J-D Grattepanche
email: jean-david.grattepanche@univ-littoral.fr

Elsa Breton

Jean-Michel Brylinski

Eric Lecuyer

Urania Christaki

coastal ecosystem dominated by Phaeocystis globosa blooms

Keywords: Phaeocystis globosa, diatoms, micrograzer community, eastern English Channel Phaeocystis globosa, diatoms, micrograzer community, eastern English Channel

The community structures and succession of phytoplankton, protozooplankton and copepods were 16 studied from February 2007 to July 2009 in a coastal area of the eastern English Channel subject to 17 Phaeocystis globosa blooms. While diatom blooms preceded P. globosa blooms each year, the 18 community structure and stock of heterotrophic protists appeared to be related to the dominant P.

19 globosa life cycle stages. In 2007 the dominance of large colonies (>100 µm, 375 µg C L -1 ) which 20 resulted in a high biomass of healthy free cells (163 µg C L -1 ) accompanied high spirotrich ciliate 21 stocks (up to 58 µg C L -1 ) and high abundances of the copepods Acartia clausi and Temora 22 longicornis (up to 11 ind L -1 ). In 2008, the bloom which lasted a shorter period of time, was 23 dominated by large colonies (328 µg C L -1 ), and fewer free cells (131 µg C L -1 ). This corresponded 24 with a lower abundance of grazers, with stocks of heterotrophic protists and copepods 1.6 times and 25 2.2 times lower, respectively. In 2009, the P. globosa bloom was again dominated by large colonies 26 and <100 µm diatoms. This corresponded to a dominance of heterotrophic dinoflagellates among the 27 protists (62% of the total heterotrophic protist biomass) and Acartia clausi (55% of the copepod 28 abundance). Overall, heterotrophic dinoflagellates appeared to be likely the most important group of 29 phytoplankton grazers. 30 31 Lancelot et al., 1998). P. globosa, a species of ephemeral occurrence alternates between a colonial 36 stage in the earlier phase and solitary cells during the decline of the bloom (Rousseau et. al., 2007).

37

In the colonial form, P. globosa can represent over 90% of phytoplankton biomass (Lancelot, 1995; 38 Lamy et al., 2009), and be responsible for the massive load of organic matter into the ambient water, 39 often resulting in foam accumulation along the shoreline (Van Boekel et al., 1992).

40

Generally speaking, phytoplankton blooms occur as a result of growth greatly exceeding 41 mortality, often through escaping control by grazers (Strom 2002; Irigoien et al., 2005). In the 42 particular case of P. globosa, experimental and modelling studies suggest that in early stages of the 43 bloom, solitary cells are well-grazed by the microzooplankton but control ceases when colonies start 44 to form (Verity, 2000). Culture experiments have shown that the smaller forms of P. globosa, free

INTRODUCTION

32

In the North Sea and in the eastern English Channel, gelatinous colonies of Phaeocystis globosa 33 Scherffel, 1900 (Prymnesiophyceae) several mm in size (Rousseau et al., 2007) 3 cells of 4-8 µm, can support the growth and reproduction of protists, but not copepods (Tang et al., weights and converted into carbon units assuming a 40% carbon content (Gorsky et al., 1988). A 171 minimum of 400 copepods were used to calculate conversion factors (401, 1153 and for Temora longicornis, Acartia clausi and other copepods). The averages of carbon per individual 173 copepod were 3.56±1.73, 1.59±0.41 and 2.34±2.63 µg C copepod -1 for Temora longicornis, Acartia 174 clausi, and other copepods, respectively. These empirical conversion factors determined from our 175 samples were then used to convert abundance into biomass data.

177

Data analysis 178

To portray temporal patterns of different phytoplankton and heterotrophic compartments considered 179 in this study the method of cumulated function (Ibanez et al., 1993) was used. This method can be 180 applied to portray trends in data series with missing values and does not require special conditions.

181

The calculation consists of subtracting a reference value (here for a biomass parameter we used the 182 annual mean of the series) from the data; the resulting residuals are then successively added, early May and lasted about one month each year (37, 27 and 29 days in 2007, 2008 and 2009, 220 respectively, Fig. 3b,c). During the blooms, P. globosa represented up to 93% of the The plots of log transformed data of biomass of major phytoplankton groups and their potential 335 predators indicated curvilinear relationships. The biomass of total protists increased linearly with 336 total phytoplankton and levels around 70 µg C L -1 (Fig. 6a). The same type of relationship was 337 observed with ciliates vs PNF and dinoflagellates vs diatoms levelling around 50 and 30 µg C L -1 , 338 respectively (Fig. 6b,c). The calculated regressions for the linear part of the relations, showed a 339 stronger relation for total phytoplankton vs protists, followed by PNF vs ciliates and dinoflagellates 340 vs diatoms (Fig. 6,a,b,c). The relationship between dinoflagellates and P. globosa colonies 341 suggested a curvilinear relationship, with dinoflagellate biomass decreasing for biomass higher than 342 1 µg C L -1 (Fig. 6d). The log-log plots of copepod biomass and auto-and heterotrophic protists did 343 not show any significant relationship. our data suggests a significant role as consumers of Phaeocystis as well.

399

Copepods dominated the mesozooplankton assemblage (68.4%, Table II) with the usual copepod 400 species found in the eastern English Channel and in the North Sea [START_REF] Breton | Qualité du pool nutritive et nutrition des copépodes pélagiques en Manche 471 orientale[END_REF], Rousseau et al. 401 2000[START_REF] Brylinski | Method of detecting faunistic gradients: FCT curves. Zooplankton 479 distribution off Cape Gris-Nez (France)[END_REF]). Abundances of copepods (0.03 -10.9 ind. L -1 , Table II) were similar to those 402 previously recorded for the study site, November 1995 to July 1997 [START_REF] Breton | Qualité du pool nutritive et nutrition des copépodes pélagiques en Manche 471 orientale[END_REF]. In our samples,

403

Acartia clausi and Temora longicornis were the most abundant species found during this study 404 (Table II). [START_REF] Brylinski | The pelagic copepods in the Strait of Dover (eastern English Channel). A 481 commented inventory 120 years after Eugène Canu[END_REF] The log-log plots displayed curvilinear relationships between phytoplankton and predator. Irigoien unsuitable for copepods, this could intensify predation on dinoflagellates (Fig. 6d). The cumulated 440 sum analysis showed some significant temporal relationships between copepods and phytoplankton 441 and between copepods and heterotrophic protists. While phytoplankton and protists have similar 442 growth rates, the absence of log-log relation between copepods and protists (autotrophic and 443 heterotrophic) can be attributed to the time lags between the appearance of prey and the predator (of 444 the order of days to weeks).

446

The more than two year's sampling allowed assessment of the variability found in a "regular 447 and recurrent event", the phytoplankton blooms of the eastern English Channel. We found 448 differences in the phytoplankton blooms as well differences in the grazer assemblages, notably a 449 marked variability from one year to the other in abundances of ciliate microzooplankton and the 450 identity of the dominant copepod species. In contrast, heterotrophic dinoflagellates appear to be a

  commonly dominate 34 the phytoplankton community during spring, following the decline of an earlier diatom bloom (e.g.,

  183 forming a cumulative function. Successive positive residuals produce an increasing slope indicating 184 higher values than the overall mean, whereas successive negative residuals produce a decreasing 185 slope indicating values lower than the overall mean. A succession of values similar to the mean consecutive terms of the cumulative sums 189 x t = value for each sampling date (t) 190 p k = annual mean 191 Spearman correlations were calculated using series of cumulative sums (Sp). These correlations 192 have an informative rather than an absolute value since the terms of cumulative sums are 193 autocorrelated. For this reason correlations can be relevant only if the correlation coefficient (r) is 194 highly significant (p = 0.01 so 1%) for the degrees of freedom considered. 195 Log-log plots of total phytoplankton, diatoms, colonies and free P. globosa cells were used to 196 investigate linkages with grazers, in particular ciliates and dinoflagellates (Irigoien et al. 2005).

8

  Salinity ranged from 33 to 35 and the seawater temperature from 4.6°C to 18.2°C (Fig.2a).201Concentrations of inorganic nutrients exhibited typical seasonal patterns for this temperate coastal 202 area: Highest concentrations were recorded at the end of winter before the onset of the 203 phytoplankton bloom reaching 37.23 µM for NO 3

221

  microphytoplankton and up to 100% of the nanophytoplankton biomass and large colonies (>100 222 µm) constituted most (56 to 93%) of the P. globosa biomass. With regard to inter-annual 223 differences, from 2007 to 2009 maximum biomass values increased for P. globosa colonies (from 224 316 to 392 µg C L -1 ) and free colonial cells (from 62 to 153 µg C L -1 ) while flagellated cells 225 decreased slightly (from 66 to 50 µg C L -1 ; Fig. 3c). 226 Diatoms were always present with mean biomass values of 92% of total phytoplankton 227 biomass over the study period. Diatom biomass ranged from 2 to 345 µg C L -1 (

429

  et al. (2005) using a large scale data set, observed the same type of relationship, observing a plateau 430 of microzooplankton biomass with increasing phytoplankton biomass at around 50 mg C m -3 ; which 431 they attributed to the presence of unfavourable prey and/or predation by mesozooplankton. In our 432 study microzooplankton also levelled at around this same value range (70 mg C m -3 Fig 6a). In the 433 plots of ciliates vs PNF and dinoflagellates vs diatoms, protistan biomass levelled at lower levels 434 (Fig. 6b, c; 50 and 30 mg C m -3 , respectively) suggesting predation of copepods on 435 microzooplankton which may have favoured further phytoplankton accumulation. The log-log 436 relation between dinoflagellates and P. globosa colonies (Fig. 6d) indicated that while small 437 colonies (representative of low biomass) may be suitable prey for dinoflagellates, larger colonies 438 (representative of high biomasses) are more difficult to consume. Given that large colonies are 439

451

  relatively consistent assemblage in terms of both their aggregate biomass compared to 452 phytoplankton, and their species composition. Heterotrophic dinoflagellates likely represent the 453 primary consumers of phytoplankton, but there is also indication that they suffer enhanced predation 454

640(Figure 2 :Figure 3 : 655 Figure 4 : 660 Figure 5 :Figure 6 :

 23655466056 Figure 1: Location of the SOMLIT station (•)

  Fig. 1

  Fig.3

  Fig. 4

  Fig.5

  Fig. 6

  Table I); nutrient concentrations always dropped dramatically at the end of spring. A

	205
	206	decrease in the maximum value of inorganic nutrients was observed from 2007 to 2009 and this was
	207	more pronounced for NO 3	-+ NO 2	-concentrations (Table I). POC ranged from 114 to 1675 µg C L -1
	208	in 2007 and from around 100 to 600 µg C L -1 in 2008 and 2009 (Table I)
	209	Phytoplankton
	210	Chlorophyll a (chl a) concentrations ranged from 0.8 to 20.3 µg Chla L -1 (Table I) with minima
	211	during autumn/winter (October -February) and maxima in late spring (April-May, Fig. 2b). The
	212	peak value of chl a concentration observed during spring coincided with the P. globosa bloom,
	213	except in 2009 when the chl a maximum was due to diatoms and occurred before the peak of the
	214	phytoplankton biomass (Fig. 2b). Total phytoplankton biomass ranged from 2 to 638 µg C L -1 , with
	215	a maximum in spring and a minimum in autumn/winter (from October to February Table II; Fig 2b).
	216	Based on our data a highly significant empirical relationship between POC:chl and
	217	Cphytoplankton:Chl was calculated (COP=92.0 + 47.6 [Chla], and Cphytoplankton=29.4 +
	218	23.6[Chla], r 2 =0.425 and r 2 =0.552 with p<0.0001 respectively, figures not shown).
	219	Phaeocystis globosa blooms are ephemeral and at our study site occurred from late March to

  TableII). The mean Phaeocystis colonies and diatoms (Fig.5g-i). In 2008, copepod 328 cumulated sums remained close to the annual average but with a slight increase corresponding to the 329 bloom of P. globosa colonies in May (Fig.5h). Considering heterotrophic protists as prey, Temora 330 longicornis were related to ciliate biomass (r = 0.42, n = 51, p < 0.002; data not shown) and Acartia

	regard to temporal trends of 331
	300 332	clausi to heterotrophic dinoflagellate biomass (r = 0.35, n = 51, p < 0.012; data not shown).
	301 333	less than 1 week and occurred between the two maxima of copepods (Fig. 4). Their highest
	302 334	abundance was observed in May 2007 when they reached up to 11.3 ind. L -1 (up to 82% of General Relationships
	303	zooplankton abundance) and they were absent during the rest of the year. Appendicularians
	304	(Oïkopleura dioica) feeding essentially on picoplankton, were also observed in low numbers (0 to
	305 306	F o F o 2.9 ind. L -1 , mean 15.3±11.8% of the mesozooplankton abundance). Temporal Trends based on cumulative sums F o
		r r r
		P P P
		e e r e e r e e r
		R e v i e w R e v i e w R e v i e w
	231
		12

228 of diatom biomass during the spring bloom (from March to May) was lowest in 2009 and highest in 229 2007 (Table

III

). The diatom 20-100 µm size class was the most important for all years and showed 230 the highest biomass mean during the spring bloom in 2008 (Table

III

). 9 We distinguished 3 distinct assemblages of diatoms. The first group, composed of cells 232 between 20-120 µm and characterized by Pseudonitzschia spp., and Chaetoceros spp., was present 233 during P. globosa blooms and persisted during the post-bloom period until August. In 2009 the 11 bloom (from March to May). The Acartia to Temora ratio of average biomass values increased from 296 0.25 in 2007 to 1.9 in 2009 (Table

III

, Fig.

4c

). Paracalanus parvus and Centropages hamatus were 297 also present in lower abundances and accounted for 7.0±5.4 and 13.6±13.3% of total copepod 298 abundance, respectively.

299

Pluteus and larvae of the urchin Echinocardium cordatum were present each year in spring during

307

The cumulative sums show temporal trends in terms of differences from overall averages, temporal 308 variations not easily seen in figures such as Figures

3 and 4

. We focused on the temporal trends of

  , we can speculate that nauplii maxima usually occur a few weeks before adult maxima can feed on the same range of prey as the adults (e.g. Isochrisis galbana of about 12 µm and 426 Rhodomonas marina 5-7 µm) (S. Souissi, Wimereux Marine Station, personal communication).

	in this work427
	428
		F o
		r
		P
		e e r
	415	R e v i e w
	416	preference for dinoflagellates over phytoplankton (Vargas and Gonzalez, 2004; Leising et al., 2005
	417	a,b). With regard to the impact of copepod grazing on the communities of heterotrophic protists and
	418	phytoplankton, some rough estimates can be made based on maximal reported clearance rates, 40
	419	mL d -1 Temora -1 (Tiselius, 1989) and 30 mL d -1 Acartia -1 , (Gismervik and Andersen, 1997) and our
	420	peak copepod abundances (Fig. 4c). Such calculations suggest a weak control, clearing at most
		about 15% of the water column per day in 2008 and 2009 in the Acartia dominated years compared
		15

reported that T. longicornis habitually dominate copepod abundance 405 during the spring and A. clausi during the summer. 406 During our study period, T. longicornis showed a decrease from 2007 to 2009 that 407 corresponded with the decrease of P. globosa bloom duration, fewer large Phaeocystis colonies (> 408 100 µm) and lower ciliate biomass (Table III). It is tempting to relate the decrease in Temora 409 longicornis to declines in ciliate biomass (r=0.42; cf. Results), as this species is thought to feed 410 selectively on ciliates and discriminate against both Phaeocystis (Hansen and Van Boekel, 1991; 411 Hansen et al., 1993) as well as dinoflagellates (Vincent and Hartmann, 2001). The species which 412 replaced Temora longicornis, Acartia clausi, while known to ingest ciliates (Gismervik and 413 Andersen, 1997), apparently does not selectively prey on them in natural populations (Tiselius, 414 1989). The correlation between A. clausi and dinoflagellate biomass can be attributed to A. clausi 421 to 2007 in which peak populations of Temora may have been capable of clearing about 50% of the 422 water column per day. Nauplii of the 2 dominant copepod species were not quantitatively sampled

Table II :

 II Autotrophic and heterotrophic abundance and biomass ([min -max]; mean ± sd), and % of

	636
	637	total protist biomass and total metazoan abundance, from February 2007 to July 2009 in the eastern
	638	English Channel.
	639

Table III :

 III Averages of biological stocks (biomass or abundance) during the spring bloom periods

http://mc.manuscriptcentral.com/jplankt Journal of Plankton Research

'Sepia II', N. Degros for nutrient analyses for the SOMLIT data base and D. Vincent for assistance

Acknowledgements: This work was supported by the coastal national network SOMLIT and a PhD 458 grant from the French ministry of education for JDG. We thank the captain and the crew of the RV

with laboratory analyses and advice in data analysis. We are grateful to J. Dolan for very useful 461 discussions on our data and critical reading of the manuscript. We thank F. Schmitt and E. Christou


Henrike ; Hamer

Henrike H Hamer

Arne M Malzahn

Maarten Boersma
email: maarten.boersma@awi.de

The invasive ctenophore Mnemiopsis leidyi: a threat to fish recruitment in the North Sea?

Keywords: stable isotopes, predation, Invasive species, gelatinous plankton, jellyfish, fish eggs, abundance Invasive species, gelatinous plankton, jellyfish, fish eggs, predation, abundance, stable isotopes 37

The invasive ctenophore Mnemiopsis leidyi has a strong reputation as a threat to fish stocks. Apart 19 from competitive relationships between M. leidyi and fish larvae, direct predation by the ctenophore 20 on both eggs and larvae is considered an important factor linking ctenophore and fish populations.

21

We therefore estimated abundances of both the ctenophore and its potential prey in the spring of 22 2008. No significant correlations were detected between ctenophore numbers and the abundance of 23 fish eggs. We further carried out stable isotope analyses to investigate the trophic position of M. 24 leidyi. Carbon and nitrogen stable isotope signatures of three potential prey groups (fish eggs, small 25 plankton and larger plankton) showed that M. leidyi primarily feeds on plankton, while fish eggs 26 are of minor importance. M. leidyi was located roughly one trophic level above the indigenous 27 ctenophore Bolinopsis infundibulum, whereas its trophic position was more similar to another native 28 ctenophore, Pleurobrachia pileus. A feeding selection experiment, with fish eggs and copepods 29 offered in the same proportion, corroborated these findings. M. leidyi ingested significantly more 30 copepods; feeding on fish eggs was not significantly different from zero. Based on these 31 experiments we conclude that in the North Sea M. leidyi has no serious potential as a direct predator 32 of fish eggs, but individuals of this species might compete for food with larval fish as well as with 33 the native ctenophore P. pileus.

 [START_REF] Mccutchan | Variation in trophic shift for stable isotope ratios of carbon, nitrogen, and 318 sulfur[END_REF][START_REF] Minagawa | Stepwise enrichment of 15 N along food chains: Further evidence and the 320 relation between δ 15 N and animal age[END_REF]. In cases where the mixing model yielded fractions of the diet 117 lower than 0 or higher than 1 these were set to 0 and 1 respectively, and the total of the three 118 resources scaled to 1.

119

For the food selection experiments, M. leidyi were kept in a planktonkreisel [START_REF] Greve | The "Planktonkreisel", a new device for culturing zooplankton[END_REF]Greve, 120 1970) with a 60cm diameter and a vertical current with a flow rate 2L * min -1 . These animals were 121 fed daily with one-to two-day-old Artemia salina nauplii for at least five days to assure a uniform were sufficient to avoid limitation effects and enough to achieve an optimal reduction of prey items 130 by 40% [START_REF] Gifford | Consumption of protozoa by copepods feeding on natural microplankton 285 assemblages[END_REF] A negative correlation between potential prey and predator densities could imply direct predation.

179

This negative correlation was indeed found between anchovy eggs and M. leidyi in the Black Sea 180 (Shiganova and Bulgakova, 2000) and between copepods and M. leidyi in Narragansett Bay, U.S.

181 [START_REF] Kremer | Patterns of abundance for Mnemiopsis in U.S. coastal waters: a comparative 308 overview[END_REF]. For the North Sea, our abundance estimations did not show this clear relationship.

182 Even though our net sampling method is an appropriate method to sample sensitive ctenophore 183 species, we surely did not overcome another typical problem of quantitative gelatinous plankton 184 sampling: as Purcell (Purcell, 2009) points out, the uneven distribution and temporarily rare 185 occurrence of ctenophores would have required a greatly extended sampling strategy, and as it is 186 our results rather represent a rough estimation of ctenophore abundances. Due to ambient 187 hydrography as well as the tidal currents the distributions of fish eggs around Helgoland are also 188 expected to be non-uniform and patchy. In fact, in our observations, fish egg densities showed 189 strong fluctuations, which is probably also a result of patchy spawning events, or spawning by 190 different species [START_REF] Malzahn | Year-to-year variation in larval fish assemblages of the 316 Southern North Sea[END_REF]. Since we did not identify the fish eggs to species, and Nixon, 1976), so that a serious predatory impact is even more unlikely here.

197

Many jellyfish, especially scyphozoans, have been observed to prefer fish eggs [START_REF] Fancett | Diet and prey selectivity of scyphomedusae from Port Phillip Bay[END_REF]198 Sullivan et al., 1994). M. leidyi feeds selectively too [START_REF] Javidpour | Annual assessment 299 of the predation of Mnemiopsis leidyi in a new invaded environment, the Kiel Fjord 300 (Western Baltic Sea): a matter of concern?[END_REF] [START_REF] Larson | Situ Feeding Rates of the Ctenophore Mnemiopsis mccradyi[END_REF][START_REF] Costello | Influence of prey detection on capture success for 273 the ctenophore Mnemiopsis leidyi feeding upon adult Acartia tonsa and Oithona colcarva 274 copepods[END_REF]. These mechanisms enable M. leidyi to feed on mobile 202 and immobile prey items at the same time. Capture success for mobile copepods such as Acartia sp.

203 is quite high with 74% of all encounters [START_REF] Costello | Influence of prey detection on capture success for 273 the ctenophore Mnemiopsis leidyi feeding upon adult Acartia tonsa and Oithona colcarva 274 copepods[END_REF], and the capture success for 204 immobile fish eggs should even be higher, as these lack escape abilities. However, in our study this 205 was not the case. Fish eggs were grazed significantly less than fast moving copepods; in fact 206 grazing rates on fish eggs were not significantly different from zero in our experiment. (B)

Mnemiopsis leidyi Bolinopsis infundibulum Pleurobrachia pileus

(1)

(3) (4)

(2)

(3)

(1)

(1) (4)

(1)

(1)

(3) (1) (1)
(2)

(8) (6) (4) (3) (1) (1) (2)
(1)

(1)

168leidyi,

  with only two sampling occasions in April-May where, based on the stable isotope signals, 169 fish eggs may account for around 10% of the diet of M. leidyi (Fig. 4.). The average values of the 170 stable isotope signals corroborate this (Fig. 5). In fact, based on these averages, fish eggs did not 171 occur in the diet of M. leidyi at all. B. infundibulum has a very unusual isotope signal compared to 172 its 'potential' prey. It has the same δ 15 N signal as the plankton fraction, and the δ 13 C-signal is 173 depleted compared to the plankton signals. Hence, there has to be one or more food source, which 174 we did not sample, with lower δ 15 N and δ 13 C values to produce the isotopic composition of B.

383Fig. 1 . 386 Fig. 2 . 390 Fig. 3 . 394 Fig. 4 . 399 Fig. 5 .

 13862390339443995 Fig. 1. Abundances of Mnemiopsis leidyi, Bolinopsis infundibulum, Pleurobrachia pileus (each

  Fig. 3 411 412

  Facility, California. δ-values were calculated by δ = 1000 *

	116	al. 2005), under the assumption that 15 N is enriched by 2.2 ‰ per trophic level and 13 C by 1‰
		F o r
		P
		e
		e r
		R
		e
		v i e
			w
		std R R std R -x	; R is the ratio of the amount of
			6

  especially in March/April. In contrast, fish eggs play only a minor role in the diet of M.

		pileus,
		F o r F o r
		P P
		e e
		e r e r
		R R
		e e
	133	v i e v i e
	134	limanda LINNÉ 1758 eggs of ca. 0.8mm and some Pleuronectes platessa LINNÉ 1758 eggs of ca. w w
	135	1.5mm in diameter) and from a specimen of Ciliata mustela (LINNÉ 1758, a bottom-dwelling
	136	Gadiform with ca. 0.8mm in egg diameter), which spawned in captivity. The eggs from C. mustela
	137	were not older than 48h and stored at 8°C so that most of them stayed alive and neutrally buoyant,
	138	as the other eggs did as well. The experimental temperature was 8°C, with dim light. Feeding was
	139	terminated by removing the ctenophore. The contents of the feeding chamber were then poured
	140	through a 150µm sieve, the remaining prey items were stained with Lugol's solution and counted in
	141	a Bogorov counting chamber. Samples were analysed using the equations developed by Frost
		8

. After acclimatisation for 1 hour, the experiment was started by adding 100 131 copepods (max. 1mm in length) and 100 planktonic fish eggs. Control treatments did not contain 132 ctenophores (n=5). Fish eggs were obtained from CalCOFI catches at Helgoland Roads (Limanda

  the driving factor of the changes in fish egg densities is not predation. In 194 addition, M. leidyi densities were very low compared to those reported from the Black Sea (up to 195 180 specimens per m³,[START_REF] Mutlu | Distribution and abundance of ctenophores and their zooplankton food in the 327 Black Sea. II. Mnemiopsis leidyi[END_REF] or the eastern US coast (peaks of 50 specimens per m³, Kremer 196

	densities suggest that
	F o r
	P
	e
	e r
	R
	e
	v i e
	w
	193
	9

191

we cannot evaluate whether a certain fish species might be particularly endangered by M. leidyi, but 192 the strong fluctuations in egg densities combined with the much lower ones in the ctenophore

  Most likely, as even in very high density experiments fish eggs were not 246 consumed by M .leidyi, the ctenophores were rejecting fish eggs in favour of copepods.247In conclusion, our findings give important inidcations that fish eggs might not be an important food 248 source for M. leidyi in the North Sea, nor are they for the indigenous ctenophore B. infundibulum, 249 but more so for P. pileus. Food competition of the invasive M. leidyi with planktivorous fish and 250 fish larvae is a more likely, but yet unexplored threat to North Sea fish stocks. However, densities 251 of M. leidyi were low in comparison to areas like the Black Sea, where values of up to 30400 Ind * 252 100m -³ were observed(Vinogradov, 1989). Hence, we propose that M. leidyi is at present unable to 253 affect the ecosystem in the North Sea in a similar way as it did in the Black Sea, and as a result 254 might fit into the current food web without the catastrophic impacts observed in other invaded seas.

	prey remains unclear. 255 256	F o r F o r F o r F o r F o r F o r F o r
			P P P P P P P
			e e e e e e e
	207		e r e r e r e r e r e r e r	Container
	208	effects caused by the relatively small 2L jars used here might have limited ingestion (as suggested R R R R R R R
	209	by Purcell (Purcell 2009)), but it seems unlikely that this would have affected the different prey e e e e e e e
		items differently. Hence, absolute predation rates on the different prey items might be incorrect, but v i e v i e v i e v i e v i e v i e v i e
			w w w w w w w
				11

http://mc.manuscriptcentral.com/jplankt Journal of Plankton Research

Acknowledgements

N (‰) ± SD

Mnemiopsis leidyi Bolinopsis infundibulum Pleurobrachia pileus

(1)

(2)

(2)

(3)

(2)

(1) (1) (8)


Christophe ; Brunet
email: christophe.brunet@szn.it

Johann Lavaud
email: johann.lavaud@univ-lr.fr

Stazione

Anton Dohrn

Can the xanthophyll cycle help extract the essence of the microalgal functional response to a variable light environment

Keywords: phytoplankton, photosynthesis, ecophysiology

Can the xanthophyll cycle help extract the essence of the microalgal functional response to a variable light

environment?

FAST REGULATION OF PHOTOSYNTHESIS AND 'THE PARADOX OF THE PLANKTON'

Phytoplankton live in a three-dimensional environment characterized by strong physical and chemical driving forces and a rapid attenuation of light with depth. In contrast, the terrestrial habitat is essentially two-dimensional, although it can be argued that forests put a lot of energy in catching that third dimension by forming support tissues to lift their photosynthetic tissues up towards the light and above the competition. A second important difference is that on land, higher plants have to invest a huge part of their organic products in unproductive support and transport tissues. Nonetheless, living in the plankton poses some problems that are arguably less relevant for higher land plants. Phytoplankton has to cope with a highly variable environment that continuously requires energy for maintenance of photosynthetic productivity and growth. This is 3 relevant in such aquatic ecosystems where biodiversity is high and competition for resources is strong. Indeed, in a few cubic millimeters of water, many phytoplankton species can grow together, sharing and competing for the same energy resources, especially light and nutrients [START_REF] Liess | Light, nutrients and grazing interact to determine diatom species richness via change to productivity, nutrient state and grazing activity[END_REF]. This is the 'paradox of the plankton' as discussed by [START_REF] Hutchinson | The paradox of the plankton[END_REF]. How does diversity persist in such a small spatial framework is still a matter of debate [START_REF] Bastow Wilson | Mechanisms of species coexistence: twelve explanations for Hutchinson's 'paradox of the plankton': evidence from New Zealand plant communities[END_REF]. High frequency variability of environmental cues can help in maintaining and even increasing phytoplankton biodiversity [START_REF] Sommer | An experimental test of the intermediate disturbance hypothesis using cultures of marine phytoplankton[END_REF][START_REF] Flöder | The influence of fluctuating light intensities on species composition and diversity of natural phytoplankton communities[END_REF]. Hence to be competitive, phytoplankton must be able to respond quickly to any kind of changes occurring in its habitat. The main abiotic driving forces are temperature, nutrients and light, the latter showing the highest variations in amplitude and frequency (McIntyre et al., 2000;[START_REF] Raven | Adaptation, acclimation and regulation in algal photosynthesis[END_REF][START_REF] Dubinsky | From the light to the darkness: Thriving at the light extremes in the oceans[END_REF]. Hence, the response of phytoplankton might be supported by at least one irradiance-dependent physiological process, which must be fast, flexible and efficient [START_REF] Li | Sensing and responding to excess light[END_REF][START_REF] Dubinsky | From the light to the darkness: Thriving at the light extremes in the oceans[END_REF]. [START_REF] Huisman | Towards a solution of the plankton paradox: the importance of physiology and life history[END_REF] proposed that the diversity of life history and of physiological abilities might promote the high biodiversity of phytoplankton. It has been proposed that the variability of physiological responses to light fluctuations would allow competitive exclusion and thus the spatial co-existence and/or the temporal succession of a multitude of species in both pelagic [START_REF] Meyer | Xanthophyll cycling in Phaeocystis globosa and Thalassiosira sp.: a possible mechanism for species succession[END_REF]Strzepek and Harrison, 2004;Dimier et al. 2007b;2009b;[START_REF] Lavaud | Photoprotection capacity differs among diatoms: possible consequences on the spatial distribution of diatoms related to fluctuations in the underwater light climate[END_REF] and benthic [START_REF] Serodio | Non-photochemical quenching of chlorophyll fluorescence and operation of the xanthophyll cycle in estuarine microphytobenthos[END_REF]van Leeuwe et al., 2008) ecosystems. Indeed, growth rate responds to fluctuating light in different ways as a function of groups/species of phytoplankton [START_REF] Litchman | Growth rate of phytoplankton under fluctuating light[END_REF][START_REF] Flöder | The influence of fluctuating light intensities on species composition and diversity of natural phytoplankton communities[END_REF][START_REF] Mitrovic | Unusual allometry between in situ growth of freshwater phytoplankton under static and fluctuating light environments: possible implications for dominance[END_REF]Wagner et al., 2006) and of the photoacclimation ability and light history of the cells [START_REF] Litchman | Competition of phytoplankton under fluctuating irradiance[END_REF]van Leeuwe et al., 2005;Wagner et al., 2006;van de Poll et al. 2007;[START_REF] Laurion | Growth and photoprotection in three dinoflagellates (including two strains of Alexandrium tamarense) and one diatom exposed to four weeks of natural and enhanced ultraviolet-B radiation[END_REF]. The photoresponse ultimately leading to a change in growth rate is thus a matter of both genomic plasticity and time scale [START_REF] Grobbelaar | Photosynthetic response and acclimation of microalgae to light fluctuations[END_REF][START_REF] Dubinsky | From the light to the darkness: Thriving at the light extremes in the oceans[END_REF]. In the short term (few seconds/minutes), the light fluctuations are mainly due to cloud movement, surface sunflecks and vertical mixing generating unpredictable changes.

These fluctuations, and especially their extremes (darkness and excess light), can be harmful for the photosynthetic productivity of microalgae by promoting an imbalance 4 between the harvesting of light energy and its use for photochemical processes and carbon fixation [START_REF] Long | Photoinhibition of photosynthesis in nature[END_REF][START_REF] Raven | Adaptation, acclimation and regulation in algal photosynthesis[END_REF][START_REF] Dubinsky | From the light to the darkness: Thriving at the light extremes in the oceans[END_REF]. In order to regulate photosynthesis versus rapid light fluctuations, phytoplankton has evolved a number of physiological photoprotective mechanisms such as the photosystem II (PS II) and PS I electron cycles, the state-transitions, the fast repair of the D1 protein of the PS II reaction center, the scavenging of reactive oxygen species (see Falkowski and Raven, 2007;[START_REF] Lavaud | Fast regulation of photosynthesis in diatoms: Mechanisms, evolution and ecophysiology[END_REF][START_REF] Ruban | Dynamics of higher plant photosystem cross-section associated with state-transitions[END_REF]. Among these processes, the XC and the dependent thermal dissipation of the excess light energy (NPQ for non-photochemical fluorescence quenching) play a central role [START_REF] Lavaud | Fast regulation of photosynthesis in diatoms: Mechanisms, evolution and ecophysiology[END_REF]Brunet et al., in press;[START_REF] Goss | Regulation and function of xanthophyll cycle-dependent photoprotection in algae[END_REF]. At longer time scales (hours to seasons), acclimation processes are supported by gene regulation which modifies the architecture of the photosynthetic apparatus as well as enzymatic reactions involved in photochemistry and metabolism [START_REF] Raven | Adaptation, acclimation and regulation in algal photosynthesis[END_REF][START_REF] Grobbelaar | Photosynthetic response and acclimation of microalgae to light fluctuations[END_REF][START_REF] Dubinsky | From the light to the darkness: Thriving at the light extremes in the oceans[END_REF]. These two types of responses, regulative and acclimative, are not mutually exclusive [START_REF] Lavaud | Photoprotection capacity differs among diatoms: possible consequences on the spatial distribution of diatoms related to fluctuations in the underwater light climate[END_REF]Brunet et al., in press). For instance, long-term acclimation to a prolonged light regime (low or high intensity, or intermittent light) modifies the amount of pigments involved in the XC leading to a modulation of the high light response via the kinetics and amplitude of NPQ [START_REF] Lavaud | Enrichment of the light-harvesting complex in diadinoxanthin and implications for the nonphotochemical quenching fluorescence quenching in diatoms[END_REF]van de Poll et al., 2007;[START_REF] Gundermann | The fluorescence yield of the trimeric fucoxanthin chlorophyll-protein FCPa in the diatom Cyclotella meneghiniana is dependent on the amount of bound diatoxanthin[END_REF]Dimier et al., 2009b).

XANTHOPHYLL CYCLE FUNCTIONING AND VARIABILITY

The xanthophyll cycle (XC) is one of the main processes regulating excessive photon flux in the light-harvesting complexes of photosystems since it is responsible for most of NPQ (for recent reviews, see [START_REF] Demmig-Adams | Photoprotection in an ecological context: the remarkable complexity of thermal energy dissipation[END_REF][START_REF] Lavaud | Fast regulation of photosynthesis in diatoms: Mechanisms, evolution and ecophysiology[END_REF][START_REF] Goss | Regulation and function of xanthophyll cycle-dependent photoprotection in algae[END_REF]. In microalgae, two main groups can be distinguished with regard to the pigments involved in the XC (Brunet et al., in press). The first group possesses the two-step de-epoxidation of violaxanthin (Vx) into zeaxanthin (Zx) via antheraxanthin (Ax) (a truncated Vx to Ax version also occurs in some primitive green algae). The second group shows a simpler conversion as the main XC, with only one step deepoxidation of diadinoxanthin (Dd) into diatoxanthin (Dt). Many specificities of the Dd- et al., 2006;[START_REF] Lavaud | Fast regulation of photosynthesis in diatoms: Mechanisms, evolution and ecophysiology[END_REF][START_REF] Goss | Regulation and function of xanthophyll cycle-dependent photoprotection in algae[END_REF] might explain the rapid and effective synthesis of Dt in large amounts (Lavaud et al., 2002a;[START_REF] Lavaud | General features of photoprotection by energy dissipation in planktonic diatoms (Bacillariophyceae)[END_REF]. In other groups of phytoplankton, there is no (cyanobacteria) or a questionable (red algae) XC [START_REF] Goss | Regulation and function of xanthophyll cycle-dependent photoprotection in algae[END_REF] but the involvement of various de-epoxidized forms of xanthophylls (including Zx) in NPQ [START_REF] Kirilovsky | Photoprotection in cyanobacteria: the orange carotenoid protein (OCP)-related non-photochemical-quenching mechanism[END_REF].

The photoprotective NPQ process takes place into the light-harvesting complex of PS II. When irradiance exceeds the photosynthetic capacity of the cell, NPQ dissipates part of the light energy absorbed in excess, thus decreasing the excitation pressure on PS II [START_REF] Demmig-Adams | Photoprotection in an ecological context: the remarkable complexity of thermal energy dissipation[END_REF][START_REF] Lavaud | Fast regulation of photosynthesis in diatoms: Mechanisms, evolution and ecophysiology[END_REF][START_REF] Li | Sensing and responding to excess light[END_REF]. NPQ is composed of three components (qE, qT and qI) whose respective importance varies among photosynthetic lineages, qE being essential for most of them. qE is the energy-dependent quenching which is regulated by the build-up of a transthylakoid ∆pH and the operation of the XC. qT refers to the part of the quenching which is due to state-transitions, while qI is due to photoinhibition. qT is relevant in phycobilisome-containing organisms (cyanobacteria and red algae) and green microalgae but it is not really significant in light conditions triggering maximal qE (i.e. high light; [START_REF] Mullineaux | State-transitions: an example of acclimation to low-light stress[END_REF][START_REF] Ruban | Dynamics of higher plant photosystem cross-section associated with state-transitions[END_REF]. The origin of qI is not clearly defined except for some higher plants (overwintering conifers and tropical evergreen species) and it requires special conditions (prolonged environmental stress) (Demming-Adams and Adams, 2006).

Although the relationship between qE and the accumulation of de-epoxidized xanthophylls has been reported in many algal groups [START_REF] Lavaud | Photoprotection capacity differs among diatoms: possible consequences on the spatial distribution of diatoms related to fluctuations in the underwater light climate[END_REF]Brunet et al., in press), there is still no clear picture of the functioning of qE in microalgae, although models have been proposed [START_REF] Lavaud | Fast regulation of photosynthesis in diatoms: Mechanisms, evolution and ecophysiology[END_REF][START_REF] Goss | Regulation and function of xanthophyll cycle-dependent photoprotection in algae[END_REF], with the exception of Chlamydomonas [START_REF] Peers | An ancient light-harvesting protein is critical for the regulation of algal photosynthesis[END_REF]. Even though qE has been investigated down to the molecular level in higher plants [START_REF] Cogdell | The structural basis of non-photochemical quenching is revealed?[END_REF], its level of complexity is still not fully understood in microalgae for two main reasons: 1) the joint partners of the XC for the regulation of qE and their interactions are not all identified, 2) the intricacy of qE/NPQ dependency on the light exposure (regime and duration) as well as on the light history of the cells, especially when simulated light field conditions are applied (Dimier et al., 2009a;Van de Poll et al., 2010), has been only been partially appreciated. In 6 cyanobacteria and red algae, although there is a qE quenching which is supported by the presence of xanthophylls and a ∆pH (for the red algae, [START_REF] Lavaud | Fast regulation of photosynthesis in diatoms: Mechanisms, evolution and ecophysiology[END_REF], the composition and organization of the antenna obviously support another type of qE mechanism (see [START_REF] Kirilovsky | Photoprotection in cyanobacteria: the orange carotenoid protein (OCP)-related non-photochemical-quenching mechanism[END_REF][START_REF] Bailey | Photoprotection in cyanobacteria: regulation of light harvesting[END_REF]. Nevertheless qE in cyanobacteria is not as powerful as in other phytoplankton taxa (see [START_REF] Lavaud | Fast regulation of photosynthesis in diatoms: Mechanisms, evolution and ecophysiology[END_REF] possibly because of the lack of a finely regulated XC. When necessary, cyanobacteria favour other photoprotective processes such as qT (described above) and the rapid repair of the D1 protein of the PS II reaction center [START_REF] Six | Light variability illuminates niche partitioning among marine picocyanobacteria[END_REF].

The microalgal XC activity shows striking peculiarities with respect to higher plants. It includes a high degree of variation in its regulation among the different taxa/species (Lavaud et al., 2004, Goss and[START_REF] Goss | Regulation and function of xanthophyll cycle-dependent photoprotection in algae[END_REF][START_REF] Kropuenske | Photophysiology in two major Southern Ocean phytoplankton taxa: Photoprotection in Phaeocystis antarctica and Fragillariopsis cylindrus[END_REF]Van de Poll et al., 2010), together with the growth phase [START_REF] Arsalane | Influence of the pool size of the xanthophyll cycle on the effects of light stress in a diatom: Competition between photoprotection and photoinhibition[END_REF]Lavaud et al., 2002a[START_REF] Lavaud | Enrichment of the light-harvesting complex in diadinoxanthin and implications for the nonphotochemical quenching fluorescence quenching in diatoms[END_REF]Dimier et al. 2009b), the nutrient state (Staehr et al., 2002;van de Poll et al., 2005), and the light history with both visible and UV radiation (see [START_REF] Lavaud | Fast regulation of photosynthesis in diatoms: Mechanisms, evolution and ecophysiology[END_REF][START_REF] Laurion | Growth and photoprotection in three dinoflagellates (including two strains of Alexandrium tamarense) and one diatom exposed to four weeks of natural and enhanced ultraviolet-B radiation[END_REF]Van de Poll and Buma, 2009). Also recent reports demonstrated how the XC activity and efficiency might be influenced by niche adaptation and vice versa in both pelagic [START_REF] Meyer | Xanthophyll cycling in Phaeocystis globosa and Thalassiosira sp.: a possible mechanism for species succession[END_REF]Dimier et al. 2007bDimier et al. , 2009a;;[START_REF] Lavaud | General features of photoprotection by energy dissipation in planktonic diatoms (Bacillariophyceae)[END_REF][START_REF] Lavaud | Photoprotection capacity differs among diatoms: possible consequences on the spatial distribution of diatoms related to fluctuations in the underwater light climate[END_REF] and benthic [START_REF] Serodio | Non-photochemical quenching of chlorophyll fluorescence and operation of the xanthophyll cycle in estuarine microphytobenthos[END_REF]van Leeuwe et al., 2008) species, and how it could influence species succession [START_REF] Meyer | Xanthophyll cycling in Phaeocystis globosa and Thalassiosira sp.: a possible mechanism for species succession[END_REF][START_REF] Serodio | Non-photochemical quenching of chlorophyll fluorescence and operation of the xanthophyll cycle in estuarine microphytobenthos[END_REF]van Leeuwe et al., 2008). This functional trait is part of the overall adaptive photophysiological properties of PS II, as shown for the diatoms (Strepzeck and Harrison, 2004;Wagner et al., 2006;Wilhelm et al., 2006). It highlights the narrow functional relationship between the niche adaptation and the capacity for photo-regulation/acclimation which leads to the above discussed proposal that the fast regulation of photosynthesis might be a crucial functional trait for microalgal ecology. In that respect, diatoms are currently the most studied group probably because they appear to be the best XC/NPQ performers among microalgae [START_REF] Lavaud | Fast regulation of photosynthesis in diatoms: Mechanisms, evolution and ecophysiology[END_REF]. Nevertheless, diatoms show a large inter-species XC/NPQ diversity [START_REF] Lavaud | General features of photoprotection by energy dissipation in planktonic diatoms (Bacillariophyceae)[END_REF][START_REF] Lavaud | Photoprotection capacity differs among diatoms: possible consequences on the spatial distribution of diatoms related to fluctuations in the underwater light climate[END_REF]Dimier et al., 2007b) which might take its source in the special evolution of this group [START_REF] Armbrust | The life of diatoms in the world's oceans[END_REF] leading to its successful adaptation to all aquatic habitats driven by a switch from benthic to a pelagic way of life (Kooistra et al., 2006). Especially, the decrease of accessory for an opportunistic strategy (Dimier et al., 2009b) that might be related to the high plasticity of their PS II antennae function including the XC [START_REF] Lavaud | Fast regulation of photosynthesis in diatoms: Mechanisms, evolution and ecophysiology[END_REF].

The influence of the size and shape of cells on the capacity for regulation of photosynthesis and in particular via the XC operation merits more interest [START_REF] Key | Cell size trade-off govern light exploitation strategies in marine phytoplankton[END_REF]. We observed that the size of cells could significantly affect the XC functioning [START_REF] Lavaud | General features of photoprotection by energy dissipation in planktonic diatoms (Bacillariophyceae)[END_REF]Dimier et al. 2007b;2009b). Indeed, physiological acclimation to light changes is a costly process. Cell size determines the structure of the PS II antenna and therefore the pigment content which constrains the use of light resource as well as the cell energy requirement for physiological responses to light fluctuations [START_REF] Finkel | Light absorption and size scaling of light-limited metabolism in marine diatoms[END_REF][START_REF] Raven | New light on the scaling of metabolic rate with the size of algae[END_REF][START_REF] Litchman | Trait-based community ecology of phytoplankton[END_REF][START_REF] Key | Cell size trade-off govern light exploitation strategies in marine phytoplankton[END_REF]. The influence of cell size/shape on metabolism coupled with the Metabolic Theory of Ecology [START_REF] Brown | Toward a metabolic theory of ecology[END_REF]) applied to the fast regulation of photosynthesis versus light would bring interesting insights for studying the photoadaptative strategies versus niche properties in microalgae. It would provide a background to understand how the environmental conditions affect photoregulatory capacity and efficiency and what their impact is on cell metabolism. Picoeukaryotes turned out to be interesting models to further explore this hypothesis (Dimier et al., 2007a;2009a;[START_REF] Six | Contrasting photoacclimation costs in ecotypes of the marine eukaryote picoplankter Ostreococcus[END_REF][START_REF] Six | Photosystem II and pigment dynamics among ecotypes of the Green Alga Ostreococcus[END_REF]. Dimier et al. (2009a) suggested that the energy cost of enhanced photoregulation due to high light fluctuation could be responsible for the decrease of growth rate in the shadeadapted picoeukaryote Pelagomonas. Additionally in situ studies (Brunet et al. 2006, unpublished results) showed, in agreement with laboratory experiments (Dimier et al., 2007a;2009a), that picoeukaryotes have high plasticity of PS II photoregulatory responses. This is probably related to the fact that the main limiting resource for these organisms is light (Timmermans et al., 2005) since nutrient availability seems not to significantly determine their rate of primary productivity (Brunet et al., unpubl. results).

THE XANTHOPHYLL CYCLE IN THE FIELD: A MATTER OF SCALE

Several studies have explored the response of the microalgal XC to the underwater light climate in coastal areas [START_REF] Brunet | In situ variations of the xanthophylls diadinoxanthin and diatoxanthin: photoadaptation and relationships with an hydrodynamical system of the Eastern English Channel[END_REF](Brunet et al., , 2003[START_REF] Brunet | Phytoplankton diel and vertical variability in photobiological responses at a coastal station in the Mediterranean Sea[END_REF][START_REF] Moline | Photoadaptative response during the development of a coastal Antarctic diatom bloom and relationship to water column stability[END_REF]; et al., 2003;[START_REF] Fujiki | Photoprotective response of xanthophyll pigments during phytoplankton blooms in Sagami Bay, Japan[END_REF][START_REF] Müller | Photophysiology of surface phytoplankton communities in a transect from the mouth of the Peene-strom to the Arkona Sea (Baltic)[END_REF], frontal systems [START_REF] Claustre | Phytoplankton photoadaptation related to some frontal physical processes[END_REF][START_REF] Brunet | Tidal and diel periodicities of size fractioned phytoplankton pigment signatures at an offshore station in South-Eastern English Channel[END_REF] and offshore areas (Bidigare et al., 1987;[START_REF] Olaizola | Pigment analysis of phytoplankton during a subarctic bloom: xanthophyll cycling[END_REF][START_REF] Kashino | Strategies of phytoplankton to perform effective photosynthesis in the North water[END_REF][START_REF] Brunet | Picophytoplankton diversity and photophysiology in the Strait of Sicily (Mediterranean Sea) in summer. I. Mesoscale variations[END_REF][START_REF] Brunet | Vertical variability and diel dynamics of picophytoplankton in the Strait of Sicily (Mediterranean Sea) in summer[END_REF]. Because the activation of the XC in reaction to the in situ changes in irradiance is fast, it can bring useful information on the physical properties and especially the mixing of water bodies at different time scales [START_REF] Lewis | Relationships between vertical mixing and photoadaptation of phytoplankton: similarity criteria[END_REF]. Indeed, the XC is well adapted for studying the physical-biological coupling of photosynthesis response to hydrodynamics. This is especially true for the surface mixed layer and the coastal zone. At short time scales (below an hour), the relative amount of photoprotective pigments, mainly Dt, is closely related to the light fluctuations especially due to hydrodynamics. For instance, it is possible to relate the shape of the vertical distribution of the XC pigments with light distribution and depth to highlight the mixing velocity cells have been exposed to (Brunet et al., 2003[START_REF] Brunet | Phytoplankton diel and vertical variability in photobiological responses at a coastal station in the Mediterranean Sea[END_REF][START_REF] Griffith | An algal photoprotection index and vertical mixing in the Southern Ocean[END_REF]. At longer time scales, variations of the pool size of Dd bring information on the 'average' light climate to which the cells have been exposed in the past hours/days. The amounts of Dt versus Dd can be used as tracers for microalgal cell movement within the euphotic zone, and in some cases the past light history of the phytoplankton can be extrapolated (Welschmeyer and Hoepffner, 1986;[START_REF] Moline | Photoadaptative response during the development of a coastal Antarctic diatom bloom and relationship to water column stability[END_REF]Brunet et al., 2003). Generalization from a given ecosystem/water body is impossible due the variety of biotic and abiotic driving forces acting on the XC functioning. Obviously, the impact of latitude and/or of the seasons is important, both directly through climatology and indirectly by shaping the algal community composition, structure and functioning. For instance, in coastal ecosystems, the phytoplankton community is dominated by cells of larger size whose activity is seasonally dependent thus largely modulating their photoadaptative strategy and sensitivity to light stress.

Additionally, there is a clear response of the XC to the diurnal cycle, which also depends on season and latitude [START_REF] Brunet | Vertical variability and diel dynamics of picophytoplankton in the Strait of Sicily (Mediterranean Sea) in summer[END_REF]2008). On a daily scale, the XC is a good indicator of light stress responsible for the noon decline of photosynthesis [START_REF] Long | Photoinhibition of photosynthesis in nature[END_REF]. XC operation has also been investigated in benthic estuarine systems, where diatom dominated microphytobenthos forming a dense biofilm at the surface of intertidal mudflats during emersion [START_REF] Serodio | Non-photochemical quenching of chlorophyll fluorescence and operation of the xanthophyll cycle in estuarine microphytobenthos[END_REF]van Leeuwe et al., 2008;Chevalier et al., 2010). In this special case, the dynamics of the XC can also provide information on the (van Leeuwe et al., 2008;Chevalier et al., 2010).

On a methodological level, such observation must be considered for improving the sampling strategy of phytoplankton and the evaluation of its productivity at the mesoscale as well as for larger scale studies. Indeed, the information extracted from the XC dynamics at different time scales has been shown to be useful for regional field studies of the dynamics of phytoplankton photosynthetic productivity (e.g., Brunet et al., 2003). It might be as well an additional tool for larger scale studies especially in the framework of the impact of climatology on the mixed layer and its potential effect on marine primary productivity [START_REF] Rost | Coccolithophores and the biological pump: responses to environmental changes[END_REF][START_REF] Iudicone | Seasonal variability of the mixed layer depth in the Mediterranean Sea as derived from in situ profiles[END_REF].

Recently, in the context of a trans-Mediterranean sampling program, a significant relationship between mixed layer depth, the distribution of light and the variations in XC pigments as well as the related NPQ extent was determined (Brunet et al., unpubl. results). Additionally, the impact of cell size on this relationship was demonstrated with a significant discrimination between picoeukaryotes and the rest of the phytoplankton community. Obviously further field investigations are needed in order to increase the available data set from marine areas with both different trophic status and hydrodynamic conditions. Also, there is a significant lack of modeling exercises on physical-biological coupling based on the XC as a marker for photoregulatory physiological processes. There are already enough data to begin such approach which would be a good alternative to in situ regional and large scale systematic investigations. It would help in answering the question of how far the XC is relevant for the fast regulation of photosynthetic productivity and carbon fluxes in the upper layer of the water column, and if so, in which context [START_REF] Lavaud | Fast regulation of photosynthesis in diatoms: Mechanisms, evolution and ecophysiology[END_REF][START_REF] Alderkamp | Can photoinhibition control phytoplankton abundance in deeply mixed water columns of the Southern Ocean ?[END_REF].

NEXT STEPS TOWARDS ILLUMINATION

In this paragraph, we report some gaps in understanding, in our opinion, on XC eco-physiology and its use for a better understanding of in situ microalgal ecology. (1) At a functional level, there is a need to increase the data-set on XC characteristics in as many as possible different microalgal species/groups. Especially, it is essential to increase the diversity of biological models, taking into account different functional traits (e.g., size, shape, niche occupancy) together with investigating the feedback of the photoacclimative strategy (sigma-or n-type, [START_REF] Six | Contrasting photoacclimation costs in ecotypes of the marine eukaryote picoplankter Ostreococcus[END_REF] of the taxa on the light-dependent XC responses. For instance, one relevant question in the productive lineage of the Heterokontophyta is the role of the secondary XC (the Vx cycle) in the photoregulatory response of cells: is it involved in fast regulation by increasing the capacity for NPQ and/or prevention of lipid peroxidation, and/or is it involved in long term acclimative response by increasing the pool size of precursors for Dt de novo synthesis under prolonged excess light exposure?

(2) A conceptual model of photoprotection in phytoplankton is still lacking.

Through the recent highlighting of the peculiarities of diatoms [START_REF] Lavaud | Fast regulation of photosynthesis in diatoms: Mechanisms, evolution and ecophysiology[END_REF], green microalgae [START_REF] Peers | An ancient light-harvesting protein is critical for the regulation of algal photosynthesis[END_REF] and cyanobacteria [START_REF] Kirilovsky | Photoprotection in cyanobacteria: the orange carotenoid protein (OCP)-related non-photochemical-quenching mechanism[END_REF], it appears that the fast regulation of photosynthesis and the interplay between the photoprotective processes involved is much more complex and diverse than previously thought compared to higher plants. Obviously the post-genomic era our field of research has now entered thanks to the recent publication of genomes from several eukaryotic groups in addition to the ones of photosynthetic bacteria (see http://www.jgi.doe.gov/) will strongly push forward the detailed examination of the photoprotective processes at the molecular level. It will help understanding their diversity and evolution among phytoplankton lineages [START_REF] Lavaud | Fast regulation of photosynthesis in diatoms: Mechanisms, evolution and ecophysiology[END_REF]. For instance, in diatoms, such functional investigations have already started focusing on the light-dependent regulation of photosynthetic genes [START_REF] Nymark | An integrated analysis of molecular acclimation to high light in marine diatom Phaeodactylum tricornutum[END_REF] and the production of photosynthetic mutants [START_REF] Materna | First induced plastid genome mutations in an alga with secondary plastids: psbA mutations in the diatom Phaeodactylum tricornutum (Bacillariophyceae) reveal consequences on the regulation of photosynthesis[END_REF]. [START_REF] Coesel | Evolutionary origins and functions of the carotenoid biosynthetic pathway in marine diatoms[END_REF] showed that the number of genes encoding the enzymes involved in the XC is different in Phaeodactylum tricornutm and Thalassiosira pseudonana. Is this feature functionally relevant? Could it have implications for the ecophysiology of these species? Also by manipulating the gene encoding the Dd de-epoxidase (which ensures the conversion of Dd into Dt under excess light exposure) we could highlight specific regulatory properties of the XC, i.e. the Dd de-epoxidase concentration appears to be finely regulated in order to provide fast and efficient photoprotection concomitant with the light intensity (Lavaud (Lavaud et al., 2002b;[START_REF] Lavaud | In diatoms, the transthylakoid proton gradient regulates the photoprotective non-photochemical fluorescence quenching beyond its control on the xanthophyll cycle[END_REF] could not achieve such a fine level of understanding.

(3) At an ecophysiological level, there are many in situ and experimental observations raising intriguing questions. The first point concerns the effects of UV radiation on XC which is still under debate due to opposite conclusions from different studies (see Lavaud, 2007, Laurion andRoy, 2009;van de Poll and Buma, 2009;van de Poll, 2010). It is now urgent to clarify this aspect regarding the expected growing impact of UV radiation in the upper layer of the water column due its enhanced stratification by global warming [START_REF] Rost | Coccolithophores and the biological pump: responses to environmental changes[END_REF]. The influence of nutrient depletion on the synthesis of xanthophylls (Staehr et al., 2002) and the XC functioning (van de Poll et al., 2005) will also need a deeper investigation in order to assess potential differences in the photoprotective behaviour of phytoplankton in oligo/-meso-/eutrophic waters. For instance, Dd/Dt synthesis and NPQ have been reported to dramatically increase in iron depleted coastal diatoms [START_REF] Allen | Whole-cell response of the pennate diatom Phaeodactylum tricornutum to iron starvation[END_REF] while oceanic species have adapted to low iron concentrations by sacrificing their ability for NPQ response to irradiance changes (Strzepek and Harrisson, 2004;[START_REF] Lavaud | Photoprotection capacity differs among diatoms: possible consequences on the spatial distribution of diatoms related to fluctuations in the underwater light climate[END_REF]. In this framework, the Antarctic / Arctic habitats are of special interest to better understand the environmental driving forces of XC and NPQ [START_REF] Mangoni | Photoacclimation in Antarctic bottom ice algae: an experimental approach[END_REF][START_REF] Alderkamp | Can photoinhibition control phytoplankton abundance in deeply mixed water columns of the Southern Ocean ?[END_REF]. Indeed, they allow investigation of special light features (increased UV radiations and/or prolonged continuous light and dark periods) in combination with other strongly influencing environmental cues such as nutrients (van de Poll et al., 2005;van Leeuwe et al., 2005).

The role of temperature on the enzymatic regulation of XC has additionally been only scarcely explored. The synthesis and role of Dt in habitats where the cells never experience high light is obviously relevant, as for instance in the deep-chlorophyll maximum, where Dt has been reported [START_REF] Brunet | Picophytoplankton diversity and photophysiology in the Strait of Sicily (Mediterranean Sea) in summer. I. Mesoscale variations[END_REF][START_REF] Brunet | Vertical variability and diel dynamics of picophytoplankton in the Strait of Sicily (Mediterranean Sea) in summer[END_REF]. Such observations support the finding that not all Dt molecules are involved in NPQ-driven photoprotection [START_REF] Lavaud | General features of photoprotection by energy dissipation in planktonic diatoms (Bacillariophyceae)[END_REF][START_REF] Schumann | Investigations on the quenching efficiency of diatoxanthin in cells of Phaeodactylum tricornutum (Bacillariophyceae) with different pool sizes of xanthophylls cycle pigments[END_REF]Dimier et al. 2009a); some of them might play a role as antioxidants (Casotti et al., 2005;[START_REF] Lavaud | Fast regulation of photosynthesis in diatoms: Mechanisms, evolution and ecophysiology[END_REF]. The deployment of mesocosms under different environmental conditions (trophic status, light quantity and

  the Vx-cycle (Wilhelm

  diatoms compared to other microalgal groups would be an advantage

  diatoms within the sediment together with the changes in incident irradiance versus the tidal cycle/season/latitude

  , unpubl. results). Our previous non-molecular physiological investigations

  . R., Smith, R. C., Baker, K. S., Marra, J. (1987) Oceanic primary production estimates from measurements of spectral irradiance and pigment concentrations.

  ., Mazza, S.,Brunet, C., Vantrepotte, V., Ianora, A., Miralto A. (2005) Growth inhibition and toxicity of the diatom aldehyde 2-trans-4-trans decadienal on Thalassiosira weissflogii (Bacillariophyceae). J.Phycol., 41, 7-20. Chevalier, E. M., Gévaert, F., Créach, A. (2010) In situ photosynthetic activity and xanthophylls cycle development of undisturbed microphytobenthos in an intertidal mudflat. J.Exp. Mar. Biol. Ecol., 385, 44-49. . A., Henriksen, P., Markager, S. (2002) Photoacclimation of four marine phytoplankton species to irradi.ance and nutrient availability. Mar.Ecol. Prog. Ser., 238, 47-59. Strzepek, R. F., Harrison, P. J. (2004) Photosynthetic architecture differs in costal and oceanic diatoms. Nature, 431, 689-692. Timmermans, K. R., van der Wagt, B., Veldhuis, M. J. W., Maatman, A., De Baar, H. J. W. (2005) Physiological responses of three species of marine pico-phytoplankton to ammonium, phosphate, iron and light limitation. J. Sea Res., 53,109-120. van de Poll, W. H., van Leeuwe, M. A., Roggeveld, J., Buma A. G. J. (2005) Nutrient limitation and high irradiance reduce PAR and UV-induced viability loss in the Antarctic diatom Chaetoceros brevis (Bacillariophyceae). J. Phycol., 41, 840-850. van de Poll, W. H., Visser, R. J. W., Buma A. G. J. (2007) Acclimation to a dynamic irradiance regime changes excessive irradiance sensitivity of Emiliana huxleyi and Thalassiosira weissflogii. Limnol. Oceanogr., 52, 1430-1438. van de Poll, W. H., Buma, A. G. J. (2009) Does ultraviolet radiation affect the xanthophyll cycle in marine phytoplankton? Photochem Photobiol Sci., 8, 1295-1301. van de Poll, W. H., Buma, A. G. J., Visser, R. J. W., Janknegt, P. J., Villavañe, V. E., Helbling, E. W. (2010) Xanthophyll cycle activity and photosynthesis of Dunaliella tertiolecta (Chlorophyceae) and Thalassiosira weissflogii (Bacillariophyceae) during fluctuating solar radiation. Phycologia, 49, 249-259. van Leeuwe, M. A., van Sikkelerus, B., Gieskes, W. W. C., Stefels, J. (2005) Taxon specific differences in photoacclimation to fluctuating irradiance in an Antarctic diatom and a green flagellate. Limnol. Oceanogr., 288, 9-19. van Leeuwe, M. A., Brotas, V., Consalvey, M., Forster, R. M., Gillespie, D., Jesus, B., Roggeveld, J., Gieskes, W. W. C. (2008) Photoacclimation in microphytobenthos and the role of the xanthophyll cycle. Eur. J. Phycol., 43, 123-132. Wagner H., Jakob T., Wilhelm C. (2006) Balancing the energy flow from captured light to biomass under fluctuating light conditions.New Phytol., 169, 95-108. Welschmeyer, N. A., Hoepffner, N. (1986). Rapid xanthophyll cycling: an in situ tracer for mixing in the upper ocean. EOS (Trans. Am. Geophys. Union), 67: 969.

  ., Büchel, C, Fisahn, J.,Goss, R., Jakob, T., LaRoche, J., Lavaud, J., Lohr, M., Riebesell, U., Stehfest, K., Valentin, K., Kroth, P. G. (2006) The regulation of carbon and nutrient assimilation in diatoms is significantly different from green algae. Protist, 157, 91-124.Wilson, A., Ajlani, G., Verbavatz, J.M., Vass, I., Kerfeld, C.A.,Kirilovsky, D. (2006) A soluble carotenoid protein involved in phycobilisome-related energy dissipation in cyanobacteria. Plant Cell, 18, 992-1007.

http://mc.manuscriptcentral.com/jplankt Journal of Plankton Research

ACKNOWLEDGMENTS

The authors would like to thank Dr. W.H.C.F. Kooistra for critical reading of this manuscript. The two anonymous referees are kindly acknowledged for their remarks and criticisms on the previous version of the manuscript.

FUNDING C.B. work is supported by the Stazione Zoologica A. Dohrn. J.L. work has been supported by the National French Institute for Scientific Research-CNRS, the French consortium CPER-Littoral and the German Research Foundation-DFG (grant LA 2368/2-1).


Sylvie Lardon

Salma Loudiyi

Mariassunta Galli

Elisa Marraccini

Marie Houdart

Enrico Bonari

From territory agronomy to regional planning: agricultural management in periurban areas

Keywords: agriculture, periurban areas, territory, spatial modelling, durability, changes, action

HAL is

A seminar on agricultural management in periurban areas

The joint seminar initiative originates from the opportunity of a field case study work during the two Winter Schools in Landscape Agronomy in 2007 and 2009 [START_REF] Rapey | Experiences from a winter school on landscape agronomy: stakes, difficulties, perspectives[END_REF]Moonen et al., 2010 in this book of abstracts) and a seminar on the agricultural management of periurban areas that was held in 2009. Through the Pisa plain case study [START_REF] Rizzo | Agronomes et géoͲagronomie : « relecture » de trois études de cas en Toscane[END_REF], positive interactions between agroͲenvironmental and territorial issues, especially about urbanization controlling process in periurban areas, have appeared obvious. These also emerged during the field work of the second Winter School on the Massaciuccoli basin in Pisa1 as well as during the field visit of the seminar on periurban agriculture in MassaͲCarrara. Convergent research studies in France and Italy highlight needs to see agriculture as a resource for territorial development [START_REF] Galli | Brevi riflessioni sull'agricoltura periurbana. Dal progetto agroͲurbano al parco agricolo[END_REF][START_REF] Méasson | Construction des capacités de développement territorial dans les zonesͲcharnières. L'exemple de Volvic Sources et Volcans[END_REF]. Therefore, there is an interest in a thematic convergence between agronomy and regional planning when studying the issues of agriculture in periurban areas. About such issues, agronomists are involved because of their ability to design innovative systems for agricultural development in periurban areas, e.g. multiͲfunctionality, tracking agricultural products, taking into account the diversity of stakeholders operating in agriculture and territory management [START_REF] Galli | Agronomia territoriale e sviluppo dell'agricoltura periurbana[END_REF]. However, because of the important spatial, temporal and social dynamics, it is suitable to be involved by a territory approach. Following [START_REF] Deffontaines | Les sentiers d'un géoagronome[END_REF], geography and agronomy are taking part in theoretical and methodological basis of landscape agronomy 2 (Benoît et al., 2006;[START_REF] Lardon | De la géoͲagronomie à l'agronomie des territoires : un parcours, des étapesͲclés et des prolongements[END_REF][START_REF] Rizzo | Agronomes et géoͲagronomie : « relecture » de trois études de cas en Toscane[END_REF]. Social scientists, geographers along with architects and planners are also involved.

During the seminar on the management of agriculture in periurban areas, main questions were about periurban agricultural policies, actors, agricultural land use and related planning issues, and the sustainability of periurban agriculture. The seminar was based on French and Italian case studies. These latter comprised periurban parks as well as territories situated in fringe areas (at the interface of rural and urban areas). Different levels were included, from municipalities to large regions and also new territorial arrangements, as such the association of neighbouring municipalities. In all the study cases, agriculture was a resource and a catalyst to territorial development.

The seminar aimed therefore to benefit from existing research programs regarding the above mentioned issue and to compare French and Italian experiences. One perspective was to support local actors and territorial institutions through a partnership research. To do so, we wished to involve students in the construction of such new approaches and to teach them to tackle complex issues like agriculture and its management and governance in periurban areas.

Due to our interest in both agronomy and planning, we stress the importance to point out synergies to create a better vision of agriculture as resource for the sustainable development of the territory. One important topic can be developed: the synergies associated to the proximity between agricultural areas and urban areas.

Creation of synergies: from concepts to actions …

In this field, some synergies between research and action are created through the intermediation of education.

From a research point of view, that means to explore new issues and introduce new concepts. Which are the public policies supporting the development of periurban agriculture and encouraging food provision to cities and networks between producers and consumers? How are local actors organized? What kind of rationale do they develop to control land, set up greenbelts and secure local governance for agriculture? What are practical strategic steps to conduct in order to maintain greenbelts in periurban areas, to define zoning for residence or leisure, natural, agricultural and forestry areas? Does sustainability of periurban agriculture can be secured within a double bind of product storage and transportation, while landscape and water management still remain? How to answer to divergent stakes? These are questions asked during a seminar that showed how the relevance of a crossͲ disciplinary attitude increases the understanding of complex stakes. To take advantage of current experiences is a first need, to formalise underlying development models is a second one.

From an actionͲoriented perspective, there is a need of new tools for different actors to support them to define common actions for territorial development. Thus, both field works of the seminar and Winter Schools (on three periurban areas: MassaͲCarrara hillsides and plain of Pisa Ͳ Massaciuccoli Lake and San Giuliano Terme plain) have been informative. In the Plain of Pisa a relevant topic was the quality of water; on this topic many actors were involved: natural park, environmentalists, local authority bodies (at local and regional levels), reclamation bodies and farmers. Those last were of particular importance for crop diversification to contain pollution and form irrigation practices. In the Massa Carrara case study, the topic was the proximity of the Candia wine area and of other residual agricultural activities to the city; in this case the main actors for food issues were farmers, consumers, inhabitants, local authority bodies, valorisation consortia. In any case, new actors, new activities and actions have to be supported. But who carry out these transformations? Are there new skills to be developed to ensure a global insight and to ease crosslinkage? We believe that new forms of organisation can be invented in actionͲoriented research and especially in fieldwork situations. But, how to point it out, to make good use of failures and to institutionalize success conditions? Actors come first in these learning processes. But researchers also are actors in facilitating these changes by their observations and modelling and in providing neutral rooms for discussion between stakeholders, also by education that can play an important role in setting up synergies.

Hence education is a bridge between research and action. First, education steps in action as a driving force about development issues carried out by local actors. Second, education also intervenes in research issues because it keeps raising questions about concepts and methods used by researchers to facilitate collective learning and development of skills. Third, education allows testing skills' articulation and synergies to conceive, realise and assess collectively development projects. At last, education has to answer to actors' issues and to be ahead of current changes. So, it can help partners to interpret and formalise these changes. What makes this researchͲeducationͲaction device original is that education is in the centre of the actionͲresearch. So, we argue that through education a better articulation between research and action is possible, to a new management of agriculture. Periurban areas are relevant experimental fieldwork areas because of their dynamics and fast developing issues. Other areas may be considered as fieldworks, e.g. rural and nature conservation areas, however they do not present both the same dynamics and the same concentration of different stakeholders in a so close space.

In these periurban areas, the framework consists in combining ground involvement and reflexive analysis, through interventions in a short sequence, aiming to build a common vision of a territory with stakeholders and consequently a common view on territorial development. We then have a methodological itinerary for a territorial prospective and participative diagnosis that has been constructed progressively by involving actors' participation. Therefore there is an involvement of the stakeholders at all the different steps of the actionͲresearch, from the research question building to the interpretation of the results. This involvement opens perspectives to an integration of agronomy in the territories.

The integration of agronomy deals with the capacity of this latter to be integrated in planning processes. Local administrative bodies have also to recognise that agriculture supports multiple functions (productive, landscape and social functions) within territories. Both these issues are quiet evident in periurban areas. Indeed, agriculture land in periurban areas has often been handled by planning for urban needs, even in areas with strong agricultural stakes. Nowadays, it is clear that the quality of life within territories is sometimes based on agriculture. It is also clear that the quality of life in periurban areas is supported by the neighbour agricultural systems.

Methodological basis for a future educational programme

To answer to resulting stakes in periurban agricultural management, an educational program has to be set up. We assume that this educational program for agronomy has to combine at least four themes: a prospective and processes approach of the territories, an hybridising of local and global knowledge, a participatory experimentation, a multiͲstakeholders action planning. Applying these approaches may contribute to the acquisition of relevant competencies and offer good opportunities to enhance them on the field. This future educational programme may give many openings for students, as such in research centres, local administrative bodies, public or private consultancy organisations.

A prospective and processes approach of territories

Development models are broadened. How to induce and support innovative and creative development projects (Deffontaines and Prod'homme, 2001)? We have to combine nature and technology, history and future anticipation, art and science, in a respecting way of a «socioͲdiversity» that guarantees the adaptation capacities of territorial organisations. A regional translation of national prospective of periubanisation by the DATAR [START_REF] Vanier | Les Futurs périurbains de la France en Europe[END_REF] and new forms of rurality by INRA [START_REF] Mora | Les nouvelles ruralités en France à l'horizon[END_REF] have to be done.

Territorial prospective is a way to induce participation of actors in a collective project design. It implies that not only sectoral actors (farmers and agriculture professionals) take part in the process but also all actors that are concerned by planning. Therefore, territorial prospective results in scenarios which objectives are to encourage local actors to act together and to collectively anticipate changes. Thus, this approach brings along a shift that facilitate the mobilisation of local actors and it contributes to the construction of a shared vision of the future. Territorial prospective is related to three main principles: (i) time projection is made to better act in present times by taking into account past times, (ii) a symbolic dimension is at stake because it opens possible ways through creativity and imagination and (iii) it directs to action.

A local and global knowledge hybridizing

At the local level, one observes the application of sustainability norms defined at higher levels. The local application of sustainable development norms is always specific because of actors' stakes. Local devices help to construct new networks and new knowledge, institutions and norms. These constructions can be mobilized elsewhere by other actors at different scales (much more global than farm scales and urban development scale) and contribute to drawing public policies. Similarly, concrete ways by which actors are coordinated at local scales can impulse restructuring at global scales. Experiences can be effective at multiple organisation levels.

Our research is wilfully placed at the local level where actors «are making» sustainable development. It is interested in observed local applications. It integrates institutional plurality and enlargement of scales and temporalities within the territory, revealing pluralities and tensions. Territorial inscription of governance processes and agricultural transformations shows for example breaks and evolutions we are in concern with: activity withdrawal, creations, organisation level changes (farmers networks) and actions principles. Clarifying the interaction between local and global is important in order to make generic some local observations, to qualify actions led for sustainable development and to identify ways of combining actions led at different scales.

A participatory experimentation

Actors concerned by agriculture in periurban areas are plural. How to facilitate actors' participation and the integration of new actors in the local governance [START_REF] Lardon | De la géoͲagronomie à l'agronomie des territoires : un parcours, des étapesͲclés et des prolongements[END_REF]? It seems to be important to extend the farmers realm and assert agriculture as a resource for all kinds of actors living within periurban areas. Of course these governance processes are still uncertain, they have to be locally constructed and have to be adapted to local agricultural specificities.

Actors' participation to development projects is usually effective upstream from decision making processes. Spatial representations can be useful to make explicit territorial dynamics. Spatial representation is an opportunity to show transformations to be encouraged and a way to transform actors' representation of reality.

A multistakeholder action planning

Agricultural organisation levels in periurban areas are many. How to joint different territories and to build in projects in order to bring dynamics together [START_REF] Vanier | Les Futurs périurbains de la France en Europe[END_REF]? Individual practices have to be linked with public policies by building intermediate levels. Following this assertion, municipalities, interͲmunicipalities and other project levels have to be defined as the appropriate levels for actions and must not be ignored as partners. These could be levels upon which agriculture can underlie and become a development catalyst.

In periurban areas, actors' coordination is an important issue because bringing together different actors holding on different territory visions and contrasting rationales and interests. These are basis principles for an educational program to territorial development that we seek to promote [START_REF] Angeon | Accompagner le développement territorial par la formation. Quels dispositifs d'apprentissage collectif et quelles compétences mobiliser ? valorisation d'expériences de formation et d'action[END_REF]. It is related to territorial development design and technology methods and concepts because it takes into account both territorial organisation understanding and it accompanies territorial changes [START_REF] Lardon | L'ingénierie territoriale pour les espaces periͲurbains. Proposition d'une démarche[END_REF]. International coͲoperations between Italy and France are a first result. "Wandering" fieldworks, European PhD candidates network, partnership with territorial institutions are many of the following steps to be constructed in order to work for the assertion of agriculture in periurban areas.

Moonen et al.,

A winter school in landscape agronomy and the synergies it created (in this book of abstracts) 2 "Thus, landscape agronomy can be defined as the study of farming practices and technical systems which mobilise territorial resources and organise territories supporting multiple stakes, by analysing the twoͲway relationship between practices and landscapes (practices building landscape and practices determined by landscape)"[START_REF] Moonen | Satellite session Ͳ Education in Landscape and Territory Agronomy[END_REF]

th European IFSA Symposium, 4Ͳ7 July 2010, Vienna (Austria)


Canh Anne-Marie Danna

Tran Minh

Immobilization of biocatalysts on solid

HAL is


Emmanuel Fiani

Laurent Périer-Camby

Gérard Thomas

Gaseous hydrocarbon adsorption on a granulated activated carbon. Exothermic effects

come


Florence Poncet

Françoise Valdivieso

Raymonde Gibert

Michèle Pijolat

In situ infrared spectroscopic study of uranium oxides during UO3 carboreduction

à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.


Catherine Brun

Michèle Pijolat

Michel Soustelle

Françoise Valdivieso

The influence of hydration of uranium trioxide on its following reduction by hydrogen into uranium dioxide UO2

ou non, émanant des établissements d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.