Silvia Pireddu

FOR TOURISM

Keywords: eLearning 1, ESP 2, Tourism 3, Collaborative Strategic Reading 4, Academic English5

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

INTRODUCTION

The paper describes the integration of online collaborative reading in a course about tourism discourse at the University of Turin. Collaborative Strategic Reading (CSR) allowed networking and improved the understanding of the texts used during the course. CSR is a well-known practice that combines cooperative learning and reading comprehension strategies. In this context, it improved the management of specialised and academic texts that require advanced language competence and basic knowledge of the profession [START_REF] Klingner | Using collaborative strategic reading[END_REF]. Students accessed the course on Moodle, which provided all the course material, e.g. readings, selfassessment grids, tests and recorded lectures. Moreover, the Amanote software was used as an integrated Moodle tool to support pre-reading, brainstorming activities and the reading of texts themselves (Hiver, Al-Hoorie, Mercer, 2020). Students were divided into small groups (max. five students) in parallel Webex sessions. They read part of an academic paper describing tourism-related genres or a sample of a professional text and used Amanote to share annotations, ideas and comments within the group and with the rest of the class (fig 1). As a post-reading activity, students were also asked to fill in a grid of analysis that will be illustrated in the following paragraphs to show typical behaviours. The integration of the three tools created a learning environment built online but is currently accessible to all the students enrolled as a MOOC inspired course for revision and self-study (Gao et alii, 2013). We discuss the pros and cons of this practice having evaluated students' responses, comments, and notes. We believe that the concept of sharing is a motivating element in developing professional English. In particular, collaborative tasks lower anxiety that hinder students participation and performance. Amanote proved especially useful in managing the collaborative reading activities [START_REF] Yu-Jie | A study of ESP teaching In the era of MOOCs[END_REF][START_REF] Stognieva | Exploring ESP Learners' Motivation: the Case of MOOC Integration into the University Curriculum[END_REF].

2

TEACHING TOURISM AS ESP: STUDENT'S NEEDS

The teaching of English for Specific Purposes (ESP) requires targeting students' level and, consequently, setting their goals to effectively select the course materials (Huyon, 2018, pp. 112-129). Ideally, students should be at least B2 speakers with knowledge of the professional field sufficient enough to have a general understanding of the job and its communicative needs. In fact, students may have rather diverse levels of language and professional competence, especially in large courses, yet acknowledging diversity may stimulate student's collaboration rather than being an obstacle. In other words, diversity can be turned into a stimulus to overcome emotional issues and establish confidence. Therefore students may be more likely to accept a challenging syllabus. In practice, discussing with students their background knowledge may create a more relaxed atmosphere where students feel free to ask for support and share. Collaborative activities can play a role in building confidence. CSR aims at promoting mutual engagement through the cooperative reading of a complex text with or without teacher management. Students act roles and are responsible for construing one single aspect of text understanding. They focus on one task at a time and share their interpretation. In this way, they feel supported by peers and are not overwhelmed by the complexity of the whole text (Mulligan, Garafolo, 2011). A complex text presents lexical obstacles, complex grammatical and textual organisation and needs metalinguistic competence to be understood. Students are asked to work out the content and bypass textual elements that may impair understanding depending on their level of fluency. Lexical density, morpho-syntactical complexity, implied knowledge, and length are obstacles that need to find appropriate strategies to avoid drop-outs. In this perspective, collaborative reading activities can help both in cognitive and linguistic terms to face the difficulty of professional readings. In general, an ESP course may address vocabulary and terminology or may focus on broad communicative skills. Alternatively, it may focus on understanding professional genres and using linguistics to make sense of professional discourse. In the case of tourism, both perspectives are crucial given its multidimensional nature. Tourism communication draws from diverse settings, discourse communities and hence different genresoften hybrid genres. Tourism genres range from written legal/corporate documents, professional meetings, video-phone conversations, websites, and press releases along with tourist guides, brochures, emails, advertising texts, (e-)tickets, (phone/zoom/skype/webex) conversations, blogs, promotional videos, and reviews [START_REF] Maci | English tourism discourse: Insights into the professional, promotional and digital language of tourism[END_REF]. The richness of tourism discourse needs a vast set of competencies and compels teachers to balance authenticity and readability. As a matter of fact, authenticity is necessary for Tourism teaching as it prepares students to deal with a global, varied and unmediated language. They must be acquainted with the complexities of pragmatics, intercultural communication and discourse, i.e. they have to learn both the language for tourism and the language of tourism (Hunyon, 2018, p. 157;[START_REF] Ennis | Teaching English for tourism: Bridging research and praxis[END_REF]. Therefore, readings should be selected with a more holistic vision of tourism. Rather than starting from terminology, course planning should work on genres' overall structure and then develop a more analytical in-depth understanding of individual texts and vocabulary in context. Language for specific purposes can be engaging if focused on the analysis of professional genres in relation to a professional community, as aspects of pragmatics and genre conventions can be transferred and reused in other contexts and taken in as individual skills. In other words, students need to see that by learning specialised language and studying (tourism) genres, they are acquiring abilities such as reading that will impact them as this is deeply motivating (Kelly, 2020).

CASE STUDY

In the context here analysed, students learned tourism language as ESP via two channels: the socalled lettorato (80 hours language classes) and a course in linguistics (60 hours). The lettorato developed B2 grammar knowledge with a focus on specialised vocabulary. The linguistics course required students to grasp the basics of genre analysis and tourism discourse. Students were in their second year (BA) and built on previous knowledge of linguistics to understand the structural mechanisms of (multimodal) texts (fig 2). The first part of the course was delivered in the form of traditional lectures. Students were taught how to recognise lexical and grammatical cohesion; identify theme and rheme; understand specialised discourse, identify specimens of meta-discourse, author visibility, and moves. Six hours were spent on specific ESP features relevant in tourism discourse, i.e. popularisation, Legal English and multimodality. The second part of the course focused on academic articles that described tourism communication.

Here CSR was applied to develop a more independent understanding of the content and overcome academic writing complexities. The articles were selected on the basis of both content and conciseness, while topics ranged from EU tourism normative guidelines, press releases, destination branding, promotional websites to multimodality, e.g. travel videos, and tourism blog writing. The third part of the course examined authentic texts to apply the notions learned in the first two sections. The texts provided an additional set of examples that could be described and analysed by students independently. For example, a vacation home rental contract provided instances of legal English, the British Airways media centre provided examples of press releases, institutional sites like Mooc2Move Conference on "MOOCs, Language learning and Mobility: design, integration, reuse" 9 -10 April 2021 4 Visit Bratislava and Visit Tuscany were used to retrieve itineraries, the Lonely Planet Guide to Rome was examined as an example of a tourist guide. A set of promotional videos were used to discuss sustainability and green tourism. Finally, a vlog allowed students to propose their views about postpandemic tourism. In other words, during each segment of the course, similar genres were seen from a different perspective: legal language was presented in its general characteristics, then a paper about EU normative guidelines was read within a CSR lesson to pick up examples of complex syntax, archaic language, jargon etc., then the same type of language was observed in the rental contract as the object of class discussion. In other cases, the basics of visual analysis were introduced in the frame of multimodal analysis and then observed in a paper analysing promotional videos. Students were then asked to write their observations about a given example of a travel video. Adding layers of knowledge allowed students with low competence or familiarity with tourism language to revise and learn by building gradual expertise while stimulating students more confident with professional English to improve and expand their knowledge, either in the direction of the applied linguistic analysis or in the direction of discourse understanding. Students with specific knowledge (e.g. semiotics or photography, or video making) could also actively contribute to general understanding.

CSR IN PRACTICE: INTEGRATING MOODLE TOOLS

The integration of CSR developed collaboration in the e-learning environment and helped overcome the sense of isolation that is regarded as one of the challenging aspects of e-interaction. CSR was designed to teach students how to avoid lexical obstacles and understand ESP features such as encapsulation of meaning in long noun phrases or complex syntax. The background knowledge provided by the first part of the course enabled students to spot the problems and retrieve the functional tools to understand both the article content and the academic language. Moreover, CSR improved meta-cognitive and self-monitoring skills that are especially relevant to implement fluency among intermediate students and stimulate more focused language learning in advanced students too. In our context, C1 students level were stimulated by the complexity of the texts, while B1 and B2 students found it hard to work within and around these texts but became conscious of their need to improve vocabulary and enhance reading to get used to authentic materials and 'real English'. The activity comprising CSR was organised as follows: at first, the instructor enhanced a brainstorming and prediction moment (collecting ideas and making predictions about the content). Then the instructor provided basic scaffolding (pre-knowledge of specialised vocabulary) and a general overview of the parts of the text (focus on the title, paragraphs). Students were then asked to recognise the genre and the topic they were reading about by resorting to previous knowledge. At that point, they were divided into small collaborative sessions and became involved in cooperative learning. In each group, roles were assigned but with no obligation so that each could feel free to collaborate spontaneously and choose a role according to their preferencessomething that appeared more appropriate with adult students. A student took the role of the reader. Some got the gist of the paragraph, while others monitored lexical obstacles and suggested fixup strategies by retrieving meaning from the context, observing word structure or suggesting bypassing the obstacle according to its relevance in the overall context.

1 Students then summarised the main idea of each paragraph. It was essential to identify keywords in each paragraph so that understanding was worked out gradually, layer after layer. At the end of each session, the instructor ensured that students had recognised the essential ideas discussed in the text and/or identified their various components. Moreover, genre description, function, and the relationship between the addresser and addressee were also investigated. Texts were annotated with Amanote by every group member and shared in the software virtual workspace (fig. 3).

Figure 3 Amanote page with students annotations.

Annotation and highlighting of the original text can be done on paper, of course, but with Amanote, students worked quickly during the session and ended up sharing and visualising what they had done. This visual representation of the reading process provided a form of text analysis that all the group members could easily understand and facilitated discussion. Furthermore, it provided more handy management of the text for revision and self-study. Finally, there followed the wrap-up stage, which was meant to stimulate self-monitoring and a better understanding of the whole process (What have I learnt? What do I need to expand on? What obstacles did I face? How could I improve?). Students were allowed to revise their work. Ideas were collected in a 'traditional' chart that every student had to fill in and then submit on Moodle. The aim was to allow each student to focus on his/her own understanding and enhance self-evaluation. One of the aspects that were fore-fronted to the class was the importance of developing a methodology to read and understand textual complexity, whatever the context and channel. Moreover, they could list new vocabulary and tourism terminology in a specific section of the chart. The chart ensured that even non-attending students had the chance to survey the methodology offline. In this way, both group work and individual work could be subsequently discussed with the instructor to monitor and control course outcomes 2 . The examples below are taken from students charts that were filled in after reading an Academic paper about Legal English and Tourism. One of the problems with teaching tourism discourse is the hybridity of genres and embedded lexicon from other domains, especially Business English, Media language, Advertising and Legal English. Therefore the text presented a double layer of complexity, being a specimen of Academic English discussing legal English in EU directives. The results prove that students responded well even when the chart received the very basic filling. The collective work allowed students with low competence to participate and get the ideas to fill in the chart, highlighting issues in personal understanding or weaknesses in the reading process itself [START_REF] Vaughn | Collaborative strategic Reading: Findings from Experienced Implementers[END_REF][START_REF] Zoghi | Looking into ELF reading comprehension[END_REF]  Complex syntax.

What I think I will learn:  Normative guidelines given by European Union to avoid ambiguity and vagueness.  Legal English applied to tourism. In fig. 5 instead, one can observe how the first and second students identified general problems and solved them with three different strategies (contextualisation, dictionary and review of previous knowledge), although they provided only a general response. In contrast, the third student identified lexical obstacles and clunks common in the text and highlighted the complexity of Academic writing. The obstacles were then solved without using a dictionary but with the application of syntactic analysis.

In fig. 6, there are examples of how students filled in the wrap-up stage (metadiscourse). In all cases, the charts show that students become aware of their reading method. Moreover, students suggested rewritings and edited versions of paragraphs, others commenting on the necessity of clarity, transparency in communication, others showing their interest in plain style and clarity in professional contexts.

In general, the observation of student's charts and their feedback indicate the effectiveness of the integrated approach and collaborative work that overcome the passive listening-only method provided either by the traditional lecture or the passive listening/ viewing of a video/slides presentation with voiceover.

Quite obviously, some students provided inadequate responses. However, the overall engagement was positive.

Mooc2Move Conference on "MOOCs, Language learning and Mobility: design, integration, reuse" / 1) I had difficult in understanding the sentence "On the other hand, legal language has been extensively analysed, with particular regard to the analysis of metatextual markers, of questioning and from both a forensic perspective as well an ethnographic viewpoint."

2) "The Euro -lex search -engine" / 3.1. The clunk is the sentence " (…) against the interests of the party responsible for drafting the guidelines.

/ 1) I solved the clunk by searching difficult words on vocabulary and reconstructing the sentence in context.

2) I searched the expression on the dictionary. / 3.1. I solved the clunk by breaking down the sentence in small parts to improve its understanding.

Mooc2Move Conference on "MOOCs, Language learning and Mobility: design, integration, reuse" 9 -10 April 2021 8 By reading this document, I learned that: 1. Some genres of tourism writing are easily recognizable as specialized discourse; it is characterized by complex sentences, modality, technical terminology, ancient crystallized legal forms whose purpose is to convey an impression of semantic objectivity and legal impartiality. The generic conventions deriving from legal discourse convey a more ruled image of the tourist community. 2. The important role of tourism has been recognized since the early 1980s. 3. The EU provides guidelines meant to be "locally-translated" by each member state. 4. Legal texts express regulation creating, modifying or terminating the rights of and obligations towards individuals and institutions. 5. A text so schematically organized, and apparently easier to understand from a semantic viewpoint, is actually denser and more cognitively demanding because of the frequent use of nominalized forms in pre-modifying position. 6. The legal register is called "legalese".

Questions about the important ideas in the passage (to clarify/ understand more in depth):

Vocabulary

New Vocabulary:

By analyzing the text, I learned new general technical vocabulary and the meaning of the term "legalese".

Tourism terminology:

I was not able to extrapolate vocabulary related to tourism that I did not know before reading; I have found more technical vocabulary related to the language, and less about tourism.

My notes and observation (was it difficult? Why? How could I improve my reading strategy?):

As this is the first time I analyze a text in this way, I have found it a little difficult, especially for the fact that I am not used to reading complex English texts. I could improve my reading skills by keeping the focus all on the sentences I am reading at each moment. As you can read above, in some passages I did not find any clunks, because the sentences could all be understood by reading them more times.

CHALLENGES

Numerosity represented one of the main obstacles. In my case study, more than 270 students enrolled, but only about 85 attended regularly. The reason is that many students work full or part-time, some in tourism, and despite the pandemic, they continued to do so. In some cases, there may have been an overlapping of other academic activities. In both cases, the availability of recorded lessons made the course available to non-attendant students, yet only very motivated ones took part in the interactive sessions. The heterogeneity of the language level was another issue. Scaffolding, foregrounding of themes, comments to text segments or direct reading by the lecturer were proposed as preparatory activities. Explanations were provided as feedback and discussed as a wrap up of the activity. However, despite the lesson's pre and post framing, it was clear that some of the students with low linguistic competence were somewhat reluctant to take an active part in the course. Finally, there were problems linked to the online dimension, such as an inadequate setting/ connection reported as a reason for not attending the collaborative sessions. Networking among students is undoubtedly one of the main problems and overcoming isolation needs lots of support. Tutors organised meetings and informal study sessions that were positively undertaken by a few, but for the most part, informal activities faced the overload of screen work and were perceived as demanding. In general, the texts' complexity required a 'strong' presence of the teacher to either prepare the activity or provide adequate explanation and feedback. Students needed to be guided and trained to select the most relevant points in terms of content and text structure. Identifying keywords, recognising the paragraph as a unit of meaning and identifying moves as textual strategies prepared the ground for CSR with (positive) effort.

CONCLUSION

Karabuga and Kaya note that students face reading problems in a foreign language because of a lack of reading methods and a lack of awareness and independence [START_REF] Karabuga | Collaborative Strategic Reading Practice with Adult EFL Learners: A Collaborative and Reflective Approach to Reading[END_REF]. As they rely on the teacher as in traditional lecturing, they are passive, which contradicts a core need of ESP teaching, i.e., being tailored to adults/ professional learning needs and participation. In the case study examined, reading sessions stimulated comments, questions and encouraged a shared understanding of the texts. Students were asked to extract keywords, terminology, and concepts into the discussions of other readings for the course, thus building a net of ideas around the various genres analysed in the tourism discourse frame. Reformulation of what was displayed in the academic readings also enabled students to develop their own authentic texts analysis. In this way, the course changed from being a mere knowledge provider to a collaborative learning environment. In general, the distance learning setting slowed down the rhythm and allowed students to focus more on reading than in a classroom organised for traditional lecturing. The Webex setting, far from being an obstacle, favoured cooperative work bypassing noise, static room facilities, and overall distractions that would hinder collaboration in a typical class. Amanote enabled a substantial sharing of information, allowing file annotation and note-taking, which, in practice, entailed a visualisation of text structure and the partition of the text in its components. Therefore we advocate for the integration of multiple tools to create an engaging learning environment. Finally, the structure of the course was based on a gradual development of genre awareness. Discourse rather than vocabulary was the focus, and institutional communication and web dynamics became the object of investigation by using academic readings, direct experience, and the analysis of authentic materials. Text linguistics was the starting point to construe complex forms of textuality. Academic readings provided models and the tools to understand tourism discourse. Collaborative practices were used to allow students to share their difficulties in understanding authentic professional texts and then retrieve textual, linguistics and contextual information to overcome them. Students were stimulated to search for more examples as a learning community, especially in blogs, vlogs, and multimedia items as a follow-up of their class activity. The use of technology in University (in-class, hybrid and blended courses) will only increase, and this should be seen as an opportunity to activate students, develop their expertise and skills (Gani et al. ii, 2016;[START_REF] Mcloughlin | E-Learning[END_REF]Sancassani et alii., 2019;[START_REF] Sallam | Research trends in language MOOC studies: a systematic review of the published literature (2012-2018)[END_REF]. Learning to read analytically and retrieve selected information should be integrated with language learning to develop a critical understanding of communication per se (Bruce, 2019: chap. 8). From this point of view, CSR proves to be an excellent strategy to combine soft skills and instruction. For this reason, the teaching of Tourism English and the understanding of Tourism Discourse should integrate and not offered as a separate option, as students need to get used to a multidimensional, multimodal communicative environment. Traditional classroom teaching is teacher-based and somewhat 'autocratic': a more participatory style where learners play an active role can be but motivating and can be seen as a form of professional training via language awareness.

Figure 1

 1 Figure 1 Integration of teaching tools to optimise the learning environment.

Figure 2

 2 Figure 2 Second Year English Language Course.

  one can observe three examples of the pre-reading stage where students focused on their previous knowledge showing existing awareness and predicting the text's content retrieved by the instructor's feed and the overall observation of the text. know about the topic: nothing What I think I will learn: I think I will learn something more about concepts and aspects of legal language of tourism. BEFORE READING Preview What I already know about the topic: I know Tourism is a specialized discourse but I don't know its relationship with Legal English What I think I will learn: -How to write properly in tourism discourse -Hoe to recognize legal formulae in tourism texts BEFORE READING Preview What I already know about the topic:  Specialized language.

Figure 4 .

 4 Figure 4. Samples of students' charts CSR stage 1.

Figure 5

 5 Figure 5 Samples of students' charts CSR stage 2.

Mooc2MoveFigure 6

 6 Figure 6 Samples of students' charts CSR stage 3.

We base comprehension on the understanding of syntax. Pre and post modifications may be non-essential at a first skimming but can be investigated at second reading.

It should be noted that the get the gist moment and the final wrap up were also used to check the overall understanding by a direct discussion with the students and by the use of a Moodle forum that allowed them to interact after the end of the course.


Jessica Kojadinovic
email: jessica.kojadinovic@univ-nantes.fr

Matthieu Le Corre

Richard P Cosson

Paco Bustamante

Trace elements in three marine birds breeding on Reunion Island (Western Indian Ocean) Part 1 : Factors influencing their bioaccumulation

Keywords: Metals, Tissue distribution, Feathers, Tropical seabirds, Contamination

This work aims to use seabirds as bioindicators of trace element levels in the tropical waters and food webs of the Western Indian ocean. The accumulation patterns of selected toxic (Cd and Hg) and essential (Cu, Fe, Mn, Se and Zn) elements were determined in liver, kidney and pectoral muscles of three species of 162 marine birds collected in Reunion Island between 2002 and 2004. These pelagic seabirds belong to the following species : Barau's Petrel (Pterodroma baraui), Audubon's Shearwater (Puffinus lherminieri bailloni) and the White-tailed Tropicbird (Phaethon lepturus). Mercury levels were also measured in breast feathers. Highest mean kidney Cd and liver Hg levels (respectively 27.79 ± 13.78 µg.g -1 d.w. and 24.31 ± 14.13 µg.g -1 d.w.) were found in the squid-eating Barau's Petrel. Barau's Petrel feather Hg levels fell in the 0.6-2.7 µg.g -1 d.w. range previously reported for other petrels and shearwaters. The values of the other elements were also in the same range as those previously reported in the published literature concerning related seabirds, although Se and Zn burdens in the Reunion birds were amongs the highest values. Levels of Zn, Fe and, to a lesser extent, Cu appeared to be regulated in seabird tissues. Uptake and pathways of metabolism and storage seemed to be similar for the five essential elements. The reproductive status of the bird did not seem to affect elemental levels which, moreover, were not significantly different between males and females. However, trace elements in sampled birds varied according to the tissue considered, the age of the animal and its species. The diet was seemingly a major influencing factor. The health status also appeared to have an impact on elemental levels.

Introduction

Contaminants such as metals and metalloids reach oceans through natural erosion, geochemical cycles and human activity. Once in the marine environment, they can enter the food web where bioaccumulation and/or biomagnification can occur. Top-predators such as marine birds, are particularly exposed to high levels of these trace elements through their food [START_REF] Bearhop | Bioamplification of mercury in Great Skua and Catharacta Skua chicks: the influence of trophic status as determined by stable isotope signatures of blood and feathers[END_REF]. Because of their trophic position and bioaccumulation capacities, seabirds are often used as bioindicators of elemental levels in the marine environment [START_REF] Walsh | The use of seabirds as monitors of heavy metals in the marine environment[END_REF][START_REF] Furness | Birds as Monitors of Environmental Changes[END_REF][START_REF] Monteiro | Seabirds as monitors of mercury in the marine environment[END_REF][START_REF] Gray | Biomagnification in marine systems: the perspective of an ecologist[END_REF].

In spite of the great variety and number of seabirds present in the southern hemisphere, most studies have been carried out on species inhabiting the northern hemisphere. The few studies conducted on trace elements in the southern hemisphere focused on temperate and subantartic species, i.e. from Chile [START_REF] Ochoa-Acuna | Mercury in feathers from chilean birds: influence of location, feeding strategy, and taxonomic effiliation[END_REF], New Zealand [START_REF] Fiona | Influence of phylogeny, diet, moult schedule and sex on heavy metal concentrations in New Zealand Procellariiformes[END_REF], Gough island [START_REF] Muirhead | Heavy metal concentrations in the tissues of seabirds from Gough Island, South Atlantic Ocean[END_REF], the Kerguelen islands [START_REF] Bocher | Influence of the diet on the bioaccumulation of heavy metals in zooplankton-eating petrels at Kerguelen archipelago, Southern Indian Ocean[END_REF]) and the Antarctic Ocean [START_REF] Szefer | Concentration of selected metals in penguins and other representative fauna of the antartic[END_REF][START_REF] Ancora | Assumption and elimination of trace elements in adélie penguins from antartica: a preliminary study[END_REF][START_REF] Gonzalez-Solis | Metals and selenium as bioindicators of geographic and trophic segregation in Giant Petrels Macronectes spp[END_REF]. The tropical zone of the Indian Ocean has, up to the present day, received very little attention from researchers in reference to biocenosis trace element contamination. Overall, tropical waters are less monitored than marine environments from temperate and polar regions, more particularly southern tropical oceans which are often considered as less polluted than the northern ones [START_REF] Fiona | Influence of phylogeny, diet, moult schedule and sex on heavy metal concentrations in New Zealand Procellariiformes[END_REF]. However, the study of unpolluted sites can be of great interest, allowing an estimation of the "background" levels of contaminants to be made and can thus be used as a reference in space and time.

Through the study of trace element levels in marine birds from Reunion Island, this paper presents novel data on elemental contamination in seabirds of the western part of the tropical Indian Ocean. This work focuses on three seabird species chosen for their contrasting dietary ecology. Barau's Petrel (Pterodroma baraui) is a pelagic bird which feeds almost exclusively on cephalopods. Aububon's Shearwater (Puffinus lherminieri bailloni) which forages closer to the coast feeds as much on cephalopods as it does on fish. Finally, the White-tailed Tropicbird (Phaethon lepturus) also forages over oceanic waters but at intermediate distances from the island compared to the other two species, and is less specialized on squid than Barau's Petrel.

In the organism, elements are transported in the blood, deposited in various tissues and excreted or stored. Understanding the global patterns of accumulation and excretion is useful in evaluating the sources of contamination and the potential risks to an individual species. In the first part of this article, we examine the levels of two non-essential elements (cadmium and mercury) and five essential elements (copper, iron, manganese, selenium and zinc) in liver, kidney and muscle, as well as mercury levels in feathers. We also studied the factors influencing the elemental burdens and the correlations among these trace elements' levels.

Materials and methods

Study site and species

The seabirds used in this study originated from colonies on Reunion Island (21 • 7'S, 55 • 33'E), a French territory (2 512 km 2 ) located 700 km east of Madagascar in the Western Indian Ocean.

Barau's Petrel, described for the first time in 1963 [START_REF] Jouanin | Un pétrel nouveau de La Réunion Bulweria baraui[END_REF], is endemic to Reunion Island, where its population is estimated at 4 000 to 6 500 pairs (Le Corre et al. 2001b). This pelagic bird is present on the island from September (courtship and mating) to April (fledglings' first flight) [START_REF] Bretagnolle | Status of Barau's Petrel Pterodroma baraui: colony sites, breeding population and taxonomic affinities[END_REF]. The eggs are laid in November. During its reproduction season, Barau's Petrel scatters to feed in the tropical and sub-tropical waters as far as several hundred kilometers south of Reunion Island. Its diet consists of 98% cephalopods (Stenoteuthis oualaniensis and Taonius sp., given as percentage of the total number of prey items) and 2% fish (Gigan & Lebon, pers. comm.). From March to September, Barau's Petrel leaves Reunion waters and migrates towards the north and the east of the Indian Ocean (Barré et al. 1996, Stahl and[START_REF] Stahl | Distribution, abundance and aspects of the pelagic ecology of Barau's Petrel (Pterodroma baraui) in the south-west Indian Ocean[END_REF].

Aububon's Shearwater (Puffinus lherminieri) is a pantropical seabird but the subspecies P. l. bailloni is found only on the islands of Reunion and Europa (22 • 20'S and 40 • 21'E, 1 650 km from Reunion island) [START_REF] Barré | Oiseaux de la Réunion[END_REF][START_REF] Corre | Taxonomic affinities of Audubon's shearwater from Europa Island[END_REF]. Three thousand to 5 000 pairs breed in 235 colonies located in the interior of Reunion Island at altitudes ranging from 50 to 1 500 m as well as on the coastal cliffs [START_REF] Bretagnolle | Status of Barau's Petrel Pterodroma baraui: colony sites, breeding population and taxonomic affinities[END_REF]. This species breeds all year round with a peak of laying between August and November. During the breeding season, Aububon's shearwater does not seem to forage further than 50 km from the coast [START_REF] Bailey | The pelagic distribution of seabirds in the Western Indian Ocean[END_REF][START_REF] Jaquemet | Seabird community structure in a coastal tropical environment: importance of natural factors and fish aggregating devices (FADs)[END_REF]). During that time, its diet consists of 50% Stenoteuthis oualaniensis and 50% fish (Gigan & Lebon, pers. comm.).

Two thousand to 5 000 pairs of White-tailed Tropicbirds breed in ravines or on coastal cliffs of Reunion Island. They do not form true colonies (Le Corre, unpublished data). This indigenous species breeds on the island all year long. During this period its diet consists of 80% Stenoteuthis oualaniensis and 20% fish, mainly of the Mollidae and Dactylopteridae families (Gigan & Lebon, pers. comm.).

Outside their breeding period individuals scatter in the tropical waters of the Indian Ocean [START_REF] Barré | Oiseaux de la Réunion[END_REF]. During that time, dietary habits of the three species remain unknown.

Bird sampling

Fifty two Barau's Petrels, 61 Audubon's Shearwaters and 49 White-tailed Tropicbirds were sampled. All birds in this study died accidentally. Petrels and shearwaters are known to be attracted by urban lights. This is particularly common in Reunion (Le Corre et al. 2001b). Of the hundreds of fledgling Petrels and Shearwaters found stranded annually, 90% are rescued successfully (Le Corre et al. 2001b). The remaining 10% are usually found dead or fatally injured. The adult Procellariiformes died of various causes including light attraction, collisions and poaching. Poaching was also one of the main causes of the death of the White-tailed Tropicbirds. Since these birds were found before or shortly after their death, we are confident that the conditions in which the birds died had no effect on the elemental levels in their tissues.

Each bird was measured, weighed and aged. Two age classes were determined (juvenile or adult) using characteristic features of the beak and the feathers. For adults, the presence of an incubation patch was an indicator of the reproductive status of the individual. Since these birds do not show any sexual dimorphism, their sex was determined during dissection. Only adults were sexed. Gonads were not developed enough in fledglings to differentiate males from females. The liver, kidneys and pectoral muscles were removed and refrozen for freeze drying. Breast feathers were also sampled on each bird. Emaciation was estimated by evaluating the muscular condition (MC) which was given a range from 1 to 3 in relation to the shape of the pectoral muscles : 1, well developed pectoral muscles ; 2, slight pectoral muscle atrophy ; 3, severe pectoral muscle atrophy [START_REF] Bolton | An improved technique for estimating pectoral muscle protein condition from body measurements of live gulls[END_REF]. Body condition (BC) was also evaluated using a condition index proposed by [START_REF] Wenzel | The suitability of oiled Guillemots (Uria aalge) as monitoring organisms for geographical comparisons of trace element contaminants[END_REF]. This condition index is the ratio of liver to kidney masses. It is significantly negatively correlated to the degree of emaciation of the bird : the smaller the index, the more emaciated is the bird (Debacker et al. 2001a).

Sample preparation

Livers, kidneys and muscles were blended, dried and ground to a fine powder. Muscles were dried in an oven at 55 • C to constant mass for 72 h, whereas liver and kidney samples were lyophilized. The moisture content was 66 to 72% in liver, 73 to 78% in kidney and 65 to 71% in muscle.

The analysis of cadmium (Cd), copper (Cu), iron (Fe), manganese (Mn), selenium (Se) and zinc (Zn) calls for an extra step in the preparation protocol. Two aliquots of 50 to 400 mg of each sample were digested with 3.5 ml of 15 N nitric acid at 60 • C for 48 h before being diluted in 10 ml of deionized water. Accuracy and reproducibility of the preparation were tested by preparing 28 replicates of lobster hepatopancreas (TORT-2), dogfish liver (DOLT-2) and dogfish muscle (DORM-2) reference standards (National Research Council, Canada) and 11 blanks along with each set of samples. Glass and plastic utensils were washed with detergent, plunged in a bath of mixed nitric acid (35 ml.l -1 ) and hydrochloric acid (50 ml.l -1 ) for a minimum of 24 h, rinsed 3 times in deionized (Milli-Q quality) water and dried in an oven at 50 • C before use.

Pectoral feathers were washed vigorously in triple baths of 0.25 N sodium hydroxide solution alternated with triple baths of deionized water in order to remove adherent external contamination and airborne contamination [START_REF] Walsh | The use of seabirds as monitors of heavy metals in the marine environment[END_REF][START_REF] Burger | Diving depths of shearwaters[END_REF]) which could alter the results of the analysis of Hg sequestered in the feathers. Feathers were then dried in an oven for 24 h at 50 • C and analyzed for Hg content.

Metal analysis

Cadmium, Cu, Fe, Mn, Se and Zn were analyzed by Inductively Coupled Plasma Atomic Emission Spectrometry (ICP-AES Varian Vista Pro CCD). Total Hg analyzes were carried out with an Advanced Mercury Analyzer (ALTEC AMA 254) on aliquots ranging from 5 to 20 mg of dried sample weighed to the nearest 0.01 mg.

Detection limits and recovery rates were respectively equal to 0.322 µg.g -1 and 98% for Cd, 0.32 µg.g -1 and 94% for Cu, 0.64 µg.g -1 and 89% for Fe, 0.0025 µg.g -1 and 94% for Hg, 0.32 µg.g -1 and 90% for Mn, 6.45 µg.g -1 and 85% for Se and 1.29 µg.g -1 and 101% for Zn. Element levels are expressed in µg.g -1 of dry weight (d.w.).

Statistical analysis

Statistical analyzes were performed using the GNU R statistical system (R Development Core Team 2005). All statistical samples submitted to tests were first checked for normality by means of Shapiro-Wilk tests. In the case of non-departure from normality, parametric tests were used in the subsequent analyzes, otherwise, non-parametric analogues were used.

The validity of the replicates of the level measures was tested by means of t-tests for paired samples. The significance of differences of trace element levels among tissues was tested by one way repeated measures analysis of variance (ANOVA) or Friedman tests and followed by Tukey's HSD (Honest Significant Difference) tests. The influence of species, age, sex, MC and reproductive status on elemental levels was tested by means of ANOVA or Kruskal-Wallis tests followed, when necessary, by Tukey's HSD tests. Prior to the use of ANOVA for independent samples, besides normality, the homogeneity of the variances of the tested samples was checked by means of Bartlett tests. In case of departure from normality or non-homogeneity of the variances, Kruskal-Wallis tests were applied instead.

For each species, associations among elemental levels in different tissues were studied by means of Pearson's linear correlation coefficient. The resulting correlation matrices were represented by dendrograms built using the average linkage as aggregation criterion.

Levels of significance of the null hypotheses associated with these tests will be divided into classes of p-values represented by the following codes : NS ≥ 0.05 ; * < 0.05 ; * * < 0.01 ; * * * < 0.001. SD will stand for standard deviation and CV for coefficient of variation.

Results

Levels of Cd, Cu, Fe, Hg, Mn, Se and Zn in liver, muscle, kidney and Hg in feathers of each species/age subgroup are presented in Table 1 and their dispersion illustrated in Figures 1, 2 and3.

With the exception of Cu which presented particularly high coefficient of variation (CV) values in Barau's Petrel liver (115%) and the White-tailed Tropicbird kidneys (up to 117%), essential elements showed little variability in seabird tissues. In contrast, Cd and Hg levels showed high variability in all three species. For Cd, CV values ranged from 38% to 134%. For Hg, the highest fluctuations were found in the soft tissues of the juvenile White-tailed Tropicbirds (196%), and the lowest in their feathers (8%). In the soft tissues, CV values were higher in juvenile than in adult tropicbirds (up to 3 times higher), whereas they were higher in adult than juvenile Procellariiformes.

Elemental levels varied from one tissue to the other, except for Cu for which the differences were not significant between liver and muscle (Table 1). The general pattern, in all 3 species, showed that liver (followed by kidney, then muscle) accumulated the highest levels of Fe, Hg and Mn. This was also the case for Zn, except in juvenile petrels where the highest levels were found in kidney. Cadmium and Se accumulated mostly in kidney. Furthermore, muscle and feather Hg levels were equivalent in juvenile shearwaters and tropicbirds. In petrels, juveniles showed higher Hg levels in feathers than in muscle whereas opposite results were found for adults.

Table 1: Levels (Mean ± SD, µg.g -1 d.w.) and inter-specific comparison results for 7 trace elements in the tissues of juvenile and adult seabirds from Reunion Island.

Factors influencing trace element levels

Influence of age-classes, sex and reproductive status

Clear morphological traits differentiate fledgling from adults, therefore, elemental burdens differences were tested between these two age-classes. The type of test and level of signif- icance are given in Figures 1, 2 and 3. Significantly higher elemental levels were revealed in adult petrels than in juveniles, except for hepatic Cu. In the same way, levels were significantly higher in adult shearwaters than in juveniles, except for Fe in liver and kidney. In tropicbirds differences between juvenile and adult were less systematic with, in some cases (i.e. Fe, Mn and Zn), higher levels in juveniles than in adults. In all three species, significant differences between juvenile and adults were observed in the three tissues for Hg and Se, for Cd in muscle and kidney, for Mn in muscle and liver as well as for Fe and Zn levels in liver.

The influence of sex on elemental levels was tested on adult birds. Gender did not seem to influence elemental levels among adults of each species with the exception of hepatic Se which was higher in tropicbird males than in females (P W ilcoxon : * * * ). This latter result suggests that eggs may constitute an excretion path for Se in female White-tailed Tropicbirds.

Reproductive status, defined by the presence or absence of an incubation patch, did not significantly influence trace element levels among adults for all species.

Inter-specific differences

Elemental levels also differed among species (Table 1). In juveniles, significant differences were found for every element in every tissue of the three species except for renal Mn. Mercury levels were significantly higher in Barau's petrels and White-tailed Tropicbirds than in Audubon's Shearwaters. The highest levels of Cd were found in the petrels. Essential metals (Cu, Fe, Mn and Zn) levels were highest in the tropicbirds.

As far as the adults were concerned, there were fewer differences among species. Mercury was the only element for which there were differences between adults of all species. The highest Hg levels were found in Barau's Petrel and the lowest in Audubon's shearwater. Adult Barau's Petrel also had the highest Fe and Se levels. The highest levels of Cu and Mn were found in the White-tailed Tropicbird. There were no significant differences between Cd and Zn levels in the three species.

Relationships between trace element levels

The correlation matrices among elemental levels in the various tissues of each species were not presented in this paper. However, two types of linear correlations were obvious : (i) correlations between different elements in the same tissue and, (ii) correlations of levels of one element in various tissues. (i) Mercury and Cd stood out by their strong tissue-to-tissue correlations in all species. Selenium and Mn were also well correlated in the liver, kidney and muscle of Barau's petrel. (ii) The following significant correlation between elements were common to the three species: Cu, Fe and Zn in muscle, and Fe and Zn in liver. Other relationships were more species-specific, such as correlations between Mn and Se in muscle, Cu and Mn in kidney in the tropicbird and renal Cu, Fe, Mn, Se and Zn in the shearwater.

Discussion

4.1 Bioaccumulation in Barau's Petrel, Audubon's Shearwater and the White-tailed Tropicbird

Tissue distribution

As it has often been shown, trace elements are not all identically distributed in the different tissues of the organism. The preferential accumulation of Fe, Hg, Mn and Zn in the liver of Reunion birds reflects the usual trends, as does the preferential accumulation of Cd in kidney [START_REF] Furness | Heavy metals in the marine environment[END_REF][START_REF] Furness | Birds as Monitors of Environmental Changes[END_REF][START_REF] Thompson | Environmental contaminants in wildlife. Interpreting tissue concentrations[END_REF]. Indeed, liver and kidney are considered as long-term storage tissues for Hg and Cd in seabirds [START_REF] Walsh | The use of seabirds as monitors of heavy metals in the marine environment[END_REF], implying that large birds with long life span accumulate high burdens of these elements [START_REF] Fiona | Influence of phylogeny, diet, moult schedule and sex on heavy metal concentrations in New Zealand Procellariiformes[END_REF]. This is obvious in Procellariiformes, for which the albatrosses are the best example [START_REF] Hindell | Mercury and cadmium concentrations in tissues of three species of southern albatrosses[END_REF], and seems to apply to this study where Barau's Petrel is the largest of the two Procellariiforme species and shows the highest levels.

The equal distribution of Cu between liver and muscle in all three studied species is an unexpected result. This accumulation pattern has, however, already been observed, although not explained, in the Common Diving Petrel (Pelecanoides urinatrix), the South Georgian Diving Petrel (Pelecanoides georgicus) and the Antarctic Prion (Pachyptila desolata) from the Kerguelen archipelago [START_REF] Bocher | Influence of the diet on the bioaccumulation of heavy metals in zooplankton-eating petrels at Kerguelen archipelago, Southern Indian Ocean[END_REF]. Selenium also differs from the usual distribution pattern as it is mostly accumulated in the kidneys of the studied birds. There are few data on the distribution of Mn among seabird tissues. It was found mainly in the liver and kidney of Procellariiformes studied by [START_REF] Kim | Distribution of 14 elements in tissues and organs of oceanic seabirds[END_REF] and mainly in the liver of Reunion birds. Further studies are needed to determine the bioaccumulation pattern of Mn in seabird tissues.

Influence of phylogeny

Tropicbirds belong to the Phaethontidae family whereas the other two species are from the Procellariidae family. Only in the tropicbirds did juveniles have higher essential metal levels than adults. This same pattern has already been observed in various species [START_REF] Kim | Distribution of 14 elements in tissues and organs of oceanic seabirds[END_REF][START_REF] Stewart | Influence of phylogeny, diet, moult schedule and sex on heavy metal concentrations in New Zealand Procellariiformes[END_REF] in which the young accumulate essential elements to meet particularly high nutritional needs [START_REF] Thompson | Environmental contaminants in wildlife. Interpreting tissue concentrations[END_REF]. This strategy may have evolved in order to survive the fast caused by the abandon of the fledglings by their parents several days before their first flight. Since young Procellariiformes also undergo a long fasting period before fledging, but do not have high essential elemental levels, the White-tailed Tropicbird may differ from the two Procellariiforme species in the way its metabolism deals with the accumulation of such essential elements.

Procellariiformes have been cited for their particular ability to concentrate trace elements, resulting in much higher elemental burdens than many other seabirds [START_REF] Walsh | The use of seabirds as monitors of heavy metals in the marine environment[END_REF]). However, within the Procellariiformes order, phylogeny is thought to explain relatively little of the inter-specific variations [START_REF] Fiona | Influence of phylogeny, diet, moult schedule and sex on heavy metal concentrations in New Zealand Procellariiformes[END_REF]. Other than intrinsic differences in bioaccumulation linked to phylogeny, several characteristics of a species may explain part of the inter-specific variability.

Size and life span obviously have an impact on the quantity of trace elements concen-trated in the body because of a dilution effect and because longer living species have more time to accumulate larger burdens. Among the three species, Barau's petrel is the largest (400 g) and very likely the longest living seabird since its phylogenetically and geographically closest parent, the Galapagos Petrel Pterodroma phaeopygia, lives more than 25 years. Barau's Petrel is followed by the White-tailed Tropicbird, 260 g, and Audubon's Shearwater, 200 g, both having a life span superior to 20 years [START_REF] Weimerskirch | Seabird demography and its relationship with the marine environnement[END_REF]). This pattern is respected for most trace element levels analyzed here, especially non-essential elements.

Diet is considered as one of the most important factors of trace element variability since it is the major contamination path in marine vertebrates [START_REF] Stewart | Influence of phylogeny, diet, moult schedule and sex on heavy metal concentrations in New Zealand Procellariiformes[END_REF][START_REF] Thompson | Seabirds as biomonitors of mercury inputs to epipelagic and mesopelagic marine food chains[END_REF][START_REF] Kim | Distribution of 14 elements in tissues and organs of oceanic seabirds[END_REF]. Of the three Reunion species, Barau's Petrel has, by far, the highest Hg content in the studied tissues. Fish prey are known to be a source of contamination for top predators because they accumulate high levels of Hg [START_REF] Honda | Metal concentrations in pelagic seabirds from the north Pacific Ocean[END_REF], mainly in a bioavailable form, i.e. methylmercury [START_REF] Bloom | A survey of size-specific mercury concentrations in game fish from Maryland fresh and estuarine waters[END_REF]). However, Barau's Petrel only includes 2% fish in its diet but feeds on cephalopods of the Taonius genus (Le Corre, unpubl. data). These are meso-pelagic squids which live in depth ranging from 500 to 700 m [START_REF] Clarke | A Handbook for the identification of cephalopod beaks[END_REF][START_REF] Nesis | Cephalopods of the World[END_REF]. It is thought that Barau's Petrel feeds on their floating carcasses. The deep, poorly oxygenated waters promote the methylation of Hg which is easily transfered to living organisms [START_REF] Thompson | Seabirds as biomonitors of mercury inputs to epipelagic and mesopelagic marine food chains[END_REF]. Recently, relatively high Hg levels were reported in mesopelagic cephalopods from the north-eastern Atlantic waters, in which a major proportion of Hg was in an organic form [START_REF] Bustamante | Total and organic Hg concentrations in cephalopods from the North East Atlantic waters: influence of geographical origin and feeding ecology[END_REF]). These findings are consistent with the fact that Hg levels found in pelagic marine birds are higher than those found in terrestrial birds [START_REF] Monteiro | Mercury concentrations in prey fish indicate enhanced bioaccumulation in mesopelagic environments[END_REF][START_REF] Thompson | Seabirds as biomonitors of mercury inputs to epipelagic and mesopelagic marine food chains[END_REF]. High Hg levels in Taonius could be responsible for the higher Hg levels found in Barau's Petrel.

Procellariiformes are also known for having high Cd levels due to their diet, which is essentially composed of cephalopods, and cephalopods have been shown to be responsible for the high Cd levels in top predators [START_REF] Smith | Concentrations of the elements Ag, Al, Ca, Cd, Cu, Fe, Mg, Pb and Zn, and the radionuclides 210pb and 210po in the digestive gland of the squid Nototodarus gouldi[END_REF], Bustamante et al. 1998a, Bustamante et al. 1998b). This seems to be the case in Reunion Procellariiformes and especially in Barau's Petrel since 98% of its diet is composed of cephalopods (Gigan & Lebon, unpublished data). The study of Hg and Cd burdens of the various prey species of the three birds would be useful in confirming these hypotheses.

Inter-individual differences

The high individual fluctuations observed for Cd, Cu and Hg could have many causes such as individual variation in diet (see 4.1.2), body condition and age (within an age-class).

The White-tailed Tropicbird was the only species for which the individual variations of Hg burdens were higher in juveniles than in adults. This may be explained by a difference in their breeding cycle. Contrary to the Procellariiformes species which breed on Reunion Island at definite periods, Tropicbirds breed individually thoughout the year. As Hg intake originates from diet, young Tropicbirds collected in various periods of the year would show more inter-individual variations than young Petrels or Shearwaters which were all collected roughly at the same time. Furthermore, these large inter-individual differences would not be as apparent in adult Tropicbirds which would have integrated Hg over a longer period, thus minimizing the variability.

Individual fluctuation in elemental levels was also found to be induced by a variability in the nutritional condition of the Common Guillemots (Uria aalge) at death (Debacker et al. 2001b). The influence of muscle condition (MC) and body condition (BC) on elemental levels was studied to determine whether the body condition of these birds had an influence on the results. As a general trend, most significant differences in trace element levels existed between the MC indices 1 and 3, which are two extreme cases, i.e. well fed and starving birds (P W ilcoxon : * ). Only renal Fe, muscular Mn, and Se levels in liver and kidney seemed unaffected by the bird's muscular condition. The higher elemental levels in the starving birds were most probably due to the loss of weight of the tissue rather than to a raise of the elemental levels. Surprisingly, very few significant correlations were found between the BC index (which ranged from 0.7 to 4.5) and trace element levels.

It is not possible to estimate the age of adult seabirds unless they are marked, yet trace elements are known to be accumulated in the organism over the lifetime. Age can therfore be considered as a possible cause of individual fluctuation among adults of each species.

Relationships between trace element levels

The evolution of Hg tissue-to-tissue correlations in Barau's Petrel juveniles and adults is a good illustration of the bioaccumulation of this element. Indeed, significant correlations of Hg levels were observed between feathers, liver, kidney and muscle in juvenile petrels (r = 0.371 * to r = 0.717 * * * ; n = 32). In adults, Hg levels in liver, kidney and muscle remained correlated (r = 0.58 * * to r = 0.786 * * * ; n = 20) whereas feather Hg levels were no longer significantly correlated to the others. Once the feather is formed, the blood irrigation subsides, implying that no further metal is deposited. In adult Barau's Petrel, Hg burden in the feathers had not evolved since the last plumage growth, whereas Hg levels in the other organs had increased with Hg accumulation.

Correlations between elements, such as Cu, Fe and Zn in muscle and Fe and Zn in liver of the three species, suggested that uptake and pathways of metabolism and storage are relatively similar for these trace elements.

Comparison with other species and locations

Table 2 draws a parallel between elemental levels in liver, kidney and feathers in seabirds from Reunion Island and phylogenically related species from other locations in the world. Elemental burdens in juveniles and adults are presented separately.

Most ecotoxicological works are based on the study of adults, as they have integrated the environmental contamination over a longer period of time. Metal levels obtained for adults in this study are generally comparable to those reported for petrels and shearwaters studied in other oceanic islands [START_REF] Muirhead | Heavy metal concentrations in the tissues of seabirds from Gough Island, South Atlantic Ocean[END_REF][START_REF] Stewart | Seasonal variation in heavy metals in tissues of Common Guillemots, Uria aalge from northwest Scotland[END_REF], Stewart et al. 1997a[START_REF] Stewart | Influence of phylogeny, diet, moult schedule and sex on heavy metal concentrations in New Zealand Procellariiformes[END_REF]). Nevertheless, Se and Zn values observed in these birds were fairly high. In kidney, Se levels exceeded 3.6 to 4.5 times the value of 10 µg.g -1 wet weight (≈ 40 µg.g -1 d.w) considered as the level above which Se may have harmful effects on birds [START_REF] Thompson | Environmental contaminants in wildlife. Interpreting tissue concentrations[END_REF]. This indicates that regulation mecanisms must exist in Reunion birds. Similar Se concentrations have been observed in other wild seabirds such as Leach's Storm-petrel (Oceanodroma leucorrhoa, 78 µ.g -1 d.w.) from the Atlantic coast of Canada (Elliott et al. 1992), the Black-footed Albatross (Diomedea nigripes, 113 µ.g -1 d.w.) from the Northern Pacific as well as birds from relatively pristine areas such as the Grey Petrel (Procellaria cinerea, 100 µ.g -1 d.w.) from the Southern Indian Ocean (Kim et al. 1996a[START_REF] Kim | Distribution of 14 elements in tissues and organs of oceanic seabirds[END_REF].

Table 2: Trace element levels (Mean±SD, µg.g -1 d.w.) in seabirds from different biogeographical areas: 1: Tropical ; 2: Subtropical ; 3: Temperate ; 4: Subpolar. * designates species for which data have been converted from "wet weight" to "dry weight" assuming a tissue water content of 70%.

The Phaethon genus has received very limited attention regarding elemental bioaccumulation. Feather Hg levels in Reunion's White-tailed Tropicbird are more than seven times inferior to those found in Red-Tailed Tropicbirds from Midway Island [START_REF] Burger | Metal levels in feathers of 12 species of seabirds from Midway Atoll in the northern Pacific Ocean[END_REF]. In Barau's Petrel feathers, Hg levels fit in the 0.6-2.7 µg.g -1 range that has been reported for petrels and shearwaters [START_REF] Burger | Metals in feathers of brown noddy (Anous stolidus): Evidence for bioaccumulation or exposure levels?[END_REF]. For Hg in feathers, a range of 5 -40 µg.g -1 d.w. can be considered as associated with adverse effects (Eisler 1987, Burger and[START_REF] Burger | Risk, mercury levels, and birds: relating adverse laboratory effects to field biomonitoring[END_REF]. In this study, the highest Hg level recorded among all birds was more than five times inferior to this toxicity limit. It can therefore be presumed that the marine birds considered during this work do not suffer from any adverse effects of Hg.

Contrary to Hg, means for renal Cd were above the 10 µg.g -1 wet weight adverse effects level determined by [START_REF] Eisler | Cadmium hazards to fish, wildlife, and invertebrates: a synoptic review[END_REF]. However, [START_REF] Furness | Cadmium in birds[END_REF] suggested that levels above which adverse effects occur in pelagic seabirds may be higher than for other birds, and that no adverse Cd effects have been documented in wild seabirds. Cadmium and Hg levels in soft tissues of adult Barau's Petrels are very close to those found in the squideating Great-winged Petrel (Pterodroma macroptera) from New Zealand. Metal burdens in Audubon's Shearwaters are similar to those found in the piscivorous Cory's Shearwaters from the Azores islands (Stewart et al. 1997a). Although seabirds feeding on similar prey tend to show closer metal burdens than species which diets are different, the geographical origin of the bird is important. For example, the Atlantic Petrel (P. incerta) from Gough Island is very close to the Great-winged Petrel in size and is also a squid-eater. However, its hepatic Hg (respectively, renal Cd) levels are almost 4 (respectively 2) times higher than those found in the Great-winged Petrel and Barau's Petrel. These comparisons suggest the existence of large differences in elemental levels even among non-industialized, isolated oceanic islands. Besides, these values remain far below levels that can be attained in polluted areas, such as the Saint Lawrence Gulf, where small, 50 g, plankton-eating Leaches Storm Petrels accumulates 3 to 4 times more renal Cd (183 ± 65 µg.g -1 ) than the Reunion birds which are larger and feed at a higher trophic level.

Conclusion

Our study has revealed some similarities and differences which exist between Barau's Petrel, Audubon's Shearwater and the White-tailed Tropicbird in terms of intake and pathways of metabolism and storage of certain elements among age-classes. Diet stood out as a major factor of elemental level variation. Among prey, cephalopods appeared to contribute importantly to the Cd and Hg intake of Reunion marine birds. The study of the excretion and storage of Cd, Cu, Fe, Hg, Mn, Se and Zn in these three seabirds would be most valuable in order to understand the detoxification strategies employed by these birds. Indeed, Reunion seabirds bioaccumulated fairly high levels of Cd, Hg, Se and Zn, especially considering the remoteness of Reunion island in respect to anthropic activity. However, for each element, similar or higher levels have been observed in parent species originating from other pristine areas. In this context, two scenarios can be considered: the levels of trace elements measured during this study correspond to (i) backround levels whose sources are natural (volcanism, erosion, etc.), or (ii) the echo of distant pollution which has reached this part of the Wester Indian Ocean by aereal and/or marine currents, or indirectly though the migration of prey species from polluted zones. Physiological studies of the Reunion seabird species would be useful to distinguish healthy birds from those in bad physiological condition in relation to their body condition index [START_REF] Wenzel | The suitability of oiled Guillemots (Uria aalge) as monitoring organisms for geographical comparisons of trace element contaminants[END_REF] in order to better apprehend the influence of the bird's physiological condition on elemental levels.

Acknowledgments

This research was supported by the Conseil Général de La Réunion. J.K. also benefited from support of the Conseil Régional de La Réunion and the European Social Fund through a PhD grant. The authors would like to thank E. Robert, M. Rouquette, P. Grondin and N. Ghanem in La Réunion for their help in the tissue preparation and C. Churlaud, Centre Commun d'Analyse (La Rochelle), for her assistance with the analyzes on the ICP-AES. We would also like to thank the numerous volunteers who actively participate in the SEOR Petrel rescue program. We are also grateful towards the referees for their helpful comments on the manuscript.

Figure 2 :

 2 Figure 2: Comparison of elemental levels (µg.g -1 d.w.) in kidneys of adult (A) and juvenile (J) seabirds (PB: Pterodroma baraui, PLB: Puffinus l. bailloni, PQ: Phaethon lepturus).Outliers are represented as individual points. For each species, the significances of the level differences between juveniles and adults are indicated below the boxplots. t : t-test ; W : Wilcoxon test.

Figure 3 :

 3 Figure 3: Comparison of elemental levels (µg.g -1 d.w.) in pectoral muscles and breast feathers of adult (A) and juvenile (J) seabirds (PB: Pterodroma baraui, PLB: Puffinus l. bailloni, PQ: Phaethon lepturus). Outliers are represented as individual points. For each species, the significances of the level differences between juveniles and adults are indicated below the boxplots. t : t-test ; W : Wilcoxon test.