Ziqi Jiang

Linbo Shang
email: shanglinbo@vip.gyig.ac.cn

Haihao Guo

Xin-Song Wang

Chen Chen

Yunhe Zhou

An experimental investigation into the partition of Mo between aqueous fluids and felsic melts: Implications for the genesis of porphyry Mo ore deposits

Keywords: partition coefficient, porphyry molybdenum deposit, hydrothermal fluid, felsic melt

Most of the world's large molybdenum (Mo) deposits are genetically related to magmas that underwent significant fractional crystallization and fluid exsolution, and the residual silicate melts are commonly peralkaline. To understand the relationship between melt compositions and the genesis of porphyry Mo mineralization, the partition coefficients of molybdenum (D Mo ) between fluid and felsic melt were determined at 850 °C, 900 °C, and 100 MPa with various values of A/NK [molar Al 2 O 3 / (Na 2 O + K 2 O) in the melt] under an oxygen fugacity around the Ni-NiO (NNO) buffer.

The results show that D Mo decreases from 4.23 to 0.4 with increasing A/NK from 0.75 to 1.36 in the carbon dioxide series (fluid composed of = 0.096 [molar CO 2 / (CO 2 X CO2 + H 2 O)] and 17.5 wt.% NaCl). A similar trend was observed in pure water, with A/NK varying from 0.72 to 1.23, D Mo decreases from 0.54 to 0.15. Significantly, D Mo in peralkaline melt is consistently higher than that in peraluminous melt, even with the same NBO/T (the ratio of non-bridge oxygen and tetrahedron ion). Our study therefore reveals that Mo is easily distributed into fluids that exsolved from peralkaline magmas. This finding explains why highly fractionated magmas are critical for porphyry Mo mineralization.

Introduction

Porphyry molybdenum deposits, the world's most important source of Mo, are commonly genetically related to high-K calc-alkaline granites generated by extensive fractional crystallization [START_REF] Sinclair | Porphyry deposits:Mineral deposits of Canada: A synthesis of major deposit-types, district metallogeny, the evolution of geological provinces, exploration methods: Geological Association of Canada[END_REF][START_REF] Pettke | The magma and metal source of giant porphyry-type ore deposits, based on lead isotope microanalysis of individual fluid inclusions[END_REF][START_REF] Sillitoe | Porphyry Copper Systems[END_REF][START_REF] Audétat | The genesis of Climax-type porphyry Mo deposits: Insights from fluid inclusions and melt inclusions[END_REF]Chen et al., 2017 and references therein). The efficient extraction of Mo from high-K calc-alkaline melt during the exsolution of magmatic fluids is an important step in Mo enrichment [START_REF] Sinclair | Porphyry deposits:Mineral deposits of Canada: A synthesis of major deposit-types, district metallogeny, the evolution of geological provinces, exploration methods: Geological Association of Canada[END_REF][START_REF] Pettke | The magma and metal source of giant porphyry-type ore deposits, based on lead isotope microanalysis of individual fluid inclusions[END_REF][START_REF] Sillitoe | Porphyry Copper Systems[END_REF][START_REF] Tattitch | Cu-Mo partitioning between felsic melts and salineaqueous fluids as a function of X NaCleq , ƒ O2 , and ƒ S2[END_REF]. The partition coefficient of Mo between aqueous fluid and melt is a key Previous studies on the partition behaviors of Mo in natural and experimental samples have found that D Mo varies from 0.06 to 135, with most values being less than 10 ( [START_REF] Tingle | Transport and concentration of molybdenum in granite molybdenite systems: Effects of fluorine and sulfur[END_REF][START_REF] Candela | The partitioning of copper and molybdenum between silicate melts and aqueous fluids[END_REF][START_REF] Keppler | Partitioning of Cu, Sn, Mo, W, U, and Th between melt and aqueous fluid in the systems haplogranite-H 2 O-HCl and haplogranite-H 2 O-HF[END_REF]Chevychelov and Chevychelova, 1997;[START_REF] Webster | Exsolution of magmatic volatile phases from Cl-enriched mineralizing granitic magmas and implications for ore metal transport[END_REF][START_REF] Bai | The distribution of Na, K, Rb, Sr, Al, Ge, Cu, W, Mo, La, and Ce between granitic melts and coexisting aqueous fluids[END_REF][START_REF] Kravchuk | Molybdenum partition between melts of natural and synthetic aluminosilicates and aqueous-salt fluids[END_REF][START_REF] Lerchbaumer | The Metal Content of Silicate Melts and Aqueous Fluids in Subeconomically Mo Mineralized Granites: Implications for Porphyry Mo Genesis[END_REF][START_REF] Zajacz | Determination of fluid/melt partition coefficients by LA-ICPMS analysis of co-existing fluid and silicate melt inclusions: Controls on element partitioning[END_REF][START_REF] Tattitch | Cu-Mo partitioning between felsic melts and salineaqueous fluids as a function of X NaCleq , ƒ O2 , and ƒ S2[END_REF]. Generally, HCl, NaCl, and KCl in aqueous fluids can increase D Mo [START_REF] Keppler | Partitioning of Cu, Sn, Mo, W, U, and Th between melt and aqueous fluid in the systems haplogranite-H 2 O-HCl and haplogranite-H 2 O-HF[END_REF][START_REF] Webster | Exsolution of magmatic volatile phases from Cl-enriched mineralizing granitic magmas and implications for ore metal transport[END_REF][START_REF] Bai | The distribution of Na, K, Rb, Sr, Al, Ge, Cu, W, Mo, La, and Ce between granitic melts and coexisting aqueous fluids[END_REF][START_REF] Schaefer | Determination of trace-element partitioning between fluid and melt using LA-ICP-MS analysis of synthetic fluid inclusions in glass[END_REF][START_REF] Tattitch | Cu-Mo partitioning between felsic melts and salineaqueous fluids as a function of X NaCleq , ƒ O2 , and ƒ S2[END_REF]. In particular, in high-salinity brine (NaCl eq = 62 wt.%), D Mo can reach up to 130 [START_REF] Tattitch | Cu-Mo partitioning between felsic melts and salineaqueous fluids as a function of X NaCleq , ƒ O2 , and ƒ S2[END_REF]. In contrast, HF in aqueous fluids has no discernible effect on D Mo [START_REF] Candela | The partitioning of copper and molybdenum between silicate melts and aqueous fluids[END_REF][START_REF] Keppler | Partitioning of Cu, Sn, Mo, W, U, and Th between melt and aqueous fluid in the systems haplogranite-H 2 O-HCl and haplogranite-H 2 O-HF[END_REF].

Most of the melt used in previous experiments were peraluminous, and only a few experimental studies investigated the effect of the melt composition on the partition coefficient (Chevychelov and Chevychelova, 1997;Kracchuk et al., 2000). For example, with the melt composition changing from granodioritic to leucogranitic (A/NK ratio from 1.53 to 1.32,where A/NK= (Al 2 O 3 )/ (Na 2 O + K 2 O) in mole), D Mo values increases from 0.2 to 0.7 at 1 kbar and from 1.4 to 2.2 at 5 kbar, respectively (Chevychelov and Chevychelova 1997). There is no noticeable correlation between D Mo and Al 2 O 3 content of melts (Kracchuk et al., 2000).

To better understand the relationship between high-K calc-alkaline granites and Mo mineralization, we carried out equilibrium experiments on high silica melts with varying A/NK ratio and aqueous fluids with H 2 O ± NaCl ± CO 2 . The experimental results show that D Mo increases with increasing alkalis and decreases with increasing A/NK in the melt. This study also demonstrates that coexisting fluid in highly evolved felsic magma has high potential for extracting Mo.

Method

Starting materials

The compositions of starting materials are given in Table 1. Felsic glasses were synthesized from dehydrated TEOS and high-purity Na 2 CO 3 , KHCO 3, and Al 2 O 3 .

These samples were ground in an agate mortar to attain a grain size of <200 μm, and then mechanically mixed with about 600 ppm Mo in the form of high-purity MoO 3 .

Then, the powders (<2 grams) were placed into Pt crucibles and heated to 1350 °C at a rate of 150 °C/h. After annealing the powders at this temperature for 8 h, the Pt crucibles were quenched in cold water. The contained quenched glasses were ground several times in an agate mortar as starting materials.

Three different series of experiment with various fluid compositions were conducted in this study (Table 1): (1) the carbon dioxide series ( = 0.096, 17.5 wt.% NaCl), X CO2

(2) the water series (pure water with ~1000 ppm each of Rb, Cs, and B), and (3) the contrast series (11.73 wt.% NaCl and 8.34 wt.% KCl). Oxalate (H 2 C 2 O 4 ) was used to generate CO 2 ( = 0.096) in the carbon dioxide series experiments and different X CO2 content of water and solid NaCl were added to control the mole fractionation of CO 2 .

Aqueous solutions containing various amounts of NaCl, KCl, RbCl, CsCl, and H 3 BO 3 were prepared from analytical-grade chemicals and deionized water. The water series experiments were conducted in pure water containing 1000 ppm each of Cs, Rb, and B.

Experimental procedures

The capsule design is illustrated in Fig. 1. Approximately 200 mg of synthetized glasses and 200 mg of aqueous solutions as described above were loaded into gold capsules of 4.8 mm inner diameter (I.D.), 5.0 mm outer diameter (O.D.), and 25 mm length. The capsules were sealed with argon arc welding and placed in a drying oven (110 °C) for 24 h to check for potential leaks. Subsequently, the capsules were loaded into rapidly quenched cold-seal pressure vessels made of Ni-base alloy. All experiments were conducted at 850, 900 °C and 100 MPa, with water as pressure medium.

Temperatures were measured with a K-type thermocouple in a hole at the end of the vessels. Pressures were measured with a Bourdon-type gauge with an uncertainty of 5 MPa. Oxygen fugacity was controlled by the material of the autoclave and was approximately the value of the nickel-nickel oxide (NNO) buffer [START_REF] Chou | Oxygen buffer and hydrogen sensor techniques at elevated pressures and temperatures[END_REF]. Based on previous experiments (e.g., [START_REF] Candela | The partitioning of copper and molybdenum between silicate melts and aqueous fluids[END_REF][START_REF] Keppler | Partitioning of Cu, Sn, Mo, W, U, and Th between melt and aqueous fluid in the systems haplogranite-H 2 O-HCl and haplogranite-H 2 O-HF[END_REF][START_REF] Webster | Exsolution of magmatic volatile phases from Cl-enriched mineralizing granitic magmas and implications for ore metal transport[END_REF][START_REF] Tattitch | Cu-Mo partitioning between felsic melts and salineaqueous fluids as a function of X NaCleq , ƒ O2 , and ƒ S2[END_REF], a duration of 10 days was selected to guarantee experimental equilibrium. After these experimental durations, the vessels were rotated 90° to force the capsules to drop to the cold-water zone, and therefore allow the samples to reach room temperature within a few seconds. Capsules were then removed from the vessels, cleaned with dilute hydrochloric acid and deionized water, and then dried and weighed to determine whether the capsules had remained sealed during the experiments. Capsules with a mass change of less than 0.005 g were used for the subsequent analyses.

In the carbon dioxide series experiments, the quenched fluid and glass phases were separated following the procedure given by [START_REF] Wang | Copper partitioning between granitic silicate melt and coexisting aqueous fluid at 850 ℃ and 100 MPa[END_REF]. The pierced capsules were opened with surgical scissors, and then the opened capsules and quenched glasses were eluted in 50 ml centrifuge tubes with 10% HNO 3 for 12 h. Molybdenum that was precipitated on the surfaces of Au capsules and quenched glasses was leached three times, and all of the leaching solutions were collected for ICP-MS analysis. The quenched glasses were ground to 200 mesh in an agate mortar for ICP-MS analysis, and the analyzed data of quenched glasses were defined as "bulk glass data".

For the water series and contrast series experiments, the quenched samples were treated using different procedures compared with the carbon dioxide series experiment.

After quenching, dilute HCl solution was used to clean the surfaces of the gold capsules.

The capsules were placed into liquid nitrogen for a few seconds to freeze the liquid inside and then cut using surgical scissors. The broken capsule was put into a Teflon beaker with 10 ml deionized water, and then annealed on an electric hot-plate at 80 ℃ for 8 h. This process was repeated three times, and all solutions were collected into a tube for analysis, similar to the procedure given by [START_REF] Guo | Experiments on Cu-isotope fractionation between chlorine-bearing fluid and silicate magma: implications for fluid exsolution and porphyry Cu deposits[END_REF]. LA-ICP-MS was used to analyze the quenched glasses, which are free of fluid bubbles (Fig. 1). This strategy avoided the effect of such bubbles on the concentration of Mo in the glass phase, and the analyzed data were defined as "pure glass data". In addition, some of the quenched glasses (~20 mg) were also ground and analyzed using ICP-MS in the contrast series experiments. We compared values of D Mo obtained from bulk glass data and pure glass data, which was used to evaluate the effect of bubbles containing in quenched glass on the concentration of Mo estimated using the different analytical methods.

Analysis of experimental products

Major elements of synthetic glasses were analyzed using LA-ICP-MS at the State Key Laboratory of Ore Deposit Geochemistry, Institute of Geochemistry Chinese Academy of Sciences, Guiyang, China. The Mo concentrations of quenched glasses (the carbon dioxide series and the contrast series) and leaching solutions were analyzed by a Finnigan MAT ELEMENT ICP-MS instrument using the procedures described by [START_REF] Qi | Determination of trace elements in granites by inductively coupled plasma mass spectrometry[END_REF] at the State Key Laboratory of Ore Deposit Geochemistry. A working curve using standard solutions of different concentrations was utilized to calculate absolute concentrations of Mo in quenched glasses and leaching solutions. Rhodium was used as an internal standard to monitor signal drift during counting.

For the water series and contrast series experiments, the quenched glasses without fluid inclusions were analyzed by LA-ICP-MS. Laser sampling was performed using a GeoLas Pro 193 nm ArF excimer laser. An Agilent 7900 ICP-MS instrument was used to acquire ion-signal intensities. Helium was used as the carrier gas, which was mixed with Argon via a T-connector before entering the ICP-MS instrument. Each analysis incorporated a background acquisition of approximately 30 s (gas blank) followed by 50 s of data acquisition from the sample. Element concentrations were calibrated against multiple reference materials (NIST 610, BCR-2G, BIR-1G, and BHVO-2G) without applying internal standardization [START_REF] Liu | In situ analysis of major and trace elements of anhydrous minerals by LA-ICP-MS without applying an internal standard[END_REF]. Off-line selection and integration of background and analyte signals, as well as time-drift correction and quantitative calibration, were performed using ICPMSDataCal [START_REF] Liu | In situ analysis of major and trace elements of anhydrous minerals by LA-ICP-MS without applying an internal standard[END_REF].

Results

All of the data of the carbon dioxide series, pure water series, and contrast series experiments are reported in Table 2. The ratio A/NK was used to quantify the composition of felsic melts. The results of this study show that D Mo in all cases decreases with increasing A/NK and D Mo is generally higher in the carbon dioxide series than that in the pure water series (Fig. 2a andb).

In the carbon dioxide series, D Mo decreases from 4.13 to 0.56 as the molar ratio of A/NK increases from 0.75 to 1.36 under conditions of the starting solution containing = 0.096 and 17.5 wt.% NaCl (Fig. 2a). A typical double-eyelid structure of fluid X CO2 inclusions containing CO 2 appears in the quenched melt of the carbon dioxide series (Fig. 1). We also analyzed fluid inclusions of the sample using Raman spectroscopy, which showed the presence of CO 2 (Fig. 1).

For the water series, all values of D Mo are below 1.0 (Table 2), and D Mo decreases from 0.54 to 0.15 as A/NK increases from 0.72 to 1.23 (Fig. 2b). Compared with D Mo of the carbon dioxide series, D Mo in the water series at the same A/NK is smaller, which suggests that the salinity of the carbon dioxide series enhances the extraction of Mo from the melt phase into fluids.

Quenched glasses of the water series and contrast series experiments were randomly analyzed by LA-ICP-MS. As revealed in the data listed in Table 3, the relative standard deviation (RSD) of major element contents was very small (typically <0.5%), and the RSD of the concentration of Mo was slightly higher, but with the maximum being <20% and most analyses being <10%. These results suggest that all the elements in quenched glasses are homogeneous in content and also confirm that experimental equilibrium attained in 10 days.

For the contrast series, the partition coefficients that were calculated on the basis of the concentration of Mo in the bulk glasses and pure glasses data coincide (Table 2), which demonstrates that in our experiments, there was a negligible effect of trapped bubbles on the concentration of Mo in silicate glasses, and therefore the Mo concentration data from quenched glass obtained from ICP-MS can be used to represent the concentration of Mo in melts.

The sources of experimental error involve two main aspects. First, it may be hard to remove all precipitated Mo from the surface of Au capsules and quenched glasses.

However, the experiments conducted by Borchert et al. (2010aBorchert et al. ( , 2010b) ) showed a good correlation in element concentration between leaching solutions and in situ determined fluid. In this study, we used the same method to leach Mo from capsules in the water series experiments. Therefore, the precipitated Mo in quenched glasses and Au capsules has little effect on the concentration of Mo in the fluid. Second, when melt cools through the glass transition temperature, some fluid will be trapped as glass-hosted fluid inclusions [START_REF] Romano | Kinetics of quenching of hydrous feldspathic melts: quantification using synthetic fluid inclusions[END_REF][START_REF] Simon | An evaluation of synthetic fluid inclusions for the purpose of trapping equilibrated, coexisting, immiscible fluid phases at magmatic conditions[END_REF]. In the present study, we found from the double-polished wafer that only 1 vol.% fluid phase was trapped in quenched glass (Fig. 1). The contrast series experiments were conducted to estimate the experimental error from the trapped fluid on the Mo concentration of quenched glasses.

LA-ICP-MS was used to analyze the quenched glasses without bubbles, and ICP-MS was used to analyze the ground quenched glasses containing fluid bubbles. The results show that values of D Mo calculated using the two different methods (pure glasses or bulk glasses) coincide on the whole, and the deviation is in the range of the experiment error. (Table 2).

Discussion

Comparison with previous results

As mentioned above, values of D Mo in natural and experimental samples encompass a wide range from 0.06 to 135 (Fig. 3a), but are mostly <10. In situ composition analyses of fluid and melt inclusions in quartz from intrusions of porphyry Mo deposits have shown that D Mo values of natural samples were in all cases larger than 1, varying from 1 to 24, with the melt compositions being metaluminous and slightly peralkaline (A/CNK [A/CNK=Al 2 O 3 / (CaO + Na 2 O + K 2 O) in mole] ranging from 0.9 to 1.1) [START_REF] Audétat | The Composition of Magmatic-Hydrothermal Fluids in Barren and Mineralized Intrusions[END_REF][START_REF] Zajacz | Determination of fluid/melt partition coefficients by LA-ICPMS analysis of co-existing fluid and silicate melt inclusions: Controls on element partitioning[END_REF][START_REF] Audétat | Source and Evolution of Molybdenum in the Porphyry Mo(-Nb) Deposit at Cave Peak, Texas[END_REF][START_REF] Lerchbaumer | The Metal Content of Silicate Melts and Aqueous Fluids in Subeconomically Mo Mineralized Granites: Implications for Porphyry Mo Genesis[END_REF]2013). The relationship of D Mo versus A/CNK from natural samples shows that D Mo is high for melts with low A/CNK relatively. Some previous experiments confirmed the influence of melt composition on D Mo . Chevychelov and Chevychelova (1997) reported values of D Mo for aqueous fluids (H 2 O-NaCl-HCl) and various synthetic gels. All of the gels were peraluminous and contained 5.2 wt.% CaO in granodioritic gel and 2.0 wt.% CaO in leucogranitic gel. D Mo decreased with increasing A/NK at around 900 °C. Specifically, D Mo ranged from 0.65 to 0.25 at 100 MPa and from 2.1 to 1.45 at 500 MPa. [START_REF] Kravchuk | Molybdenum partition between melts of natural and synthetic aluminosilicates and aqueous-salt fluids[END_REF] conducted experiments to study D Mo between fluid with 1m NaCl and various synthetic melts under conditions of 800 °C and 1.0-2.0 kbar. The melts were prepared using albite and other peraluminous glasses. We reprocessed their experimental data and found that D Mo decreased from 7.33 at A/NK = 0.98 to 0.22 at A/NK = 1.52 (Fig. 3b).

Our experimental results clearly show the same trend of D Mo increasing with decreasing A/NK, and values of D Mo are in the established range for natural samples (Fig. 3b).

The main differences between our experiments and those of Chevychelov and Chevychelova (1997) and [START_REF] Kravchuk | Molybdenum partition between melts of natural and synthetic aluminosilicates and aqueous-salt fluids[END_REF] were that our starting melt did not contain CaO and some of comparison experiments were conducted at higher pressure (e.g., 500 MPa). In addition, the melt composition of Chevychelov and Chevychelova (1997) and [START_REF] Kravchuk | Molybdenum partition between melts of natural and synthetic aluminosilicates and aqueous-salt fluids[END_REF] were peraluminous, and only the highest value of D Mo of 7.33 was obtained using albite as the starting melt, which may be caused by the degree of polymerization of albite. This is because albite is fully polymerized, the solubility of molybdenite in highly polymerized melts is very low [START_REF] Isuk | Behavior of molybdenum in alkali silicate melts: Effects of excess SiO 2 and CO 2[END_REF], which will allow more Mo to dissolve into the coexisting solution, in turn leading to a high D Mo . In some of our experiments, D Mo is very small (e.g., 0.25) and may be explained by the existence of CaO in the melt and the starting solution didn't contain salinity.

CaO is known to prevent Mo from being distributed into magmatic fluids [START_REF] Kravchuk | Molybdenum partition between melts of natural and synthetic aluminosilicates and aqueous-salt fluids[END_REF], although Chevychelov and Chevychelova (1997) considered that Ca enhances the concentration of Mo in fluids and is precipitated as a crystalline phase. In contrast, magma forming porphyry Mo is in all cases highly evolved, and the melt composition is high-K calc-alkaline. The data of Chevychelov and Chevychelova (1997) and [START_REF] Kravchuk | Molybdenum partition between melts of natural and synthetic aluminosilicates and aqueous-salt fluids[END_REF] obtained from peraluminous melt cannot explain the relationship between the causative magma and high-K calc-alkaline granite.

We also note that fluid salinity affects D Mo in both natural and experimental samples.

The highest reported value of D Mo can reach 135 in hypersaline fluids [START_REF] Tattitch | Cu-Mo partitioning between felsic melts and salineaqueous fluids as a function of X NaCleq , ƒ O2 , and ƒ S2[END_REF], which is in good agreement with results from an earlier experiment [START_REF] Webster | Exsolution of magmatic volatile phases from Cl-enriched mineralizing granitic magmas and implications for ore metal transport[END_REF]. In a system involving low to medium salinity fluids, values of D Mo are in all cases less than 10. In our study, carbon dioxide series experiments using fluids with 17.5 wt.% NaCl resulted in higher D Mo values than those of the pure water series.

Effect of melt composition on D Mo

Our results reveal that D Mo decreases with increasing A/NK and that D Mo is higher in peralkaline melts than that in peraluminous melts, which can be attributed to the change of the structure of melt and the Mo species in melt.

The basic units of felsic melts are a silicon-oxygen tetrahedron and an aluminumoxygen tetrahedron. The oxygen linking the Si 4+ "network-forming" cations is denoted as "bridging O" (BO), and the oxygen linking Si 4+ and other cations (networkmodifying) is denoted as "non-bridging oxygen" (NBO). The ratio NBO/T is defined by Equation ( 1), in which all elements are represented as molar concentrations in silicate melt [START_REF] Mysen | The effect of melt composition on trace element partitioning: an experimental investigation of the activity coefficients of FeO, NiO, CoO, MoO 2 and MoO 3 in silicate melts[END_REF]:

(1) NBO/T = (2 × A -4 × T)/T where T represents the total number of tetrahedral central cations, and A represents the total number of anions. Mo is present primarily as molybdate moieties ( ) in Mo(Ⅵ)O 2- 4 most silicate melt [START_REF] Farges | Structural environments around molybdenum in silicate glasses and melts. I. Influence of composition and oxygen fugacity on the local structure of molybdenum[END_REF], which suggests that chemically active oxygen, also referred to as NBO, would be required to form the molybdate moieties in melt.

In peraluminous melt, there are two types of aluminum: one type that forms Al-O-Al tetrahedra with charge-balancing cations; and another type that modifies the silicate network, acting as network-modifying cations and decreasing the degree of polymerization and increasing the number of NBOs of silicate melt [START_REF] Stebbins | Glass structure, melt structure, and dynamics: Some concepts for petrology[END_REF].

The increasing number of NBOs in melt favors the formation of molybdate moieties and leads to a decrease in D Mo .

In our experiments, D Mo is higher in all cases for the peralkaline melts than for the peraluminous melts, even for the same NBO/T (Fig. 2c andd). In addition, D Mo increases with an increasing alkali content of melt (Fig. 2e andf). In the peralkaline melt, the excess alkali and alkaline earth metal ions may form complexes with the molybdate moieties to form Na 2 MoO 4 , K 2 MoO 4 , or CaMoO 4 [START_REF] Farges | Structural environments around molybdenum in silicate glasses and melts. I. Influence of composition and oxygen fugacity on the local structure of molybdenum[END_REF]O'Neill and Eggins, 2002). D Mo is controlled predominantly by the nucleation of molybdate rather than the NBO/T ratio of the melt (Fig. 2c andd). Molybdate is the main species of Mo in saline fluids [START_REF] Cao | Solubility of molybdenite and the transport of molybdenum in hydrothermal solutions[END_REF][START_REF] Kudrin | Behavior of Mo in aqueous NaCl and KCl solutions at 300-450 ℃[END_REF][START_REF] Bali | The mobility of W and Mo in subduction zone fluids and the Mo-W-Th-U systematics of island arc magmas[END_REF][START_REF] Zhang | Solubility of molybdenite (MoS 2 ) in aqueous fluids at 600-800 °C, 200 MPa: A synthetic fluid inclusion study[END_REF][START_REF] Tattitch | Cu-Mo partitioning between felsic melts and salineaqueous fluids as a function of X NaCleq , ƒ O2 , and ƒ S2[END_REF][START_REF] Shang | An Experimental Study of the Solubility and Speciation of MoO 3 (s) in Hydrothermal Fluids at Temperatures up to 350 °C[END_REF]. The higher salinity in our carbon dioxide series relative to the other experiments enhances the solubility of molybdate moieties such as Na 2 MoO 4 and K 2 MoO 4 in fluids and increased D Mo . NaMoO 3 Cl is favored as the main species in hypersaline fluids [START_REF] Tattitch | Cu-Mo partitioning between felsic melts and salineaqueous fluids as a function of X NaCleq , ƒ O2 , and ƒ S2[END_REF].

A trend similar to that observed for the carbon dioxide series was investigated in the water series experiments (Fig. 2b andd

Implications for porphyry deposits

During the evolution of a porphyry system, exsolved fluid will extract metallogenic metals from magma and transport them to the shallow crust, where they are precipitated to form a porphyry deposit [START_REF] Sinclair | Porphyry deposits:Mineral deposits of Canada: A synthesis of major deposit-types, district metallogeny, the evolution of geological provinces, exploration methods: Geological Association of Canada[END_REF]. In the early stage of the formation of Mo deposits, the degree of evolution of felsic magma is low and the magma contains large amounts of volatiles and NBOs, resulting in a relatively small D Mo between fluid and melt. At the same stage, the viscosity of magma is very low, and large volumes of magma are easy to form [START_REF] Zhang | Chemistry, Mineralogy and Crystallization Conditions of Porphyry Mo-forming Magmas at Urad-Henderson and Silver Creek, Colorado, USA[END_REF]. Subsequently, the residual melt will undergo Mo enrichment as the magma ascends to the shallow crust and crystallization differentiation occurs [START_REF] Wang | Petrogenesis of Early Cretaceous post-collisional granitoids at Shapinggou, Dabie Orogen: Implications for crustal architecture and porphyry Mo mineralization[END_REF][START_REF] Zhang | Chemistry, Mineralogy and Crystallization Conditions of Porphyry Mo-forming Magmas at Urad-Henderson and Silver Creek, Colorado, USA[END_REF]. If the magma undergoes sufficient crystal-melt segregation, such as the crystallization of amphibole [START_REF] Du | Early sulfide saturation is not detrimental to porphyry Cu-Au formation[END_REF], the residual melt will be depleted in aluminum and enriched in alkalis. Similar magma compositional variations may be induced by assimilating alkali-rich strata or by mixing with an alkali-rich magma injected into the magma chamber. With decreasing A/NK of the residual melt, D Mo will increase markedly, and more Mo will be distributed into coexisting fluids.

To evaluate the effect of melt composition on the formation of porphyry Mo deposits, we modeled fluid exsolution processes in the magma chamber. In a hypocritical felsic chamber, we assumed that the magma volume is about 100 km 3 , the concentration of Mo is 15 ppm (Audétat and Li, 2017, and references therein), the water content of the magma is about 5 wt.%, and the magma density is 2.5 g/cm 3 . Molybdenum may be hypothetically deposited in a hydrothermal environment with 100% precipitation efficiency [START_REF] Pokrovski | Speciation and Transport of Metals and Metalloids in Geological Vapors[END_REF]. The amount of Mo in the magmatic fluid is thus essential for the grade and scale of porphyry Mo deposits. Using the partition coefficients established in the present study, simple mass balance calculations show that carbon dioxide saline solution (850 °C, 100 MPa, = 0.096, and 17.5 wt.% X CO2

NaCl) extracts about 6.3 times more Mo from peralkaline magma (for A/NK = 0.75 and 51.35 ppm Mo in the fluid phase, 6.4 × 10 5 ton of Mo will be deposited in the porphyry metallogenic stage) than from peraluminous magma (for A/NK = 1.2 and 8.17 ppm Mo in the fluid phase, 1.1 × 10 5 ton of Mo will be deposited in the porphyry metallogenic stage). For fluid composed of pure water (900 °C and 100 MPa), the fluid can extract about 3.5 times more Mo from peralkaline magma (A/NK = 0.72, 7.88 ppm Mo in the fluid phase, 9.8 × 10 4 ton Mo) than from peraluminous magma (A/NK = 1.23, 2.23 ppm Mo in the fluid phase, 2.8 × 10 4 ton Mo) in a closed system. Therefore, a porphyry magma containing excess alkali is a key factor for Mo enrichment and for forming a granite-related Mo ore deposit. Furthermore, we also used the Rayleigh fractionation model to calculate the efficiency of Mo extracted from magma by fluids (Fig. 4).

According to our calculations, in the case where 10% of the fluid is extracted from felsic magma, the concentration of Mo in coexisting fluid is 1058 ppm (D Mo = 4.13, A/NK = 0.75). In the case where D Mo changes to 0.56 (A/NK = 1.2), as obtained for peraluminous melt, the concentration of Mo in coexisting fluid is 171 ppm. The Rayleigh fractionation calculation is consistent with our mass balance calculation results, supporting our interpretation that a peralkaline melt composition favors the formation of porphyry Mo deposits.

A highly evolved magma that is enriched in alkali favors more Mo being distributed into coexisting magmatic fluids, which can explain why magma forming porphyry Mo deposits is typically highly evolved.

Conclusion

Our experimental results show that the partition coefficient of Mo between fluid and felsic melt (D Mo ) decreases with increasing A/NK in melt. D Mo is higher in peralkaline melt than in peraluminous melt, and peralkaline melt is therefore more favorable for the enrichment of Mo during magmatic-hydrothermal processes. This finding improves our understanding of the transport of Mo in magmatic-hydrothermal systems. Any geological processes that act to increase the alkali concentration of melts, such as crystal-melt segregation (e.g., amphibole), assimilation of alkali-rich strata into the magma, and mixing with alkali-rich magma in the magma chamber, favor the formation of porphyry Mo deposits.

Captions for Figures and Tables

Fig. 1 The experimental process and sample assembly used for this study. Pure gold was used for the capsule for the experiments. The capsule was filled with synthetic glass and aqueous solution. The photomicrograph shows double-polished quenched glass. Raman spectroscopy verified the existence of CO 2 . [START_REF] Khitarov | Partition of Zn, Cu, Pb and Mo between the fluid phase and silicate melt of granitic composition under high-temperature and pressure[END_REF], [START_REF] Candela | The partitioning of copper and molybdenum between silicate melts and aqueous fluids[END_REF], [START_REF] Tingle | Transport and concentration of molybdenum in granite molybdenite systems: Effects of fluorine and sulfur[END_REF], [START_REF] Keppler | Partitioning of Cu, Sn, Mo, W, U, and Th between melt and aqueous fluid in the systems haplogranite-H 2 O-HCl and haplogranite-H 2 O-HF[END_REF], Chevychelov and Chevychelova (1997), [START_REF] Webster | Exsolution of magmatic volatile phases from Cl-enriched mineralizing granitic magmas and implications for ore metal transport[END_REF], [START_REF] Bai | The distribution of Na, K, Rb, Sr, Al, Ge, Cu, W, Mo, La, and Ce between granitic melts and coexisting aqueous fluids[END_REF], [START_REF] Schaefer | Determination of trace-element partitioning between fluid and melt using LA-ICP-MS analysis of synthetic fluid inclusions in glass[END_REF], [START_REF] Kravchuk | Molybdenum partition between melts of natural and synthetic aluminosilicates and aqueous-salt fluids[END_REF], [START_REF] Tattitch | Cu-Mo partitioning between felsic melts and salineaqueous fluids as a function of X NaCleq , ƒ O2 , and ƒ S2[END_REF], and this study. Melt and fluid compositions differ among studies. Values of the partition coefficient for natural samples were collected from [START_REF] Zajacz | Determination of fluid/melt partition coefficients by LA-ICPMS analysis of co-existing fluid and silicate melt inclusions: Controls on element partitioning[END_REF], [START_REF] Audétat | The Composition of Magmatic-Hydrothermal Fluids in Barren and Mineralized Intrusions[END_REF], [START_REF] Audétat | Source and Evolution of Molybdenum in the Porphyry Mo(-Nb) Deposit at Cave Peak, Texas[END_REF], and [START_REF] Lerchbaumer | The Metal Content of Silicate Melts and Aqueous Fluids in Subeconomically Mo Mineralized Granites: Implications for Porphyry Mo Genesis[END_REF]. (b) A comparison of experimental data between the present study and Chevychelov and Chevychelova (1997) and [START_REF] Kravchuk | Molybdenum partition between melts of natural and synthetic aluminosilicates and aqueous-salt fluids[END_REF]. A/NK is the molar ratio of Al 2 O 3 / (Na 2 O + K 2 O) in the starting materials. Solid blue circles and squares represent the carbon dioxide series (fluid composition of H 2 O-NaCl-CO 2 ) and water series (pure water containing 1000 ppm each of Rb, Cs, and B) experiments, respectively. Unfilled blue diamonds represent experimental data from [START_REF] Kravchuk | Molybdenum partition between melts of natural and synthetic aluminosilicates and aqueous-salt fluids[END_REF]. Unfilled red hexagons represent experimental data from Chevychelov and Chevychelova (1997) at 1 kbar, and hexagons with a cross represent their experiments conducted at 5 kbar. Table 1 Starting materials of the three series of experiments.

Table 2 Element concentrations of quenched glasses and solutions, and the calculated distribution coefficient (D Mo ) between solutions and quenched glasses. Table 3 The average composition and relative standard deviation (RSD) of quenched glasses of the contrast and water series glasses using data obtained at randomly selected points using LA-ICP-MS. Notes: a The concentration of Mo in the fluid phase. All leaching solution was collected and then analyzed using ICP-MS.

b The concentration of Mo in quenched glass. The glass was dissolved by HNO 3 and HF and then analyzed using ICP-MS.

c The concentration of Mo in quenched glass. LA-ICP-MS was used to avoid analyzing the fluid phase that was trapped in quenched glasses.

σ represents the 1 sigma standard deviation of the measurements.

D Mo bulk means that the partition coefficient was calculated using a/b. D Mo pure means the partition coefficient was calculated using a/c. n.a. data were not analyzed. = CO 2 / (CO 2 + H 2 O) in mole; NBO/T is the ratio of non-bridge oxygen to tetrahedron ions, as X CO2 defined in the discussion section (4.2). The concentrations in parentheses are those of the starting solutions.

  parameter for quantitively understanding Mo enrichment in the process of hydrothermal fluid extraction from fractionated granitic melts. The coefficient is defined as D Mo = , where and are the concentrations of Mo in the aqueous fluid C

  ), whereby in peraluminous melt, D Mo decreases with increasing NBO/T. In contrast, in peralkaline melt, D Mo increases with increasing NBO/T, where the nucleation of Na 2 MoO 4 and K 2 MoO 4 is a critical factor, as the solubility of molybdate controls the partition of Mo between melt and coexisting fluids. In other words, peralkaline residual magma can promote the partitioning of Mo into hydrothermal fluids.

Fig. 2

 2 Fig. 2 The relationship between D Mo and A/NK, NBO/T, and Na 2 O + K 2 O, where A/NK is calculated as Al 2 O 3 /(Na 2 O + K 2 O) (in mole of the starting materials), and Na 2 O + K 2 O is in wt.%. (a) shows the variation in D Mo for the carbon dioxide series experiments. The concentration of Mo in quenched glasses was analyzed by dissolving the glass in HNO 3 and HF and then using ICP-MS for analysis. Error bars are smaller than the scale of the icons. (b) shows the variation in D Mo for the water series experiments. The concentration of Mo in quenched glasses was analyzed using LA-ICP-MS. The dotted red frame represents D Mo in peralkaline melt (d), and the dotted blue frame represents D Mo in peraluminous melt (c and d). (e) and (f) show variation in D Mo with respect to the alkali concentration of melt in carbon dioxide series and water series.

Fig. 3 (

 3 Fig.3(a) Experimental partition coefficients collected from[START_REF] Khitarov | Partition of Zn, Cu, Pb and Mo between the fluid phase and silicate melt of granitic composition under high-temperature and pressure[END_REF],

Fig. 4 A

 4 Fig. 4 A schematic illustrating the exsolution of fluid from magma (left), and the concentration of Mo in coexisting fluid calculated using Rayleigh fractionation with different partition coefficients (right). For the right-hand diagram, the x-axis represents the degree of extraction of fluid from melt, and the y-axis represents the concentration of Mo in coexisting fluids. In Rayleigh fractionation, "F" represents the extraction ratio of fluid, so (1 -F) was used to calculate the concentration of Mo in residual felsic magma.

FiguresFig. 1

 1 Figures

  Fig. 1.

Fig

  Fig. 2.

Fig. 3 .

 3 Fig. 3.

Fig

  Fig. 4.

  Fig. 1.

Fig

  Fig. 2.

Table 1

 1 Starting materials of the three experiments

	Run	T °C	P MPa	Na 2 O wt.%	Al 2 O 3 wt.%	SiO 2 wt.%	K 2 O wt.%	A/NK	NBO/T	Mo ppm
	The carbon dioxide series ( XCO2 = 0.096, 17.5wt.% NaCl)
	M1-1	850	100		5.47	10.86	78.12	5.05	0.75	0.05	952
	M1-2	850	100		4.47	12.46	78.20	3.88	1.08	0.03	805
	M1-3	850	100		5.12	13.05	76.00	4.27	1.00	0.00	693
	M1-4	850	100		4.70	14.42	75.88	3.94	1.20	0.09	717
	M1-6	850	100		5.45	15.06	75.70	3.68	1.16	0.08	576
	The water series (pure water with 1000ppm Rb, Cs, B)
	J-039	900	100		5.28	11.10	77.12	6.41	0.71	0.06	592
	J-040	900	100		5.01	11.86	77.08	5.98	0.81	0.04	497
	J-041	900	100		4.23	14.25	76.15	5.30	1.12	0.06	529
	J-042	900	100		3.92	12.44	77.59	5.95	0.96	0.01	656
	J-043	900	100		3.99	15.26	75.61	5.06	1.27	0.13	591
	J-044	900	100		5.28	11.10	77.12	6.41	0.71	0.06	592
	The contrast series (11.73 wt.% NaCl, 8.34 wt.% KCl)
	J-003	900	100		4.23	14.25	76.15	5.30	1.12	0.06	529
	J-010	900	100		3.99	15.26	75.61	5.06	1.27	0.13	591
	J-016	900	100		5.28	11.10	77.12	6.41	0.71	0.06	592
	A/NK= (Al 2 O 3 )/ (Na 2 O + K 2 O) in mole;	X CO2	= CO 2 / (CO 2 + H 2 O) in mole; NBO/T is the ratio of non-bridge oxygen to tetrahedron ions, as
	defined in the discussion section (4.2). The concentrations in parentheses are those of the starting solutions.

Table 2

 2 Compositions of quenched glasses and leaching solution, and the calculated partition coefficient (D Mo ) between leaching solution and quenched glasses.

	Run.	Na 2 O wt.% Al 2 O 3 wt.% SiO 2 wt.% K 2 O wt.% A/NK NBO/T Mo ppm	Mo ppm	Mo ppm		D Mo D Mo D Mo
								Quenched	Bulk	Pure	σ	Bulk Pure σ
								solution a	glasses b	glasses c
	The carbon dioxide series
	M1-1	n.a.	n.a.	n.a.	n.a.	0.75	0.05	861	208	n.a.		4.13 n.a.
	M1-2	n.a.	n.a.	n.a.	n.a.	1.08	0.03	539	363	n.a.		1.49 n.a.
	M1-3	n.a.	n.a.	n.a.	n.a.	1.00	0.00	367	174	n.a.		2.11 n.a.
	M1-4	n.a.	n.a.	n.a.	n.a.	1.20	0.09	240	428	n.a.		0.56 n.a.
	M1-6	n.a.	n.a.	n.a.	n.a.	1.16	0.08	353	356	n.a.		0.99 n.a.
	The water series
	J-039	5.40	11.52	75.56	6.65	0.72	0.06	174	n.a.	322	36.0	n.a. 0.54 0.06
	J-040	4.78	11.74	76.61	6.12	0.81	0.04	124	n.a.	315	13.0	n.a. 0.39 0.02
	J-041	4.11	13.67	76.09	5.36	1.09	0.04	96	n.a.	482	10.8	n.a. 0.20 0.00
	J-042	3.76	12.19	77.22	5.98	0.96	0.01	139	n.a.	503	25.7	n.a. 0.28 0.01
	J-043	3.89	14.61	75.67	5.01	1.23	0.11	78	n.a.	521	19.5	n.a. 0.15 0.01
	J-044	5.63	12.14	74.21	7.03	0.72	0.06	136	n.a.	337	87.8	n.a. 0.40 0.11
	The contrast series
	J-003	5.12	14.20	73.96	6.61	0.91	0.02	121	302	351	19.4	0.40 0.34 0.02
	J-010	4.51	14.36	74.70	6.28	1.01	0.00	203	437	492	20.3	0.46 0.41 0.02

Table 1

 1 Starting materials of the three experiments

	Run	T °C	P MPa	Na 2 O wt.%	Al 2 O 3 wt.%	SiO 2 wt.%	K 2 O wt.%	A/NK	NBO/T	Mo ppm

Acknowledgments

Financial support for the study was provided by the National Key Research and Development Program of China (2016YFC0600204), the National Natural Science Foundation of China (U1812402, 41673067, and 91955209), and the Open Research Fund of the State Key Laboratory of Ore Deposit Geochemistry to Haihao Guo. We gratefully acknowledge the help of Yanwen Tang and Yinghua Chen during LA-ICP-MS analyses, and Jin Hu and Yan Huang in conducting ICP-MS analyses.

Table 3

The average composition and the relative standard deviation (RSD) of the quenched glasses of the contrast and water series glasses at randomly different points using LA-ICP-MS.

N is the number of analysis points.

σ is the 1 sigma standard deviation of the measurement. Notes: a The concentration of Mo in the fluid phase. All leaching solution was collected and then analyzed using ICP-MS.

b The concentration of Mo in quenched glass. The glass was dissolved by HNO 3 and HF and then analyzed using ICP-MS.

c The concentration of Mo in quenched glass. LA-ICP-MS was used to avoid analyzing the fluid phase that was trapped in quenched glasses.

σ represents the 1 sigma standard deviation of the measurements.

D Mo bulk means that the partition coefficient was calculated using a/b. D Mo pure means the partition coefficient was calculated using a/c. n.a. data were not analyzed.

Table 3

The average composition and the relative standard deviation (RSD) of the quenched glasses of the contrast and water series glasses at randomly different points using LA-ICP-MS.

N is the number of analysis points.

σ is the 1 sigma standard deviation of the measurement.


Lauric Thiault

Matthew I Curnock

Georgina G Gurney

Scott F Heron

Nadine A Marshall

Erin Bohensky

Nao Nakamura

Petina L Pert

Joachim Claudet

Convergence of stakeholders' environmental threat perceptions following mass coral bleaching of the Great Barrier Reef

Keywords: attitudes, climate change, coastal communities, environmental change, environmental threats, Great Barrier Reef, media, public perceptions, risk assessment

come

Introduction

Stakeholder support for conservation and environmental management initiatives is key to their successful implementation [START_REF] Bennett | Why local people do not support conservation: Community perceptions of marine protected area livelihood impacts, governance and management in Thailand[END_REF][START_REF] Alexander | Public attitudes and decision making in environmental resource planning -a perception gap[END_REF]. Failure to secure community support can lead to public resistance and backlash from stakeholders, non-compliance and ultimately, a lack of achievement of social and ecological objectives [START_REF] Pollnac | Marine reserves as linked social-ecological systems[END_REF][START_REF] Gurney | Poverty and protected areas: An evaluation of a marine integrated conservation and development project in Indonesia[END_REF]. Different perceptions among different users and audiences about the relative seriousness of environmental threats is often at the heart of such resistance, affecting public support for management strategies designed to respond to those threats [START_REF] Voyer | Who cares wins: The role of local news and news sources in influencing community responses to marine protected areas[END_REF].

People perceive environmental threats in diverse ways. Complex threats like climate change are characterized by great variation in perceptions and experience, such that no unifying theory is applicable [START_REF] Wolf | Individual understandings, perceptions, and engagement with climate change: insights from in-depth studies across the world[END_REF]. This is because risk judgement, where individuals assess risks based on the probability of a threat and its relative consequences, incorporates considerations such as personal worldviews, affiliation and proximity, emotional affect, and trust [START_REF] Slovic | Trust, emotion, sex, politics, and science: Surveying the risk-assessment battlefield (Reprinted from Environment, ethics, and behavior, pg[END_REF][START_REF] Elliott | Risk perception frames in environmental decision making[END_REF]. These risk assessments are mediated by a variety of societal determinants including experiential and sociocultural factors like social norms and cultural cognition [START_REF] Slovic | Trust, emotion, sex, politics, and science: Surveying the risk-assessment battlefield (Reprinted from Environment, ethics, and behavior, pg[END_REF][START_REF] Kahan | Cultural cognition and public policy[END_REF][START_REF] Gattig | Judgmental discounting and environmental risk perception: dimensional similarities, domain differences, and implications for sustainability[END_REF]. Furthermore, they are amplified or attenuated by institutions such as the media and political systems [START_REF] Kasperson | The Social Amplification and Attenuation of Risk[END_REF][START_REF] Voyer | Who cares wins: The role of local news and news sources in influencing community responses to marine protected areas[END_REF][START_REF] Foxwell-Norton | Saving the Great Barrier Reef from disaster, media then and now[END_REF]. As a result, perceptions may differ greatly among social subgroups (e.g. livelihood groups).

The socially constructed nature of environmental threat perceptions also raises the question of how sensitive such perceptions are to contextual change, including environmental change. Indeed, in addition to potentially affecting individuals' personal experiences, environmental crises often attract increased levels of media coverage of the threat in question, which may lead to shifts in public concern over certain issues [START_REF] Carmichael | Elite cues, media coverage, and public concern: an integrated path analysis of public opinion on climate change, 2001-2013[END_REF]Curnock et al. 2019). However, the social effects of such crises are context-dependent, and such shifts in concern only happen in amenable public arenas, where widely shared cultural, institutional and political conditions enable sustained attention to the crisis [START_REF] Ungar | Media context and reporting opportunities on climate change: 2012 versus 1988[END_REF]. Analyzing how threat perceptions within a community change in response to events or shocks within a social-ecological system can help to better understand the emergence and dissipation of common and conflicting perceptions, and identify the key drivers of these changes [START_REF] Siegrist | The necessity for longitudinal studies in risk perception research[END_REF]. Such knowledge is valuable for resource managers seeking to engage successfully with communities to raise awareness and encourage participation in the design and implementation of socially relevant management actions [START_REF] Kochalski | Public perception of river fish biodiversity in four European countries[END_REF].

However, despite recognition of the potential plasticity of community perceptions of environmental threats, most assessments of perceptions are static and the temporal dynamics are rarely studied explicitly [START_REF] Siegrist | The necessity for longitudinal studies in risk perception research[END_REF].

In order to fill this gap, we set out to evaluate changes in stakeholders' perceptions of key environmental threats in the context of a major environmental disruption. Specifically, we examine the prioritization of environmental threats within and among three distinct stakeholder groups (commercial fishers, tourism operators, and coastal residents) in the Great Barrier Reef (GBR or Reef) region, Australia, before and after the unprecedented and wide-spread climate-change induced coral bleaching events in 2016 and 2017 (Hughes et al. 2018a(Hughes et al. , 2018b)). We ask: (1) Do fishers, tourism operators, and coastal residents perceive environmental threats differently? (2) What are the positive and negative associations between the identified threats? (3) Did threat prioritization and associations within and among stakeholder groups change following the mass coral bleaching events? The GBR represents an important case study to help improve our understanding of the responsiveness of environmental threat perceptions to major risk events among interest groups and the general public. This importance is underpinned by its World Heritage and iconic status, the multiple uses and dependencies of adjacent communities and industry sectors, the complexity of threats it faces from local to global scales, and the myriad intangible social and cultural values with which it is associated [START_REF] Gurney | Redefining community based on place attachment in a connected world[END_REF]Marshall et al. 2019a;Curnock et al., 2019). It is hoped that our study will provide social scientists, conservation practitioners and resource managers with an improved understanding of the dynamic nature of environmental threat perceptions, to facilitate more purposeful and effective public engagement around threat mitigation in their responses to future risk events.

Methods

The Great Barrier Reef

The Great Barrier Reef (GBR) is the largest coral reef system in the world, spanning 2,300 km along the east coast of Queensland, Australia. Despite being considered one of the best managed systems globally [START_REF] Mccook | Adaptive management of the Great Barrier Reef: a globally significant demonstration of the benefits of networks of marine reserves[END_REF], live coral cover has declined by an average of 0.67 %/year since 1996 as a result of cumulative impacts from multiple, interacting threats [START_REF] Mellin | Spatial resilience of the Great Barrier Reef under cumulative disturbance impacts[END_REF]. Through an evidence-based assessment process, the Great Barrier Reef Marine Park Authority (GBRMPA) has consistently identified climate change as the greatest threat to the GBR since 2009 (GBRMPA, 2009;2014;2019a). Other major threats identified through this process include poor water quality (i.e., nutrient, sediment and pesticide runoff), coastal development, some remaining impacts of fishing and illegal fishing and poaching, and outbreaks of Crown-of-Thorns Starfish (COTS). Collectively these threats have resulted in a downgrading of the overall outlook for the GBR from "poor" (GBRMPA 2009(GBRMPA , 2014) ) to "very poor" in recent years (GBRMPA 2019a).

In response to these assessments, a series of management interventions aimed at protecting biodiversity and increasing ecosystem resilience have been developed (Great Barrier Reef blueprint for resilience 2017). Further, a variety of community engagement initiatives and programs led by GBRMPA (e.g. Eye on the Reef, Reef Guardian, Reef Joint Field Management Program, Local Marine Advisory Committees, Reef Advisory Committees) have provided avenues to foster stakeholders' support for management and engagement in stewardship activities.

GBR stakeholder groups

We compared threat perceptions among three key stakeholder groups of the GBR region, namely commercial fishers, tourism operators and coastal residents. These groups have different levels and types of direct interaction with the GBR and therefore, we hypothesized may have different threat perceptions. The former two groups represent the two largest reef-dependent industries on the GBR region, but they engage with the Reef in different ways and have distinct socio-demographic and political characteristics [START_REF] Curnock | The Social and Economic Long Term Monitoring Program (SELTMP) 2014 Tourism in the Great Barrier Reef[END_REF][START_REF] Tobin | The Social and Economic Long Term Monitoring Program (SELTMP) 2014 -Commercial Fishing in the Great Barrier Reef[END_REF]. GBR tourism operators tend to be entrepreneurial, have achieved a high level of education, and are sensitive to tourists' perceptions and media representations of GBR threats [START_REF] Curnock | The Social and Economic Long Term Monitoring Program (SELTMP) 2014 Tourism in the Great Barrier Reef[END_REF](Curnock et al. , 2019;;Curnock & Marshall 2019). Commercial fishers have been found to be a relatively homogeneous male-dominated group, and tend to be older and more politically conservative than tourism operators [START_REF] Tobin | The Social and Economic Long Term Monitoring Program (SELTMP) 2014 -Commercial Fishing in the Great Barrier Reef[END_REF]Marshall & Curnock 2019a).

Data collection and coding of threats

Data on environmental threat perceptions was elicited through surveys with 5,254 individuals in 2013 (n=3,304) and 2017 (n=1,950) as part of the Social and Economic Long-Term Monitoring Program (SELTMP) for the GBR [START_REF] Marshall | Advances in monitoring the human dimension of natural resource systems: An example from the Great Barrier Reef[END_REF]). In the 2013 survey, respondents included 2,975 coastal residents, 210 commercial fishers and 119 owners and managers of marine and island tourism businesses operating in the GBR. In the 2017 survey, they included 1,765 coastal residents, 91 commercial fishers and 94 tourism operators.

National and international tourists were also surveyed in the SELTMP but were not included in this analysis because this paper focuses on local stakeholders. Coastal residents and tourists were surveyed using face-to-face interviews in the main population centers along the GBR, and tourism operators and commercial fishers were interviewed by telephone. For both the 2013 and 2017 sampling periods, the research was reviewed and approved by the CSIRO Social Science Human Research Ethics Committee, and was conducted in accordance with the Australian National Statement on Ethical Conduct in Human Research (2007).

To elicit threat perceptions, respondents were asked to list the "three most serious threats to the GBR" in a short, open-ended format. Responses were collated and then each was numerically coded (1=yes; 0=no) into 13 broad thematic categories (Table 1; these categories are described further in Curnock et al. (2019)). The coding and analysis did not take into account the ranking or order of threats as listed by the respondents. The SELTMP surveys also obtained information on gender and age, which have been shown to influence perceptions [START_REF] Jefferson | Public perceptions of the UK marine environment[END_REF]) and were thus used to control for unbalanced sampling across years (Supporting Information). Additional details on survey design and administration in the SELTMP are available at (CSIRO 2019).

Data analysis

We explored changes in threat perceptions through three distinct analyses. First, we focused on the change in occurrence of threats over time within stakeholder groups. For each of the 12 threat categories ("other" was excluded), we used a general linear model (GLM) with a binomial fit, where the response variable was threat occurrence and the predictor variables were stakeholder group membership, year, gender and age. An interaction between group membership and year was examined to elucidate whether perceptions of the threat differed significantly across the two time periods for different groups. Demographic variables were included to control for bias in unequal distribution of samples on both years.

Second, for each threat category we assessed the variation in threat occurrences in each year among stakeholder groups. We used GLMs with a binomial fit of threat occurrence as a function of stakeholder group, gender, and age and quantified the variation in the response that was explained by the 'stakeholder group' covariate using the models' estimated variance.

Third, we examined the associations between perceived threats in each stakeholder group using probabilistic models of threat co-occurrence. Expected frequency of co-occurrence was determined based on the distribution of each threat being random and independent of the other threats. We compared the observed and expected frequencies of co-occurrence between each pair of threats to determine which threats tended to be statistically more or less identified together than expected by chance. All analyses were implemented in R statistical analysis software version 3.6.2 (R Core Team 2017).

Results

Analysis of within-stakeholder group perception changes revealed both significant increases and decreases in the occurrence of several threats from 2013 to 2017 (Fig. 1). The direction of these changes was generally consistent across the three stakeholder groups. Between 2013 and 2017, most notably, there was an increase in the perceived threat of 'climate change' across all groups (though not significant for tourism operators because it was already considered a priority threat by this group in 2013), with commercial fishers showing the largest relative shift. 'Pollution' also became more frequent among the three threats perceived as most serious to the GBR, although increases were only significant for coastal residents and tourism operators. The proportion of respondents perceiving 'coastal development' and 'shipping' among the top three threats fell significantly across all groups.

The occurrence of 'fishing' increased sharply among fishers, and decreased slightly (but significantly) among residents. Over the four-year sampling interval, the occurrence of 'poor water quality' also decreased for all stakeholder groups, but the change was only significant for residents. Although significant for residents, the magnitude of the changes in occurrence probability remained relatively low for other threat categories (Fig. 1).

In 2013, threats that were perceived as being the most serious for the GBR differed between stakeholder groups (Fig. 2). Fishers were primarily concerned with 'coastal development' (p=0.38), while tourism operators were most concerned about 'poor water quality' (p=0.40), and coastal residents indicated 'shipping' as the most serious threat (p=0.36). In 2017, however, 'climate change' became the threat most likely to be identified among the top three most serious threats to the GBR by all stakeholder groups (fishers: p=0.43; operators: p=0.53; residents: p=0.55). 'Fishing' was the second threat most likely to be mentioned by fishers (p=0.42) and ranked third for tourism operators (p=0.23) and residents (p=0.26).

Other environmental threats that ranked high in 2017 included poor water quality (fishers: p=0.30; operators: p=0.27; residents: p=0.22), governance (fishers: p=0.21; operators: p=0.23) and pollution (residents: p=0.45).

In 2013, it was also noted that there was significant variation among stakeholders in their perceptions for all threats except 'poor water quality', with stakeholder group accounting for 12%-34% of the variation in threat perceptions (Fig. 3). Fishers tended to list 'climate change' significantly less frequently than tourism operators and coastal residents. Residents listed 'pollution' and 'shipping' more frequently than other groups. Although not statistically significant, tourism operators tended to identify 'poor water quality' and 'climate change' more frequently than fishers and residents. The variation among stakeholders decreased markedly in 2017, with the variable 'stakeholder group' accounting for just 6%-16% of the variation in environmental threat perceptions (Fig. 3). The largest variations in 2017 were in 'pollution' and 'fishing', which occurred more frequently among residents and fishers, respectively.

In 2013, interactions between the perceived key threats did not overlap among the stakeholder groups and revealed more negative associations than positive associations for all three stakeholder groups (Fig. 4). For example, 'climate change' was negatively associated with 'natural disasters', 'coastal development' and 'pollution' for fishers; with 'fishing' and 'mining' for tourism operators; and with 'COTS' for coastal residents (Fig. 4). In the fishers' network, two other negative associations ('pollution' with 'poor water quality'; and 'fishing' with 'governance') and one positive association ('natural disasters' with 'mining') were evident. In the tourism operators' network, 'coastal development' was negative associated with 'governance', while 'pollution' significantly co-occurred with 'shipping'. In the residents' network, negative associations between 'COTS' and 'governance', and between 'fishing' and the 'pollution'-'humanity' positive association cluster were identified. Contrary to 2013, interactions between the key perceived threats in 2017 revealed more positive than negative associations, with clear overlap between stakeholder groups (Fig. 4). 'Climate change' formed new positive associations with 'fishing' and 'poor water quality' for all stakeholder groups. In the fishers' network, 'fishing' and 'poor water quality' became also positively associated. Tourism operators' and residents' networks both displayed a negative association between 'climate change' and 'COTS'; for the operators' network, this negative association was part of an interactions cluster of 'COTS' (negative) with 'climate change' and 'poor water quality' (positive).

Discussion

Community and stakeholder support is often critical for conservation success.

Understanding community perceptions of environmental threats, and how these may vary between social subgroups and over time is therefore important for guiding strategic engagement and policy development. Our analysis of environmental threat perceptions of commercial fishers, tourism operators, and coastal residents with respect to the GBR across two time periods revealed three key results. First, environmental threat perceptions can shift in a relatively short time in response to contextual changes. Second, following a major environmental disturbance event, stakeholder groups increasingly identified similar threats, both between and among groups. Lastly, the perceived threat of climate change rose to become the most prominent source of concern for each of the stakeholder groups.

Plasticity of environmental threat perceptions

The major shift in threat perceptions over a relatively short time period in our case study points to the plasticity of these perceptions. Whilst recent studies indicate that people do not consider the media a trusted source of information about the GBR [START_REF] Mackeracher | Who trusts whom in the Great Barrier Reef? Exploring trust and communication in natural resource management[END_REF], they also acknowledge the media's centrality in communication about environmental issues (Foxwell-Norton & Lester 2017). The majority of the public, including those who live closest to the GBR, have little direct experience of the Reef and rely on visual representations largely shaped by information and knowledge communicated through the media. In our case, the observed changes in threat perceptions appear to reflect the relative prominence of different threats communicated in the media. For example, the grounding of a coal carrier on a shoal in the GBR in 2010 and controversy over the Abbot Point Capital Dredging Project in 2013 received extensive media coverage at the time, and were considered likely to have influenced public perceptions of the risks posed by shipping and coastal development to the GBR [START_REF] Lankester | Media representations of risk: the reporting of dredge spoil disposal in the Great Barrier Reef Marine Park at Abbot Point[END_REF]. We suspect that the visibility of these two events in the media influenced the high degree of concern about these threats in the 2013 survey. In the 2017 survey, however, our results reveal that climate change became the foremost issue for all local stakeholder groups. The extent, magnitude and ecological impact of the 2016 and 2017 mass bleaching events (Hughes et al. 2018a(Hughes et al. , 2018b) ) and the considerable attention from the media that explicitly attributed the events to climate change likely increased people's concerns about this issue [START_REF] Eagle | Competing and conflicting messages via online news media: Potential impacts of claims that the Great Barrier Reef is dying[END_REF]Curnock et al. 2019;Boudet et al. 2019). Together, these results indicate that shifts in perceptions were related in part to changes in the predominance of particular issues in the media [START_REF] Lee | Predictors of public climate change awareness and risk perception around the world[END_REF]Boudet et al. 2019), and are suggestive of the media's importance and likely influence on public perceptions.

Media constructions of threats to the GBR have been implicated in the divergence of perceptions held by the public and those of managers regarding which threats are most critical [START_REF] Moscardo | Exploring public awareness of threats to the Great Barrier Reef environment[END_REF]. The contribution of journalistic norms, whereby some issues are given primacy in reporting over others [START_REF] Boykoff | Climate change and journalistic norms: A case-study of US mass-media coverage[END_REF], may provoke or further exacerbate such incongruity [START_REF] Voyer | Who cares wins: The role of local news and news sources in influencing community responses to marine protected areas[END_REF]). For instance, some have proposed that increased attention to plastic pollution in the media over recent years may have a "crowding-out effect" on the urgency of other threats for which the consensus among scientists and managers is better established, such as climate change [START_REF] Stafford | Viewpoint -Ocean plastic pollution: A convenient but distracting truth?[END_REF]. However, our results from 2017 do not show a negative association between 'pollution' and 'climate change' (or any other threat), disputing the presence of such an effect in our case. Although it should be noted that a high proportion of residents cited plastic pollution as a key threat to the GBR (Supporting Information).

Climate change as a primary source of concern for the GBR

In 2017, after the GBR experienced some of the worst and most widespread effects of climate change on live coral (Hughes et al. 2018a) and associated fish assemblages [START_REF] Richardson | Mass coral bleaching causes biotic homogenization of reef fish assemblages[END_REF], climate change was the most frequenlty mentioned threat for all stakeholder groups (42-55% of the 2017 sample). Our finding that 55% of coastal residents perceive climate change in the top three threats to the GBR only partly aligns with results from a report (based on data from the same survey that we employed) that found that 68% of respondents considered climate change "an immediate threat requiring action"; Marshall & Curnock 2019). This discrepancy may be because the latter question relates the threat of climate change in general terms, while our paper examines the threat of climate change to the GBR specifically.

While many news media representations of the 2016-17 mass coral bleaching events attributed climate change as the cause [START_REF] Eagle | Competing and conflicting messages via online news media: Potential impacts of claims that the Great Barrier Reef is dying[END_REF], there was a concurrent "alternative facts" campaign in Australia run by vested-interest groups and conservative news media that denied the climate change attribution [START_REF] Opray | Peter Ridd and the climate sceptics[END_REF]. Survey respondents' political orientation and their primary sources of news in relation to the coral bleaching event could have influenced their threat perceptions and acceptance of climate change as the cause of recent mass bleaching [START_REF] Lee | Predictors of public climate change awareness and risk perception around the world[END_REF]. As climate-related environmental communication campaigns are susceptible to polarization and misinformation, managers and scientists face serious challenges in a media landscape that is increasingly susceptible to the intentional dissemination of misleading content (van der Linden 2019). In Australia, this is confounded by a highly concentrated media ownership [START_REF] Holmes | Climate change communication in Australia: the politics, mainstream media and fossil fuel industry nexus[END_REF] and increasingly skeptical climate change reporting [START_REF] Bacon | Sceptical climate part 2: Climate Science in Australian Newspapers[END_REF].

We note that in the Austral summer of 2020, a third climate-induced mass coral bleaching event occurred in the GBR, coinciding with the onset of the global COVID-19 pandemic. The concurrence of these two major events raises questions about whether public perceptions about the threat of climate change have increased in prominence, or if the pandemic has "crowded-out" such concerns by affecting reporting opportunities related to this last bleaching event. Further studies may be able to elucidate the relative effects of these historically significant events.

Convergence of threat perceptions within the community

Achieving consensus among stakeholders is a persistent challenge with consequences that can affect the success of decision-making [START_REF] Hicks | Synergies and tradeoffs in how managers, scientists, and fishers value coral reef ecosystem services[END_REF]. Shared perceptions within the community can help practitioners identify joint management goals and reduce disagreement between different stakeholder groups that potentially hold dissimilar knowledge and values [START_REF] Sutton | Recreational fishers' attitudes towards the 2004 rezoning of the Great Barrier Reef Marine Park[END_REF]de Nooy 2013). Increased similarity in perceptions of the most serious threats to the GBR across stakeholder groups in 2017 suggests that GBR managers may be better situated to develop management strategies that are likely to receive broad-based support [START_REF] Horowitz | Investigating stakeholder perceptions of fish decline: making sense of multiple mental models[END_REF]. Our findings also suggest which strategies are likely to work well in public communication because they are directed towards threats that resonate with the majority of stakeholders. In particular, climate change, which now ranks at the top of the list across all stakeholder groups, may represent a relevant entry point for engagement with other relevant issues that also ranked high among fishers, tourism operators and residents, such as water quality and fishing. This also suggests that most people would accept GBRMPA's framing that links climate change resilience to improved water quality and strong fishing regulation (GBRMPA 2019b), and highlights a potential window of opportunity for managers to engage with synergistic policy interventions to protect the Reef and other ecosystems [START_REF] Morrison | Save reefs to rescue all ecosystems[END_REF].

Although threat perceptions held by the different stakeholder groups became more aligned in 2017, some differences remained. Commercial fishers were increasingly concerned about the threat posed by fishing, with concerns centered around overfishing (~50% of fishing threats were related to overfishing; Supporting Information). Whether they considered themselves as contributing to overfishing was not explored further in our survey. However, given that 40% of identified fishing threats related to recreational fishing, it appears that many commercial fishers did not consider their group responsible for the threat. Coastal residents were substantially more concerned about pollution (Fig. 1), including plastic pollution (Supporting Information). This may be because residents' first-hand experience of the GBR is generally limited to local beaches where the most visible threat is marine debris [START_REF] Marshall | Changes among coastal residents of the Great Barrier Reef region from 2013 to 2017[END_REF]). Further, recent years have seen significant media coverage of the threat of plastic pollution to global ocean environments [START_REF] Stafford | Viewpoint -Ocean plastic pollution: A convenient but distracting truth?[END_REF].

Identifying and engaging key stakeholder groups is important, but such groups are rarely homogenous (D'Anna 2016). As a result, decision-makers looking for consensus by focusing engagement on the most serious threats may neglect potentially complex interactions that could lead to sub-optimal outcomes. For example, there is a risk that apparent similarities between stakeholder groups may mask conflicts within these groups that, if not addressed, would ultimately affect whether individuals support management actions. Our analysis of the associations between threats found that most negative associations present in 2013 were absent four years later. Instead, positive associations between high-priority threats (i.e. 'climate change', 'poor water quality', and 'fishing') became evident within all groups, suggesting that addressing these threats may now be perceived as complementary.

While the most frequently mentioned threats were increasingly identified together, some negative associations remained in the post-coral bleaching period. The perception of COTS as a serious threat tended to be negatively associated with those of climate change (among tourism operators and residents) and water quality (for residents). In such cases, a key challenge is to ensure that communications with stakeholder groups focused on one threat do not undermine or detract from what is being communicated about the others. Two approaches for overcoming this challenge warrant examination. First, separate the communication of policies to diminish the tension. For example, policies to address water quality (e.g. grants to farmers to implement best water management practice) and COTS (e.g. COTS control) could be communicated as separate programs, even if they are linked in the management strategy. A second approach is to ensure communication, and policies themselves, explicitly address these tensions; for example, explaining how culling COTS will have positive impacts on the Reef's resilience to climate change [START_REF] Anthony | Operationalizing resilience for adaptive coral reef management under global environmental change[END_REF] or how addressing water quality will reduce COTS outbreaks [START_REF] Wooldridge | Environmental triggers for primary outbreaks of crown-ofthorns starfish on the Great Barrier Reef, Australia[END_REF].

Given the 2017 landscape of threat perceptions, a focus on the most widely recognized threats that has positive associations across stakeholders could inform communication of the integrated management strategies to the community, and could have additive effects through providing extra justifications. This means placing most emphasis on the risk posed by climate change, poor water quality, and certain aspects of fishing, and the need for a management approach that articulates multiple threat-mitigating strategies. For example using land-based management in combination with marine protected area networks [START_REF] Mccook | Adaptive management of the Great Barrier Reef: a globally significant demonstration of the benefits of networks of marine reserves[END_REF][START_REF] Macneil | Water quality mediates resilience on the Great Barrier Reef[END_REF]. For engagement with particular stakeholders, however, we recommend close consideration of the dominant priorities within each group.

Consistent and balanced messaging in response to an environmental crisis can help to achieve attitudinal and behavioral change when framed in accordance to people's values [START_REF] Kochalski | Public perception of river fish biodiversity in four European countries[END_REF]van der Linden et al. 2019). Indeed, in the case of the GBR, this has been suggested in relation to different forms of place attachment [START_REF] Gurney | Redefining community based on place attachment in a connected world[END_REF]. Given the strong attachments that people hold for the GBR and the negative emotions or grief they are exhibiting in response to its degradation (Marshall et al. 2019c(Marshall et al. , 2019a)), engagement relating to threats that leverages different forms of attachment to the GBR may hold promise [START_REF] Smith | The role of emotion in global warming policy support and opposition[END_REF]. Further, targeting messages about the impact of threats on particular habitats (e.g. beaches, estuaries, and iconic reef sites) and species (e.g. whales, turtles, and corals) that stakeholders value [START_REF] Marshall | Changes among coastal residents of the Great Barrier Reef region from 2013 to 2017[END_REF]) holds additional potential.

Finally, leveraging other information channels (e.g. opinion leaders and change agents) and highlighting evidence of effectiveness may have the potential to facilitate impactful messaging that fosters greater stakeholder support for conservation initiatives [START_REF] Reynolds | Communicating the effectiveness and ineffectiveness of government policies and their impact on public support: a systematic review with meta-analysis[END_REF].

Conclusion

Understanding stakeholders' perceptions of key threats to the natural environment provides critical insights into what kind of management and communication strategies are most likely to resonate with the relevant community. High-profile environmental crises appear to have an important influence on shaping perceptions and may create new opportunities to engage people with mitigation and adaptation. Our approach provides an empirical account of the plasticity of perceptions and shows how stakeholders associate different environmental threats in relation to an iconic natural asset. These findings highlight the importance of further research on this topic and of social monitoring for natural resource management, to understand evolving threat perceptions (and drivers) among different stakeholder groups and communities, providing insights for improved community engagement in threat mitigation policies and actions. Our study further provides guidance for social scientists on conceptual and empirical approaches and analytical tools to elucidate environmental threat perceptions.

Figure 1 :

 1 Figure1: Changes in the environmental threat perceptions of stakeholder groups between 2013 and 2017. Solid points represent occurrence probability estimates and error bars the bootstrapped 95% confidence intervals. Red and blue colors respectively indicate significant increases and decreases in threat occurrence probability within the stakeholder groups over time. OR: odds ratio. OR>1 indicates increased odds of identifying a given threat among the three most serious threats to the GBR. Only the eight most frequently reported threats are displayed. See Supporting Information for results for all threat categories (n=12) except 'other'.

Figure 2 :

 2 Figure2: Changes in the rankings of perceived threats to the GBR between 2013 and 2017 across stakeholder groups. The thickness of a band indicates the probability of a particular threat being identified as one of the three most serious threats to the GBR (thicker band means higher probability).

Figure 3 :

 3 Figure 3: Variation in threat perceptions among stakeholder groups in 2013 (yellow) and 2017(green). Different letters at the top of bars indicate significant differences among stakeholder groups within each year, as revealed by generalized linear models. N.S.: not significant; F: commercial fishers; O: tourism operators; R: coastal residents. The eight most frequently identified threats are displayed. See Supporting Information for results for all 12 threat categories except 'other'.

Figure 4 :

 4 Figure4: Network diagrams showing interactions among threats prioritized as most serious to the Great Barrier Reef by commercial fishers, tourism operators, and residents in 2013 and 2017, based on co-occurrence analysis. The size of the node reflects the threat's occurrence probability (larger node means higher probability). Green ties (interactions) indicate nonrandom tendencies to co-occur and orange ties indicate non-random tendencies to be associated negatively between pairs of threats (nodes). Ties are only highlighted where the observed frequency of interaction differs from expected random frequency.

FiguresFigure 1 :

 1 Figures

Figure 2 :

 2 Figure 2: Changes in the rankings of perceived threats to the GBR between 2013 and 2017 across stakeholder groups. The thickness of a band indicates the probability of a particular threat being identified as one of the three most serious threats to the GBR (thicker band means higher probability).

Figure 3 :

 3 Figure 3: Variation in threat perceptions among stakeholder groups in 2013 (yellow) and 2017(green). Different letters at the top of bars indicate significant differences among stakeholder groups within each year, as revealed by generalized linear models. N.S.: not significant; F: commercial fishers; O: tourism operators; R: coastal residents. The eight most frequently identified threats are displayed. See Supporting Information for results for all 12 threat categories. except 'other'.

Figure 4 :

 4 Figure 4: Network diagrams showing interactions among threats prioritized as most serious to the Great Barrier Reef by commercial fishers, tourism operators, and residents in 2013 and 2017, based on co-occurrence analysis. The size of the node reflects the threat's occurrence probability (larger node means higher probability). Green ties (interactions) indicate nonrandom tendencies to co-occur and orange ties indicate non-random tendencies to be associated negatively between pairs of threats (nodes). Ties are only highlighted where the observed frequency of interaction differs from expected random frequency.

TableTable 1 :

 1 Threat categories used to categorize survey participants responses to the open-ended question "what are the three most serious threats to the Great Barrier Reef?". See Supporting Information for distribution of sub-categories andCurnock et al. (2019) for the process for identifying the categories.

	Threat categories	Example responses
	Climate change	Climate change; global or ocean warming; rising temperatures; sea
		level rise; ocean acidification; coral bleaching
	Pollution	Pollution; marine debris; litter; plastic; rubbish
	Poor water quality	Agricultural, urban and industrial runoffs; sediments; pesticides;
		sewage; fertilizers
	Coastal development	Port expansions; dredging; infrastructures; harbors; coastal
		development
	Crown-of-thorns starfish	COTS; the starfish
	(COTS)
	Fishing	Commercial and recreational fishing and collecting; illegal foreign
		and domestic fishing; overfishing; poaching
	Shipping	Shipping traffic; collisions; oil spills; big tanker ships; ballast waters
	Natural disaster	Natural disasters; storms; cyclones; floods; tsunamis; earthquakes
	Governance	Mismanagement; bureaucracy; politics; lack of enforcement;
		corruption; lack of government support or involvement
	Tourism	Tourism; trampling; diver impacts; unsustainable tourism
	Mining	Mining industry; Adani; coal
	Humanity	Overpopulation; damage from humans; human activities; bad
		human behavior; people; societal attitudes
	Other	Habitat loss; invasive species; other

Supporting Information

Community information and survey sample (Appendix S1), the proportion of threat subcategories across stakeholder groups (Appendix S2), within-and among-stakeholder group variation in threat perception between 2013 and 2017 (Appendix S3), and extend methods for data analysis (Appendix 4) are available online. The authors are solely responsible for the content and functionality of these materials. Queries (other than absence of the material) should be directed to the corresponding author.