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Programme National Environnement CôtierNew Caledonia Pilot Site ProgrammeAbstract presentation1999-2002 activitiesObjectivesThe aim of the New Caledonia pilot site programme is to assess how human activities affectthe transport and transformation of terrigeneous and anthropogenic inputs and the structureand functioning of marine organisms and populations. The high island coral reef lagoonstudied is an original ecosystem with some significant specificity in its geomorphology,environmental conditions, trophic status or ecosystem composition (Labrosse et al., 2000).The programme is organised according to 5 combined research actions.• Action 1 « Circulation and transport of terrigeneous and anthropogenic inputs » focus onthe study of the physico-chemical environment by characterising and modelling watercurrents, the subsequent distribution of water chemistry and particle transport anddeposition.• Action 2 « Biogeochemical functioning of the lagoon system » focus on interactionsbetween the non living environment and planktonic and benthic populations on the basisof biogeochemical and geochemical approaches.• Action 3 « Transfer of metals through the trophic food chain » prolongs the metalgeochemistry work from the 2 previous actions by assessing how metals are incorporatedin the benthic biota.• Action 4 « Variations in growth of lagoon organisms » assess how human activities andassociated environmental alteration affect the growth of fishes and ...
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Programme National Environnement Côtier
New Caledonia Pilot Site Programme
Abstract presentation
1999-2002 activities
Objectives The aim of the New Caledonia pilot site programme is to assess how human activities affect the transport and transformation of terrigeneous and anthropogenic inputs and the structure and functioning of marine organisms and populations. The high island coral reef lagoon studied is an original ecosystem with some significant specificity in its geomorphology, environmental conditions, trophic status or ecosystem composition ( Labrosse et al., 2000 ). The programme is organised according to 5 combined research actions. • Action 1 « Circulation and transport of terrigeneous and anthropogenic inputs » focus on the study of the physico-chemical environment by characterising and modelling water currents, the subsequent distribution of water chemistry and particle transport and deposition. • Action 2 « Biogeochemical functioning of the lagoon system » focus on interactions between the non living environment and planktonic and benthic populations on the basis of biogeochemical and geochemical approaches. • Action 3 « Transfer of metals through the trophic food chain » prolongs the metal geochemistry work from the 2 previous actions by assessing how metals are incorporated in the benthic biota. • Action 4 « Variations in growth of lagoon organisms » assess how human activities and associated environmental alteration affect the growth of fishes and invertebrates. • Action 5 « Indicators of reef-lagoon environmental and resource status » largely synthesise the programme outcomes to identify and define ecological indicators.
Participants In 2002, the New Caledonia pilot site programme gathered a total of 102 participants corresponding to slightly more than 25 full time equivalents. Regarding student training, 26 graduate and undergraduate students have been formed over the 1999-2002 period and as much reports were published; 14 PhD thesis have been conducted or are currently underway. International collaboration has been reinforced especially as New Caledonia has a specific position both due to its coral reef lagoon environments and geographic situation in the Pacific Ocean. Collaborative work has beeen especially developped with Australia where coral reef is a key issue. Additionally, scientific transfer has been conducted through the ongoing collaboration between IRD and the regional University of the South Pacific based in Fidji, the latter being in charge of student formation from 12 Pacific island states. The list of research institutions and universities involved in each research action is presented bellow. Action 1 - Circulation and transport of terrigeneous and anthropogenic inputs ANSTO, Australia . Radioecology and tracers (Peck G.., Szymczack R.) Centre dOcéanologie de Marseille . DIC-CO 2 system (Romano, Bensoussan). CNRS Banyuls . Nutrients and dissolved carbon by HTCO (Cauwet, Deliat, Pujo-Pay). IRD, Nouméa. Hydrodynamic modelling (Douillet), water chemistry (Chifflet, Fichez, Pagès). Université de Perpignan . Particle mineralogy (Courp). Université de Toulon . Particle transport modelling and wave turbulence (Ouillon, Schmied). Action 2 - Biogeochemical functioning of the lagoon system Centre dOcéanologie de Marseille . Fluxes at the water sediment interface (Grenz), Biogeochemical modelling (Bujan, Faure, Grenz, Pinazo). CNRS, Banyuls . Organic matter, primary production (Cauwet, Pujo-Pay, Conan). CNRS, Paris. Fluxes at the water sediment interface (Boucher).
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Ecole Pratique des Hautes Etudes, Perpignan. Phytoplankton (Delesalle) Institut Pasteur, Paris . Genetics & toxicology (Tandeau de Marsac, Iteman, Rippka, Herdmann). IRD, Nouméa. Water sediment fluxes (Chevillon, Chifflet, Fichez), micro & phytoplankton (Pagès, Torréton), Trichodesmium (Le Borgne, Le Bouteiller, Neveux, Rodier, Tenorio). James Cook University, Townsville, Australie . Sédimentology (Larcombe, Ridd). Observatoire Océanologique Européen (OOE), Monaco . Protists (C. Ferrier-Pagès). Université de Bretagne Occidentale, Brest . Fluxes at the water sediment interface (Clavier, Chauvaud), iron analysis (Blain). Université de Lille .Fluxes at the water sediment interface (Denis). Université de Montpellier . Pelagic communities, modelling (Trousselier). Action 3 Transfer of metals through the benthic trophic food chain ANSTO, Australia . Metal incorporation in bivalve shells (Jeffree). IAEA, Monaco . Radioecology (Cotret, Fowler, Teyssié, Warnau). Ifremer, Nouméa. Metal bioaccumulation in shrimps (Lemonier, Munier). IRD, Nouméa. Metal bioaccumulation (Breau, Fichez), microbiology (Pringault, Viret). Université Bretagne Occidentale, Brest . Bivalve growth (Chauvaud, Clavier, Thébault). Université de la Rochelle. Metal ecotoxicology (Fichet, Miramand, Radenac). Université de Nantes . Biomarkers of metal contamination (Amiard, Berthet). Action 4 - Variations in growth of lagoon organisms Ifremer, Brest . Otoliths analysis (de Pontual) Ifremer, Sète . Fish genetics (Dietrich) IRD, Nouméa . Fish ecology (M. Kulbicki). IRD, Brest . Otoliths analysis, bivalve growth (Marec, Morize, Stéquert) Université de Bretagne Occidentale, Brest . bivalve growth (Chauvaud, Clavier, Lorrain, Paulet, Thébault, Thouzeau) Ecole Pratique des Hautes Etudes, Perpignan . Fish genetics (Planes) CNRS, Perpignan . Fish parasitology (Morand, Sasal) Action 5 - Indicators of reef-lagoon environmental and resource status Centre dOcéanologie de Marseille. Fish ecology and fisheries (Letourneur). Commission du Pacifique (CPS), Nouméa . Fish ecology and fisheries (Labrosse, Clua). Ecole Pratique des Hautes Etudes, Perpignan . Fish ecology (Galzin). IRD, Nouméa . Biostatistic, fisheries, ecology, indicators (Ferraris, Garrigue, Kulbicki, Breau). Université de Montréal, Canada . Ecology (Legendre) Université Paris VI, Fish ecology (Bozec). University of South Florida, St Petersburg, USA . Remote sensing (Andréfouët)
Implementation Operations in New Caledonia were conducted with the logistic support of the Nouméa IRD Centre that has extensive sea going and laboratory facilities. A total of 7 scientific cruises occured between 1999 and 2002 on board R.V. Alis (Nouméa 3 to 7 and Camecal 1 and 2). Smaller boats (Dawa, Coris) were used for lighter field operation. The network of scientific collaboration progressively grew up during this 4 years period and now offers a very signifcant potential in terms of scientific expertise and analytical capacity. Application of research actions, such as 3D current modelling, particulate transport modelling, metal bioaccumulation, integrated indicator studies, to a coral reef lagoon environment may be considered as pioneer scientific initiatives and are therefore producing original results.
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Practical difficultie mainly aroused from the remoteness of the site, transport representing a very a significant part of the necessary budget. As a consequence, additional funding was needed to support the research programme and all involved partners significantly participated to minimize and take charge of those costs.
Main results
Action 1 - Circulation and transport of terrigeneous and anthropogenic inputs Scientific questions • What are the relationships between the main forces (tide, wind, river runoff) and water circulation in the lagoon? • What are the consequences of lagoon hydrodynamics on the transport of dissolved and particulate material? • What are the main pathways for particulate material and is it possible to assess and model particle transport? Circulation Hydrodynamic modelling was initiailly based on a 2D model for tidal currents ( Douillet 1998 ) and a 3D model for wind driven currents. Since 2001, computing improvements make it possible to combine tidal and wind forcing within the sole 3D model ( Douillet et al, 2001 ). Finally, as part of the coupling with transport modelling, a wave modelling module was combined to the 3D model. In the meantime, field measurements of currents and water physics were conducted to feed and validate modelling outputs. The bottom mooring of doppler current profilers prooved extremely usefull in validating the vertical structure of currents and since the end of 2001 the use of a recorder measuring average wave height and period provided data essential to the developpment of wave modelling. Transport and fate of terrigeneous and anthropogenic inputs Transport modelling of dissolved and particulate material A first transport model for suspended cohesive particles ( Douillet et al, 2001 ) demonstrated that wind had a major influence on deposition vs. erosion processes in shallow water areas especially over 20 m depth. Tide being a permanent forcing largely control long term particle transport, vertical mixing in the water column and finally fine sediment deposit in areas where wind induced current are minimum ( Fig. 1 ). Particle transport and teledetection Visible teledetection provide a global and instantaneous view of Suspended Mater (SM) distribution of great use to test and validate particle transport model outputs. A preliminary study of bottom reflectance was conducted in 2001 to assess the respective optical contributions from the bottom and from the water column, a necessary step before reliable suspended matter distribution can be gained from air-borne images. ( Ouillon et al., 2002 ). It was followed by a joint action combining Landsat image acquisition and measurements at sea using an hyperspectral radiometer. This approach as been additionally supported since 2001 by the French Ministry of Research (ACI « Earth Observation », programme BISSECOTE). Another model developed in 2001 for non-cohesive particles showed a good agreement between the distribution of erosion and coarse sediments. All model outputs were at equilibrium, deposition and erosion being locally balanced, except for those rare areas where strong gradients or strong temporal variability in sheer stress were recorded.
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Figure 1 : Modelling of fine particle deposition after a tidal cycle with a 8 m/s trade winds, comparison with fine sediment distribution in the south west lagoon of New Caledonia. Hydrology River flow rates from the 3 main rivers were recorded in continuous and combined with continuous suspended load recording and discrete samples to calculate dissolved and particulate fluxes entering the lagoon. Results from lagoon water studies ( Deliat, 2001 ; Douillet et al., in prep ; Fichez et al., in prep ) identified two main factors explaining more than 70 % of spatial variability. The terrigeneous versus oceanic gradient generated moderate variability but affected all sites. Human induced eutrophication conversely appeared as a major source of variability but only affected a limited number of sheltered coastal sites. Significant depth enrichment in chlorophyll a was ofen observed ( Fichez et al., in prep ) despite an absence of temperature and salinity stratification ( Douillet et al., in prep ). This enrichment was attributed to nutrient benthic recycling and reinjection in the water column demonstrating a major interaction between the pelagic and benthic compartments. Temporal variability was studied at various time scales by combining various and complementary sampling strategies. Two main patterns occurring at very different time scales were observed ( Fichez et al., in prep ). At the seasonal scale, we observed a chlorophyll a maximum during the austral winter period (June), the development of this winter bloom and its controlling factors is now conducted within Action 2. At an hourly scale, we observed very strong variations in the trophic status especially in inshore areas, a variability related to the rapid displacement of water bodies with contrasting characteristics. Particle vertical residence time The 238 U/ 234 Th and 210 Pb/ 210 Po isotopic ratios were used to assess a vertical residence time of particles before deposition and the respective importance of physical versus biological processes in vertical particle transfer. This radioecology approach was conducted in collaboration with the Australian Nuclear Science and Technology Organisation and it identified a strong difference between typical lagoon sites, where residence time of 2 to 4 days were essentially controlled by physical processes, and oceanic sites where residence time of around 22 days were essentially controlled by biological processes ( Szymczack, 2002 ). Bottom mapping Bottom mapping was conducted by acoustic classification coupled to in situ sampling and observations. This approach allows to precisely delimit sediment and habitat distributions and to identify areas of fine sediment deposit to be linked with particle transport modelling and terrigeneous and anthropogenic inputs deposition ( Chevillon & Legendre, in prep; Larcombe et al., in prep. ).
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Sediment archives The vertical distribution of excess 210 Pb and metals (Fe, Mn, Al, Ni, Cr, Co, Cu, Zn) in different geochemical phases were studied in sediment cores sampled in 1997 and 1998. From the results it was inferred that significant hypersedimentation occurred in the inshore part of the lagoon due to post war mining prospecting ( Fernandez et al., 2002a ; 2002b ; 2002c ). On the contrary, canyons essentially acted as traps for carbonated sediments and were not significantly influenced by terrigeneous inputs. Action 2 - Biogeochemical functioning of the lagoon system Scientific questions • What is the contribution of terrigeneous and anthropogenic inputs to interactions between the pelagic and benthic systems? • How are terrigeneous and anthropogenic inputs transformed and deposited? • What controls the first pelagic trophic levels (autotroph and heterotroph picoplankton) and what are the consequences of those controls on carbon cycling? • Do terrigeneous inputs influence the development and potential toxicity of Trichodesmium filamentous cyanobacteria? • How can we combine existing data to gain a synthetic and predictive view on the biogeochemical functioning of the system? Exchanges at the water - sediment interface Vertical particle fluxes Vertical particle fluxes were measured on various occasions by poisoned sequential acquisition sediment traps. Results obtained on the elementary and mineralogy composition of collected sediments were combined with sediment studies to assess the respective contribution of authigenic versus terrigeneous sediment sources ( Magand et al., in prep ). Benthic cycling Oxygen and nutrient fluxes at the water-sediment interface were measured along gradients of increasing terrigeneous and anthropogenic influences. The first results permitted to validate ex situ measurement techniques ( Grenz et al., 2002 ) and to define adapted strategy such as the weekly to fortnightly survey of 2 typical sites (middle lagoon & eutrophic bay). An experiment was also conducted to assess the impact of ammonia inputs on benthic production and respiration ( Clavier et al., in prep ). Response of pelagic biocenosis In situ approaches. Four compartments have been studied: heterotrophic picoplankton (heterotrophic bacteria), autotrophic picoplankton (procaryotes and eucaryotes), autotrophic nanoplankton and microplankton and heterotrophic nanoplankton (heterotrophic flagellates and ciliates), to assess the influence of environmental conditions on the structure and functioning of pelagic communities and identify controlling factors ( Torréton 2002 ). The results demonstrate that dissolved mineral nitrogen (DIN) is the environmental factor that best correlates with variations in bacterial and phytoplankton biomass and activities. Average phytoplankton size increases with increasing DIN concentrations ( Fig. 2 ) and it was further observed that as DIN increases: (i) chlorophyll a ratio and primary production increase in the 2-10 µm fraction, (ii) the autotrophic picoplankton /Chl.a ratio decreases, (iii) the nano algaes / Chl.a ratio increases. The composition of autotrophic nanoplankton and picoplankton communities is similarly affected by DIN increase. Those changes in community composition are of great consequence to trophic pathways.
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0 0.0 0.4 0.8 1.2 1.6 2.0 Figure 2 : Percentage contribution (y-axis) for the 3 main groups of nanoalgae (85+ 11 % of total abundance) as a function of chlorophyll a concentrations (x-axis in µg/l). Diatoms ( z ), coccolithophorids ( ✚ ), dinoflagelates ( ). In vitro approaches. In vitro experiments mainly based on growth and N/P competition were conducted in parallel to in situ studies to analyse some essential functioning mechanisms. Comparison between DOC decrease and bacterial growth provided data on bacterial growth efficiency ( Jacquet, 2001 ). 33 PO 4 , and 15 NH 4 uptake experiments were conducted to analyse relationships between nutrients and plankton population and between discrete light uptake measurements and daily integration. Bacterial growth precludes 12 to 24 hours incubation in a vial as it is commonly done for oceanic environments. Uptake measurements as a function of class size provided essential data to biogeochemical modelling, confirmed that DIN was the factor limiting primary production and invalidated some concepts extracted from the existing literature (NH 4 affinity, phyto/bacterioplankton competition for NH 4 ). Modelling of biogeochemical functioning A preliminary work was conducted on box modelling ( Bujan, 2000 ; Bujan et al., 2000 ) but we rapidly shifted on 3D hydrodynamic and biogochemical coupled modelling. One of the biggest advantages of this later approach is to offer a spatial resolution which is compatible with the spatial variability observed in the inshore part of the lagoon ( Bujan, 2000 ; Pinazo et al., submitted ). However, the first 3D modelling account of mineralisation processes was not adapted enough to the specificity of tropical coastal environments such as the microbial loop ( Torréton, 2002 ). Therefore, another step was conducted to develop a 0D model providing an optimum numerical solution to the complex trophic status of the New Caledonia lagoon ( Faure, 2002 ). Coupling of this 0D model with the 3D hydrodynamic model is currently underway through a IRD/COM co-chaired PhD thesis. Determinism and potential toxicity of Trichodesmium Blooms of Trichodesmiu m filamentous cyanobacterai are observed in the New Caledonia lagoon and offshore but no information exists on their origin and consequences on coastal ecosystem. A daily survey was conducted from January to March 2002 in the Bay of Ouiné on the east coast. Even though no significant Trichodesmium bloom occurred, this study provided a first extensive description of lagoon phytoplankton and established the links between phytoplankton structure and environmental conditions ( Le Borgne et al., 2002 ). The system shifted from an oligotrophic population with Trichodesmium as the dominating microplanktonic gender during dry periods to a mesotrophic system dominated by diatoms and dinoflagellates and with almost no Trichodesmium during rainy periods with additional
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terrigeneous nutrient inputs. The lack of Trichodesmium bloom was attributed to those rainy episods and this survey therefore has to be replicated during a longer dry period. Action 3 Transfer of metals through the benthic trophic food chain Scientific questions • How can we assess the proportion of metals associated to sediments that are still available to benthic organisms? • Do metal concentrations in benthic organisms relates to contrasted terrigeneous and anthropogenic input conditions?. • Is it possible to identify physiological effects due to metal inputs in benthic organisms? Metal bioavailability In vitro simulation of digestive metal desorbtion Surface sediment sampled from sites subject to various input sources (urban, industrial, terrigeneous, lagoonal) were subject to desorption test using a pH 4 buffer solution (acetic acid 1 % + ammoniac), which was considered as representative of ambient conditions for bivalves digestive system. The bioavailable fraction was compared with geochemical sequential extraction (carbonate + organic fractions) and further comparison with metal bioaccumulation in G. tumidum are currently underway. Bio-assay on larval stages Investigations were conducted on metal concentrations in tropical marine invertebrate larvae and display of larval malformation as an early detection of the metal toxicity of a solution (i.e. sediment desorption or effluent).. The preliminary technical experiments demonstrated that Diadema setosum and Trochus niloticus could be targeted as potential early bioindicators of metal. Additional work is needed to establish the scientific bases for a strongly needed environmental bio-monitoring tool in tropical environments. Metal bioaccumulation in soft tissues This essential operation gathered most of the energy devoted to Action 3 as it aimed at establishing the scientific bases of metal bioaccumulation in the soft tissue of benthic organism in the New Caledonia lagoon. We followed 4 successive steps. Selection of target species After preliminary database studies and prospection of coastal sites subject to contrasted inputs, 13 common species belonging to various systematic groups and displaying a range of trophic strategies were selected and sampled for metal analysis: • Algae : Halimeda macroloba, Halimeda incrassata, Caulerpa taxifolia, Caulerpa sertularioides, Lobophora variegata • Bivalves : Isognomon isognomon, Gafrarium tumidum, Hyotissa hyotis • Echinoderms : Holothuria (Halodeima) edulis, Diadema setosum • Gasteropode : Strombus (Laevistrombus) canarium • Alcyonarians : Sinularia leptoclados, Sarcophyton sp Metal concentrations Determination of metal concentrations (Al, Co, Cr, Cu, Fe, Mn, Ni, V et Zn) in soft tissues was conducted by ICP-OES detection after micro-wave exposure and the results were compared to assess the bioaccumulation potential of each species. G. tumidum, I. isognomon (bivalves) L. variegata (brown algae) presented the highest potential in term of quantitative bio-indicator of metal contamination ( Magand 2000, Breau et al., in prep ). Further statistical analyses are underway to assess the significance of biometric variables on metal
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contamination in order to propose standardisation procedures that would limit inter-individual variability, a necessary step to establish a suitable tool for environmental monitoring. Metal incorporation and depuration kinetics The kinetics of dissolved metal accumulation and depuration was experimentally assessed in the target species G. tumidum, I. isognomon and L. variegata using metal radiotracers and beta ( 63 Ni) or gamma ( 54 Mn, 57 Co, 65 Zn, 109 Cd, 110 Ag) spectrometry. Specimens were incubated in mesocosm under ambient tropical similar to those of the lagoon. Radiotracing techniques, which allow working at ambient concentrations, provided results ( Fig. 3 ) supporting those from in situ bioaccumulation as the three species presented very significant concentration factors, L. variegata unambiguously appearing as a top ranking bioaccumulator. Similar work was conducted on metal accumulation from food and sediment sources. 250 600 3500 Co-57 Co-57 Co-57 3000 200 500 2500 400 1502000 300 100 1500 200 1000 50100 500 0 0 0 0 3 6 9 12 15 18 21 24 27 30 0 3 6 9 12 15 18 21 24 27 30 0 3 6 9 12 15 18 21 24 27 30 Durée d'exposition (j.) Durée d'exposition (j.) Durée d'exposition (j.) G. tumidumI. isognomonL. variegata Figure 3 : Dissolved Co accumulation rate using radiotracing technique in 3 target species, values en y-axis are expressed as a concentration factor related to ambient level in the water. Biomarker of physiological status A last step study was conducted to assess the physiological status of the bivalve G. tumidum using methellothionein as a biomarker. The digestive and respiratory organs were separated from the rest of the soft tissue and analysed separately. The results obtained on specimen from 3 sites with contrasted metal inputs showed no significant differences and metallothioneins therefore appeared unfit to trace metal exposure in the considered species. Bivalve shell recording An additional study associated to a PhD work was initiated in 2002 considering the potential capacity of pectinid bivalves shells in registering high frequency (daily) variations in environmental conditions. Among 3 selected species Comptopallium radula was retained as it potentially displayed daily growing layers. Past activities included identification and location of C. radula environment, building of constraining underwater parks and specimen transplantation, environmental weekly survey (including DGT measurement of available dissolved metals) on park sites. Action 4 Growth variations of lagoon organisms Scientific questions • What are the main factors affecting fish and invertebrate growth and what is the contribution of environmental status to growth variations? • What are the consequences of growth variations on fish communities and their habitats? 8
Fish growth After a preliminary global study of fish population structure and of their sensitivity to anthropogenic disturbances ( Rossier & Kulbicki, 2000 ; Kulbicki, 2002 ), the work focused on sedentary species with special attention to Chaetodontidae which were identified as good indicators of environmental status ( Bozec et al., submitted ). A study conducted in 2000 further permitted to select Chaetodon speculum as a target. Morphology It was demonstrated that fish size and weight (sampling and underwater census) were lower in the 2 bays subject to significant anthropogenic inputs than in the unimpacted bays and reference lagoon site. A covariance analysis further demonstrated that for a similar size, fishes were leaner in anthropogenically impacted bays than elsewhere. Genetics This operation investigated the genetic structure of Chaetodon speculum sampled in various places of the lagoon and subject to contrasted conditions of terrigeneous and anthropogenic inputs. The goal was to establish whether micro-scale genetic variations could be observed or not. Electrophoresis was conducted on subsamples of muscle and liver. The results identified 6 polymorph loci that displayed no intra-site differences. Similarly, no differences were observed in the heterozygote or polymorphism ratios. In conclusion it can be inferred that no genetic differentiation was observed between impacted and non-impacted sites. Parasitology Parasite is more and more acknowledged as powerful indicators of environmental alteration. Fish blood samples were taken and blood parasites were fixed and coloured before identification. Studies were conducted on the infestation ratio and parasite species composition and interpretation was conducted on the following points: • For all Chaetodontidae species, the influence of inshore-offshore transects was interpreted as a function of fish species, trophic status and size. • Chaetodon speculum alone was used to assess the influence of small-scale geographical distribution. • For Apogonid fishes, species with similar ecological and biological characteristics were used to assess the influence of bay transects and the nature of antrhopogenic inputs. No significant relationship could be evidenced between hematocrit and parasitism except for Sainte Marie Bay were a significant inverse correlation was established for Paradiscogaster sp1 (n=27, R 2 =0.17, p=0.03). In general, it was considered that hematocrit ratio did not unambiguously identified anthropogenic alterations in the lagoon of New Caledonia. The total number of parasites per fish is highly variable ( Morand et al., 2000 ), highest values were measured at Sèche Croissant and in Sainte Marie Bay and lowest in Grande Rade. The percentage of infested fishes was also lower in Grande Rade than elsewhere. Most parasite-infested fishes were infested by digenes and monogenes while nematodes were infrequent. Grande Rade, subject to a combination of urban and industrial inputs, was clearly identified from all other site by lower parasite infestation and a specific parasite species composition. Otoliths A first work established a significant correlation between fish size and otolith parameters (length, weight etc.) but no significant differences could be identified as a function of sample location ( Fig. 4 ). Lapilli were easier to study than sagitta especially on young specimens as growth rings were more visible and counting variability lower. However, preparation of lapilli had to be handled with extreme carefulness to obtain usable thin slices. Tracer experiments were conducted to validate counting results. Micro-scale sampling and microanalysis are
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