Effects of the duration of exposure to mercuric chloride on the embryogenesis of the estuarine teleost, Fundulus heteroclitus

Embryos of Fundulus heteroclitus in the 4–8 cell stage were exposed nine Hg⁺⁺ (as mercuric chloride) concentrations from 0 to 100 μg/litre (ppb) for 32 days, 5 days, 2 days and 1 day. All but the chronically (32-day) exposed embryos were allowed to continue development in mercury-free water (20% S) after the exposure period to determine the effect of duration of exposure on three parameters of development. Ninety-six hour survival, total hatching success and per cent incidence of lateral spinal curvature were measured. Only embryos exposed to mercury for a single day showed a significant increase in survival in comparison with embryos exposed for a longer period of time after four days of development. Under all conditions of exposure, survival was reduced at concentrations greater than 40 ppb Hg⁺⁺. Hatching success of chronically exposed embryos was significantly reduced at concentrations greater than 10 ppb Hg⁺⁺. Significant increases in total hatchability were effected by reducing the duration of exposure to five days and one day. Of eleutheroembryos emerging following chronic exposure to mercury, increases in the incidence of lateral spinal curvature were noted at all concentrations above 20 ppb Hg⁺⁺. Significant reductions of this disorder were observed among eleutheroembryos exposed to mercury for 5 days, 2 days or 1 day. Of the three parameters measured, the incidence of lateral spinal curvature and the resulting VH₅₀ value gave a more sensitive evaluation of the embryotoxic effects of Hg⁺⁺ as mercuric chloride on the estuarine teleost, Fundulus heteroclitus.     

Benzo(a)pyrene induced glycine N-methyltransferase messenger RNA expression in Fundulus heteroclitus embryos

Glycine N-methyltransferase (GNMT) is a mediator in the methionine and folate cycles, and is responsible for the transfer of a methyl group from S-adenosylmethionine (SAM) to glycine forming S-adenosylhomocysteine (SAH) and sarcosine. All the known DNA methyltransferases use SAM as a methyl donor thus, GNMT is critically involved in regulation of DNA methylation. Altered GNMT activities have been associated with liver pathologies including hepatocellular carcinoma. The homotetramer form of GNMT is enzymatically active, but the homodimeric form has been suggested as the 4S PAH-binding protein which may mediate CYP1A expression. To further understand the role of GNMT in benzo(a)pyrene (BaP)-related toxicity, full length Fundulus heteroclitus GNMT cDNA was cloned from adult liver. The open reading frame (ORF) of GNMT is 888 base pairs long and encodes a deduced protein of 295 amino acids which has 74% identity with human GNMT. Expression of GNMT mRNA was determined by quantitative RT-PCR. In unfertilized, 2 days postfertilization (dpf), and 3 dpf embryos GNMT was constitutively higher than in 4, 7, 10 or 14 dpf embryos. Embryos were also exposed to waterborne BaP at 10 and 100 μg L⁻¹, and by 10 dpf the higher BaP dose caused increased expression of GNMT mRNA. These results suggest that PAH exposure may alter expression of an important physiological methylation mediator. Future work will be necessary to determine enzyme level effects of BaP exposure as well.     

Exposure of pink salmon embryos to dissolved polynuclear aromatic hydrocarbons delays development,prolonging vulnerability to mechanical damage

Exposure to dissolved polynuclear aromatic hydrocarbons (PAHs) from crude oil delays pink salmon (Oncorhynchus gorbuscha) embryo development, thus prolonging their susceptibility to mechanical damage (shock). Exposure also caused mortality, edema, and anemia consistent with previous studies. Hatching and yolk consumption were delayed, indicating the rate of embryonic development was slowed by PAH exposure. The net result was that exposed embryos were more susceptible to shock than normal, unexposed embryos. Susceptibility to shock was protracted by 4–6 d for more than a month in embryos exposed to exponentially declining, dissolved PAH concentrations in water passed through oiled rock; the initial total PAH concentration was 22.4 μg L⁻¹ and the geometric mean concentration was 4.5 μg L⁻¹ over the first 20 d. Protracted susceptibility to shock caused by exposure to PAHs dissolved from oil could potentially increase the reported incidence of mortality in oiled stream systems, such as those in Prince William Sound after the Exxon Valdez oil spill, if observers fail to discriminate between direct mortality and shock-induced mortality.     

A simple and reliable in vivo EROD activity measurement in single Fundulus heteroclitus embryo and larva

Dioxin-like compounds (DLC) induce toxic responses in early life stages of fish through activation of the aryl hydrocarbon receptor (AhR) which is frequently assessed by ethoxyresorufin-O-deethylase (EROD) activity. A novel spectrofluorimetric method was developed to quantitatively assess EROD activity in individual living embryos and prolarvae of a marine model fish species, the mummichog Fundulus heteroclitus. This in vivo method is based on the measurement of the production of resorufin by single live embryos or prolarvae after 5 h incubation with ethoxyresorufin. Freshly fertilized eggs were treated topically from 2.5 to 50 pg egg⁻¹, with 3,3′,4,4′,5-pentachlorobiphenyl (PCB126), a prototypical DLC. EROD activity was assessed in embryos (7 days post-fertilization) and prolarvae (16 days post-fertilization). Resorufin was measured both in the culture medium (25‰ seawater) and in whole fish homogenates, to assess the percentage retained in the body. Approximately 95% and 17% of the resorufin produced in vivo was retained in embryos and prolarvae respectively. EROD activity in homogenates of embryos and in the culture medium of prolarvae increased linearly with dose. EROD activity measured by the in vivo method was highly correlated to that measured by a traditional in vitro technique using S9 fractions for both embryos and prolarvae. Both in vivo and in vitro EROD activity were higher in prolarvae than in embryos pretreated with PCB126. EROD induction measured in prolarvae by the in vivo and in vitro methods were similar whereas higher induction was measured in vivo than in vitro in embryos. The in vivo method was more sensitive and as reliable as the in vitro technique, and required a lower number of fish (4 compared to 3 pools of 5). This in vivo method is useful to link EROD induction in individual embryos or prolarvae to other organism-level responses. Further studies with other categories of xenobiotics should be performed to assess potential toxic effects on resorufin absorption/excretion processes which could affect in vivo measurements.     

Effects of tributyltin on salmon interrenal CYP11β, steroidogenic factor-1 and glucocorticoid receptor transcripts in the presence and absence of second messenger activator,forskolin

The mechanisms by which TBT produces modulations of the endocrine systems are not fully described. In this study, juvenile salmon were force-fed diet containing TBT (0: solvent control, 0.1, 1 and 10 mg/kg fish) for 72 h. Subsequently, fish exposed to solvent control and 10 mg/kg TBT were exposed to waterborne concentration of the adenyl cyclase stimulator forskolin (200 μg/L) for 2 and 4 h. Tissue and blood were sampled from individual fish (n = 6). Gene expression patterns of CYP11β, steroidogenic factor-1 (SF-1), and glucocorticoid receptor (GlucR) were determined by qPCR. TBT generally decreased mRNA levels of CYP11β, GlucR and SF-1, compared to the solvent control and these effects were differentially modulated by the presence of forskolin. This study suggests that TBT may exert broader endocrine disrupting effects through possible modulation of cAMP/PKA second messenger systems.     

Lindane toxicity: Histopathological,behavioural and biochemical changes in Etroplus maculatus (Bloch, 1795)

The effects of sub-lethal concentrations of lindane on behavioral, hematological and histological parameters in Etroplus maculatus were investigated. The LC₅₀ value of lindane for E. maculatus was estimated using the Probit method and was found to be 0.028 mg/L. The red blood cell count (RBC) and the hemoglobin (Hb), hematocrit (Ht), mean corpuscular hemoglobin (MCH), mean corpuscular volume (MCV) and mean corpuscular hemoglobin concentration (MCHC) were significantly reduced (p > 0.0001) in fish exposed to the toxicant concentrations compared to the control groups. However, the white blood cell count (WBC) was observed to be significantly higher (p < 0.0001). Observations of the tissues showed that lindane had profound destructive effects on the gills, liver and kidney of the fish. The gills showed proliferation of the lamellar epithelium and lamellar fusion, the liver showed necrosis and the kidneys had constriction of the tubular lumen. The frequency of observed behaviors had the same levels of significance throughout the period of study. There was a reduction in the frequency of occurrence between test concentrations, but remained significantly higher than the control. The study shows that lindane is harmful to E. maculatus at sub-lethal concentrations and that the application of this pesticide close to bodies of water is a dangerous threat to aquatic life.     

Effects of benzo[a]pyrene on DNA damage and histological alterations in gonad of scallop Chlamys farreri

To investigate the biological impact of polycyclic aromatic hydrocarbons (PAHs) on reproductive system, scallops Chlamys farreri were continuously exposed to benzo[a]pyrene (BaP) (0.5, 3, 10 μg L^?1) during 15 days. DNA damage and histological alterations were examined in female gonad. DNA strand break levels significantly increased after 12 h exposure, and remained high and significantly different from control values until the end of the exposure. In the ovaries of the scallops exposed to 10 μg L^?1 BaP for ten days, histological analysis showed that the cytoplasts of the oocytes in the outer layer of the ovaries became sparse, and the nuclear membranes were obscure. Damaging effects on ovaries and oocytes were more severe after 15 days exposure. Degenerating oocytes increased and the connective tissue of the ovary envelops became loose. Electron microscopic examination revealed ultrastructural aspects of degenerating oocyte and degenerated oocyte after 15 days exposure.     

Plasma steroid levels in female flounder (Platichthys flesus) after chronic dietary exposure to single polycyclic aromatic hydrocarbons

The chronic effects of polycyclic aromatic hydrocarbons (PAHs) on ovary development, total hepatic lipids and plasma sex- and corticosteroid levels in female flounder (Platichthys flesus) were examined. Sexually mature feral female flounder were exposed via the diet to phenanthrene (0.5, 2.5 or 12.5 nmol/g food) or chrysene (0.4 nmol/g food) for 12 weeks, during the previtellogenic phase of the annual reproductive cycle. PAH exposure did not directly affect germ cell development since no structural and/or developmental differences were observed between control and exposed fish. On the contrary, all treatments resulted in altered plasma steroid levels. The most pronounced effect was the significant decrease in plasma 17β-estradiol to 19±11%, 27±7%, 63±20% and 61±12% in relation to control fish, respectively, in flounders exposed to 12.5, 2.5 or 0.5 nmol phenanthrene/g food and 0.4 nmol chrysene/g food. Impaired ovarian growth was not observed, most likely because experiments were ended before the period of vitellogenesis, even though a non-significant general decline in total hepatic lipids could be observed. Moreover, all exposed flounders, except fish fed with the highest amount of phenanthrene, showed a negative correlation between plasma 17β-estradiol and 17α-hydroxyprogesterone levels (r=−0.46). One possible explanation is that PAH action may be mediated by a specific inhibition of steroidogenic enzymes. These findings provide evidence that selected PAHs are antiestrogenic xenobiotics with the capability to impair female teleost reproductive function.     

Distribution and Habitat Preferences of the Introduced MummichogFundulus heteroclitus(Linneaus) in South-western Spain

The distribution and apparent habitat preference of the common mummichog (Fundulus heteroclitus) in south-western Spain were examined during summer–autumn 1996. This introduced species was more or less continuously distributed along the Atlantic coast of Spain, being more abundant in sites near the coastline (usually <10 km inland), mainly in four extensive marshes. The species preferred marsh-related mesohabitats, such as salt lagoons, saltmarsh fish ponds and marsh channels, both natural and man-modified.Fundulus heteroclituswas mostly found at salinities >25. It was the most frequently captured fish species, occurring at 81 of the 272 sites sampled; their frequency of occurrence was almost twice that of the second ranked species (Gambusia holbrooki). However, in over 80% of cases,F. heteroclituswas found alone or with only one sympatric fish species, which usually belonged to a group composed ofGobius niger,mugilids,Anguilla anguilla, Blenniussp.,Lebias ibera, Pomatoschistussp. andDicentrarchus labrax. Finally, the origin and dispersal of mummichog in the Iberian peninsula and the potential effects of this species on native fish populations is discussed.     

Genotoxicity of copper oxide and silver nanoparticles in the mussel Mytilus galloprovincialis

Though there is some information on cytotoxicity of copper nanoparticles and silver nanoparticles on human cell lines, there is no information on their genotoxic and cytotoxic behaviour in bivalve molluscs. The aim of this study was to investigate the genotoxic impact of copper oxide and silver nanoparticles using mussels Mytilus galloprovincialis. Mussels were exposed to 10 μg L⁻¹ of CuO nanoparticles and Cu²⁺ and Ag nanoparticles and Ag⁺ for 15 days to assess genotoxic effects in hemocytes using the comet assay. The results obtained indicated that copper and silver forms (nanoparticles and ionic) induced DNA damage in hemolymph cells and a time-response effect was evident when compared to unexposed mussels. Ionic forms presented higher genotoxicity than nanoparticles, suggesting different mechanisms of action that may be mediated through oxidative stress. DNA strand breaks proved to be a useful biomarker of exposure to genotoxic effects of CuO and Ag nanoparticles in marine molluscs.     

Effect of feeding selectivity on the transfer of methylmercury through experimental marine food chains

The present study established an experimental marine food chain of three levels (microalgae → zooplankton → fish) to investigate the effect of feeding selectivity on the transfer of methylmercury (MeHg) through the food chain. Total Hg concentrations in Chlorella sp., Nitzschia closterium and Isochrysis galbana exposed to 1 μg L⁻¹ MeHg for three days were 27.91, 32.74 and 40.03 μg g⁻¹ respectively and were significantly different (p < 0.05) between species. Moina mongolica and Artemia sp. primarily selected Chlorella sp. as the sole diet, though the Artemia sp. partly grazed on I. galbana as well. Harpacticus uniremis, however, preferred to graze N. closterium and I. galbana and avoided Chlorella sp. The varying concentration of Hg in the microalgae species as well as the selectivity of zooplankton to the algal diet resulted in varying Hg accumulation in three zooplankton species (M. mongolica < Artemia sp. < H. uniremis with total Hg concentrations of 0.14, 0.66 and 0.82 μg g⁻¹, respectively). Scophthalmus maximus and Paralichthys olivaceus mainly preyed on H. uniremis and partly on M. mongolica, while Fugu rubripes primarily preyed on M. mongolica and secondarily on Artemia sp. Thus, similar reasoning as above could explain the significant difference in Hg accumulation in the fish (S. maximus > P. olivaceus > F. rubripes with total Hg concentrations of 0.0042, 0.0031 and 0.0020 μg g⁻¹, respectively). These investigations suggested feeding selectivity plays a key role in the transfer of MeHg along marine food chains.     

Home range and diel behavior of the ballan wrasse,Labrus bergylta,determined by acoustic telemetry

Effective fisheries management needs to consider spatial behavior in addition to more traditional aspects of population dynamics. Acoustic telemetry has been extensively used to provide information on fish movements over different temporal and spatial scales. Here, we used a fixed-receiver array to examine the movement patterns of Labrus bergylta Ascanius 1767, a species highly targeted by the artisanal fleet of Galicia, NW Spain. Data from 25 individuals was assessed for a period of 71 days between September and November 2011 in the Galician Atlantic Islands Maritime-Terrestrial National Park. Fish were present within the monitored area more than 92% of the monitored time. The estimated size of individual home ranges, i.e. the area where fish spent most of their time, was small. The total minimum convex polygons area based on all the estimated positions was 0.133 ± 0.072 km², whereas the home range size estimated using a 95% kernel distribution of the estimated positions was 0.091 ± 0.031 km². The core area (50% kernel) was 0.019 ± 0.006 km². L. bergylta exhibited different patterns of movement in the day versus the night, with 92% of the fish detected more frequently and traveling longer distances during the daytime. In addition, 76% of the fish displayed a larger home range during the day versus during the night. The linearity index was less than 0.005 for all fish suggesting random movements but within a relatively small area, and the volume of intersection index between consecutive daily home ranges was 0.75 ± 0.13, suggesting high site fidelity. The small home range and the sedentary behavior of L. bergylta highlight the potential use of small MPAs as a management tool to ensure a sustainable fishery for this important species.     

Toxicological effects induced by the nanomaterials fullerene and nanosilver in the polychaeta Laeonereis acuta (Nereididae) and in the bacteria communities living at their surface

Fullerene (nC₆₀) and nanosilver (nAg) are nanomaterials with bactericide properties. The increments in their use raise questions about their potential environmental impacts, including estuarine ones. The polychaete Laeonereis acuta (Nereididae) secretes mucus that is colonized by bacteria communities. We analyzed the antioxidant and oxidative damage responses of anterior, middle and posterior region of L. acuta and bacteria communities after nC₆₀ or nAg exposure during 24 h. Molecular analysis showed a prevalence of Vibrio genera in the communities. Bacteria biomass was lowered in worms exposed to 1.0 mg/L of nAg. nC₆₀ reduced total antioxidant capacity of bacteria from worms exposed to 0.1 mg/L. Worms anterior region presented lower antioxidant capacity after exposure to 1.0 mg nC₆₀/L, and the same was observed in the posterior region of worms exposed to 1.0 mg nAg/L. Lipid peroxidation was reduced in the anterior region of worms exposed to nC₆₀ and the opposite was observed in the posterior region.     

Inter-season and interannual variations in fish and macrocrustacean community structure on a eastern English Channel sandy beach: Influence of environmental factors

The intertidal zone of an exposed sandy beach on the French coast of the English Channel was sampled with a 1.5 m beam-trawl over five years (2000 and 2003–2006) at weekly intervals. The fish and macrocrustacean catches were analysed to determine the inter-season and interannual variation in community structure and relate these variations to changes in the major environmental variables. Only six species (plaice Pleuronectes platessa, common goby Pomatoschistus microps, sprat Sprattus sprattus, sand eel Ammodytes tobianus, brown shrimp Crangon crangon and shore crab Carcinus maenas) from the 27 species captured can be considered as dominant species of the intertidal zone, and they accounted for >90% of total numbers. Most individuals caught were young-of-the-year or juvenile. Analysis of similarities (ANOSIM) and similarities percentage (SIMPER) indicated that inter-season variability of community structure (mean average similarity = 47%) was more pronounced than interannual variability (mean average similarity = 65%). Canonical correspondence analysis (CCA) indicates that a substantial component (32.2%) of the measured inter-season variation in community structure can be explained by environmental factors (mainly water temperature). The main inter-season changes in the abundance and community structure were due to the variation of the six key species and reflect the different times of their recruitment. During the five years of the study, the structure of the fish and macrocrustacean spring community persisted from year to year, with the dominant species reappearing consistently even though their abundances fluctuated from year to year. This interannual variation probably reflects variable recruitment success influenced by physico-chemical conditions. In spite of the considerable interannual variation (40 times) in the spring bloom of the prymnesiophyte alga Phaeocystis globosa we found no effect of this bloom on either fish and macrocrustacean species densities or diversity index.     

Fish scales in sediments from off Callao,central Peru

We study fish scales as a proxy of fish abundance and preservation biases together with phosphorus from fish remains (P_fish) in a sediment core retrieved off Callao, Peru (12°1′S, 77°42′W; water depth=179 m; core length=52 cm). We interpret our results as a function of changing redox conditions based on ratios of redox-sensitive trace elements (Cu/Al, Mo/Al, Ni/Al, Zn/Al, V/Al), terrigenous indicators (Fe in clays, Ti, Al), and biogenic proxies (CaCO₃, biogenic opal, total nitrogen, organic carbon, barite Ba). The core covers roughly 700 years of deposition, based on ²¹⁰Pb activities extrapolated downcore and ¹⁴C dating at selected intervals. Our fish-scale record is dominated by anchovy (Engraulis ringens) scales followed by hake (Merluccius gayii) scales.The core presented an abrupt lithological change at 17 cm (corresponding to the early 19th century). Above that depth, it was laminated and was more organic-rich (10–15% organic carbon) than below, where the core was partly laminated and less organic-rich (<10%). The lithological shift coincides with abrupt changes in dry bulk density and in the contents of terrigenous and redox-sensitive trace elements, biogenic proxies, and fish scales. The remarkable increase in redox-sensitive trace elements in the upper 17 cm of the core suggests more reducing conditions when compared with deeper and older horizons, and is interpreted as an intensification of the oxygen minimum zone off Peru beginning in the early 19th century. Higher fish-scale contents and higher P_fish/P_total ratios were also observed within the upper 17 cm of the core. The behavior of biogenic proxies and redox-sensitive trace elements was similar; more reduced conditions corresponded to higher contents of CaCO₃, C_org, total nitrogen and fish scales, suggesting that these proxies might convey an important preservation signal.     

Influence of summer conditions on the larval fish assemblage in the eastern coast of Tunisia (Ionian Sea,Southern Mediterranean)

The structure of the summer larval fish assemblage off the eastern coast of Tunisia and its relation to environmental conditions was studied, from ichthyoplankton samples taken during a survey conducted between 23rd June and 9th July 2008. A total of 68 larval fish taxa were identified, 52 to species level. The taxonomic composition and abundance of the larval fish assemblage showed high spatial heterogeneity. Mesoscale hydrographic features, such as eddies, seem to play an important role in the spatial distribution of fish larvae in the area, enhancing concentration and retention. The larval fish assemblage was dominated by the small pelagic species Sardinella aurita (26.6% of the total larval fish abundance), followed by Engraulis encrasicolus (22.6%), Spicara spp. (8.6%) and Mullus barbatus (6.8%). Shannon–Weaver index (H′) ranged between 0 and 2.62. The highest values were found offshore, at 95 miles east of Sousse, over depths around 250 m. The diversity was higher in this region as a result of transport by currents and retention by eddies. It has also been shown that the eastern coast of Tunisia is a spawning ground for the tuna species Auxis rochei, Thunnus thynnus and Thunnus alalunga. Larvae of mesopelagic fishes represented 5.46% of the total abundance, with Cyclothone braueri, Ceratoscopelus maderensis and Lampanyctus crocodilus being the most important species. Canonical correspondence analysis (CCA) indicated that depth was the most important environmental factor in explaining species distribution.     

Assessing waterbird habitat use in coastal evaporative systems using stable isotopes (δC, δN and δD) as environmental tracers

Isotopic patterns of biota across salinity gradients in man-made evaporative systems could assist in determining the use of these habitats by animals. Here we report δ¹³C, δ¹⁵N and δD measurements of a euryhaline fish, the Mediterranean toothcarp (Aphanius fasciatus), inhabiting a range of salinities in the Thyna saltworks near Sfax (Tunisia). The contribution of these salinity niches to egg formation of two typically piscivorous bird species breeding in the area and feeding within saltworks, Little Tern (Sternula albifrons) and Little Egret (Egretta garzetta), was inferred trough a triple-isotope (δ¹³C, δ¹⁵N and δD) Bayesian mixing model. Isotopic trends for fish δ¹⁵N and δD across the salinity gradient followed the equations: δ¹⁵N = e^{(1.1 + 47.68/Salinity)} and δD = −175.74 + Salinity + Salinity²; whereas fish δ¹³C increased as salinity rose (δ¹³C = −10.83 + 0.02·Salinity), after a sudden drop in fish isotopic values for salinities >60 (Practical Salinity Scale) (average fish δ¹³C for salinities <60 = −5.92‰). Both bird species fed largely on low hypersalinity ponds (salinity = 43; average contribution = 37% and 22% for Little Egrets and Little Terns, respectively), although the use of intermediate hypersalinities (salinities 63 and 70) by Little Terns also occurred (16% and 21%, respectively). Isotopic patterns across salinity gradients allow the use of isotopic measurements to inform studies of habitat occupancy within evaporative systems and provide further insights into how wildlife communities interact with them.     

Influence of exposure history on vitellogenin induction in medaka: a case of ‘estrogen memory’?

In this study, we exposed female medaka to aqueous solutions of o,p′-DDT until tissues residues reached approximately 100 g/g. Male offspring of exposed females and unexposed males that were raised to 6 months of age differed from untreated controls in their response to subsequent 4-day static exposure to 17-β-estradiol (E2; 12 μg/l as determined by steroid EIA). Homogenized liver samples from males from DDT treatments, females from DDT treatments, control males and control females produced two vitellogenin bands on a Western blot with no qualitative differences in band size and location between the groups. To quantify the relative level of vitellogenin, 5 μg of protein from each sample was analyzed by slot blot. A statistical comparison revealed a significant difference in optical density of the slots between control males and DDT exposed males (analysis of variance, n=18, P=0.021; Tukey test, n=9, P=0.047) indicating that previous transgenerational exposure to DDT enhanced the vitellogenic response to E2 exposure in males. These results indicate that exposure to estrogenic chemicals may produce an ‘estrogen memory’ which potentiates the response to a subsequent exposure event.     

Behavioral effects in mummichog larvae (Fundulus heteroclitus) following embryonic exposure to methylmercury

Embryos of the mummichog, Fundulus heteroclitus, were exposed to concentrations of methylmercury (meHg) below those that can cause morphological abnormalities. After hatching, larvae were kept in clean water and tested periodically for ability to capture prey (Artemia salina) or for their swimming performance and predator avoidance. Embryonic exposure to 10 μg/liter meHg resulted in reduced prey capture ability by early larvae, measured as total Artemia caught in 1 and 5 min. However, older larvae recovered from the behavioral deficits, perhaps owing to a compensation for early CNS insult. Fish from a chronically polluted environment (Piles Creek (PC), a tributary of the Arthur Kill), previously shown to have high tolerance to the teratogenic effects of higher concentrations of meHg, proved to be less susceptible to these behavioral effects than fish from a relatively uncontaminated site (EH). Also, the PC control larvae captured prey far more effectively than the EH larvae, although they made more miscues. When tested for swimming performance after embryonic exposure to 10 μg/liter, EH larvae had increased performance when compared to controls. This effect was also transitory. The improved swimming performance did not correspond to improved ability to avoid predation by grass shrimp (Palaemonetes pugio). The increased swimming performance may correspond to greater total activity, making them more likely to attract the predator's attention and resulting in increased capture. Thus, negative, though temporary, effects were observed in both prey capture and predator avoidance after embryonic exposure to meHg.     

Size matters: experimental partitioning of the strength of fish herbivory on a fringing coral reef in Moorea,French Polynesia

While the importance of top‐down control by grazers in maintaining tropical reef community structure is well known, the effect of ‘fishing down the food web’, which simultaneously changes the abundance and size of herbivorous fishes, has received less attention. As many fishing practices target the biggest fish and regulations often set minimum size limits, understanding size‐dependency of this controlling force is important. We evaluated the hypothesis that reduction in the abundance and size of fish, regardless of species identity, reduces the role of herbivory in controlling algal abundance on reefs and assessed variation in efficacy of this top‐down control on different types of common macroalgae. We quantified herbivory rates within cages of differing opening sizes on assemblages of four common algal species (Padina boryana, Dictyota bartayresiana, Halimeda opuntia and Galaxaura fasciculata) on two fringing reefs in Moorea, French Polynesia. Small acanthurids (<15 cm length) were the dominant herbivorous fish while other herbivorous fish were rare. For the two most palatable algae, the majority of herbivory occurred in open plots, with herbivory reduced by >50% in the largest opening cages (6 × 6 cm) where the maximum size fish entering was 12 cm in length (mean = 7.6, SE = 0.4). Fish entering medium (4.5 × 4.5 cm openings, maximum fish length = 8 cm, mean = 6.3, SE = 0.4) and small (3 × 3 cm openings, no fish observed entering) cages had herbivory rates approximately equal to the control treatment (1 × 1 cm openings). Consumption varied among algal species, with minimal consumption of physically and chemically defended algae and no pattern across treatments. Our results demonstrate a need for management plans to not only maintain the overall abundance of herbivorous fish but to protect the largest sizes for effective top‐down control of algal communities.