Atlantic Croaker Research Articles

Daily variation in ingress of fall-spawned larval fishes into Delaware Bay in relation to alongshore and along-estuary wind components

Identifying factors that affect ingress of larval fishes from offshore spawning areas into estuarine nurseries is important to improve understanding of variability in recruitment of many coastal marine species. This study investigated the ingress of larval Atlantic croaker (Micropogonias undulatus), Atlantic menhaden (Brevoortia tyrannus), and summer flounder (Paralichthys dentatus) at Roosevelt Inlet, near the mouth of Delaware Bay, USA in relation to short-term wind events. Nightly abundances, from November 15 to December 15, 2010, were analyzed with alongshore and along-estuary wind components (direction and speed) using cross-correlation analysis to determine if winds affect larval ingress. Ingress of Atlantic croaker and summer flounder correlated with along-estuary winds, whereas Atlantic menhaden showed no significant correlations with either alongshore or along-estuary winds. Although along-estuary winds during this period were predominantly down-estuary, Atlantic croaker ingress was correlated with positive along-estuary winds (blowing up-estuary), with a three-day lag; and a particularly large ingress peak occurred following the largest up-estuary wind peak. Ingress of summer flounder was correlated with negative along-estuary winds (blowing down-estuary), with a two-day lag. These results suggest that species-specific vertical position in the water column influenced ingress into Delaware Bay. The lag results also suggest that ingressing Atlantic croaker and summer flounder may have a pooling stage outside the mouth of Delaware Bay.

Identification and characterization of membrane androgen receptors in the ZIP9 zinc transporter subfamily: I. Discovery in female atlantic croaker and evidence ZIP9 mediates testosterone-induced apoptosis of ovarian follicle cells.

Rapid, cell surface-initiated, pregenomic androgen actions have been described in various vertebrate cells, but the receptors mediating these actions remain unidentified. We report here the cloning and expression of a cDNA from Atlantic croaker (Micropogonias undulatus) ovaries encoding a 33-kDa, seven-transmembrane protein with binding and signaling characteristics of a membrane androgen receptor that is unrelated to any previously described steroid receptor. Instead, croaker membrane androgen receptor has 81-93% amino acid sequence identity with zinc transporter ZIP9 (SLC39A9) subfamily members, indicating it is a ZIP9 protein. Croaker ZIP9 is expressed in gonadal tissues and in brain and is up-regulated in the ovary by reproductive hormones. Croaker ZIP9 protein is localized to plasma membranes of croaker granulosa cells and human breast cancer (SKBR-3) cells stably transfected with ZIP9. Recombinant croaker ZIP9 has a high affinity (dissociation constant, Kd, 12.7 nM), limited capacity (maximal binding capacity 2.8 nM/mg protein), displaceable, single binding site-specific for androgens, characteristic of steroid receptors. Testosterone activates a stimulatory G protein coupled to ZIP9, resulting in increased cAMP production. Testosterone promotes serum starvation-induced cell death and apoptosis in transfected cells and in croaker ovarian follicle cells that is associated with rapid increases in intracellular free zinc concentrations, suggesting an involvement of zinc in this nonclassical androgen action to promote apoptosis. These responses to testosterone are abrogated by treatment with ZIP9 small interfering RNA. The results provide the first evidence that zinc transporter proteins can function as specific steroid membrane receptors and indicate a previously unrecognized signaling pathway mediated by steroid receptors involving alterations in intracellular zinc.

Managing a Marine Stock Portfolio: Stock Identification, Structure, and Management of 25 Fishery Species along the Atlantic Coast of the United States

AbstractIn this review, stock identification methods used, resulting stock numbers and boundaries, and assessment and management context were explored for all 25 species managed by the Atlantic States Marine Fisheries Commission (ASMFC). This included invertebrates and vertebrates distributed between Maine and Florida, with a few species ranging across all these states and some ranging into the Gulf of Mexico and the Canadian Maritimes. The effects of larval dispersal or mixing of adults in the marine environment were evident. Marine and catadromous spawners were recognized and treated as a unit stock (e.g., northern shrimp Pandalus borealis, American Eel Anguilla rostrata, Atlantic menhaden Brevoortia tyrannus, Bluefish Pomatomus saltatrix, Tautog Tautoga onitis), a metapopulation (American lobster Homarus americanus, Atlantic Herring Clupea harengus), or two stocks, north and south of Cape Hatteras, a major biogeographic boundary, (Black Sea Bass Centropristis striata, Scup Stenotomus chrysops, Red Drum Sciaenops ocellatus, Summer Flounder Paralichthys dentatus). Estuarine and anadromous spawners were structured and managed at a finer spatial scale (horseshoe crab Limulus polyphemus, Atlantic Sturgeon Acipenser oxyrinchus, American Shad Alosa sapidissima and the river herrings Blueback Herring A. aestivalis and Alewife A. pseudoharengus, and Spotted Seatrout Cynoscion nebulosus). A broad suite of stock identification methods have been applied to ASMFC species and reviewed here in five categories: life history traits, other phenotypic traits, genetic traits, natural marks, and applied marks. An interdisciplinary mix of methods has been achieved for a few species (Striped Bass Morone saxatilis, Winter Flounder Pseudopleuronectes americanus), but only a few or no stock identification methods have been applied to others (Spiny Dogfish Squalus acanthias, Hickory Shad A. mediocris, Spot Leiostomus xanthurus, Spanish Mackerel Scomberomorus maculatus). Clinal phenotypic variation has contributed to several long‐standing debates about stock structure; some of these have been recently reevaluated as a unit stock (Atlantic Croaker Micropogonias undulatus, Weakfish Cynoscion regalis), and others are still debated. For some ASMFC species, other priorities (e.g., bycatch) dominate the uncertainty of the assessment or management process. Otherwise, stock identification remains a research priority for most of these species. Continued research of this subject should consider (1) research priorities tabulated by ASMFC review panels, (2) strategic use of interdisciplinary stock identification methods, (3) use of experiments or reaction norms to separate phenotypes from genotypes, (4) genetic surveys at a seascape scale, (5) demonstration of contingent (nongenetic) structure and its implications for management, and (6) simulation modeling. Obstacles to adopting finer‐scale structure into assessments or management of ASMFC fisheries include: (1) multiple stock units are apparent but boundaries are not clear, (2) monitoring requirements for smaller areas or for mixed‐stock catches are not cost effective, or (3) mixing rates within a metapopulation or across biogeographic boundaries are poorly described.Received May 8, 2013; accepted March 3, 2014

Restoration of tryptophan hydroxylase functions and serotonin content in the Atlantic croaker hypothalamus by antioxidant treatment during hypoxic stress.

Antioxidants are prototypical scavengers of oxygen-free radicals and have been shown to prevent neuroendocrine dysfunction in vertebrates during oxidative stress. In the present study, we investigated whether antioxidant treatment can reverse hypoxia-induced down-regulation of hypothalamic tryptophan hydroxylase (TPH) and serotonergic functions in Atlantic croaker. Hypothalamic neuronal contents of TPH-1 and TPH-2 proteins, serotonin (5-hydroxytryptamine, 5-HT) and its precursor, 5-hydroxytryptophan (5-HTP) as well as hypothalamic TPH-1 and TPH-2 mRNA expression and TPH activity were measured in croaker after exposure to hypoxia and treatment with pharmacological agents. Multiple injections of N-ethylmaleimide, a sulfhydryl alkylating agent, caused comparable decreases in hypothalamic TPHs functions and 5-HT contents to that induced by hypoxia exposure (dissolved oxygen: 1.7 mg/L for 4 weeks) which were partially restored by repeated injections with a nitric oxide synthase (NOS)-inhibitor and/or vitamin E. Double-labeled immunohistochemical results showed that TPHs and 5-HT neurons were co-expressed with neuronal NOS (nNOS, a neuroenzyme) that catalyzes the production of nitric oxide, a free radical, in hypothalamic neurons. These results suggest that hypoxia-induced impairment of TPH and serotonergic functions are mediated by nNOS and involve the generation of free radicals and a decrease in the antioxidant status. This study provides, to our knowledge, the first evidence of a protective role for an antioxidant in maintaining neural TPHs functions and 5-HT regulation in an aquatic vertebrate during hypoxic stress.

Activation of the Pi3k/Akt Pathway and Modulation of Phosphodiesterase Activity via Membrane Progestin Receptor-Alpha (mPRalpha) Regulate Progestin-Initiated Sperm Hypermotility in Atlantic Croaker1

Rapid progestin stimulation of sperm motility is a widely observed phenomenon in vertebrates, but the mechanisms governing these effects are still poorly understood, especially in teleosts, amphibians, and birds, which do not express CatSper. Here we show that progestin-stimulated sperm hypermotility in a teleost, Atlantic croaker (Micropogonias undulatus), is initiated though membrane progestin receptor-alpha (mPRalpha, also known as Paqr7b) and involves activation of the Pi3k/Akt pathway and increased phosphodiesterase (Pde) activity. The specific mPRalpha agonist 10-ethenyl-19-norprogesterone (Org OD 02-0) mimicked the stimulatory actions of the endogenous progestin in this species, 17, 20beta, 21-trihydroxy-4-pregnen-3-one (20beta-S), on sperm motility. Inhibition of Pi3k (1 nM Wortmannin; 25 μM LY294002) and Akt (25 μM ML-9) effectively abolished progestin-initiated sperm hypermotility. Surprisingly, treatment with the PDE inhibitors Cilostamide (100 nM) and Rolipram (1 μM) also blocked progestin stimulation of sperm motility. Whereas treatment with 20beta-S increased sperm Pde activity, pretreatment with Wortmannin eliminated this response to the progestin and also resulted in elevated cAMP levels, indicating that Pdes are at least partially under Pi3k/Akt control. The results suggest that mPRalpha-mediated progestin stimulation of sperm motility in croaker through Pi3k/Akt is dependent on maintenance of Pde activity and a reduction in internal cAMP concentrations. However, a previous study showed that progestin stimulation of sperm hypermotility in this species is also dependent on membrane adenylyl cyclase (Acy) activation and increased intrasperm cAMP concentrations. Collectively, these findings indicate that progestin-mediated hypermotility through mPRalpha in teleost sperm involves modulation of intracellular cAMP concentrations through multiple signaling pathways.

Sex change and morphological transitions in a marine ectoparasite

AbstractThe fitness of parasitic organisms is strongly driven by their ability to infect potential hosts. Although transmission to a host organism is a key component to the parasitic lifestyle, surviving and reproducing within a host poses additional challenges. Cymothoa excisa is a parasitic isopod that infects Atlantic croaker, Micropogonias undulatus, along the Texas coast and has evolved mechanisms to successfully survive and reproduce within its host. Cymothoa excisa is known to exhibit sex‐change strategies but limited information exists on morphological changes, reproductive output and the timing at which sex change becomes optimal. This study collected Atlantic croaker during a 22‐month survey period and identified parasite prevalence and intensity in the host fish population. Infection rates were constant throughout the year at 19.88% and intensity increased through the season up to a maximum of four parasites. Following collection, isopod morphological parameters were quantified for each life stage (including female, transitional, male and juvenile), identifying shape and size transitions through ontogeny and sex change. Transitional C. excisa isopods only occurred when only one isopod was present in a fish, suggesting that isopods change sex from male to female if they are the first to recruit to an uninfected host. As isopods transition to females they have a large increase in size, legs, and pleotelson (which influence fecundity and anchoring ability), whereas the gonopod, eyes and uropod show a reduction (which are no longer needed for swimming and finding hosts). Data suggest that C. excisa sex change is related to the timing of infection and brood size increases with female size and host size. Therefore, it would be advantageous to be the first isopod to infect a host, as it could change into a female and increase reproductive potential. We discuss hypotheses that could explain the mating behavior of parasitic isopods.

Membrane progestin receptor alpha mediates progestin-induced sperm hypermotility and increased fertilization success in southern flounder (Paralichthys lethostigma)

Progestin hormones stimulate sperm motility in teleosts but their mechanisms of action remain unclear. Preliminary results suggest that progestin upregulation of sperm motility in southern flounder and several other marine species is mediated through a sperm membrane progestin receptor with the characteristics of membrane progestin receptor alpha (mPRα, also known as Paqr7b). The hypothesis that mPRα has an important role in progestin regulation of southern flounder sperm motility and fertility was tested in the present study. The specific mPRα agonist, 10-ethenyl-19-norprogesterone (Org OD 02-0, 100nM), mimicked the stimulatory actions of the endogenous progestin, 17,20β, 21-trihydroxy-4-pregnen-3-one (20β-S, 100nM) on flounder sperm motility. The concentration of the mPRα protein on sperm plasma membranes was positively correlated to sperm motility as well as the responsiveness of sperm to progestin stimulation. Acute in vitro progestin treatment of sperm with high mPRα protein levels increased both sperm motility and fertilization success in strip spawning experiments. However, in vitro progestin treatments were ineffective on sperm with low receptor abundance. A single injection of the superactive gonadotropin-releasing hormone analog (LHRHa, 100μg/kg) increased sperm motility and fertilization success in strip spawning experiments 72h post-injection which was accompanied by an increase in mPRα protein concentrations on sperm plasma membranes. These results provide clear evidence that southern flounder sperm hypermotility is mediated through mPRα. Stimulatory G proteins, but not inhibitory G proteins, were identified in flounder sperm plasma membrane fractions. The finding that treatment of flounder sperm plasma membrane fractions with either 20β-S or Org OD 02-0 increases cAMP levels suggests progestins stimulate flounder sperm motility by activating an mPRα/stimulatory G protein/membrane adenylyl cyclase pathway. A similar mechanism has been identified in Atlantic croaker, suggesting that the signaling pathway mediated by mPRα in sperm is highly conserved in advanced teleosts. Collectively, our results indicate that progestin-stimulation of flounder sperm hypermotility and fertility is dependent on a sufficient concentration of mPRα which can be upregulated by in vivo LHRHa treatments. These findings potentially have practical applications for enhancing the fertility of male flounder broodstock.

Effects of hypoxia-induced habitat compression on growth of juvenile fish in the Neuse River Estuary, North Carolina, USA

Hypoxia is thought to have negative effects on fish in coastal ecosystems, but quan- tifying those effects can be difficult. Direct exposure to hypoxia can reduce fish growth or survival, but fish can also rapidly detect and avoid low dissolved oxygen levels. However, avoidance behavior may result in indirect effects that reduce fish growth. For example, when hypoxic condi- tions expand, fish densities may increase in nearshore oxygenated refuges, potentially causing density-dependent reductions in growth. We evaluated this hypothesis for juvenile demersal fish species (primarily spot Leiostomus xanthurus and Atlantic croaker Micropogonias undulatus). By monitoring water quality and fish density across the Neuse River Estuary, North Carolina, USA, under varying water quality conditions during summer 2007, we showed that fish effectively avoided hypoxia despite rapidly changing conditions (minutes to hours), moving away from incur- sions of hypoxic water and then rapidly redistributing into affected areas after these events passed. Fish densities in nearshore oxygenated refuges increased nearly 2-fold when habitat was compressed by hypoxic waters. Spot in compressed refuges also had significantly less food in their stomachs during June. Based on published estimates of density-dependent spot growth, we esti- mated that average spot growth rate was reduced 17% during habitat compression events, which occurred 21.5% of the time, translating into an average reduction in growth rate of 4% over the summer. This likely is a conservative estimate of indirect hypoxia effects on growth, as hypoxia was relatively mild in 2007, and density dependence is only one indirect mechanism by which hypoxia may potentially reduce growth.

Derelict fishing gear in Chesapeake Bay, Virginia: Spatial patterns and implications for marine fauna

Derelict fishing gear is a source of mortality for target and non-target marine species. A program employing commercial watermen to remove marine debris provided a novel opportunity to collect extensive spatially-explicit information for four consecutive winters (2008–2012) on the type, distribution, and abundance of derelict fishing gear and bycatch in Virginia waters of Chesapeake Bay. The most abundant form of derelict gear recovered was blue crab pots with almost 32,000 recovered. Derelict pots were widely distributed, but with notable hotspot areas, capturing 40 species and over 31,000 marine organisms. The target species, blue crab, experienced the highest mortality from lost pots with an estimated 900,000 animals killed each year, a potential annual economic loss to the fishery of $300,000. Important fishery species were captured and killed in derelict pots including Atlantic croaker and black sea bass. While some causes of gear loss are unavoidable, others can be managed to minimize loss.

Influence of constant and periodic experimental hypoxic stress on Atlantic croaker otolith chemistry

The chemical composition of fish otoliths may provide information on the environmental expo- sure histories of fishes if 'vital effects' on element incorporation are minimal. In order to use redox-sensi- tive geochemical proxies, such as manganese, in otoliths to quantify sublethal exposure to hypoxia, the relative influence of endogenous and exogenous controls on otolith composition must first be vali- dated. Controlled laboratory experiments were con- ducted on Atlantic croaker Micropogonias undulatus to examine the response of otolith Sr:Ca, Ba:Ca, Mg:Ca, Mn:Ca, and Na:Ca ratios to either constant or periodic hypoxia treatments for 4 and 10 wk, respec- tively. Although fish somatic growth and condition were affected by constant hypoxia, no difference in otolith chemistry relative to normoxic control treat- ments was detected. Similar to the 4 wk study, there was no difference in otolith chemistry between fish (males and females combined) exposed 10 wk to con- stant hypoxia and control normoxic fish. Periodic hypoxia significantly decreased otolith Ba:Ca and Mg:Ca in both males and females and reduced Sr:Ca in males, and there was a slight effect of sex on otolith Mn:Ca. Significant interactions between treat - ment and sex were detected for otolith Sr:Ca and Na:Ca, possibly related to combined stresses of gona - dal development and periodic hypoxic stress. Although responses to treatments were observed for some ele- ments, the magnitudes of responses were minimal compared to exogenous variation driven by water chemistry composition reported in previous labora- tory and field investigations. The otolith chemistry of Atlantic croaker is therefore minimally influenced by endogenous factors in response to hypoxic stress, which has important implications for interpreting otolith chemical chronologies of wild fish collected within natural hypoxic regions.

In search of climate effects on Atlantic Croaker (Micropogonias undulatus) stock off the U.S. Atlantic coast with Bayesian state-space biomass dynamic models

Atlantic Croaker (Micropogonias undulatus) production dynamics along the U.S. Atlantic coast are regulated by fishing and winter water temperature. Stakeholders for this resource have recommended investigating the effects of climate covariates in assessment models. This study used state-space biomass dynamic models without (model 1) and with (model 2) the minimum winter estuarine temperature (MWET) to examine MWET effects on Atlantic Croaker population dynamics during 1972–2008. In model 2, MWET was introduced into the intrinsic rate of population increase (r). For both models, a prior probability distribution (prior) was constructed for r or a scaling parameter (r0); imputs were the fishery removals, and fall biomass indices developed by using data from the Multispecies Bottom Trawl Survey of the Northeast Fisheries Science Center, National Marine Fisheries Service, and the Coastal Trawl Survey of the Southeast Area Monitoring and Assessment Program. Model sensitivity runs incorporated a uniform (0.01,1.5) prior for r or r0 and bycatch data from the shrimp-trawl fishery. All model variants produced similar results and therefore supported the conclusion of low risk of overfishing for the Atlantic Croaker stock in the 2000s. However, the data statistically supported only model 1 and its configuration that included the shrimp-trawl fishery bycatch. The process errors of these models showed slightly positive and significant correlations with MWET, indicating that warmer winters would enhance Atlantic Croaker biomass production. Inconclusive, somewhat conflicting results indicate that biomass dynamic models should not integrate MWET, pending, perhaps, accumulation of longer time series of the variables controlling the production dynamics of Atlantic Croaker, preferably including winter-induced estimates of Atlantic Croaker kills.

Development of a Methodology for Intensive Larviculture of Atlantic Croakers

AbstractThe Atlantic Croaker Micropogonias undulatus (Sciaenidae) is a candidate species for marine baitfish aquaculture in the southeastern United States because of its high value and common use as live bait by recreational fishers. However, an efficient larviculture procedure has not been reported to date; development of such a procedure was the impetus for this study. Embryos were obtained from captive broodstock that were induced to spawn volitionally by using a single injection of a luteinizing hormone releasing hormone agonist. Larvae were cultured at low density (initial density = 6.4 larvae/L) via intensive culture methods, including the use of recirculating filtration systems and of rotifers, brine shrimp Artemia spp., and micropellets as larval foods. The trial was performed in six 1,100‐L tanks at a salinity of 14–29‰, with average rearing temperatures of 23.6°C and 24.6°C. At the completion of the study (39 d posthatch), mean SLs were 24.7 mm (SE = 0.738) for larvae cultured at 24.6°C and 23.0 mm (SE = 0.624) for larvae cultured at 23.6°C. Mean survival at 39 d posthatch was 25.9% and did not differ significantly between temperature groups. This work demonstrated a successful methodology for intensive larviculture of Atlantic Croakers and can serve as a platform for the experimentation that will be necessary to develop economically viable procedures for intensive production of this species.

Patterns of saccular afferent innervation in sciaenids

In this study, saccular afferent arborization patterns in Atlantic croaker Micropogonias undulatus, red drum Sciaenops ocellatus and spot Leiostomus xanthurus were characterized. Leiostomus xanthurus showed the simplest configuration while M. undulatus displayed the most complex. In addition, hair-cell densities at sites sampled along the rostro-caudal axis of the saccular epithelia correlated with the observed patterns of arborization.

Examination of an Estuarine Fish Assemblage Over an Inshore Artificial Reef

The perceived value of oyster reefs as fish habitat has led to many restoration projects in areas of historically high oyster populations. This study evaluated fish usage of a limestone cobble mimic oyster reef in Barataria Bay, Louisiana, as compared to a mud-bottom reference site. Emphasis was given to species of economic and ecological importance, including spotted seatrout (Cynoscion nebulosus), Atlantic croaker (Micropogonias undulatus), and bay anchovy (Anchoa mitchilli). There were no observed differences in community structure or catch per unit effort (CPUE) between habitats, likely due to high variability in the data, though seasonal differences were observed. CPUE of spotted seatrout, Atlantic croaker, and bay anchovy did not differ between habitats. Seasonal differences in abundance were detected, with significantly higher CPUE of spotted seatrout in summer, of Atlantic croaker in spring and summer, and of bay anchovy in winter. Spotted seatrout and Atlantic croaker were both significantly larger over the artificial reef, while bay anchovy were significantly larger over the mud bottom. Spotted seatrout, a prized recreational fishing species in Louisiana, appeared to be the only species that showed higher biomass, determined by numbers and size, at the the artificial reef. This is important in the context of managing habitat enhancement projects. While the reef did not increase numbers or species richness of the overall fish community, it did have an effect on one recreationally important species. Therefore, the success of such projects is based as much on the intended purpose, as its affect on the overall community.

Response of Lake Pontchartrain Fish Assemblages to Hurricanes Katrina and Rita

To assess possible impacts on Lake Pontchartrain fishes from the 2005 hurricanes, we compared trawl, beach seine, and gillnet collections taken before (2000–2003, 2005) and after (2006–2009) to determine if significant assemblage changes occurred. We also compared basic environmental variables to test for hurricane-related changes. Significant post-hurricane changes in fish assemblages occurred in trawl (analysis of similarity (ANOSIM), R < 0.090, p < 0.05) and beach seine (ANOSIM, R < 0.120, p < 0.05) collections across all seasons. Gillnet assemblages exhibited changes in only one season (ANOSIM, R = 0.045, p < 0.05). These consistently low global R values (all R < 0.120) across all gears suggest only minor compositional changes in species. When peak abundance periods were compared for individual species, Gulf menhaden (Brevoortia patronus) declined in trawl collections after the hurricanes (Friedman's test, χ 2 = 6.00, p = 0.014) but increased in gillnet collections (Friedman's test, χ 2 = 5.00, p = 0.025). Hardhead catfish (Ariopsis felis) increased in trawl collections, but Gulf pipefish (Syngnathus scovelli), naked gobies (Gobiosoma bosc), and rough silverside (Membras martinica) all declined in beach seine samples and Atlantic croakers (Micropogonias undulatus), Spanish mackerel (Scomberomorus maculatus), and sand seatrout (Cynoscion arenarius) all declined in gillnet samples. In general, salinity increased and water clarity and dissolved oxygen decreased after the hurricanes. While the overall composition of Lake Pontchartrain fish assemblages remains stable, the significant decline of some species and changes in certain environmental variables are cause for concern. Future monitoring should determine if all elements of this estuary will recover from these impacts.

Effects of an Inshore Artificial Reef on the Trophic Dynamics of Three Species of Estuarine Fish

Estuarine habitats are important in the life history of many fish species, yet are being degraded at an alarming rate. Habitat loss is often mitigated by the addition of artificial reefs. Understanding how artificial habitat affects the trophic dynamics of associated fish communities is important to understanding their role in estuarine environments. This study compared the trophic dynamics of spotted seatrout, Cynoscion nebulosus (Cuvier, 1830), Atlantic croaker, Micropogonias undulatus (Linnaeus, 1766) , and bay anchovy, Anchoa mitchilli (Valenciennes, 1848), at an inshore artificial reef and a nearby mud-bottom site. Trophic dynamics were assessed using a combination of gut content analysis and stable isotopes for spotted seatrout and Atlantic croaker, and stable isotopes alone for bay anchovy. No significant differences were found in the either the diets or mean values of (delta)13C, (delta)15 N, or (delta)34S of spotted seatrout between habitats. Differences were seen in both the centroid distance and total area of the (delta) 13 C- (delta)15N biplot for spotted seatrout indicating greater trophic niche breath at the artificial reef. Diets of Atlantic croaker differed significantly between habitats and specimens were more enriched in (delta)15N at the artificial reef; however, no differences in trophic niche breadth were observed. Bay anchovy were more depleted in both (delta)13C and (delta)34S over the artificial reef and differences in the trophic niche breadth were observed. Results suggest that habitat alterations can affect trophic dynamics of estuarine species in different ways. Therefore, foraging strategy should be considered when evaluating estuarine artificial reefs.

Simulating the effects of global climate change on Atlantic croaker population dynamics in the mid-Atlantic Region

Projecting global climate change (GCC) effects on fish populations has primarily focused on temperature, while non-temperature effects are rarely simulated. In this study, we used a non-linear matrix population projection model of Atlantic croaker (Micropogonias undulatus) in the mid-Atlantic Bight to illustrate how global climate change effects, in addition to temperature, can be incorporated into population projections. The model was a multiple time step, stage-within-age matrix projection model with two nursery regions (Virginia and North Carolina estuaries) for young-of-the-year (YOY, egg to age-1) life stage development and a single ocean spatial box for adults. Late juvenile mortality was density-dependent and calibrated to generate a spawner-recruit relationship similar to observed values. Model simulations were for 160 years. Global climate change effects were estimated for 2020, 2050, and 2080, which resulted in three new sets of parameter values of the matrix model. The first 40 years of the 160 years were baseline, followed by 40 years of 2020 parameter values, 40 years of 2050 values, and 40 years of 2080 values. Changes in the parameters of the matrix model were based on changes in annual and seasonal temperatures generated by global circulation models, as well as presumed changes in precipitation causing increased hypoxia, increased variability in salinity, rising sea level, and changes in ocean circulation causing increased northward and offshore transport. Global climate change resulted in increased croaker abundance with lower inter-annual variability. Sensitivity analysis with each GCC effect imposed singly showed that the increase in croaker abundance under GCC was due to the complex suite of positive and negative responses across multiple life stages. The major positive response was due to warmer temperatures, and the major negative effects were due to increased variability in salinity, increased offshore transport, and sea level rise. A second sensitivity analysis showed that important, but highly uncertain, effects produced smoothly increasing population responses with increasing magnitude. We discuss how effects other than temperature can be important to projecting population responses to GCC, and the strengths and weaknesses of our analysis. Our analysis demonstrates how a variety of GCC-related effects can be incorporated into traditional population models; what is needed is sufficient empirical information to quantify the effects in terms of growth, mortality, movement, and reproduction.

An Ecologically Framed Mercury Survey of Finfish of the Lower Chesapeake Bay

Total mercury (THg) and methylmercury (MHg) concentrations and determents of mercury (Hg) accumulation were examined for muscle tissues of 10 finfish from the lower Chesapeake Bay (LCB) and its tributaries. There was no suggestion of potential human harm from Hg due to LCB fish consumption: None of the sampled fish had THg concentrations approaching the United States Environmental Protection Agency human health screening value. Hg concentrations in different fish species generally increased with the increasing stable isotope of nitrogen 15 (δ(15)N) but not the stable isotope of carbon 13 (δ(13)C), thus suggesting that trophic position but not dietary carbon source is a dominant determinant. An MHg biomagnification model was built to estimate a food web magnification factor of approximately 10-fold increase per trophic level. Based on otolith strontium-to-calcium ratios, Atlantic croaker inhabiting less saline waters might accumulate more Hg than those inhabiting more saline waters. The SAS mixed procedure identified significant positive intraspecies relationships between MHg concentration and δ(13)C for summer flounder, weakfish, American eel, Atlantic croaker, and spot.

Temporal and Spatial Effects on the Diet of an Estuarine Piscivore, Longnose Gar (Lepisosteus osseus)

Chesapeake Bay is the largest estuary in the USA and comprises vast areas of polyhaline to freshwater, tidal fish habitat. The Bay experiences large temperature differences between winter and summer, which in combination with the variety of salinities enables approximately 240 species of fish to be temporary inhabitants. This dynamic environment leads to an ever-changing prey field for predators. The goal of this study was to characterize the diet of one of the few resident, euryhaline predators within the tidal rivers in Virginia, Lepisosteus osseus (longnose gar). The top five prey species were Morone americana, Brevoortia tyrannus, Fundulus spp., Micropogonias undulatus, and Leiostomous xanthurus. The diet composition varied with the seasonal fish assemblages, length of L. osseus, water temperature, and salinity. L. osseus consumed a greater amount of marine and anadromous fishes (%W = 59.4 % and %N = 56.5 %) than resident fishes (%W = 40.6 % and %N = 43.5 %). The seasonal influx of anadromous or coastal spawning fishes appears to be an important prey source for L. osseus and most likely other piscivores in the tributaries of Chesapeake Bay.

Diversity of the skin microbiota of fishes: evidence for host species specificity

Skin microbiota of Gulf of Mexico fishes were investigated by ribosomal internal spacer analysis (RISA) and 16S rRNA gene sequencing. A total of 102 fish specimens representing six species (Mugil cephalus, Lutjanus campechanus, Cynoscion nebulosus, Cynoscion arenarius, Micropogonias undulatus, and Lagodon rhomboides) were sampled at regular intervals throughout a year. The skin microbiota from each individual fish was analyzed by RISA and produced complex profiles with 23 bands on average. Similarities between RISA profiles ranged from 97.5% to 4.0%. At 70% similarity, 11 clusters were defined, each grouping individuals from the same fish species. Multidimensional scaling and analysis of similarity correlated the RISA-defined clusters with geographic locality, date, and fish species. Global R values indicated that fish species was the most indicative variable for group separation. Analysis of 16S rRNA gene sequences (from pooled samples of 10 individual fish for each fish species) showed that the Proteobacteria was the predominant phylum in skin microbiota, followed by the Firmicutes and the Actinobacteria. The distribution and abundance of bacterial sequences were different among all species analyzed. Aeribacillus was found in all fish species representing 19% of all clones sequenced, while some genera were fish species-specific (Neorickettsia in M. cephalus and Microbacterium in L. campechanus). Our data provide evidence for the existence of specific skin microbiota associated with particular fish species.