Naked Goby Research Articles

A new species of Ellipsomyxa Køie, 2003 (Bivalvulida) infecting the gall bladder of Pangasius macronema Bleeker (Siluriformes: Pangasiidae) from the Mekong River Delta, Vietnam.

During a parasitological survey of freshwater fishes in the Mekong River Delta, Vietnam, disporic plasmodia containing myxospores morphologically consistent with Ellipsomyxa Køie, 2003 (Bivalvulida) were observed infecting the gall bladder of Pangasius macronema Bleeker (Siluriformes: Pangasiidae). Herein, we use morphology and small subunit ribosomal DNA (SSU rDNA, 18S) sequence data to describe Ellipsomyxa intravesica Ksepka & Bullard n. sp. and relate it to other myxozoans. The new species resembles Ellipsomyxa adlardi Whipps & Font, 2013, which infects the naked goby, Gobiosoma bosc (Lacepede) (Gobiiformes: Gobiidae) in Lake Pontchartrain, Louisiana, but differs from it by having a longer myxospore (mean = 13.3; range = 12.0-15.0 vs. 12.4; 11.3-14.4) and shorter polar capsules (3.7; 3.0-4.0 vs. 4.3; 3.9-4.9). The 18S phylogenetic analysis recovered the sequence of the new species sister to those ascribed to Ellipsomyxa ariusi Chandran, Zacharia, Sathianandan & Sanil, 2020 and Ellipsomyxa sp. (MK561979); both of which infect the gall bladder of the threadfin sea catfish, Arius arius (Hamilton) (Siluriformes: Ariidiae) from the southwest coast of India. Consistent with previous phylogenetic analyses of Ellipsomyxa spp., Ellipsomyxa was recovered as monophyletic. The new species is the first species of Ellipsomyxa reported from a freshwater fish in Asia and the first myxozoan reported from P. macronema.

Invasiveness risks of naked goby, Gobiosoma bosc, to North Sea transitional waters

In recent decades, gobies have dispersed or introduced from the Ponto-Caspian region of eastern Europe in a westerly direction to North American and western European waters. By contrast, the naked goby, Gobiosoma bosc, is the only known gobiid species to have been introduced in an easterly direction from North American to western Europe. The potential invasiveness of G. bosc was assessed using the Aquatic Species Invasiveness Screening Kit (AS-ISK) for rivers and transitional waters for the western and eastern sides of the North Sea. Using globally-derived thresholds, G. bosc was assessed as low-medium invasiveness risk for both sides of the North Sea under current climate conditions. Under future climate conditions, potential invasiveness will increase for both risk assessment areas. Environmental suitability assessment indicated an increase in environmental suitability for G. bosc on the eastern coastline of the North Sea under climate change scenarios and suitability remained unchanged on the western coastline, reflecting the authors' expectations of invasiveness risk.

Site Fidelity of Oyster Reef Blennies and Gobies in Saltmarsh Tidal Creeks

Blennies and gobies are among the most abundant fishes in western Atlantic and Gulf of Mexico estuaries. They establish nests and maintain territories in oyster reefs and around other shallow-water structures during warm months. In this study, site fidelity and movements were determined for adult striped blenny, naked goby, freckled blenny, crested blenny, and feather blenny, in descending order of abundance. Recaptures among 221 tagged fishes at nine intertidal oyster reefs in a southeastern U.S. saltmarsh estuary provided information about fidelity for individual oyster reefs and nest sites as well as the size of territories (areas used) around nest sites. An overall recapture rate of 94% for fishes on reefs where they were tagged indicated high fidelity. Total recapture rates for the four blenny species ranged from 38 to 50%, but the naked goby recapture rate was only 9%. Within a breeding season, fidelity for specific nest sites was 58% for all blennies and 17% for gobies. Movements away from nest sites were limited with 56% of all fishes re-occurring ≤ 1 m from the original tagging site. Territories of 84% of the recaptured fishes. Differences in species composition and abundance between reefs suggested species-specific preferences for habitat features. Crested blenny and freckled blenny were recaptured at nest sites with significantly more oyster cover than nest sites occupied by striped blenny. Blennies occupied nest sites for several months and across annual breeding seasons suggesting continued residency within small areas of individual oyster reefs throughout their lives. Strong fidelity for reefs and nest sites potentially makes blennies more susceptible to disturbances than gobies, but both may be vulnerable to habitat disturbance at scales < 5 m. Thus, blennies and gobies may be useful indicator species for changes within estuarine habitats and ecosystems.

Ontogeny of Otolith Formation in Two Demersal Estuarine Reef Fishes

Abstract Planktonic reef fish larvae locate and orient to reefs during settlement. Consequently, metamorphosis occurs in appropriate juvenile and/or adult habitats. Larval fish use otoliths for hearing (sagittae and asterisci) as well as equilibrium (lapilli) required for directional swimming. Striped blenny (Chasmodes bosquianus) and naked goby (Gobiosoma bosc) larvae, settled individuals, and juveniles were used to describe otolith ontogeny from hatching through settlement, the transition from pelagic to benthic habitats, and metamorphosis. Larvae hatched from nests collected in North Inlet estuary, SC, were cultured from May through July in 2012 and 2013 at ambient temperatures. Sagittae and lapilli were present at hatching in both species. Asterisci were only observed in settlement (gobies and blennies) or metamorphosis (blennies) stage fishes, regardless of age (days post-hatch). Otoliths within a pair were symmetrical. Fish total length increased faster than sagittae otolith length in settlement stage blennies and postflexion gobies. The allometric model explained ∼90% of the variability in sagittae otolith length with total length for both species. Settlement occurred 15–20 days post-hatch in striped blennies and 19–27 days post-hatch in naked gobies. Asterisci were found in 100% of settlement stage striped blennies and 67% of naked gobies. We hypothesize that the presence of asterisci in settlement stage demersal oyster reef fishes facilitates identification of and orientation to suitable settlement habitats thereby enhancing recruitment success.

Distribution and population structure in the naked goby Gobiosoma bosc (Perciformes: Gobiidae) along a salinity gradient in two western Atlantic estuaries.

Many species of fish produce larvae that undergo a prolonged dispersal phase. However, evidence from a number of recent studies on demersal fishes suggests that the dispersal of propagules may not be strongly correlated with gene flow. Instead, other factors like larval behavior and the availability of preferred settlement habitat may be more important to maintaining population structure. We used an ecologically important benthic fish species, Gobiosoma bosc (naked goby), to investigate local and regional scale population structure and gene flow along a salinity gradient (∼3 ppt to ∼18 ppt) in two North Carolina estuaries. G. bosc is an abundant and geographically widespread species that requires complex but patchy microhabitat (e.g. oyster reefs, rubble, woody debris) for reproduction and refuge. We sequenced 155 fish from 10 sites, using a common barcoding gene (COI). We also included recent sequence data from GenBank to determine how North Carolina populations fit into the larger biogeographic understanding of this species. In North Carolina, we found a significant amount of gene flow within and between estuaries. Our analysis also showed high predicted genetic diversity based upon a large number of rare haplotypes found within many of our sampled populations. Moreover, we detected a number of new haplotypes in North Carolina that had not yet been observed in prior work. Sampling along a salinity gradient did not reveal any significant positive or negative correlations between salinity and genetic diversity, nor the proportion of singleton haplotypes, with the exception of a positive correlation between salinity standard deviation and genetic diversity. We also found evidence that an introduced European population of naked gobies may have originated from an Atlantic source population. Altogether, this system offers a compelling way to evaluate whether factors other than dispersal per se mediate recruitment in an estuarine-dependent species of fish with a larval dispersal phase. It also demonstrates the importance of exploring both smaller and larger scale population structure in marine organisms to better understand local and regional patterns of population connectivity and gene flow.

Cryptic lineage divergence in marine environments: genetic differentiation at multiple spatial and temporal scales in the widespread intertidal goby Gobiosomabosc.

The adaptive radiation of the seven‐spined gobies (Gobiidae: Gobiosomatini) represents a classic example of how ecological specialization and larval retention can drive speciation through local adaptation. However, geographically widespread and phenotypically uniform species also do occur within Gobiosomatini. This lack of phenotypic variation across large geographic areas could be due to recent colonization, widespread gene flow, or stabilizing selection acting across environmental gradients. We use a phylogeographic approach to test these alternative hypotheses in the naked goby Gobiosoma bosc, a widespread and phenotypically invariable intertidal fish found along the Atlantic Coast of North America. Using DNA sequence from 218 individuals sampled at 15 localities, we document marked intraspecific genetic structure in mitochondrial and nuclear genes at three main geographic scales: (i) between Gulf of Mexico and Atlantic Coast, (ii) between the west coast of the Florida peninsula and adjacent Gulf of Mexico across the Apalachicola Bay, and (iii) at local scales of a few hundred kilometers. Clades on either side of Florida diverged about 8 million years ago, whereas some populations along the East Cost show divergent phylogroups that have differentiated within the last 200,000 years. The absence of noticeable phenotypic or ecological differentiation among lineages suggests the role of stabilizing selection on ancestral phenotypes, together with isolation in allopatry due to reduced dispersal and restricted gene flow, as the most likely explanation for their divergence. Haplotype phylogenies and spatial patterns of genetic diversity reveal frequent population bottlenecks followed by rapid population growth, particularly along the Gulf of Mexico. The magnitude of the genetic divergence among intraspecific lineages suggests the existence of cryptic species within Gobiosoma and indicates that modes of speciation can vary among lineages within Gobiidae.

Effects of within-season temperature variations on the early life history of two estuarine demersal fishes

Cultured naked goby (Gobiosoma bosc) and striped blenny (Chasmodes bosquianus) larvae were used to compare life history parameters for early and late periods within a long spawning season during which temperature increased by approximately 10 °C. Hatch lengths, growth rates, larval period duration, settlement length, survivorship, and other metrics of these serial spawners were determined for larvae hatched during early and late time periods with ambient average weekly water temperatures of 20.8 (standard deviation ±2.1 °C) and 29.0 (±1.0), respectively. Cultured fishes provided parameter estimates in the absence of predation mortality and with constant prey availability. Four hypotheses were tested for each species: 1) total length at hatch is not related to temperature, 2) pelagic larval period (PLD) is negatively related to temperature, 3) growth rates and survivorship are positively related to temperature, and 4) flexion and settlement lengths are negatively related to temperature. For both gobies and blennies, hatch length decreased with increasing temperature, but was not significantly related to survivorship. Larval blennies retained the yolk-sac longer than gobies. At higher temperatures, striped blenny flexion length, settlement length, PLD, and instantaneous mortality significantly decreased while instantaneous growth in length increased. Naked goby flexion lengths, settlement lengths, PLD, and mortality rates also declined with increasing water temperatures while instantaneous growth rates increased with increasing water temperatures. Average growth in length did not change significantly with temperature for either species. Survivorship in both fishes was lowest during 0 to 6 days post hatch (dph) coincident with the yolk-sac and first feeding stages. Survivorship significantly increased with larval fish total length and age (dph) for both species and time periods. Average estimated striped blenny percentage survival increased by an order of magnitude (~3 to ~32 %) with increasing temperature while average naked goby percentage survival increased from ~3 % (early) to ~11 % (late) over the 8.3 °C temperature range examined. The observed life history parameter variation with seasonal temperature changes likely function to ensure survival to settlement for at least some cohorts within a year class as part of a bet-hedging life history strategy. Data from cultured fishes provide a baseline for future evaluation of demographics and rates from field collections.

New Host Record (Gobiosoma bosc, Teleostei), forHomalometronsp. (Digenea: Apocreadiidae) in the Charleston Harbor, South Carolina, U.S.A.

During a dietary study of the naked goby, Gobiosoma bosc, collected from Charleston Harbor, South Carolina, in 2011–2012, gut content analyses showed the presence of several digenean species. The identity of one of the digenean species was investigated using molecular and morphological techniques. A comparison of 374 base pairs of an internal transcribed spacer region of ribosomal DNA (ITS2) with the GenBank database revealed that the digenean was a Homalometron sp., most likely Homalometron palmeri or an undescribed sister taxon. Specimens examined for morphology were immature, less than 1 mm in length, and had an oral to ventral sucker width ratio of 1:1.15–1.29. This is the first record of Homalometron sp. parasitizing a Gobiosoma bosc host, and it represents the first potential occurrence of H. palmeri outside of the Gulf of Mexico.

Ontogenetic changes in predator–prey interactions between two species of larval fishes and oyster veligers

The naked goby (Gobiosoma bosc), striped blenny (Chasmodes bosquianus), and eastern oyster (Crassostrea virginica) are common resident species in temperate Atlantic tidal waters. All three species produce planktonic larvae, and interactions between their early life stages likely influence recruitment success. Fish predation on oyster veligers requires co-occurrence as well as a match between prey behavior, size, and morphology and the ability of the predator to capture and engulf the veliger (prey). Wild plankton, oyster veligers, and wild plankton enriched with oyster veligers (mixed) were fed to cultured larval fishes during laboratory experiments. Three hypotheses were tested: (1) no fish species-specific differences in oyster veliger consumption exist within similar predator–prey development stage combinations, (2) postflexion blennies and gobies consume more veligers than preflexion fishes, (3) veligers reach a size refuge from fish predation by the umbo developmental stage. The resulting data provide a quantitative description of larval fish feeding behavior with respect to fish (preflexion, postflexion) and veliger (straight hinge, umbo) developmental stage. Selectivity for bivalve veligers as well as ontogenetic effects on the predator–prey interaction were examined. Fish nests were cultured to provide larval fish predators of known age. Overall, 70% of striped blennies and 59% of naked gobies consumed at least one prey item during the 3h experiments. There were fish species-specific differences in oyster veliger consumption between striped blennies and naked gobies. Striped blennies consumed more prey items including a wider range of veliger ages than larval naked gobies of the same developmental stages, regardless of the prey treatment. Fish selectivity was high for copepod nauplii and bivalve veligers and usually low for polychaete larvae, barnacle nauplii, and diatoms. There was a significant positive relationship between standardized consumption and predator development stage in the wild treatment for both fishes and in mixed and veliger treatments for blennies. All fishes consumed straight hinge veligers more often than umbo stage veligers. The largest veligers appear to reach a predation refuge from both fishes. Larval gobies and blennies are generalist predators that use seasonal pulses of zooplankton prey within temperate estuaries. Potential mismatches between predator–prey spatial and temporal overlap that might reduce fish recruitment are likely offset by adult spawning strategies that result in multiple nests within a long spawning season.

Spatial and Temporal Distribution of Larval Naked Goby Gobiosoma bosc (Pisces, Gobiidae) in the Middle St. Johns River, Florida

Naked goby (Gobiosoma bosc) larvae were collected from February 2008 through September 2009 at six sites located from 100 to 255 km upstream of the lower St. Johns River estuary. A total of 49,995 G. bosc larvae were collected making it the fourth most abundant species present. Preflexion larvae (3–5 mm standard length (SL)) were collected at all sites and comprised of >55 % of all G. bosc larvae collected. The dominance of preflexion larvae, estimated to be about 2 weeks old, validated that G. bosc were spawning at all sampling sites. Because of the distance involved, and the lack reverse flows due to tidal influence, larval presence was not a result of upstream transport from the estuary. Throughout the study, salinity at all sampling sites averaged between 0.2 and 1.2 practical salinity units (psu), which is below the lower limit of salinity at which this species has been previously reported to spawn. Spawning by G. bosc in the middle St. Johns River in 2008 and 2009 occurred from late March through early August. Spawning in the middle basin appeared truncated compared to the estuary, where reproduction appears to occur well into the fall. Larval G. bosc larvae began appearing in our samples as water temperatures approached 20 °C. Larval density varied significantly both spatially and temporally, but was poorly explained by instantaneous measures of dissolved oxygen, salinity, pH, temperature, Secchi depth, or sampling depth. At sampling sites, where G. Bosc larvae were most abundant, average seasonal densities declined from 74 to 95 % between 2008 and 2009. In August 2008, heavy rains from Tropical Storm Fay caused dramatic flooding over the entire study area and dissolved oxygen concentration at all sampling sites fell to <0.8 mg L−1 from periods ranging from several days to several weeks. We believe this anoxic event caused high larval and juvenile mortality resulting in a nearly complete recruitment failure of the 2008 year class. Since G. bosc rarely survive past age I, recruitment failure of the 2008 year class could explain the between-year decline in larval densities observed. In addition, frequent anoxic events associated with increased streamflow at our most upstream sites during the late summer wet season may also help explain low larval densities at these sites.

Diet composition and feeding ecology of the naked goby Gobiosoma bosc (Gobiidae) from four western Atlantic estuaries.

The feeding ecology of the small-bodied benthic naked goby Gobiosoma bosc, a western Atlantic species that occurs in estuaries and other inshore habitats from Connecticut to Texas U.S.A., was investigated in a total of four estuaries spanning South Carolina, North Carolina, Maryland and New Jersey. Gut content analysis of 391 individuals revealed that G. bosc is a benthic microcarnivore that feeds primarily on polychaetes, gammarid amphipods and harpacticoid copepods. Diet composition varied with body size, tidal creek within an estuary and geographic region. Analyses of gut fullness suggest that G. bosc is a daytime visual predator and that nest and egg guarding during the reproductive season reduce foraging activity in mature males. Additionally, G. bosc infected with adult digenean parasites of the gut foraged more intensely than uninfected individuals, a relationship that was strongest for reproductively mature males. Regionally, significant variation in dietary breadth was documented and may reflect a foraging response to a decrease in prey diversity moving from estuaries of higher salinity and lower latitude to estuaries of lower salinity and higher latitude. These results contribute to an understanding of the life history of G. bosc and the role played by this common species in estuarine food webs.

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.

Interaction of Two Myxozoan Parasites from Naked GobyGobiosoma bosc, in Lake Pontchartrain, Louisiana

During a parasitological survey of naked gobies ( Gobiosoma bosc ) in Lake Pontchartrain, Louisiana, U.S.A., 2 myxozoan parasites were found infecting the gall bladders of 84 of 90 fish. Parasite plasmodia of each were morphologically distinct; plasmodia bearing Ellipsomyxa-like spores were elongate and fusiform (1,126 by 403 μm), and those bearing Sphaeromyxa-like spores were large and discoid (1,400 μm diameter). Neither parasite conformed to any described species of myxozoan, and both are described here. Sphaeromyxa kenti n. sp. bears boomerang-shaped spores ranging 17.5-19.8 μm long by 3.8-5.2 μm wide. Two unequal sized polar capsules contain ribbon-like polar filaments characteristic of this genus. Ellipsomyxa adlardi n. sp. bears ovoid spores 11.3-14.4 by 7.1-8.8 μm, with 2 rounded polar capsules oriented in opposite directions relative to the longitudinal plane of the spore. Phylogenetically both species cluster with sequenced members of their respective genera. Plasmodia of E. adlardi n. sp. were encountered in 72.2% of gobies examined, and S. kenti n. sp. in 25.6%. Overall, 6.7% of animals were uninfected, and only 4.4% of the 90 fish examined were infected with both species. The observed co-occurrence was lower than expected by chance, strongly suggestive of an interaction between these species.

First record of the naked goby Gobiosoma bosc (Lacepède, 1800) in European waters

The naked goby Gobiosoma bosc (Lacepede, 1800), a western Atlantic gobiid species, has been recorded for the first time in European waters in October 2009. Seven specimens were caught by a stow net vessel at river km 45 in the Weser estuary (Germany) close to Sandstedt.

Passive acoustics as a monitoring tool for evaluating oyster reef restoration.

Passive acoustics uses naturally occurring sounds produced by marine organisms to study their behavior, biology, and location. Ambient marine sounds are known to vary from place to place, and these sounds can be used to detect differences in habitats. Oyster toadfish, naked goby, mud crabs, and snapping shrimps inhabit oyster reefs, and they are known to produce sounds. In an oyster reef, the combination of sounds produced by organisms’ communication, feeding, or moving may produce a unique acoustic signature. Therefore, individual acoustic signatures of oyster reefs may convey information about the habitat quality and the organisms that inhabit them. Three sites along the Saint Lucie Estuary, Florida were acoustically monitored. Restored and natural reefs were recorded for 5-min using a hydrophone. Acoustic signatures were compared using spectra [(frequency (Hz) versus intensity (dB)] overlays. Preliminary results showed that shortly after restoration, acoustic signatures from the natural and restored reefs differed. As time progresses, the acoustic signature of a fully restored reef may resemble that of the natural reef, representing a convergence of restored and natural habitats. Passive acoustics has the potential to provide a new methodology to rapidly monitor oyster reefs and other ecosystems such as coral reefs and rocky reefs.

Effects of hypoxia on Mnemiopsis leidyi, ichthyoplankton and copepods: clearance rates and vertical habitat overlap

Differences in predator and prey tolerances to low dissolved oxygen (DO) concentra- tions influence planktonic food web interactions in seasonally hypoxic environments. We examined low-DO effects on predation by hypoxia-tolerant ctenophores, Mnemiopsis leidyi, on less hypoxia- tolerant ichthyoplankton prey in laboratory experiments. We also examined the relationship between bottom DO concentrations and vertical distributions, and considered potential effects of biotic (pre- dators and competitors) versus abiotic factors (low DO concentration, temperature, salinity, time of day) on vertical habitat overlaps between gelatinous zooplankton and their prey during summer in a Chesapeake Bay subestuary. Laboratory clearance rates of M. leidyi feeding on bay anchovy (Anchoa mitchilli) eggs and yolk sac larvae, and naked goby (Gobiosoma bosc) larvae were as high at low DO (1.5 mg l -1 ) as at high DO concentrations (7 mg l -1 ). Multiple years of field sampling at 2 sites revealed that the proportions of motile species in the bottom layer of the water column, espe- cially fish larvae and copepods, increased with increasing bottom DO concentrations during both day and night. Ctenophore densities remained high in the bottom layer even at low DO concentrations. Vertical habitat overlaps among 4 motile predator-prey pairs (M. leidyi-copepods, M. leidyi-naked goby larvae, bay anchovy larvae-copepods, and naked goby larvae-copepods) increased with increasing bottom DO concentrations (1st- or 2nd-order regression models). Vertical overlap between M. leidyi and fish eggs was significantly higher during the day than at night. Statistical models sug- gest that both bottom DO concentration and scyphomedusan predators influenced M. leidyi-fish egg nighttime and M. leidyi-copepod combined day-night overlaps. Hypoxia influences food web inter- actions more through altered habitat use and encounter rates than by directly affecting predation. Strong behavioral responses of larval fish and copepods to low bottom DO concentrations may decrease habitat overlap between M. leidyi predators and their prey.

Nekton use ofVallisneria americana Michx. (Wild celery) beds and adjacent habitats in Coastal Louisiana

We compared nekton use ofVallisneria americana Michx. (submerged aquatic vegetation, SAV) with marsh shoreline vegetation and subtidal nonvegetated bottom (SNB) using a 1-m2 drop sampler in the oligohaline area of Barataria Bay, Louisiana. Mean densities of most abundant species were significantly different among six habitat types. Harris mud crabRhithropanopeus harrisii, Ohio shrimpMacrobrachium ohione, blue crabCallinectes sapidus, daggerblade, grass shrimpPalaemonetes pugio, white shrimpLitopenaeus setiferus (fall), rainwater, killifishLucania parva, naked gobyGobiosoma bosc, code gobyGobiosoma robustum (fall), speckled worm eelMyrophis punctatus (fall), and gulf pipefishSyngnathus scovelli (spring), were much more abundant, and species richness also was greater, inVallisneria than over SNB.Vallisneria supported densities of most species that were similar to those in marsh vegetation, although naked goby and gulf pipefish were more abundant inVallisneria, and speckled worm eel and saltmarsh topminnowFundulus jenkinsi were more abundant in marsh. Within theVallisneria bed, densities of Harris mud crab, rainwater killifish, and speckled worm eel were higher at sites near the marsh (SAV Inside Edge) than at sites more distant from the marsh (SAV Outside Edge), and Ohio shrimp (fall) densities were higher in the interior of the bed than along the edges. The mean size of blue crab was larger in marsh thanVallisneria and large inVallisneria than SNB. White shrimp did not differ in size among habitat types.Vallisneria beds may provide an important nursery habitat for young blue crab and white shrimp that use oligohaline estuarine areas. These SAV beds can provide an alternative structural habitat to emergent vegetation during periods of low water, becauseVallisneria occurs in the subtidal and generally persists throughout the year on the Gulf coast. Species whose young thrive in low-salinity waters and also depend on structure would benefit most fromVallisneria habitat in estuaries.

Does bioturbation by a benthic fish modify the effects of sediment contamination on saltmarsh benthic microalgae and meiofauna?

A microcosm experiment was conducted using a replicated factorial design to determine if a benthic fish modifies the effects of sediment-bound contaminants (diesel fuel and two levels of a Cu, Cr, Pb, Hg and Cd mixture) on saltmarsh benthic primary producers and consumers. The naked goby, Gobiosoma bosc, a burrowing fish that preys on small macrofauna, was added to experimental microcosms. Goby burrowing and foraging significantly increased turbidity and disrupted the sediment surface. Results were typified by complex and varied responses with many statistically significant effects and interactions among treatments. Although G. bosc modified the responses to both diesel and metal pollution in invertebrates (but not microalgae), bioturbation did not increase or decrease the toxic effects of metals or diesel, and diesel–metal interactions did not vary in response to G. bosc. Specifically, G. bosc inhibited a trend toward diesel-induced increases in nematode abundance, and diesel toxicity inhibited increases in ostracod abundance stimulated by G. bosc. Diatoms, nematodes and the copepod Pseudostenhelia wellsi decreased in treatments with G. bosc. However, G. bosc lead to increases in cyanobacteria and ostracods and a trend toward increases in the copepod Pseudobradya sp. Our findings suggest that microcosm experiments are potentially poor mimics of natural systems without bioturbation. Conclusions about the direct and indirect effects of contaminants may differ with and without bioturbation. Finally, our work suggests that the direct effects of toxicants may inhibit or mask bioturbation effects that stimulate population growth of some meiofauna.

Effects of environmental variables upon the spatial and temporal structure of a fish community in a small, freshwater tributary of the Indian River Lagoon, Florida

A survey to monitor the distribution and abundance of fishes and selected invertebrates in the St. Sebastian River, Florida, was conducted from March 1999 through June 2000. We recorded a total of 181,854 individuals (representing 77 taxa) in 128 seine samples, and a single species, bay anchovy ( Anchoa mitchilli), accounted for 84.4% of the animals collected. Seasonally, the species compositions of spring and fall samples were most similar (percent similarity index (PSI)=95.3%), whereas those of summer and winter samples were most dissimilar (PSI=54.0%). The spring samples contained the greatest mean number of taxa (N0=59 taxa), and the fall samples had the fewest (N0=38). In addition, spring samples had the highest index of abundant taxa (Hill's N1=10.6) and summer samples had the lowest (Hill's N1=6.4), suggesting that approximately four more taxa were caught in greater abundance during spring than during summer. Community composition determined via canonical correspondence analysis revealed four assemblages: two seasonal groupings and two spatial groupings. Seasonal species assemblages were composed of a spring-summer group characterized by recruits of Irish pompano ( Diapterus auratus), snook ( Centropomus undecimalis), and naked goby ( Gobiosoma bosc), and a fall–winter group characterized by recruits of mullet ( Mugil cephalus), spot ( Leiostomus xanthurus), and croaker ( Micropogonias undulatus). Spatial groupings were composed of a north prong group which included taxa with estuarine affinities, and a south prong group which included taxa with freshwater affinities. Community composition recorded during periods of controlled water releases and during periods of naturally high-water-flow differed, primarily because abundant estuarine taxa disappeared during the controlled release. The loss of these taxa suggests that when large amounts of fresh water enter the system during relatively short periods of time, the estuarine component of the community does not have time to adjust to the rapid decrease in salinity.

Mechanisms promoting upriver transport of larvae of two fish species in the Hudson River estuary

Bay anchovy Anchoa mitchilli and naked goby Gobiosoma bosc larvae have been reported to move up-estuary. In the present study, we examined depth preferences and periodic vertical move- ments that might promote such along-estuary transport in these 2 species. We conducted 2 cruises of 3 d each in the Hudson River estuary, USA. The cruises were 1 wk apart, coinciding with spring and neap tides. We sampled every 2 h with an ichthyoplankton trawl to permit tests of time, depth, and lateral position on larval concentration. We also collected data on water-column structure with a CTD, and cur- rent velocity with an acoustic Doppler current profiler (ADCP). We briefly sampled at several sites over a distance of 25 km along the river, and found that larvae of both species were uniformly abundant along this section although salinity decreased sharply with increasing distance upriver. Bay anchovy larvae were more abundant than goby larvae (median concentration 234 vs 6.6 ind. 100 m -3 ). Most sampling was conducted at an oligohaline location (mean salinity = 3 to 5 psu). Larvae were typically more concentrated at greater depths; among anchovy larvae during neap tide conditions, and goby larvae during neap and spring tide conditions, larvae were more concentrated at 6 and 8 m than at the surface by a factor of 2 to 9. Large larvae showed a stronger depth preference than small larvae. During spring tide, the water column was less stratified, and anchovy larvae under these conditions were uniformly distributed vertically. There were slight lateral differences in larval concentration, with fewer larvae in shallow water over the shoals than in similar depths in the main channel. We evaluated periodic cycles in flow and larval dis- tributions via harmonic regression. Tidal constituents of the depth-averaged current flow included the K1 (period = 23.9 h), M2 (period = 12.4 h), and the M4 (period = 6.2 h) tides. Harmonic regression explained >95% of the observed variability in mean flow. Diel periodicity in depth-averaged larvae con- centration was evident, particularly among large anchovy and goby larvae during neap tide conditions. Larvae were more abundant in the sampled depths at night than during the day by a factor of 3 to 10. There was also diel periodicity in the mean depth of goby larvae, such that larvae were about 2 m shal- lower at night than during the day. There was no periodic variability in the mean depth of anchovy larvae. We suggest that diel periodicity in larval concentration and mean depth reflects diel migration to shallower water at night, noting that temporal variability in net avoidance may also contribute to the periodicity. We conclude that anchovy and goby larvae exhibit a depth distribution and vertical migra- tion behavior that promotes upriver transport. Transport should be most rapid during neap tide periods.