Explore the vast range of titles available.

The flow regime of a river is an important driver of many ecosystem components. However, few studies explore how differences in flow rates and water chemistry can influence communities of parasites and their hosts. Here, we investigate the impact of dissolved oxygen, pH, salinity, water temperature, and river flow on the abundance and prevalence of cymothoid isopod parasitism (Lironeca ovalis) of the Bay Anchovy (Anchoa mitchilli) in the Alafia and Hillsborough rivers of Tampa Bay (Florida). We also explore seasonality by comparing monthly samples preserved throughout 2005–2007. Although both the Alafia and Hillsborough rivers had similar average water temperatures and salinity, and similar wet and dry season cycles, the upstream damming of the Hillsborough River had numerous negative effects on water flow rate, dissolved oxygen content, and acidity. This disruption in water quality corresponded with a lower abundance of anchovy hosts, fewer free-swimming cymothoids, and low prevalence of anchovy parasitism. Anchovies were much more abundant in the Alafia River, but flow negatively affected abundance—a negative effect that could be mitigated by positive changes in water temperature, salinity, and pH. Flow rates also negatively affected free-swimming cymothoid abundance; however, water flow was less important in predicting their parasitism of anchovies. In Alafia, fewer anchovies were parasitized when dissolved oxygen was high and water acidity was low, but more were parasitized during the wet season. These findings corroborate predictions that flow can moderate habitat stability and complexity which, in turn, can impact opportunities for parasitism of host communities.

Greater nutrient loads since the 1950s have increased the extent and duration of hypoxic conditions in the Patuxent River and the Chesapeake Bay (Maryland, USA). We linked watershed, water quality, and individual-based predation models to predict how changes in local (Patuxent River watershed) and regional (bay-wide) nutrient loading rates would affect bay anchovyAnchoa mitchilliegg and larval mortality rates in the lower region of the Patuxent River. Nutrient loadings affected hypoxic volume and the degree of spatial overlap between anchovy and their predators. Mortality rates were simulated during June and July under combinations of a wet or dry year, reduced and increased nutrient loadings from the Patuxent River watershed, and increased and decreased nutrient loadings into the Patuxent River at the Chesapeake Bay boundary. Chesapeake Bay water quality at the downstream boundary had a much larger effect on egg and larval mortality rates than nutrient loading rates from the Patuxent River watershed, and these responses were consistent with the downstream boundary condition having a greater effect on hypoxia. Water column structure, year type (wet/dry), and location within the lower Patuxent River had smaller effects on egg and larval mortality. Due to indirect effects, the effect of the Chesapeake Bay boundary condition on larval mortality rates during June was opposite to that predicted for egg mortality rates. Our results illustrate that statements and justifications about the benefits of nutrient loading reductions on estuarine ecosystems should avoid oversimplification, be specific, and recognize that species responses to changes in environmental conditions can be complex and variable.

Predicting future changes in species distributions due to climate change and sea-level rise are critical for informing adaptive management of large-scale estuarine ecosystem restorations. In this study, we used binomial generalized additive models (GAMs) to predict suitable habitat for 24 species groups under current conditions and projected conditions for 2060 in Florida Bay, a large and shallow estuary subject to one of the largest hydrological restoration efforts in the world, the Comprehensive Everglades Restoration Plan (CERP). Overall, potential sea-level rise due to climate change had a large influence in the system, driving the biggest reduction in habitat suitability in both magnitude and spatial extent. In contrast, the impacts of increased freshwater flows (and localized changes in salinity and salinity variation) from restoration influenced a greater number of species, but are predicted to have a relatively smaller influence on future habitat suitability for the majority of species in Florida Bay. The broadest positive changes in occurrence probabilities were found for spotted seatrout, pink shrimp, hardhead halfbeak, scaled sardine, common snook, and great barracuda. Negative changes occurred in numerous small-bodied species such as hardhead silverside, goldspotted killifish, rainwater killifish, and bay anchovy, as well as larger-bodied Crevalle jack, gray snapper, and white mullet. The model results predicted winners and losers, thereby providing an opportunity to ensure management strategies are designed appropriately to best achieve the desired results for the future of the Florida Bay ecosystem.

Anchovies are species of ecological and economic importance that inhabit coastal waters, where they are very abundant. The objective of the study was, through high-frequency temporal sampling, to analyze the diversity, seasonal and diel distribution patterns of anchovies and their relationships with environmental variables. For 19 months, 24-h monthly cycles were carried out, taking samples every two hours. Permutational analysis of variance (PERMANOVA) and redundancy analysis (RDA) were used for data analysis. Seven species were captured, of which, Anchoa mitchilli, Anchoa hepsetus, Anchoa lyolepis, Anchoa lamprotaenia and Cetengraulis edentulus are common in brackish waters; however, Anchoviella perfasciata and Engraulis eurystole rarely occur in these systems. For these species, no major threats are known; therefore, they are listed as ‘Least Concern’. A seasonal succession shows pulses during the closed-mouth phase and during the late warm-rainy season. At diel level, A. mitchilli, C. edentulus and A. lamprotaenia showed a markedly nocturnal pattern. RDA correlations showed that salinity, day/night effect, inlet state and rainfall were the most important factors related to anchovy distribution. Segregation along a salinity gradient was observed, in which A. mitchilli was captured mainly at low salinities, while other species occurred mainly at intermediate to high salinities. High-frequency sampling allowed a better understanding of the species richness and abundance patterns of anchovies in the system.

Temperate lagoonal estuaries contain a mosaic of subtidal habitats including salt marsh creeks, sand, and seagrass. Studies comparing fish use of estuarine habitats have focused disproportionately on sand and seagrass habitats, and along the U.S. east coast, previous studies that have made the direct comparison between subtidal salt marsh creeks, sand, and seagrass habitats were spatially narrow in scope. Here, we performed a comprehensive comparison of fish species composition, abundance, diversity, richness, and fish lengths across subtidal salt marsh creek (upper creek and creek mouth sites), sand, and seagrass habitats within a temperate lagoonal estuary. Daytime otter trawl sampling occurred at 45 sites within Barnegat Bay (New Jersey) in April, June, August, and October during 2012–2014. Seventy species representing estuarine transients, residents, southern strays, and shelf strays were observed, and juvenile and small adult fishes dominated the collections. There were some differences in species composition between habitats, with the assemblages in upper creek and seagrass habitats being the most dissimilar. Fish abundance, diversity, and richness were often higher in creek mouth and seagrass habitats than in sand habitat. Similar to seagrass habitats, creek mouths were shallow, more saline, and contained complex physical structure (macroalgae, marsh banks). Many fishes used all habitats (e.g., bay anchovy Anchoa mitchilli), but others were partial to certain habitats (e.g., fourspine stickleback Apeltes quadracus in seagrass). This study reaffirmed that many interacting factors shape fish assemblages and demonstrated the significance of marsh creeks to the subtidal habitat mosaic of this temperate lagoonal estuary.

The bay anchovy Anchoa mitchilli is the most abundant fish in Chesapeake Bay (USA) and is a vital link between plankton and piscivores within the trophic structure of this large estuarine ecosystem. Baywide distributions and abundances of bay anchovy eggs and larvae, and larval growth, were analyzed in a 5 yr program to evaluate temporal and spatial variability based on research surveys in the 1995–1999 spawning seasons. Effects of environmental variability and abundance of zooplankton that serve as prey for larval bay anchovy were analyzed. In the years of these surveys, 97.6% of eggs and 98.8% of larvae occurred in the polyhaline lower bay. Median egg and larval abundances differed more than 10-fold for surveys conducted in the 5 yr and were highest in the lower bay. Within years, median larval abundance (ind. m−2) in the lower bay was generally 1–2 orders of magnitude higher than upper-bay abundance. Salinity, temperature, and dissolved oxygen explained 12% of the spatial and temporal variability in egg abundances and accounted for 27% of the variability in larval abundances. The mean, baywide growth rate for larvae over the 5 yr period was 0.75 ± 0.01 mm d−1, and was best explained by zooplankton concentration and feeding incidence. Among years, mean growth rates ranged from 0.68 (in 1999) to 0.81 (in 1998) mm d−1 and were fastest in the upper bay. We identified environmental factors, especially salinity, that contributed to broadscale variability in egg and larval production.

Carbon (δ13C) and nitrogen (δ15N) isotopes were used to evaluate spatial, temporal, and interspecific differences in trophic relationships of four fish species (Paralichthys dentatus, Anchoa mitchilli, Leiostomus xanthurus, and Bairdiella chrysoura) in Maryland’s coastal bays. The δ13C values for all species were more enriched in 2017 than in 2018, a year of higher-than-average rainfall that likely caused higher amounts of terrestrial carbon to enter the estuary. There were significant differences among species in the δ13C values, with L. xanthurus being the least depleted (−17.2‰ in 2017; −18.8‰ in 2018). Spatially, the δ13C values of the species, particularly P. dentatus and B. chrysoura, were more depleted in the northern bays, which have a higher nutrient content and receive more freshwater inflow directly from tributaries, than the southern bays. The observed δ13C values (−19.5 ± 0.2‰ to –17.2 ± 0.3‰), however, indicate that marine phytoplankton was the primary carbon source of the fishes. Overall, A. mitchilli was the most enriched in δ15N (13.0‰), and L. xanthurus was the most depleted (10.2‰). δ15N was more enriched in fish from the more human-impacted northern bays than in fish from the southern bays, though this might also have stemmed from the differences in the diet composition of the species in the northern and southern bays. A. mitchilli had the highest trophic level, while L. xanthurus and P. dentatus had the lowest trophic levels. Niche breadth was widest in L. xanthurus compared to the other fish species, suggesting a higher variability in diets among L. xanthurus individuals, leading to specialized diets. There was a high niche overlap between B. chrysoura, A. mitchilli, and L. xanthurus, which indicates they fed on similar prey resources.

Lernaeenicus radiatus is a pennellid copepod with a 2-host life cycle that exhibits high host-specificity to their first host, black sea bass Centropristis striata. This parasite was prevalent in the gills of black sea bass juveniles and adults along the coast of New Jersey, USA, April to December 2019. Parasite incidence was high in the summer and fall in near-shore areas and dropped significantly in fish from deep waters further off-shore in December. Heavy infections of L. radiatus occurred in gills of adult black sea bass inhabiting reef-associated structures, in which parasite incidence rate was 2−3.7 times higher than in non-structure habitat. Less hostspecificity occurred in second hosts which support female metamorphosis. In total, 7 fish species were confirmed as second hosts, with the most common being Atlantic menhaden Brevoortia tyrannus and bay anchovy Anchoa mitchilli. Incidence of L. radiatus depends on host abundance and habitats that support interactions of the preferred fish hosts, which may explain the heavy infections in reef habitats. The L. radiatus anchor process in metamorphosed females was highly polymorphic, depending on tissue tropism. Parasite length varied considerably, with neck and trunk measurements of L. radiatus from adult menhaden being 2–4 times larger than those from smaller host species. Mitochondrial cytochrome oxidase c subunit I (COI) sequences demonstrated all parasites to be L. radiatus, with sequence divergence limited to 0.3%. These findings show that morphology of the metamorphosed females has poor taxonomic value, and polymorphisms instead are related to attachment site and host characteristics.

Coastal shoreline hardening is intensifying due to human population growth and sea level rise. Prior studies have emphasized shoreline-hardening effects on faunal abundance and diversity; few have examined effects on faunal biomass and size structure or described effects specific to different functional groups. We evaluated the biomass and size structure of mobile fish and crustacean assemblages within two nearshore zones (waters extending 3 and 16 m from shore) adjacent to natural (native wetland; beach) and hardened (bulkhead; riprap) shorelines. Within 3 m from shore, the total fish/crustacean biomass was greatest at hardened shorelines, driven by greater water depth that facilitated access to planktivore (e.g., bay anchovy) and benthivore-piscivore (e.g., white perch) species. Small-bodied littoral-demersal species (e.g., Fundulus spp.) had greatest biomass at wetlands. By contrast, total biomass was comparable among shoreline types within 16 m from shore, suggesting the effect of shoreline hardening on fish biomass is largely within extreme nearshore areas immediately at the land/water interface. Shoreline type utilization was mediated by body size across all functional groups: small individuals (≤60 mm) were most abundant at wetlands and beaches, while large individuals (>100 mm) were most abundant at hardened shorelines. Taxonomic diversity analysis indicated natural shoreline types had more diverse assemblages, especially within 3 m from shore, although relationships with shoreline type were weak and sensitive to the inclusion/exclusion of crustaceans. Our study illustrates how shoreline hardening effects on fish/crustacean assemblages are mediated by functional group, body size, and distance from shore, with important applications for management.

Hurricanes are important ecological disturbances that maintain biodiversity. We investigated the short-term impacts of Hurricane Irma, a category 4 storm that passed through south Florida on September 10, 2017, on fish and macroinvertebrate communities of western and north-central Florida Bay, FL, USA. Spatiotemporal trends in physical water conditions (temperature, salinity, water depth, dissolved oxygen, chlorophyll a, and turbidity) as well as rainfall and coastal discharge were assessed to characterize hurricane-induced habitat changes. Dramatic but ephemeral changes in water depth and rainfall were observed. Longer lasting reductions of salinity regime and increases in turbidity and chlorophyll a were also observed. The prevailing hypersalinity (≥ 40 ppt) conditions, ongoing since March 2017, were abruptly ended by the storm. Hurricane Irma significantly altered fish and macroinvertebrate communities. Analysis of community spatiotemporal trends revealed spatially distinct temporal community shifts. Cluster analysis distinguished four groups among nine highly abundant species identified as exerting the most influence on pre- and post-hurricane total community differences. Reductions in relative abundance of two groups were coincident with Irma’s passage while a third group, comprised solely of pelagic, zooplanktivorous Anchoa mitchilli, exhibited rapid population growth that started 2 months after the passage of the storm. These faunal disruptions are reminiscent of a prior Florida Bay community shift that followed a similar sequence of consecutive disturbances: hypersalinity, seagrass die-off, and a category-5 hurricane. Recovery from this prior community shift cascade took many years.