Spatial and temporal variation in estuarine fish and invertebrate assemblages: Analysis of an 11-year data set

Protocols for monitoring wetland mitigation and restoration projects call for routine counts of animals, yet long-term spatial and temporal patterns are rarely examined. An analysis of monitoring data from three southern California estuaries spanning 11 years, four seasons, and multiple stations within the estuaries revealed differences in spatio-temporal patterns between fish and invertebrates. Ordination analysis showed that fish assemblages were more predictable from environmental variables than were invertebrate assemblages. Variation in the fish assemblage was, primarily due to seasonal differences that were driven by changes in temperature. Invertebrates showed little seasonal variation, but a much higher degree of interannual variation than fish. Streamflow and dissolved oxygen were significant predictors of the invertebrate assemblage, indicating that irregular disturbances such as flooding events had a more important effect on the invertebrate assemblage than predictable seasonal cues such as temperature. Variation in fish and invertebrates was high both between and within the three estuaries, indicating that differences exist on multiple spatial scales. The influence of spatial and temporal factors on estuarine invertebrate and fish communities should be considered in planning monitoring programs for wetland mitigation or restoration sites.     

Patterns in use of estuarine habitat by juvenile English sole (Pleuronectes vetulus) in four Eastern North Pacific estuaries

English sole (Pleuronectes vetulus) is one of a few commercially important marine fishes on the Pacific coast of North America that use estuarine areas as nurseries for juvenile stages. Trawl surveys of four United States Pacific Northwest estuaries were conducted to determine spatial patterns of juvenile English sole residence in estuaries during 1998–2000. Additional data from 1983–1988 were also analyzed. Two size classes of juvenile English sole were identified during surveys, with densities of small (Total length [TL] <50 mm) sole ranging from 0 to 11,300 fish ha^?1 across all sites, and densities of large (TL 50–150 mm) sole ranging from 0 to 33,000 fish ha^?1 across all sites. Principal components analysis of static habitat data collected at each trawl survey site was used to define habitat types within each estuary, and discriminant function analysis was used to test the resulting classification scheme. Both small and large cohort English sole used lower side channel locations at significantly higher densities than other estuarine areas. Small English sole also showed significant relationships with both bottom temperature and depth. These patterns in habitat use were consistent across all estuaries and indicate that English sole used shallow depth areas surrounded by extensive tidal flats, where temperatures were optimal for growth. The analysis also suggested a carrying capacity may exist for large English sole in nursery estuaries.     

Effects of hypoxic disturbances on an estuarine nekton assemblage across multiple scales

Disturbances influence ecological communities over a wide range of scales. We investigated the effects of localized hypoxic disturbances on an estuarine fish assemblage at several spatial (m² and 10s km²) and temporal (days, seasons, years) scales in a multivariate framework (temperature, salinity, depth, dissolved oxygen). We examined whether seasons, years) scales in a multivariate framework (temperature, salinity, depth, dissolved oxygen). We examined whether there were consistent changes in fish and crustacean estuarine assemblage characteristics along environmental gradients and whether these relationships were altered by hypoxic disturbances. We also investigated at what scale dissolved oxygen concentration may be influencing the structure of motile estuarine assemblages and whether the size of the hypoxic zone altered its effects on the estuarine assemblage. Hypoxic disturbances altered fish and crustacean assemblages along the depth gradients that were present during well-oxygenated periods. Species diversity, richness, and catch rates were lower in hypoxic patches than in oxygenated areas. Dissolved oxygen concentration remained an important explanatory variable for patch-level assemblage dissimilarity, species richness, and diversity when data were aggregated across seasons. When we examined the data at a larger scale, by aggregating information across the study area, we did not detect influences of hypoxia on assemblage structure. Fish moved out of local hypoxic zones, but remained within the estuary even in years with extensive hypoxia. There was no effect of size of the hypoxic distrubance on whether organisms responded to hypoxia or on diversity or richness of the study site. These results suggest that these local disturbances play an important role in structuring motile species assemblages at a patch-level within an estuary, but regional factors such as recruitment and migration are important in influencing species assemblages for the entire estuary over months and years.     

Spatiotemporal Models of an Estuarine Fish Species to Identify Patterns and Factors Impacting Their Distribution and Abundance

Understanding the distribution and abundance of organisms can be exceedingly difficult for pelagic fish species that live in estuarine environments. This is particularly so for fish that cannot be readily marked and released or otherwise tracked, such as the diminutive delta smelt, Hypomesus transpacificus, endemic to the San Francisco Estuary. The environmental factors that influence their distribution operate at multiple scales, from daily tidal cycles and local perceptual fields to seasonal and annual changes in dominant environmental gradients spanning the entire San Francisco Estuary. To quantify scale-specific patterns and factors shaping the spatiotemporal abundance dynamics of adult delta smelt, we fit a suite of models to an extensive, spatially resolved, catch survey time series from 13 annual cohorts. The best model included cohort-specific abundance indicators and daily mortality rates, a regional spatial adjustment, and haul-specific environmental conditions. The regional adjustment identified several density hot spots that were persistent across cohorts. While this model did include local environmental conditions, the gain in explained variation was relatively slight compared to that explained by the regional adjustment. Total abundance estimates were derived by multiplying habitat volume by catch density (design-based) and modeled density (model-based), with both showing severe declines in the population over the time period studied. The design-based approaches had lower uncertainty but potentially higher bias. We discuss the implications of our results for advancing the science and improving management of delta smelt, and future data collection needs.     

Distribution of Diatoms Along Environmental Gradients in the Charlotte Harbor,Florida (USA), Estuary and Its Watershed: Implications for Bioassessment of Salinity and Nutrient Concentrations

The relative abundance of diatom species in different habitats can be used as a tool to infer prior environmental conditions and evaluate management decisions that influence habitat quality. Diatom distribution patterns were examined to characterize relationships between assemblage composition and environmental gradients in a subtropical estuarine watershed. We identified environmental correlates of diatom distribution patterns across the Charlotte Harbor, Florida, watershed; evaluated differences among three major river drainages; and determined how accurately local environmental conditions can be predicted using inference models based on diatom assemblages. Sampling locations ranged from freshwater to marine (0.1–37.2 ppt salinity) and spanned broad nutrient concentration gradients. Salinity was the predominant driver of difference among diatom assemblages across the watershed, but other environmental variables had stronger correlations with assemblages within the subregions of the three rivers and harbor. Eighteen indicator taxa were significantly affiliated with subregions. Relationships between diatom taxon distributions and salinity, distance from the harbor, total phosphorus (TP), and total nitrogen (TN) were evaluated to determine the utility of diatom assemblages to predict environmental values using a weighted averaging-regression approach. Diatom-based inferences of these variables were strong (salinity R ²?=?0.96; distance R ²?=?0.93; TN R ²?=?0.83; TP R ²?=?0.83). Diatom assemblages provide reliable estimates of environmental parameters on different spatial scales across the watershed. Because many coastal diatom taxa are ubiquitous, the diatom training sets provided here should enable diatom-based environmental reconstructions in subtropical estuaries that are being rapidly altered by land and water use changes and sea level rise.     

Ingress of Brachyuran Crab Post-larvae to the Newport River Estuary

Planktonic larvae of estuarine species often develop in the coastal ocean and return to estuaries using favorable currents. This study investigated spatial distributions of brachyuran crab post-larvae during ingress to the Newport River estuary, North Carolina, USA (34°41′ N, 76°40′ W). Nearshore plankton tows were conducted across the inlet to the estuary. Settlement on passive ‘hog’s hair’ collectors was simultaneously monitored in each of four estuarine channels. Callinectes sapidus density was highest east of the inlet, whereas relative estuarine abundance was higher in western channels. In separate sampling with collectors at coastal and estuarine locations, spatial distributions of post-larvae were consistent through time but differed for C. sapidus, Uca spp., and Pachygrapsus transversus. The diel timing of C. sapidus settlement on collectors was determined at the coast and compared to previous studies of settlement in the estuary. Behavioral responses to environmental cues may alter transport pathways from those predicted by hydrodynamic models.     

The importance of autotroph distribution to mussel growth in a well-mixed,temperate estuary

In this study, we explored the extent to which secondary production in a well-mixed estuary reflects local differences in biotic and physical characteristics of habitats, or larger-scale, estuary-wide characteristics governed by a freshwater-marine gradient. We addressed the following questions: To what extent do organic components of seston within habitats in an estuary reflect distributions of local autotrophs and to what extent do estuarine consumers such as sessile filter-feeders, respond to small-scale, local differences in habitat characteristics in a wellmixed estuary? We contrasted habitat quality and consumer growth at four sites within Padilla Bay estuary, Washington, representing the major autotrophic sources of organic carbon in Pacific Northwest estuaries (i.e., phytoplankton, eelgrass (Zostera marina), epibenthic and macro-algal species, and marsh macrophytes.) The natural abundances of stable carbon isotopes {ie898-1} were used to resolve origins of organic carbon in diets of blue mussels (Mytilus edulis), a representative suspension feeder. To assess consumer responses to habitat, quality, we combined measures of sestonic food quantity and quality and physical parameters with in situ determination of mussel growth. We used measures of food quality {ie898-2} and consumer response (growth of transplanted mussels) to integrate the effects of high variability in estuarine physical and biological characteristics on primary and secondary production. Using ANOVA, we detected significant differences in the concentrations of sestonic food, seston composition as indicated by {ie898-3}, and mussel {ie898-4} values and growth rates among the four representative habitats. That significant differences in {ie898-5} values of mussel tissue corresponded to the significant differences in {ie898-6} values of local autotrophs and seston among habitats suggests that mussels in Padilla Bay rely primarily on local sources of carbon for food. Mussel growth throughout, the estuary was significantly correlated with both sestonic {ie898-7} and salinity. We conclude that differences in local seston composition and mussel growth rates reflect in part the heterogeneous, distribution of benthic primary producer habitats in Padilla Bay, despite its well-mixed nature. In addition, local differences in salinity levels, as opposed to the bay-wide freshwater-marine, gradient, explained a significant proportion of the variance in mussel growth within the bay. Our results counter the prediction that seston quality and consumer production are comparable throughout well-mixed estuaries, and suggest that the paradigm of physically and chemically determined gradients in estuarine secondary production needs to be broadened to include local biotic factors as well.     

Integrating Multiple Natural Tags to Link Migration Patterns and Resource Partitioning Across a Subtropical Estuarine Gradient

Establishing links between migration patterns and trophic dynamics is paramount to ecological studies investigating the functional role habitats provide to resident and transient species. Natural tags in fishes, such as otolith chemistry and tissue stable isotopes, can help reconstruct previous environmental and dietary histories, although these approaches are rarely combined. A novel multiproxy natural tag approach was developed to estimate immigration patterns of juvenile Atlantic croaker Micropogonias undulatus, across contrasting salinity gradients in three subtropical estuaries of the western Gulf of Mexico. Juvenile young-of-year Atlantic croaker were collected along a latitudinal gradient that included positive, neutral, and negative estuaries, based on physicochemical (temperature, salinity, dissolved element) and isotopic (δ¹⁵N and δ¹³C) parameters. Otolith elemental chronologies of Sr/Ca and Ba/Ca were used to classify migratory types within each estuary, while tissue-specific isotope ratios revealed time since recent (liver~weeks) and longer term (muscle~months) diet shifts. Nitrogen isotopes in both liver and muscle tissues were highly correlated, suggesting tissue equilibrium and estuarine residence of at least 3 months, with geographic δ¹⁵N gradients reflecting the magnitude of anthropogenic nutrient enrichment within each estuary. Differences in isotopic equilibrium of muscle-liver δ¹³C values and variation in marginal edge otolith Sr/Ca and Ba/Ca suggested recent shifts in carbon source and habitat utilization, reflecting individualized movement across seascapes and connectivity of habitat mosaics. The multiproxy approach presented here identified diverse migration patterns and linked feeding and movement on regional (inter-estuary), local (intra-estuary), and individual scales to improve our understanding of habitat function across estuarine gradients.     

Challenges and strategies for better use of scientific information in the management of coastal estuaries

Numerous studies have concluded that better use of scientific information could improve the quality of coastal and estuarine environmental management. Approaches for effecting such a change include ecosystem-based, integrated, and adaptive management, but such basic re-orientation of estuarine and coastal management has proved difficult to achieve. Even environmental indicators, seemingly straightforward ways of injecting scientific information into decision making, have achieved broad on-the-ground use in relatively few instances—principally the largest estuary management programs. A conceptual framework useful for examining environmental management systems affecting the five PNCERS (Pacific Northwest coastal Ecosystems Regional Study) estuaries conceives of environmental managers, researchers, and interested and affected parties in the public as interacting through the multi-layered institutional arrangements that currently promote the utilization, management, or protection of coastal and estuarine resources. Considerable variation exists in the approach and effectiveness of the region's environmental management organizations. Interaction between science and management in the region appears to be limited to an extent by high transaction costs; a cultural divide between environmental scientists and environmental managers is perceived by members of both groups who work with the PNCERS estuaries as inhibiting communications between them. Mechanisms that both groups identify as useful for improving the flow of information between science and management are little used, perhaps as a result. The two groups have very different patterns of information dissemination and acquisition, and though both chose agency archives and databases as their top methods for disseminating information, neither group relies much on these vehicles for information they seek. Both residents' and practitioners' perceptions of threats to the PNCERS estuaries show patterns of estuary-to-estuary variation. One theme that emerges is that problems associated with poor land management in adjacent uplands are common to most of these estuaries, potentially providing a sense of commonality through which a more regional approach to estuary management could emerge. A common set of estuarine environmental indicators implemented for all estuaries could help instigate such a regional approach, but resource constraints, especially at the local level, will have to be overcome for that to occur. There is currently substantial lack of common vision among coastal practitioners as to the purpose and desirability of indicators, and relatively little experience or knowledge of their use, particularly at the local level. Use of estuarine science in the management of these estuaries appears to be greatest during periods in which the largest programmatic shifts in environmental management approaches occur, an observation consistent with other studies that have concluded that the use of environmental science in environmental management tends to be episodic.     

Tectonic Subsidence of California Estuaries Increases Forecasts of Relative Sea-Level Rise

Even along the generally uplifting coast of the Pacific US, local geologic structures can cause subsidence. In this study, we quantify Holocene-averaged subsidence rates in four estuaries (Carpinteria Slough, Goleta Slough, Campus Lagoon, and Morro Bay) along the southern and central California coast by comparing radiocarbon-dated estuarine material to a regional sea-level curve. Holocene-averaged rates of vertical motion range from subsidence of 1.4?±?2.4, 1.2±0.4, and 0.4?±?0.3 mm/year in Morro Bay, Carpinteria Slough, and Goleta Slough, respectively, to possible uplift in Campus Lagoon (?0.1?±?0.9 mm/year). The calculated rates of subsidence are of the same magnitude as rates of relative sea-level rise experienced over the late Holocene and effectively double the ongoing rates of relative sea-level rise experienced over the last five decades on other parts of the coast. The difference in rates of vertical motion among these four estuaries is attributed to their geological settings. Estuaries developed in subsiding geological structures such as synclines and fault-bounded basins are subsiding at much higher rates than those developed within flooded river valleys incised into marine terraces. Restoration projects accounting for future sea-level rise must consider the geologic setting of the estuaries and, if applicable, include subsidence in future sea-level rise scenarios, even along the tectonically uplifting US Pacific Coast.     

Spatial and temporal variability and drivers of net ecosystem metabolism in western Gulf of Mexico estuaries

Net ecosystem metabolism (NEM) is becoming a commonly used ecological indicator of estuarine ecosystem metabolic rates. Estuarine ecosystem processes are spatially and temporally variable, but the corresponding variability in NEM has not been properly assessed. Spatial and temporal variability in NEM was assessed in four western Gulf of Mexico shallow water estuaries. NEM was calculated from high-frequency dissolved oxygen measurements. Interbay, intrabay, and water column spatial scales were assessed for NEM, gross primary production (GPP), and respiration (R) rate variability. Seasonal, monthly, and daily temporal scales in NEM, GPP, and R were also assessed. Environmental conditions were then compared to NEM to determine which factors were correlated with each temporal and spatial scale. There was significant NEM spatial variability on interbay, intrabay, and water column spatial scales. Significant spatial variability was ephemeral, so it was difficult to ascertain which environmental conditions were most influential at each spatial scale. Significant temporal variability in NEM on seasonal, monthly, and daily scales was found and it was correlated to temperature, salinity, and freshwater inflow, respectively. NEM correlated strongly with dissolved oxygen, temperature, and salinity, but the relationships where different in each bay. The dynamics of NEM on daily scales indicate that freshwater inflow events may be the main driver of NEM in the semiarid estuaries studied. The variable nature of NEM found here is further evidence that it is not valid to use single station monitoring deployments for assessment of whole estuarine ecosystem metabolic rates in large ecosystems. The relationship between NEM and temperature, salinity, and freshwater inflow events could drive predictive models assessing the potential influence of projected climate change and watershed development scenarios on estuarine metabolic rates.     

Estuaries of the South Atlantic coast of North America: Their geographical signatures

Estuaries of the southeastern Atlantic coastal plain are dominated by shallow meso-tidal bar-built systems interspersed with shallow sounds and both low flow coastal plain and high flow piedmont riverine systems. Three general geographical areas can be discriminated: the sounds of North Carolina; the alternating series of riverine and ocean dominated bar-built systems of South Carolina, Georgia, and northeast Florida, and the subtropical bar-built estuaries of the Florida southeast coast. The regional climate ranges from temperate to subtropical with sea level rise and hurricanes having a major impact on the region's estuaries because of its low and relatively flat geomorphology. Primary production is highest in the central region. Seagrasses are common in the northern and southern most systems, while intertidal salt marshes composed ofSpartina alterniflora reach their greatest extent and productivity in South Carolina and Georgia. Nuisance blooms (cyanobacteria, dinoflagellates, and cryptomonads) occur more frequently in the northern and extreme southern parts of the region. Fishery catches are highest in the North Carolina and Florida areas. Human population growth with its associated urbanization reaches a maximum in Florida and it is thought that the long-term sustainability of the Florida coast for human habitation will be lost within the next 25 years. Tidal flushing appears to play an important role in mitigating anthropogenic inputs in systems of moderate to high tidal range, i.e., the South Carolina and Georgia coasts. The most pressing environmental problems for the estuaries of the southeastern Atlantic coast seem to be nutrient loading and poor land use in North Carolina and high human population density and growth in Florida. The future utilization of these estuarine systems and their services will depend on the development of improved management strategies based on improved data quality.     

Microbial Nitrogen Cycling in Estuaries: From Genes to Ecosystem Processes

Nitrogen (N) is one of the primary nutrients required to build biomass and is therefore in high demand in aquatic ecosystems. Estuaries, however, are frequently inundated with high concentrations of anthropogenic nitrogen, which can lead to substantially degraded water quality. Understanding drivers of biogeochemical N cycling rates and the microbial communities responsible for these processes is critical for understanding how estuaries are responding to human development. Estuaries are notoriously complex ecosystems: not only do individual estuaries by definition encompass gradients of salinity and other changing environmental conditions, but differences in physical parameters (e.g., bathymetry, hydrodynamics, tidal flushing) lead to a tremendous amount of variability in estuarine processes between ecosystems, as well. Here, we review the current knowledge of N cycling processes in estuaries carried out by bacteria and archaea, including both biogeochemical rate measurements and molecular characterizations of N cycling microbial communities. Particular attention is focused on identifying key environmental factors associated with distinct biogeochemical or microbial regimes across numerous estuaries. Additionally, we describe novel metabolisms or organisms that have recently been discovered but have not yet been fully explored in estuaries to date. While the majority of research has been conducted in the benthos, we also describe data from estuarine water columns. Understanding both the common patterns and the differences between estuaries has important implications for how these critical ecosystems respond to changing environmental conditions.     

Discovery of the “Phantom” dinoflagellate in Chesapeake Bay

Since its discovery in natural estuarine habitat of North Carolina in 1991, the widespread impact of the toxic dinoflagellate, Pfiesteria piscicida (gen. et sp. nov.), popularly called the “phantom” dinoflagellate, on North Carolina fish stocks has been established, yet little is known about its influence outside of North Carolina estuaries. Here, we document the presence of P. piscicida in Chesapeake Bay. A fish kill was observed after inoculating an aquarium containing mummichogs with sediment samples from Jenkins Creek, a brackish creek (salinity 11‰) of the Chesapeake Bay system. P. piscicida was the cause of the kill, as supported by morphological, physiological, and histological evidence. The appearance and behavior of the algae and symptoms associated with fish mortality were consistent with those previously observed in P. piscicida-associated aquaria fish kills in North Carolina. The discovery of P. piscicida in Chesapeake Bay supports the speculation that these toxic dinoflagellates have a dramatic and far-reaching impact on fish stocks in shallow, eutrophic estuaries along the eastern United States.     

Factors influencing spatial and annual variability in eelgrass (Zostera marina L.) meadows in Willapa Bay, Washington, and Coos Bay, Oregon, estuaries

Environmental factors that influence annual variability and spatial differences (within and between estuaries) in eelgrass meadows (Zostera marine L.) were examined within Willapa Bay, Washington, and Coos Bay, Oregon, over a period of 4 years (1998–2001). A suite of eelgrass metrics were recorded annually at field sites that spanned the estuarine gradient from the marine-dominated to mesohaline region of each estuary. Plant density (shoots m^?2) of eelgrass was positively correlated with summer estuarine salinity and inversely correlated with water temperature gradients in the estuaries. Eelgrass density, biomass, and the incidence of flowering plants all increased substantially in Willapa Bay, and less so in Coos Bay, over the duration of the study. Warmer winters and cooler summers associated with the transition from El Niño to La Niña ocean conditions during the study period corresponded with this increase in eelgrass abundance and flowering. Large-scale changes in climate and nearshore ocean conditions may exert a strong regional influence on eelgrass abundance that can vary annually by as much as 700% in Willapa Bay. Lower levels of annual variability observed in Coos Bay may be due to the stronger and more direct influence of the nearshore Pacific Ocean on the Coos Bay study sites. The results suggest profound effects of climate variation on the abundance and flowering of eelgrass in Pacific Northwest coastal estuaries.     

Impact of Armored Shorelines on Shore-Zone Fish Density in a Mid-Atlantic,USA, Estuary: Modulation by Hypoxia and Temperature

Anthropogenic modifications of estuarine environments, including shoreline hardening and corresponding alteration of water quality, are accelerating worldwide as human population increases in coastal regions. Estuarine fish species inhabiting temperate ecosystems are adapted to extreme variations in environmental conditions including water temperature, salinity, and dissolved oxygen across seasonal, daily, and hourly time scales. The present research utilized quantitative sampling to examine the spatiotemporal distribution of shore-zone estuarine fish species in association with four unique shoreline types across a range of water temperature and dissolved oxygen conditions. Fish were collected from the intertidal and shallow subtidal region of four shoreline types, Spartina alterniflora marsh, Phragmites australis marsh, riprap, and bulkhead, in the summer and fall of 2009 and 2010. Analyses were performed to (1) compare mean fish density among shoreline types across all water conditions and (2) explore relationships of the complete fish assemblage, three functional species groupings, and two fish species (Fundulus heteroclitus and Menidia menidia) to unique shoreline/water conditions. Significantly greater mean fish densities were found along S. alterniflora shorelines than armored shorelines. Several metrics including fish density, species richness, and occurrence rates suggest S. alterniflora shorelines may serve as a form of refuge habitat during periods of low dissolved oxygen and high temperatures for various species, particularly littoral-demersal species including F. heteroclitus. Potential mechanisms that could contribute to a habitat providing refuge during adverse water quality conditions include tempering of the adverse condition (decreased temperatures, increased dissolved oxygen), predation protection, and increased foraging opportunities.     

A comparison of mercury in estuarine fish between Florida Bay and the Indian River Lagoon, Florida, USA

Concentrations of mercury (Hg) in fish were compared between two Florida estuaries, the Indian River Lagoon and Florida Bay. The objective was to determine if differences in Hg concentration exist and to attempt to relate those differences to sources of Hg. Five hundred and thirteen estuarine fish were collected and analyzed for Hg concentration. Fish species collected were black drum, bluefish, bonnethead shark, common snook, crevalle jack, gafftopsail catfish, gray snapper, Mayan cichlid, pompano, red drum, sheepshead, southern flounder, spadefish, and spotted seatrout. Analysis of variance of species-specific Hg data among the three defined regions of eastern and western Florida Bay and the Indian River Lagoon substantiated regional differences. Proximity to known anthropogenic sources of Hg appeared to be a significant factor in the distribution of Hg concentration among the fish collected. Sufficient numbers of crevalle jack, gray snapper, and spotted seatrout were collected to permit statistical analysis among regions. Hg concentrations in all three of these species from eastern Florida Bay were higher than those collected in the other two areas. A major fraction of the estuarine fish collected in eastern Florida Bay exceeded one or more State of Florida or U.S. Food and Drug Administration fish consumption health advisory criteria. In general, fish from western Florida Bay contained less Hg than those from the Indian River Lagoon, and fish from the Indian River contained less Hg than those from eastern Florida Bay. Crevalle jack from all areas and spotted seatrout from Florida Bay were placed on a consumption advisory in Florida. Detailed study of Florida Bay food web dynamics and Hg biogeochemical cycling is recommended to better understand the processes underlying the elevated Hg levels in fish from eastern Florida Bay. This information may be vital in the formulation of appropriate strategies in the ongoing South Florida restoration process.     

Nursery Function Drives Temporal Patterns in Fish Assemblage Structure in Four Tropical Estuaries

Despite estuary-to-estuary differences in assemblage composition, fish faunas of tropical Indo-Pacific estuaries show parallel patterns of temporal change, suggesting a common set of ecological drivers. One potentially important driver is the interaction of different patterns of occupancy by functional groups that display different life-history patterns. However, most studies that have considered temporal change lack the detail needed to understand life-history utilisation. Most have focussed on changes in catch per unit effort (CPUE) or probability of encounter, with only one study going further and investigating changes in size structure and then only for a single estuary. One of the reasons for this lack of detail is the large volume of work needed to collect comprehensive data on size structures of species rich assemblages across multiple estuary systems over time. To overcome the logistical limitations on data collection, we used joint patterns of change in CPUE and mean biomass per fish (BPF) as proxies for changes in size structure. We investigated how different life-history strategies contributed to overall temporal patterns of assemblage change across four tropical Indo-Pacific estuaries. The three life-history strategies displayed characteristically different patterns in CPUE and BPF and the relationships between CPUE and BPF that reflect differences in the way that the three groups use estuaries. These different patterns interacted to produce complex assemblage patterns that are likely to be sensitive to location-specific differences in the mix of species from each group, providing at least part of the explanation for the site-specific fish assemblage structures that are characteristic of tropical estuarine fish fauna.     

A Comparison of Otolith Geochemistry and Stable Isotope Markers to Track Fish Movement: Describing Estuarine Ingress by Larval and Post-larval Halibut

Estuarine recruitment of fishes is a potential bottleneck in the life cycle of many coastal species. We investigated patterns of size-at-ingress for larval and post-larval California halibut entering the Punta Banda Estuary (PBE), Mexico, using both otolith geochemistry and carbon stable isotope ratios (SIR). Juvenile halibut (n?=?126; 38–163 mm standard length [SL]) were collected from inside PBE and the adjacent exposed coast during the fall of 2003, and otoliths (geochemistry) and muscle tissues (SIR) were analyzed to reconstruct the environmental histories of individuals. Based on geochemical analyses, nearly all fish collected from PBE were characterized by a non-estuarine signature (e.g., low Mn and Ba) in the otolith growth bands deposited when fish were <30 mm SL. Although fish collected from the coast retained that signature throughout their lives, fish collected within PBE showed elevated concentrations of Mn and Ba in the otolith growth bands deposited once halibut were 30–70 mm SL, thereby recording ingress. Carbon SIR of juvenile halibut prey also differed between the estuary and coast. Muscle δ ¹³C values of halibut captured along the coast were consistent (ca.?15‰), while those captured in the estuary were variable and generally more enriched in ¹³C (?16‰ to ?11‰). Both natural tagging approaches agreed that most halibut (~75 %) enter PBE long after settlement (>?>?8–12 mm SL), although size-at-ingress estimates were significantly larger (mean difference = 27 mm; p?<?0.001) when derived via carbon SIR than with otolith geochemistry. Potential explanations for the differences in size-at-ingress estimates involve the magnitude of isotopic and trace element gradients at this ocean–estuary boundary, the temporal resolution of environmental tags stored within otoliths and soft tissues, and the size-at-capture or somatic growth rate of juvenile halibut. We conclude by discussing the relative merits of otolith geochemistry and SIR as natural tags, and by considering the implications of secondary dispersal into estuaries by post-larval fish.