Estuarine Nursery Areas Research Articles

Quantifying larval dispersal portfolio in seabass nurseries using otolith chemical signatures

The temporal asynchronies in larvae production from different spawning areas are fundamental components for ensuring stability and resilience of marine metapopulations. Such a concept, named portfolio effect, supposes that diversifying larval dispersal histories should minimize the risk of recruitment failure by increasing the probability that at least some larvae successfully settle in nursery. Here, we used a reconstructive approach based on otolith chemistry to quantify the larval dispersal portfolio of the European seabass, Dicentrarchus labrax, across six estuarine nursery areas of the northeast Atlantic Ocean. The analysis of natal and trajectory signatures indicated that larvae hatch in distinct environments and then dispersed in water masses featured by contrasting chemical signatures. While some trace elements appeared affected by temporal changes (Mn and Sr), others varied spatially during the larval stage but remained poorly affected by temporal fluctuation and fish physiology (Ba, Cu, Rb and Zn). We then proposed two diversity metrics based on richness and variations of chemical signatures among populations to reflect spatio-temporal diversity in natal origins and larval trajectories (i.e., estimates of dispersal portfolio). Along the French coast, the diversity estimates were maximum in nurseries located at proximity of offshore spawning sites and featured by complex offshore hydrodynamic contexts, such as the Mont St-Michel bay. Finally, our findings indicate that the dispersal portfolio was positively related with the local abundance of seabass juveniles, supporting the assumption that heterogeneity in dispersal history contributes to promote recruitment success in nurseries.

Decoupling carry-over effects from environment in fish nursery grounds

Life-history trait expression not only depends on the current environmental constraints, but also on the past ones that shaped traits expressed earlier in life. Such an effect, named carry-over, can occur in fish nursery grounds when juvenile performances after settlement are influenced by their larval traits in combination with conditions experienced in nurseries. To date, the impacts of environmental and human stressors on post-settlement traits have been assessed, but independently from larval traits, so that the contributions of environmental versus carry-over constraints remain unquantified. Here, we used a reconstructive approach based on otolith microstructure to investigate how carry-over and environment affect life-history traits of the European seabass, Dicentrarchus labrax. In the northeast Atlantic Ocean, seabass juveniles were collected in six French estuarine nursery areas with contrasted environmental conditions (water temperature, salinity, food availability, and anthropogenic impacts), and five of their life-history traits across ontogenetic stages were measured (pelagic growth, larval duration, size at settlement, post-settlement growth and body condition). Piecewise structural equation model emphasized the strong co-variation of larval traits in response to food availability and temperature in the pelagic environment, stressing that fast growing larvae are characterized by shorter pelagic larval duration, but larger size at recruitment. However, the magnitude of carry-over effects greatly varied between traits, revealing that larval trait impacts on post-settlement traits remained minor as compared to the nursery environment. In estuarine nurseries, our findings suggest that resource allocation results from a trade-off between somatic growth and energy storage. Fish juveniles exposed to anthropogenic stress or risk of food limitation tended to predominantly invest in storage, whereas individuals in favourable conditions allocated their resources in somatic growth. These findings highlight the importance of heterogeneity in pelagic and nursery environments in understanding trait variations and population dynamic of estuarine dependent fish.

Seascape connectivity of temperate fishes between estuarine nursery areas and open coastal reefs

Abstract While estuaries are considered valuable nurseries for many harvested fish species, little quantitative data exist about the spatial scales over which estuaries supply individuals to coastal reefs and how this influences coastal metapopulations. Quantifying this connectivity between estuaries and coastal reefs will assist the sustainable management of fisheries and key fish habitat. This information is particularly pertinent considering estuaries world‐wide are experiencing degradation and habitat loss. We examine how the relative abundance and body length of three exploited fishes (Chrysophrys auratus, Pseudocaranx georgianus and Nemadactylus douglasii) varied in relation to the proximity and size of the nearest estuary, predicting that estuarine dependent species (i.e. C. auratus) would be smaller and more abundant on reefs close to large estuaries. As a network of ‘no‐take’ marine reserves exist across the study area, we also assessed for reserve effects and if these were influenced by the proximity and size of estuaries. Fish assemblages were surveyed using baited remote underwater video systems deployed on 629 rocky reefs across 417 km of coastline in south‐eastern Australia. As predicted, C. auratus were smaller and more abundant on reefs adjacent to estuaries (<8.5 km), which is consistent with the species being heavily reliant on estuaries as nursery habitats. Neither the length nor abundance of N. douglasii and P. georgianus were influenced by the proximity or size of estuaries. Marine reserves consistently had higher abundances and larger C. auratus, regardless of their proximity to estuaries. However, reserve effects were more variable for both N. douglasii and P. georgianus. Synthesis and applications. Our results suggest that the dispersal of subadult Chrysophrys auratus from estuarine nurseries to coastal reefs occurs across relatively small spatial scales, highlighting that conserving the ecological functioning of estuaries is paramount to sustaining recruitment to nearby coastal fisheries. Estuary size and proximity had little influence on populations of both Nemadactylus douglasii and Pseudocaranx georgianus as these species are not greatly dependent on estuaries. We also found that the proximity to estuaries did not enhance reserve effects, instead these effects were consistent across the study area.

Predation on small juvenile fishes in shallow estuarine nursery areas: Reply to Baker & Sheaves (2021)

The key criticism by Baker & Sheaves (2021; Mar Ecol Prog Ser 662:205-208) of the Whitfield (2020; Mar Ecol Prog Ser 649:219-234) estuarine littoral predation paradigm review is that shallow water fish nursery habitats contain abundant predator assemblages which may create high predation pressure on the juvenile fish cohorts that occupy these areas. The primary arguments supporting Baker & Sheaves’ criticism arise from a series of papers published by them on piscivorous fish predation in certain tropical Australian estuaries. The counter-argument that shallow littoral areas in estuaries do indeed provide small juvenile fishes with refuge from small and large piscivorous fishes is provided by published papers from 4 different estuary types in South Africa, covering both subtropical and warm-temperate systems. Based on the overall published information, the argument for shallow (<1 m depth) estuarine waters providing major protection for newly settled juveniles appears to be weak in northern Australia but strong in South Africa. The global situation, as outlined in this response, is more supportive of low piscivorous predation in shallow nursery habitats, but further targeted research is needed before we can confirm that littoral estuarine waters are indeed a universal keystone attribute in this regard.

Littoral habitats as major nursery areas for fish species in estuaries: a reinforcement of the reduced predation paradigm

For many decades, the role of estuaries as important nursery areas for fishes was accepted as fact by scientists and environmental managers. At the turn of the 21st century, a question mark was raised in relation to the reduced predation component of the nursery function, with some scientists contending that both large and small piscivorous fish species had access to the estuarine habitats that juvenile fishes in estuaries occupied. If true on a global scale, the nursery designation for these habitats would be compromised and the long-held paradigm that estuaries are important nursery areas for fishes would need to be revised. In this review, I examine the nature of fish nursery areas in estuarine littoral habitats from a mainly predation perspective and, based on a variety of ichthyofaunal and avifaunal studies, come to the conclusion that apart from a few selected estuarine systems, there is limited predation on juvenile fishes in these particular areas. This, coupled with the abundant suitable food resources for juvenile fish from different trophic categories, shelter from high-energy marine wave action and biological connectivity between a variety of submerged and emergent macrophyte communities, renders shallow estuarine littoral areas ideal nursery areas for the juveniles of mostly euryhaline marine fish species, the dominant component of estuarine ichthyofaunas globally. In addition, there are strong indications from the fossil record that these littoral estuarine nursery areas have been functioning since the Devonian, more than 350 million years ago.

Movement and Out‐Migration of Juvenile Atlantic Sturgeon in Georgia, USA

AbstractAtlantic Sturgeon Acipenser oxyrinchus, a federally endangered anadromous fish, persist along the East Coast of North America. Despite two decades of federal protection, many populations have yet to fully recover and major knowledge gaps remain, especially in the southern portion of the species’ range. The seasonal movement patterns of river‐resident juveniles (RRJs) are not well understood, and little is known about the transition from the RRJ life stage to the marine‐migratory juvenile (MMJ) life stage. During the summers of 2014–2016 we captured and acoustically tagged age‐1 RRJ Atlantic Sturgeon in the Ogeechee, Altamaha, and Satilla rivers, Georgia, to (1) describe and quantify seasonal movements of RRJ Atlantic Sturgeon in order to identify important estuarine nursery areas and (2) examined temporal patterns of out‐migration in order to better understand the critical transition from RRJ to MMJ in Georgia rivers. Movements of 79 fish were monitored using an array of stationary receivers deployed downstream from the heads of tide in each river system. During the summer months in each river, the fish congregated in upriver, freshwater reaches, but during the winter months they moved downriver and became more broadly distributed. Some fish (36.7%; n = 29) migrated back up their natal river in the spring and remained there as age‐2 RRJs. We observed the out‐migration of 30.4% (n = 24) of age‐2 MMJs only during December–March, based on detections outside their natal river. The results of this study support the assumption of the closure of age‐1 populations that underpins recent quantitative studies of Atlantic Sturgeon recruitment.

Movements of Juvenile Bull Sharks in Response to a Major Hurricane Within a Tropical Estuarine Nursery Area

Predicting the responses of animals to environmental changes is a fundamental goal of ecology and is necessary for conservation and management of species. While most studies focus on relatively gradual changes, extreme events may have lasting impacts on populations. Animals respond to major disturbances such as hurricanes by seeking shelter, migrating, or they may fail to respond appropriately. We assessed the effects of Hurricane Irma in 2017 on the behavior and survival of juvenile bull sharks (Carcharhinus leucas) within a nursery of the Florida coastal Everglades using long-term acoustic telemetry monitoring. Most of our tagged sharks (n = 14) attempted to leave the shallow waters of the Shark River Estuary before the hurricane strike, but individuals varied in the timing and success of their movements. Eight bull sharks left within hours or days before the hurricane, but three left more than a week in advance. Nine of 11 bull sharks (~ 82%) eventually returned to the array within weeks or months of the storm. Six of these returning individuals were detected in a different coastal array in nearshore waters ca. 80 km away from the mouth of the estuary during their absence. The remaining three bull sharks moved downstream relatively late (after the hurricane) and may have died. We used binomial generalized linear mixed models to estimate the probability of presence within the array as a function of several environmental variables. Departure from the array was predicted by declining barometric pressure, increasing rate of change in pressure, and potentially fluctuations in river stage. Juvenile bull sharks may weigh multiple environmental cues, perceived predation risk, their own physical size, and shifting prey resources when making decisions during and after hurricanes.

The importance of newly-opened tidal inlets as spawning corridors for adult Red Drum (Sciaenops ocellatus)

The ability to emigrate from estuarine nursery areas to spawning grounds is essential for the persistence of estuarine dependent species such as Red Drum, (Sciaenops ocellatus). Typically in this region, tidal inlets are the only mechanism for this transfer. Cedar Bayou, a natural tidal inlet, was deliberately closed in 1979 but was recently dredged and reopened. The inlet allows for direct water exchange between the Gulf of Mexico and Mesquite Bay, Texas, USA, and represents a unique opportunity to study estuarine dependent species’ migration processes. Adult Red Drum were implanted with acoustic transmitters that allowed us to track their movement patterns before and after the reopening of Cedar Bayou. The goals of this study were to: 1) determine if Red Drum choose migration routes opportunistically in Texas waters; and 2) elucidate general movement patterns and residency estimates for Red Drum in Texas bays. Red Drum showed relatively little movement during the pre-opening period and summer, even after the inlet was restored. Once open, fish actively traversed through Cedar Bayou during the months commonly associated with spawning migrations and coincident with a drop in water temperature. These results demonstrate that Red Drum choose migration corridors opportunistically, thus opening tidal inlets such as Cedar Bayou can provide maturing Red Drum with greater connectivity between estuaries and spawning grounds in the open Gulf of Mexico.

The abundance, diversity and distribution of small fishes in mangrove and non-mangrove estuaries in warm temperate South Africa

Mangroves in tropical and subtropical regions have been well documented in terms of the advantages they provide and their role in structuring ichthyofaunal assemblages, but little is known about their warm temperate counterparts. The study aimed to investigate the importance of warm temperate mangroves by comparing the abundance, diversity and distribution of small fishes in mangrove and non-mangrove estuaries in warm temperate South Africa. A 50x2 m (12-mm mesh) seine net was used over three summer seasons to sample small fishes in the Gonubie, Qora, Nahoon and Xhora estuaries (the latter two being mangrove estuaries). Fish abundance and diversity showed little variation among estuaries, despite the presence of mangroves. Estuaries in warm temperate areas are not only at the edge of mangrove distribution, but also offer alternative habitats which lend similar advantages to fish survival. It appears that warm temperate ichthyofauna have not yet evolved a dependence on mangrove systems in terms of the food, refuge and other ecological services they provide. Understanding the function of habitats and their value in enhancing fish survival in estuarine nursery areas is essential for fish conservation.

Extrinsic and intrinsic factors shape the ability of using otolith chemistry to characterize estuarine environmental histories

Reconstructing habitat use and environmental histories of fish via otolith chemistry relies on linking otolith chemical composition to the surrounding environment, as well as disentangling the consequences of ontogenetic or physiological effects that may mask environmental signals. We used multiple linear and linear mixed models to analyse the importance of environmental (temperature, salinity, water chemistry) and individual based (fish size) factors on otolith chemical composition and incorporation (Li, Mg, Mn, Sr, and Ba) of juvenile Dicentrarchus labrax, over their time within an estuarine nursery area. Multi model inference highlighted the importance of ontogeny, as well as the influence of temperature and salinity on otolith chemistry and elemental incorporation, with results indicating that intrinsic effects may potentially outweigh environmental effects. Ultimately, understanding if otolith chemistry accurately reflects fine-scale environmental variation is key to reconstruct environmental histories of juvenile fishes in estuaries and will contribute to determining the impact changing estuarine conditions may have on growth and survival.

Response of soft-bottom macrobenthic assemblages to artisanal trawling fisheries in a subtropical estuary

Bottom trawling is one of the most harmful and widespread activities affecting benthic habitats and fauna. In this study, we analyzed the impact of shrimp trawling fisheries on the densities, assemblage structure and vertical stratification of the benthic macrofauna in shallow mudflats of the Patos Lagoon Estuary (Brazil). Experimental trawls of different intensities were performed during three shrimp fishing seasons (2015–2017), comparing macrofauna among before and after trawling, and a control zone. The changes in macrofaunal assemblages were more consistently related to natural variability than to trawling impact, being mostly influenced by sediment structure and salinity variation. The trawling impact was mainly detected in the area with higher percentages of fine sediments, with different macrofaunal responses in each month and stratum. Some non-significant decreases on total densities after trawling were observed, mainly on the superficial stratum, and signs of burial activities. The response to trawling disturbance of each species was different and it highly depended on their natural variability. Only five species showed significant variation to the trawling treatment (Erodona mactroides, Heleobia australis, H. charruana, Heteromastus similis and Laeonereis acuta), with temporally different responses. Decreasing densities were more related to the high impact treatment. In some seasons, decreases on the abundance of Monokalliapseudes schubarti after high impact trawls were up to 60% of the seasonal mean densities. Trawling fisheries may reduce macrobenthic densities but not their vertical stratification. The impact of trawling on key species may compromise the ecosystem function, as benthic macrofauna provide food sources for many aquatic resources. This study highlights trawling impacts in an estuarine nursery area, which should be fully considered since they may be reflected in the trophic webs.

Temporal dynamics of condition for estuarine fishes in their nursery habitats

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 557:207-219 (2016) - DOI: https://doi.org/10.3354/meps11858 Temporal dynamics of condition for estuarine fishes in their nursery habitats R. W. Schloesser1,2,*, M. C. Fabrizio1 1Virginia Institute of Marine Science, College of William & Mary, PO Box 1346, Gloucester Point, Virginia 23062, USA 2Present address: Mote Marine Laboratory, 1600 Ken Thompson Parkway, Sarasota, Florida 34236, USA *Corresponding author: rschloesser@mote.org ABSTRACT: The condition of individuals in a year class may contribute to recruitment variability due to differential survival of poor- and well-conditioned fish, but the temporal dynamics of juvenile fish condition are poorly understood. We examined inter- and intra-annual dynamics of condition for juveniles of 3 species collected from estuarine nursery areas of Chesapeake Bay from November 2010 to June 2014. We describe temporal patterns in length-based indices, the hepatosomatic index (HSI), and relative subdermal lipid estimates for juvenile summer flounder Paralichthys dentatus (n = 1771), Atlantic croaker Micropogonias undulatus (n = 3911), and striped bass Morone saxatilis (n = 874). Multiple indices provided a more complete understanding of energy-storage strategies for juveniles because temporal patterns among condition indices were not congruent for a given species. Most juvenile summer flounder and Atlantic croaker migrate from Chesapeake Bay in the fall, and both species exhibited increases in subdermal lipids in the time period prior to migration. For all species, individuals that remained in the estuary during winter exhibited high HSI values, indicating a common energy-storage strategy during winter. Mean condition of juveniles varied among year classes, but differences were inconsistent among indices, suggesting that energy was differentially stored among tissues for these year classes. Density-dependent effects contributed to variation in mean condition for summer flounder and striped bass. Our understanding of recruitment variability may be improved by assessing annual differences in mean condition as revealed by multiple indices. KEY WORDS: Fulton’s K · Hepatosomatic index · Subdermal lipid · Fish fatmeter · Juveniles · Bioenergetics · Recruitment Full text in pdf format PreviousNextCite this article as: Schloesser RW, Fabrizio MC (2016) Temporal dynamics of condition for estuarine fishes in their nursery habitats. Mar Ecol Prog Ser 557:207-219. https://doi.org/10.3354/meps11858 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 557. Online publication date: September 28, 2016 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2016 Inter-Research.

Importance of estuarine nursery areas for the adult population of the temperate seabass Lateolabrax japonicus, as revealed by otolith Sr:Ca ratios

AbstractOtolith Sr:Ca ratios were used to evaluate the contribution of estuarine nursery areas to the temperate seabass (Lateolabrax japonicus) population in Tango Bay, the Sea of Japan. Otolith Sr:Ca ratios of juveniles collected from freshwater, brackish and coastal areas were analysed to determine a criterion for distinguishing whether individuals used estuarine or coastal areas as nurseries. Otolith Sr:Ca ratios of adult seabass collected around Tango Bay were also analysed to detect the records of salinity that juveniles experienced and to estimate the contribution of each habitat. Sr:Ca ratios of the edges of otoliths of juveniles from freshwater areas were 2.4 × 10−3 in average, which were significantly lower than those of juveniles collected from a coastal area (4.9 × 10−3 in average) owing to differences in salinity conditions among these areas. Based on the threshold criterion determined by this difference, 39 out of 107 (36%) adult seabass were estimated to have used the estuary as a nursery during their juvenile stage according to their Sr:Ca chronologies. Despite the small area covered by estuarine nurseries compared with coastal waters, the Yura River estuary contributed considerably to the adult seabass population. This indicates estuaries play an important role as nurseries for seabass juveniles, and it should be noted that the estuaries are important nurseries to conserve the stocks of coastal fishes.

Assessing reproductive behavior important to fisheries management: a case study with red drum, Sciaenops ocellatus

Spawning site selection and reproductive timing affect stock productivity and structure in marine fishes but are poorly understood. Traditionally, stock assessments measure reproductive potential as spawning stock biomass or egg production and do not include other aspects of reproductive behavior. Red drum make an excellent case study to assess these other aspects, as (1) they are highly fecund, pelagic spawners, like most exploited marine fishes; (2) their life cycle is delineated between nursery (estuarine) and adult (coastal and offshore) habitat; and (3) they are managed at these two spatial scales. This study was conducted from August 2012 to December 2013 and integrates data from multiple methods and spatial scales. Aerial surveys were used for large-scale monitoring of aggregations off two known estuarine nursery areas, Tampa Bay and Charlotte Harbor, Florida, USA. Capture-based sampling in Tampa Bay coastal (n = 2581) and estuarine waters (n = 158) was used to assess reproductive state and to confirm coastal spawning. To assess spatial dynamics, we acoustically tagged two population components in the Tampa Bay system, subadults from the estuary (n = 20) and adults from the coastal spawning site (n = 60). Behavioral plasticity was seen in subadult recruitment to coastal habitat, with some subadults maturing and recruiting before or during the spawning season and others (14 of 20 acoustically tagged fish) recruiting at the end of the 2012 spawning season. Both adults and recruited subadults (n = 29) were consequently detected in the Charlotte Harbor array, 132 km to the south. Spawning-site fidelity to the Tampa Bay spawning site occurred at both the population and individual scales. Aggregations consistently occurred in Tampa Bay coastal waters during the spawning season, and approximately two-thirds of tagged adults returned in the 2013 spawning season. A similar proportion of subadults returned to the Tampa Bay spawning site, exhibiting natal homing. However, these first-time spawners arrived later than repeat spawners and were detected over shorter time periods. This study, and others like it, demonstrates how integrating data from individuals tracked over space and time with more traditional population-based sampling is changing our understanding of ecological processes that affect marine fish productivity and our ability to manage for sustainablity.

Spawning segregation and philopatry are major prezygotic barriers in sympatric cryptic Mugil cephalus species

The flathead mullet, Mugil cephalus, is a commercially vital fish in fisheries and aquaculture worldwide. Genetic analyses have recently revealed three cryptic species of M. cephalus in the Northwest Pacific. These species are sympatric in Taiwanese waters and specific reproductive behaviors have been suggested to be a major prezygotic barrier. Species composition was evaluated in samples of M. cephalus at different growth stages collected from various habitats (offshore spawning ground, estuarine nursery and feeding areas) over several months or years. The gonadosomatic index of adults and the body length of juveniles were recorded to determine the reproductive season and recruitment periods in estuaries. The results revealed partially temporal spawning isolation between species pairs, spatial segregation on specific spawning grounds and strong philopatry preclude hybridization. Thus, the results imply that traditional fisheries of mature fish in the Taiwan Strait target only one species, whereas aquaculture in Taiwan contain juveniles of all three species collected in estuaries. The ecological niche and demography of these species must be investigated further to estimate the impact of juvenile sources on aquaculture.

Habitat- and bay-scale connectivity of sympatric fishes in an estuarine nursery

Acoustic telemetry was used to examine habitat- and bay-scale connectivity for co-occurring juvenile fishes, southern flounder (Paralichthys lethostigma) and red drum (Sciaenops ocellatus), at two spatial scales in a model estuarine seascape. An acoustic positioning system was deployed to examine habitat-scale (ca. 1 m–1 km) movement, while a larger gridded array was deployed to examine bay-scale movement (ca. 1–20 km). Both species exhibited greater use of edge habitat and seagrass beds at the habitat scale; however, rates of movement within habitats varied between species. Southern flounder movement (mean = 4.0 m min−1) increased with decreasing habitat complexity (seagrass to bare sand) and increasing temperature, while red drum rate of movement (mean = 8.4 m min−1) was not significantly affected by environmental factors at the habitat scale, indicating the use of different foraging strategies (i.e. ambush vs. active). Bay-scale distribution was influenced by physicochemical conditions and seascape composition, with both species found most frequently in areas with high seagrass coverage and relative close proximity to tidal creeks and connective channels. Response to environmental variables often differed between species and the probability of bay-scale movement (>1 km) for southern flounder was greatest on days with narrow tidal ranges (<0.4 m) and higher temperatures (>17 °C), while the probability of bay-scale movement for red drum increased in response to decreasing salinity and lower temperatures (<16 °C). Species-specific variation in movement patterns within and across habitat types observed here at both the habitat and bay scale suggest sympatric species employ different strategies to partition resources within estuarine nursery areas and highlight the importance of multi-species assessments for improving our understanding of habitat value and ecosystem function.

Linking hydrodynamics and fish larvae retention in estuarine nursery areas from an ecohydrological perspective

Global change is affecting freshwater flow into estuarine nursery areas, with effects on fish larvae retention. Until now, related studies usually considered all early phases of fishes as passive drifters. However, the swimming behaviour of temperate fish larvae in these areas with strong tides and freshwater inflow is poorly described. The goal of this study was to review the swimming abilities of temperate fish species through ontogeny, the influence of nutritional conditions and how they are able to cope with hydrodynamics changes in nursery areas (including extreme freshet events resulting from dam management), using the Guadiana Estuary as a case study. The ontogeny of the swimming behaviour of estuarine fish larvae from different taxonomic groups was analyzed using the maximum sprint or critical swimming speed (Ucrit). Those results were compared with current observations performed under various tidal and river discharge conditions. In addition, the effect of larval nutritional condition on swimming abilities was also discussed. Overall, most of the species presented skills to be retained inside nursery areas, using distinct strategies. Those involve short term directional horizontal swimming against the axial currents, vertical migration and the use of residual upstream flows, especially over shallower areas. Nevertheless, during high freshet events all the studied species larvae will be flushed out of the estuary with consequent survival threaten. Extensive investigations are needed to thoroughly explore the relation of in situ behavioural responses of fish larvae and small scale estuarine hydrodynamics, towards a sustainable ecohydrological management of nurseries in flow regulated estuaries.

Habitat quality of estuarine nursery grounds: Integrating non-biological indicators and multilevel biological responses in Solea senegalensis

Estuaries are highly valuable ecosystems that provide various goods and services to society, such as food provision and supporting nursery habitats for various aquatic species. Estuarine habitat quality assessment is thus critical in managing both ecological and economic value. In this work, various biological and non-biological indicators of habitat quality in estuarine nursery areas were determined, encompassing local environmental conditions, chemical contamination, anthropogenic pressures, juvenile Solea senegalensis condition, biomarkers response to contamination and juvenile density. The various indicators provided an integrated view on habitat quality and their responses were broadly concordant. Nursery quality assessment based on anthropogenic pressure indicators and fish biomarker responses were very similar, signaling nursery areas with higher anthropogenic pressure in Tejo and Ria de Aveiro estuaries. Yet, favorable environmental conditions across all sites could have contributed to lessen the potential hazardous biological effects of exposure to anthropogenic stressors, resulting in soles’ fairly good condition and generally high juvenile density. Nevertheless, a mismatch between high juvenile density and high estuarine contribution to adult coastal populations was observed in areas with higher anthropogenic pressures. Although a causal relationship cannot be established, the results emphasize the need to fully understand how the estuarine period spent in estuaries and local processes determine the quantity and quality of juveniles exported to marine adult populations, which is critical to achieve the full potential of the fish production service of estuaries and coastal stock replenishment.

Connectivity within estuaries: An otolith chemistry and muscle stable isotope approach

Understanding whether fish move among estuarine areas and habitats or show high site fidelity has major implications for habitat conservation and the safeguard of estuarine ecological integrity. Muscle stable isotopes (δ13C, δ15N) and otolith elemental composition (Li:Ca, Mg:Ca, Mn:Ca, Cu:Ca, Sr:Ca, Ba:Ca and Pb:Ca) were used to evaluate connectivity between two separate estuarine nursery areas in summer and autumn for juvenile age-0 Dicentrarchus labrax and Pomatoschistus microps. Distinct isotopic ratios and otolith elemental signatures were found between areas for D. labrax and P. microps, and in both sampling times. High classification accuracies to collection sites were achieved via otolith elemental signatures (80–94%), and a combined analysis using both muscle stable isotopes and otolith chemistry resulted in increased accuracy with no classification errors. Overall, low site connectivity was found for both species. The use of two distinct natural tags provided corroborative and complementary information on fish movement and intra-estuarine habitat use at different temporal scales, whilst elucidating distinct ecological and environmental linkages. Ultimately, the combined use of distinct natural tags showed great promise to unravel intra-estuarine connectivity patterns.

Small-Scale Nekton Density and Growth Patterns Across a Saltmarsh Landscape in Barataria Bay, Louisiana

Nekton on the northern Gulf of Mexico depend on estuarine nursery areas, but patterns of habitat use and the underlying processes that drive these patterns are not fully understood. We examined small-scale (1–50 m) patterns of habitat use in Barataria Bay by collecting nekton samples between 2002 and 2006 with a 1-m2 drop sampler. Habitat-specific densities were estimated for six habitat types at various distances from the shoreline in marsh (Marsh1M = 1 m and Marsh3M = 3 m) and over shallow nonvegetated bottom, SNB (SNB1M = 1 m, SNB5M = 5 m, SNB20M = 20 m, and SNB50M = 50 m). Habitat-specific growth rates also were estimated for brown shrimp Farfantepenaeus aztecus caged in SNB1M, SNB5M, and SNB20M. Nekton density patterns in Barataria Bay appeared to be clearly different from the Galveston Bay model, which predicts nekton distribution patterns relative to the marsh shoreline. Although densities in Barataria Bay were significantly higher in samples near the marsh shoreline (Marsh1M or SNB1M) for brown shrimp, blue crab, and white shrimp, highest mean densities were not always present in marsh edge vegetation. In addition, densities of brown shrimp and white shrimp in Barataria Bay declined much more steeply with distance into the marsh than in the model. Daily growth rates (1.0–1.2 mm TL day−1, 68–89 mg day−1) for brown shrimp were similar among SNB habitat types. Our results suggest that SNB in Barataria Bay may be relatively more important as habitat for fishery species than previously assumed.