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Context Oysters provide structured habitat along coastal margins, but owing to the high turbidity of many estuaries, characterising the faunal communities that utilise oyster reefs typically requires direct capture, which is potentially lethal or destructive. Acoustic imaging sonar can non-destructively sample the abundance and size of swimming organisms (nekton), but collection of data from acoustic imaging files requires substantial processing time following field sampling. Aims We compared five alternate data examination protocols that could be applied to acoustic imaging files from intertidal oyster reefs and identified a protocol (analysing randomly chosen 3 of 5 min of imagery recordings) that reduces parameter estimation bias and processing time. Methods To demonstrate the utility of this protocol, we investigated diel differences in fish use of fringing oyster reefs. Key results During day-time and night-time sampling, we respectively recorded 4535 and 1924 fish across a size range of 1–52 cm. We found no difference between day and night in relative abundance, mean size, or size-spectra of the fish community inhabiting reefs. Conclusions and implications Active acoustic imaging can be an effective, non-destructive method to characterise faunal communities in shallow, turbid habitats and can be used to test hypotheses regarding the ecology of these ecosystems.

Animal groups are known to exhibit collective behaviours that allow for effective responses to predators and environmental factors. Habitats with high levels of structural complexity have been shown to influence the collective tendencies of these animal aggregations. However, the effect of anthropogenically induced habitat complexity on collective tendency is still unknown. We examined the effect of a water control structure (WCS), located in an estuarine salt marsh system, on the collective behaviours of free ranging juvenile Gulf menhaden (Brevoortia patronus), a schooling forage fish. Using an acoustic imaging sonar, behavioural observations prior to and during predator attacks were collected in an open marsh canal as well as in the vicinity of the WCS. We found that fish in schools responded to the WCS by swimming in a less aligned and cohesive manner, while maintaining an increased ability to transfer social information. Our results demonstrate that collective tendency in schooling fish is affected by the presence of anthropogenically introduced habitat complexity, prior to and during predator attack. Our study, thus, strengthens the idea that the complex environmental conditions induced by the presence of man-made structures may play a large role in structuring collective behaviour and trophic interactions in aquatic environments.

Over the last 20 years, innovations have led to the development of exciting new technologies and novel applications of established technologies, collectively increasing the scale, scope, and quality of research possible in tidal marsh systems. Thus, ecological research on marshes is being revolutionized, in the same way as ecological research more generally, by the availability of new tools and analytical techniques. This perspective highlights current and potential applications of novel research technologies for marsh ecology. These are summarized under several themes: (1.) imagery — sophisticated imaging sensors mounted on satellites, drones, and underwater vehicles; (2.) animal tracking — acoustic telemetry, passive integrated transponder (PIT) tags, and satellite tracking, and (3.) biotracers — investigation of energy pathways and food web structure using chemical tracers such as compound-specific stable isotopes, isotope addition experiments, contaminant analysis, and eDNA. While the adoption of these technological advances has greatly enhanced our ability to examine contemporary questions in tidal marsh ecology, these applications also create significant challenges with the accessibility, processing, and synthesis of the large amounts of data generated. Implementation of open science practices has allowed for greater access to data. Newly available machine learning algorithms have been widely applied to resolve the challenge of detecting patterns in massive environmental datasets. The potential integration on digital platforms of multiple, large data streams measuring physical and biological components of tidal marsh ecosystems is an opportunity to advance science support for management responses needed in a rapidly changing coastal landscape.

Given recent trends of warming water temperatures and shifting fish distributions, detecting range expansion is important for resource management and planning. The subtropical common snook Centropomus undecimalis (hereafter referred to as snook) is an estuarine species that historically extended from the tropics to southern portions of Florida and Texas, but this range has been expanding for the past decade. We collected juvenile snook (n = 16; size range = 96–210-mm standard length [SL]) in saltmarshes of South Carolina, which is well outside their usual range but not unprecedented. Growth rates of juvenile snook in South Carolina (0.72-mm SL d−1) were similar to those reported for Florida during a cold period, but faster than rates reported for Florida during a recent period of mild winters (0.49-mm SL d−1). Based on collection and estimated hatch dates, and supported by winter water temperature records, juvenile snook overwintered for at least 1 year allowing them to grow to sizes that are typical for emigration from nursery habitats to open estuarine shorelines. Continued work is needed to determine whether there is potential for ongoing range expansion of snook to the region, and a strategy is proposed to focus on future research.

We evaluated spatial, short-term, and decadal-scale variability in the summer ichthyoplankton assemblages within the North Inlet-Winyah Bay estuarine system, Georgetown County, South Carolina, USA. Ichthyoplankton were collected weekly from late May to early September 2016 on nighttime flood tides using a 1-m diameter, 1-mm mesh plankton net at three sites of varying salinity and proximity to inlets. Nearly 30,000 fishes representing 59 taxa were collected from all three sites over the 14-week study period. Gobiidae and Anchoa spp. dominated the overall community, composing between 69 and 94% of the total catch at each of the three sites. Weekly densities of all taxa combined did not vary between sites, yet diversity metrics (richness, evenness, Shannon-Weiner index, and Simpson’s index) were greatest at the highest salinity site, and overall assemblage composition significantly varied among sites. Non-metric multidimensional scaling suggested a shift in the assemblage at all sites corresponding to an increase in water temperature throughout the summer. Differences in family-level assemblage composition between this study and previous work from the 1980s were detected, differences which may be indicative of regional-scale environmental change. Overall, the summer ichthyoplankton assemblages resembled those from other estuaries along the southeastern US Atlantic coast and temperate regions worldwide, generally dominated by a few taxa and composed of a mixture of estuarine-, estuarine and nearshore-, and continental shelf-spawning taxa.

Early life stage tarpon (Megalops atlanticus) have been collected in the western Atlantic Ocean north of Florida where it has been assumed that individuals migrate from estuarine areas at the onset of winter because water temperature during winter is too low for survival. However, there is anecdotal evidence of juvenile tarpon present during winter in this region. We conducted a tag-recapture study to examine potential overwinter survival in a tidally-restricted, upland pond in coastal South Carolina where tarpon have been observed during winter months. We also estimated the age structure of tarpon in this location to determine if age-0 fish were temporarily using this pond or if there were older individuals present, indicating the pond may be occupied for extended periods of time. We recaptured 29 of the 95 individuals tagged and released during January 2016 through October 2018. Of those 29 recaptured individuals, 13 survived one winter and two survived over two winters. Water temperature during winter in a nearby tidal creek was lower than in the pond, which appeared to provide a thermal refuge for tarpon. Estimated ages for 36 individuals ranged from 0 to 3 years (n = 10, 20, 5, 1, respectively). To our knowledge this is the northernmost documented overwintering of juvenile tarpon. Determining the extent of this type of habitat in the region and examining the population dynamics of tarpon in these locations could ultimately help determine how this region contributes to the productivity of adult tarpon populations.

Coincidental long-term changes in estuarine nekton assemblages and environmental conditions are widely reported. In this study, from a warm-temperate, high salinity, salt marsh-dominated estuary in the southeastern USA, decreases in overall abundance, shifts in species and life stage composition, and changes in seasonal patterns of occurrence coincided with increased water temperature. Biweekly trawl collections in a subtidal creek were made during two 4-year periods separated by more than 30 years. Of the total 111 taxa in the North Inlet estuary, South Carolina, 64% (71) occurred during both the historic (1981–84) and recent (2013–16) periods. The top five species and their proportions of the total annual catches changed between periods. In the recent study period, near-bottom species (Lagodon rhomboides, Bairdiella chrysoura, Litopenaeus setiferus) increased, and pelagic species (Anchoa spp. and Lolliguncula brevis) decreased. The mean abundance of total nekton in the recent period was approximately 50% of historic abundance. Large, but temporary increases in nekton abundance occurred when salinity decreased after major storms. In the recent study period, shifts in the timing of peak abundances from spring to fall, the occurrence of juveniles during winter, and increased diversity suggested responses to significantly warmer winters and summers. Over the 30 year period, the subtidal nekton assemblage transitioned to a state of lower abundance and different composition. Future increases in water temperature, incidences of major storms, and modifications of estuarine habitats due to rising sea level could lead to additional changes in the fauna of warm-temperate estuaries.

To increase our knowledge of the early life history of Megalops atlanticus (Tarpon) along the United States Atlantic coast north of Florida, we estimated the age and hatch dates of Tarpon larvae (i.e., leptocephali) recruiting to salt marsh pools in the North Inlet estuary, SC. We collected leptocephali (n = 36) from marsh pools during June through October 2016 and kept a subset (n = 24) of these individuals for aging. We were able to estimate ages for 18 individuals by counting presumed daily rings on their otoliths. We estimated hatch date by subtracting estimated age from the capture date. Mean age was 25 days post hatch (dph) and varied from 17 to 30 dph. Hatch dates spanned from 25 July to 9 September 2016. These are the first age and hatch date estimates for Tarpon leptocephali from estuaries north of Florida and provide insight into the biology and possible spawning behavior of Tarpon in this area of the US Atlantic coast.

We examined the effects of passive integrated transponder (PIT) tags on the survival, growth, and tag retention for two common estuarine fishes, mummichog (Fundulus heteroclitus) and pinfish (Lagodon rhomboides). A separate laboratory experiment was conducted for each species where individuals, ranging in initial size from 45 to 82 mm standard length (SL), were implanted with 8-mm or 12-mm PIT tags. Across both experiments, the probability of survival for tagged individuals ranged from 82 to 92%, probability of tag retention ranged from 82 to 91%, and probability of survival and tag retention ranged from 73 to 83%. For both species, most mortality and tag loss occurred for small (< 60 mm) individuals tagged with 12-mm tags, and generally early in the experiments. There was little effect of tagging on growth for individuals of either species compared to individuals in untagged control treatments. We recommend a minimum length of 55 mm SL for mummichog and 65 mm SL for pinfish when tagging with 8-mm or 12-mm PIT tags, as almost all fishes above these sizes survived and retained their tags. Direct comparison of our results with other studies was difficult because of variation in the tagging, husbandry, and experimental protocols used in experiments. A comparison among these different protocols would be useful to determine the least intrusive, most effective, and optimal procedure for a given species or group of estuarine fishes.

In marine ecosystems, predator-prey interactions are known to structure critical processes (e.g., trophic transfer, nutrient regeneration) and have important implications for mediating community dynamics. However, the temporal and spatial scales over which these processes operate remain poorly understood mainly because the resolution provided by traditional sampling techniques is low. In particular, tides and physical forcing pose challenges due to sampling dynamics in coastal ecosystems. Examining the fine-scale temporal and spatial dynamics of predators and prey in tidally driven estuarine ecosystems requires implementing techniques that are robust to these challenges. Here, we examine data from a high-resolution multibeam imaging sonar (DIDSON) at the confluence of an intertidal and subtidal creek over six ebb-flood cycles and quantify the temporal and spatial scales of variance between the density of predators and prey. Densities of both groups were strongly and inversely related to tidal stage, irrespective of time of day. The potential for an encounter between functional groups and utilization of the estuarine intertidal-subtidal complex was mediated by the tidal stage. When the intertidal creek was flooded, both predator and prey fishes occupied the channel more than the slopes adjacent to the marsh edge. In addition, our study demonstrated fine-scale asynchronous timing in the distribution of predators and prey, with prey densities generally peaking prior to those of predators. This suggests that the scale of variation of prey occupying the intertidal creek, which is often thought to provide refuge, drives coincidental utilization by predators and mediates their interactions.

The extensive use of salt marsh creeks by nekton is widely recognized, yet few investigations have quantified the extent to which tidal migratory nekton make repeated visits to the same location within creek networks. An improved understanding of nekton movements and fidelity can improve insights into the nursery function and value of creek habitats. We conducted tag-recapture experiments with young fishes to determine movements among intertidal creeks in the North Inlet estuary, South Carolina. In 2008, 3246 fishes were tagged with coded microwire tags. In 2012, 577 fishes were tagged with passive integrated transponder (PIT) tags. Based on percentages of recaptures, creek-specific fidelity was determined for spot (Leiostomus xanthurus) (78%), silver perch (Bairdiella chrysoura) (71%), pinfish (Lagodon rhomboides) (80%), and mullets (Mugil curema and Mugil cephalus) (77%). Recaptures occurred up to 79 days after release. Rates of recapture of all tagged fishes combined varied among creeks (74% to 100%). Considering earlier research that demonstrated differences in habitat quality among local intertidal creeks, we suggest that differences in fidelity reflect differences in habitat quality among creeks. Greater rates of repeated use (higher fidelity) could help explain why some creeks consistently support more tidal migratory nekton than other creeks. Changes in the strength of fidelity over time could be a useful measure of changes in habitat quality. We suggest that site fidelity be considered as another metric to use in efforts by resource managers to identify and evaluate essential fish habitat.

The marsh-mangrove ecotone along the southeastern US Atlantic coast occurs in northeast Florida within the Guana-Tolomato-Matanzas (GTM) estuary, where emergent vegetation transitions from marsh-dominated in the north to mangrove-dominated in the south. Dominant vegetation type has been shown to influence creek bank slope, nekton access to refuge, predation risk, and access to food. The northward distribution of mangroves in the estuarine mosaic is in flux in northeast Florida, and the effect on subtidal nekton, including commercially important species, is not known. To determine if estuarine nekton assemblages differ along the marsh-mangrove ecotone, a 60-km transition zone within GTM estuary was divided into 20 sub-zones where nearshore subtidal nekton communities were sampled monthly with trawls for 1 year. A total of 15,750 individuals consisting of 100 species were collected during the study period; 13 species made up 90% of the total catch. Subtidal nekton assemblages in marsh sites were dominated by typical salt marsh species (i.e., Leiostomus xanthurus, Anchoa spp., Bairdiella chrysoura) and had little overlap with assemblages in mixed and mangrove sites, which were dominated by structure-oriented species (i.e., Lagodon rhomboides and Eucinostomus spp.). Despite similar environmental conditions among the zones, there were clear differences in the subtidal nekton community along the marsh-mangrove ecotone, largely driven by fish species. This change in nekton community along the ecotone suggests that ecological processes such as food availability or predator/prey dynamics affected by changes in marsh surface habitats may result in differences in nekton species distribution and abundance across interconnected habitats such as in subtidal nekton that we observed in the GTM estuary.

Marsh pools are present in estuaries throughout the world and provide valuable habitat for fishes and decapod crustaceans (i.e., nekton). The purpose of our study was to examine the species composition and temporal variation of the nekton assemblage within marsh pools of a southeastern US estuary. We conducted weekly sampling of five marsh pools in the North Inlet estuary, SC from May to November 2016. Temporal variation in the nekton assemblage appeared to be related to the life history of individual species, tidal connectivity of pools with adjacent habitats, and environmental conditions within pools. Most transient species, which migrate into the North Inlet estuary as larvae or juveniles, were present primarily in early summer and late fall. Many transient species were absent or occurred in low abundance during July and August when water temperature was highest, salinity most variable, and tidal connectivity with adjacent habitats was lowest. In contrast, most resident species, which can complete their entire life cycle within the North Inlet estuary, were present and relatively abundant throughout the study as juveniles and adults. Based on the limited studies available, species richness and the ratio of transient to resident species in marsh pools at low latitudes (e.g., southeastern US) are higher compared to marsh pools at high latitudes (e.g., east coast of Canada). A more comprehensive understanding of the role of marsh pools in the life history of nekton would be useful for conserving, managing, and restoring salt marshes and the species found in these environments.

Much emphasis has been placed on challenges related to estimating ages of old fish, yet accurately estimating age for young individuals has proved equally challenging for some species. Indices of recruitment are often based on assigning ages to young fish to estimate the strength of a given year class. Similarly, growth is most commonly estimated using age-based methods and has been proposed as a metric for evaluating the quality of nursery habitats. Unfortunately, there is a paucity of information on the validity of age estimates for many fishes, and thus the accuracy of age-based metrics used to guide management of these species is unknown. To address such needs, we conducted a validation study of age and growth estimation methods for juvenile tarpon (Megalops atlanticus), using oxytetracycline to chemically mark otoliths and scales. Oxytetracycline marks were observed on all the otoliths of recaptured tarpon (n = 23), prior to a newly formed annulus, validating true age and that one annulus is deposited yearly. Marginal increment analysis indicated that annuli form in tarpon otoliths and scales during March–April. Annuli in scales were more easily identified by readers leading to more accurate and precise estimates of age from scales (100 % accuracy of age estimates for age-1 fish) compared to otoliths (88 % accuracy). Although annual age estimates were accurate, we observed substantial error and low accuracy for daily age estimates based on otoliths (10 % accuracy). Additionally, there was a poor relationship between otolith radius and tarpon length (R2 = 0.46), which resulted in inaccurate estimates of back-calculated length-at-age and growth rates. Our results indicate that scales can be used to differentiate between age-0 and age-1 tarpon, which will aid in conservation efforts by allowing for more accurate evaluation of the age structure within nursery habitats and the quality of these habitats. Further research is needed to better understand factors influencing daily age and growth estimates from otoliths.

Connectivity among estuarine habitats can influence nekton vital rates, and studying these processes requires the ability to track individuals effectively. Passive integrated transponder (PIT) tags have been used to evaluate movement of juvenile fishes in estuaries, yet this technique remains untested for penaeid shrimp . We evaluated survival, growth, and feeding behavior of juvenile white shrimp ( Litopenaeus setiferus ), an ecologically and economically important penaeid species along the US Atlantic and Gulf coasts, implanted with 8-mm PIT tags. Daily survival and tag retention observations and weekly length and weight measurements were made of tagged individuals (n = 18) kept in individual seawater tanks for 28 days, and compared with similarly housed untagged (control) individuals (n = 18). After four weeks, tagged and control shrimp were offered varying densities of a common estuarine prey item, grass shrimp ( Palaemonetes spp.), in feeding trials. Tagged white shrimp exhibited 100% tag retention and an estimated probability of survival after 28 d that was not significantly different from control shrimp (0.81 and 0.94, respectively). We found no evidence of a relationship between tagging treatment or initial shrimp size on the probability of survival. Tagged shrimp demonstrated growth at rates that were not significantly different from control shrimp, and tagged and control shrimp exhibited nearly identical feeding rates on grass shrimp (Palaemonetes spp.) prey. Our results suggest PIT tag technology represents an effective tool to study the movement and vital rates of juvenile white shrimp during their estuarine residence.

Field stations and marine laboratories (FSMLs) are essential institutions for natural history education and research. Recently, the National Research Council suggested goals for FSMLs and that a metric be administered for their evaluation. We surveyed a non-random cross-section of 8 southeastern US FSMLs in different ecosystems to evaluate how they provide educational opportunities in accordance with National Research Council recommendations pertaining to convergence, STEM education, and interdisciplinary education. Survey responses were provided as narrative responses and through the completion of a rubric. FSML representatives reported generally high mean scores in categories addressed in the rubric. We observed the greatest variation in responses regarding the number of interdisciplinary programs offered across FSMLs. Rubric responses associated with convergence across programs, station culture, and facilities were relatively uniform. Although the FSMLs surveyed exhibited variations in ecosyst...

The tarpon Megalops atlanticus is a tropical to subtropical species whose pole-ward distribution is thought to be limited by low water temperatures. In the western north Atlantic Ocean juvenile tarpon occur in estuaries of the South Atlantic Bight (SAB) north of Florida near the northern limit of its distribution, but it is currently unknown whether these individuals can survive winter, grow to maturity, and contribute to the adult population. As a first step to determine whether juvenile tarpon can survive winter conditions in the SAB, we conducted laboratory experiments to estimate minimum lethal temperatures of tarpon exposed to 1) ambient fluctuating winter water conditions and 2) a constant rate of temperature decline. Juvenile tarpon exposed to ambient winter water conditions had a mean ± standard deviation (SD) minimum lethal temperature of 13.7 ± 3.4 °C. When exposed to a constant rate of temperature decline (2 °C day−1), mean ± SD minimum lethal temperature (9.2 ± 0.8 °C) was lower than when tarpon were exposed to ambient fluctuating conditions. A combination of our results with all published data on the cold tolerance of juvenile tarpon resulted in an overall mean ± SD minimum lethal temperature of 12.0 ± 2.8 °C. Based on available long-term temperature records from SAB estuaries, overwinter survival of juvenile tarpon is unlikely in most aquatic habitats (e.g., tidal creeks, flats, open water). Similar to other estuarine transient fishes, juvenile tarpon likely exploit seasonably favorable nursery habitats and then migrate to other locations to overwinter.

Estuary plumes on the western Louisiana continental shelf in the Gulf of Mexico, outside of constricted channels of the Sabine and Calcasieu Lakes were observed on two RADARSAT-1 synthetic aperture radar (SAR) images. The in situ data showed a change in salinity of ~2–3 PSUs across the front on the northwest edge of the plume, corresponding to locations of vertical salinity variation of 5.5–7.5 PSU. Velocity magnitude outside of the inlet reached more than 2.3 ms $^{{\mathrm {-1}}}$ seaward and a brackish lens in the upper 4.5 m of the water column, the spread of which contributed to the development of a plume. The volume of brackish water within the plume was estimated an order of magnitude larger than the volume output from the Calcasieu River within an entire ebb tidal period. This implies that the plume was formed during multiple tidal cycles and it sustained during the flood tides because only weak diurnal tides exist. Both satellite and in situ observations showed an interesting western intensification of the plume. An analysis to the momentum/vorticity equations suggests that the western intensification is due to the asymmetry of the vorticity-divergence relationship under the Coriolis force. This can also be enhanced by an ambient coastal current that strengthens the convergence at the front. Estuary plumes are shown as bright and dark features in two SAR images. Results from a radar model simulation and in situ water temperature data showed that the SAR observed plume features were dominated by the water temperature differences.

Estuaries along the US east coast serve as essential nursery habitats for the early life history stages of many marine fishes. In the South Atlantic Bight (SAB), many studies have demonstrated the importance of these habitats for juveniles, but larval fish communities have received little attention, particularly around northeast Florida. To determine community structure, and seasonal distribution and abundance of larval fish in the Guana–Tolomato–Matanzas (GTM) estuary at its two inlets (St. Augustine and Matanzas), ichthyoplankton were sampled bi-weekly for one year at both inlets during nighttime spring flood tides. Samples were collected with a plankton net (1 m diameter, 1 mm mesh) suspended 1 m below the surface. Seventy-two taxa were collected, with four families comprising 85% of the collection: Sciaenidae (36.2%), Engraulidae (19.9%), Gobiidae (18.0%), and Gerreidae (10.7%). The two inlets differed in larval densities and taxonomic richness, although both were greatest during the summer. Spring and summer pulses in recruitment were observed for nearshore summer spawners. Marine offshore-spawned species exhibited peak recruitment in winter. The ichthyoplankton communities of the GTM estuary were most similar to those in southern SAB estuaries, and showed pronounced seasonal changes in composition, as is common in estuaries worldwide.

Salt marsh ecosystems and the seascapes in which they are embedded serve as critical habitats for species harvested by fisheries (1), which provide food and economic security for hundreds of millions of people (2). Historical marsh losses coupled with increasing pressures from coastal development and climate change place these intertidal ecosystems and surrounding uplands under growing threat (3). Preventing further losses of salt marshes and associated fisheries production will require greater public awareness and difficult choices in coastal policy and management, underpinned by greater understanding of marsh function.

Estuaries are composed of multiple interconnected habitat types used by transient fish species during their period of estuarine residency. Structural marsh management restricts habitat connectivity and impedes the movement of fishes among these habitat types by limiting access via water control structures (WCSs) between the managed area and the rest of the estuary. While some general information on fish passage rates is available, species-specific information on passage through WCSs is lacking for salt marsh fishes. We monitored tagged fishes from March 2012 through November 2013 using passive integrated transponder antenna arrays at two identical WCSs in the Calcasieu Lake estuary, Louisiana, USA, to assess the effect of slotted WCSs on fish behavior. A total of 420 individuals of 15 species was tagged and released at the WCSs; of these, 145 individuals representing 11 species were later detected at the WCSs. Five species comprised most (93%) of the detected individuals: Elops saurus (n = 60), Mugil cephalus (n = 43), Sciaenops ocellatus (n = 20), Pogonias cromis (n = 7), and Ariopsis felis (n = 5). Passage rates were low, with most of the observed fishes (n = 80) passing only once through the structures. Other than E. saurus, which was only observed migrating out of the managed marsh, no clear pattern in swimming direction was observed for the other species. Detected species were all present primarily during the summer and fall, however, diel activity at the structures varied by species. The WCSs in our study area appeared to attract and congregate fishes, functioning more like ecological hotspots, rather than simply facilitating fish passage.

Tidally driven fluctuations lead to rapid variations in hydrological properties that can have profound effects on the dynamic and functions of salt marshes. During low tides, many nektonic species find refuge from predatory fish in shallow intertidal pools. The utilization of shallow pool refuges also exposes fishes to fitness costs that fluctuate between day and night. Yet, how aggregated fish using an intertidal pool modulate their schooling behavior over the diel cycle remains unknown. Using high-resolution imaging sonar (ARIS), we monitored an intertidal pool over a 3-day period and quantified fish abundance, size, and schooling behavior relative to the diel and tidal cycles. Higher fish abundance was found during low tides than high tides when the section was connected with the subtidal waters. At low tide, no differences in fish abundance and size were detected in the pool between day and night, but larger schools formed at night than day. Our results suggest that biotic and abiotic factors affecting fish schooling behavior in the low tide refuge may vary over the diel cycle. We present possible functional explanations for the shifts in schooling tendency between nocturnal and diurnal utilization of the pool.

Water control structures (WCSs) restrict hydrological connectivity in salt marshes and thereby impede nekton movement within the greater habitat mosaic. Transient fishery species, which spawn outside salt marshes and must get past these barriers to reach spawning areas or salt-marsh nurseries, are especially vulnerable to these structures. Water control structures incorporating slots (narrow vertical openings spanning most of the water column) are thought to improve nekton passage; however, few studies have directly examined nekton passage through WCS slots. Dual-frequency identification sonar (DIDSON) acoustic imaging was used monthly (April–September 2010) on diurnal flood tides to examine nekton movement through 15-cm-wide slots at two identical WCSs located in Louisiana tidal marsh channels. Nekton behavior was compared between these WCSs and a nearby natural salt-marsh creek. Examination of 12 h of subsampled acoustic data revealed large concentrations of salt-marsh nekton at the WCSs (n = 2,...

Along the US Atlantic coast, oyster reefs support a large number of estuarine species including ecologically important and abundant mud crabs. Multiple factors including environmental conditions, the introduction of non-native species, parasites, and interspecific competition can change the structure of these communities over time. To examine long-term changes in mud crab communities, crabs were sampled quarterly for ten years in a mixed oyster/mud habitat in a northeast Florida estuary. A total of 6935 individuals comprised of 10 species were collected, including two non-native crab species: Petrolisthes armatus (Gibbes, 1850) and Charybdis hellerii (Milne-Edwards, 1867). Three species (Panopeus herbstii Milne Edwards, 1834, P. armatus, and Eurypanopeus depressus (Smith, 1869)) made up 97.3% of adult specimens collected, and were observed throughout the study period in varying abundances. Non-metric multi-dimensional scaling (MDS) conducted on species abundances revealed that the community underwent significant long-term, rather than cyclical seasonal, changes. Most noteworthy were the similarities in community assemblages observed in the years prior to, and soon after, the introduction of a non-native parasite, Loxothylacus panopaei (Gissler, 1884), which preferentially infects E. depressus. The significance of the presence/absence of the parasite on the community structure was confirmed through an analysis of similarities test (ANOSIM). While E. depressus abundance declined in the early years of the study after the introduction of L. panopaei, and never recovered, abundance of P. herbstii did not significantly change. Temperature and salinity likely only briefly impacted individual species on a seasonal or yearly basis including P. armatus, whose abundance reached an all-time low in the winter of 2010-2011 along with extreme winter temperatures.

Considered a keystone species in the southeastern US coastal plain, gopher tortoises occupy a variety of upland habitat types. Although upland pine-dominated habitats have received much attention, few studies have examined tortoises in nearby coastal beach dune habitats. To examine the distribution and abundance of gopher tortoises in northeast Florida coastal habitats, comprehensive burrow surveys were conducted 3 times during the last 8 yrs on 2 separate gopher tortoise populations near St. Augustine, Florida. The objectives for these surveys were to 1) examine changes in population size and structure in representative upland and coastal dune habitats and 2) describe the response of gopher tortoises to land management practices (i.e., prescribed fire). Total burrow density within the upland population remained stable over the 3 surveys (0.68 burrows/ha in 2005, 0.66 burrows/ha in 2007, and 0.64 burrows/ha in 2011). Burrow densities in the burned areas of the upland habitat increased in areas th...

The northern limits of three mangrove species—Avicennia germinans (Black Mangrove), Rhizophora mangle (Red Mangrove), Laguncularia racemosa (White Mangrove)—on the United States Atlantic coast are vouchered and described in comparison to previous boundaries defined in literature and herbarium collections. The location and general status of individual trees were used to delineate northern maxima and show that present ranges extend beyond historic records. The gradient structure of the ecotone within an area of uniform climate is interpreted as ongoing latitudinal movement.

article i nfo Climate change is expected to cause a poleward shift of many temperate species, however, a mechanistic un- derstanding of how temperature and species' life histories interact to produce observed adult range is often lacking. We evaluated the hypothesis that juvenile thermal tolerance determines northern range in gray snapper (Lutjanus griseus), a species commonly caught as juveniles along the US Atlantic coast well north of their adult distribution, using a combined laboratory, field and modeling approach. The cumulative degree days below 17 °C (CDDb17) survived by individuals maintained in the laboratory under ambient seasonal cooling conditions were used to quantify the chronic effects of prolonged but non-lethal low temperatures. Under ambient conditions, juveniles stopped feeding below 11.3 °C, and the mean temperature at death was 10.2 °C (+/−0.74 S.D.). The CDDb17 endured by individuals ranged from 61.9 to 138.8 (83.54+/− 22.44 S.D.), and was positively related to fish size. The relation between CDDb17 and fish size was extrapo- lated to the maximum juvenile size in fall to provide an upper limit for survival in the wild (CDDb17= 210 days). Acute low temperature tolerance was evaluated in a second experiment that exposed juveniles to a constant rate of temperature decline (3 °C d −1

Nekton tidal migration patterns were examined in oligo-mesohaline intertidal salt marsh creeks using underwater video observations collected throughout multiple tidal cycles (i.e., fl ood-ebb) during summer 2005-2006. Underwater video observations indi- cated that species composition and abundances varied with tide stage. Three intertidal salt marsh species (Fundulus heteroclitus, Morone americana, Menidia menidia) were the most abundant species observed. In general, resident species were most abundant in early fl ood and late ebb tide stages, whereas transient species were most abundant around slack high tide. F. heteroclitus displayed a consistent symmetrical tidal migration pattern and primarily occurred in early fl ood and late ebb tide stages. M. americana occurred throughout fl ood and high tides, but were largely absent from intertidal creeks during ebb tide. M. menidia was observed during all tide stages, but displayed no distinct migration patterns. The results of this study highlight the advantages and disadvantages of using underwater video for exam- ining small-scale tidal migrations of nekton in intertidal salt marsh creeks.

article i nfo Structurally complex habitats are often associated with more diverse and abundant species assemblages in both aquatic and terrestrial ecosystems. Biogenic reefs formed by the eastern oyster (Crassostrea virginica) are complex in nature and are recognized for their potential habitat value in estuarine systems along the US Atlantic and Gulf of Mexico coasts. Few studies, however, have examined the response of nekton to structural complexity within oyster reefs. We used a quantitative sampling technique to examine how the presence and complexity of experimental oyster reefs influence the abundance, biomass, and distribution of nekton by sampling reefs 4 months and 16 months post-construction. Experimental oyster reefs were colonized immediately by resident fishes and decapod crustaceans, and reefs supported a distinct nekton assemblage compared to mud-bottom habitat. Neither increased reef complexity, nor age of the experimental reef resulted in further changes in nekton assemblages or increases in nekton abundance or diversity. The presence of oyster reefs per se was the most important factor determining nekton usage.

Water control structures (WCSs) installed to regulate water levels can alter both the hydrology and ecology of salt marshes. WCSs are thought to limit nekton ingress into, and egress from, managed marshes. Slots (vertical openings that span most of the water column) incorporated into WCSs are thought to facilitate nekton passage through structures, but little research has directly examined how slot size affects passage rates. We used dual-frequency identification sonar (DIDSON) acoustic imaging to examine the effect of slot width (10, 15, 30, or 60 cm), tidal cycle, diel period, and season on nekton passage at a WCS located in a tidal salt marsh canal. Few individuals (total numbers and relative percentages) used the slots for passage through the structure during any stage of the tidal cycle, day or night, or seasonally. The number and size of migrants were similar for all four slot sizes examined. Nekton used the slots most often on flood tides to access the managed marsh (i.e., swim inside), primarily at night. Individuals entering the managed marsh were larger than those observed leaving the managed marsh. Whereas the majority of migrants were observed during winter months, season did not affect nekton passage in our study. Acoustic imaging allowed a unique and comprehensive evaluation of nekton passage by permitting an examination of factors such as swimming direction and proportion of migrants that are unobservable with other sampling techniques.

In the oligohaline Alloway Creek watershed of the upper Delaware Bay, invasive Phragmites australis (Common reed; hereafter Phragmites) has been removed in an attempt to restore tidal marshes to pre-invasion form and function. In order to determine the effects of Phragmites on nekton use of intertidal creeks and to evaluate the success of this restoration, intertidal creek nekton assemblages were sampled with weirs from May to November for 7 years (1999-2005) in three marsh types: natural Spartina alterniflora (Smooth cordgrass; hereafter Spartina), sites treated for Phragmites removal (hereafter referred to as Treated), and invasive Phragmites marshes. Replicate intertidal creek collections in all three marsh types consisted primarily of resident nekton and were dominated by a relatively low number of ubiquitous intertidal species. The Treated marsh nekton assemblage was distinguished by greater abundances of most nekton, especially Fundulus heteroclitus (Mummichog). Phragmites had little impact on nekton use of intertidal creeks over this period as evidenced by similar nekton assemblages in the Spartina and Phragmites marshes for most years. Long-term assemblage-level analyses and nekton abundances indicated that the Treated marsh provided enhanced conditions for intertidal creek nekton. The response of intertidal creek nekton suggests that the stage of the restoration may influence the results of comparisons between the marsh types and should be considered when evaluating marsh restorations.

Large-scale marsh restoration efforts were conducted to restore normal salt marsh structure and function to degraded marshes (i.e., former salt hay farms) in the mesohaline lower Delaware Bay. While nekton response has been previously evaluated for the marsh surface and subtidal creeks in these marshes, little effort has been focused on intertidal creeks. Nekton response in intertidal creeks was evaluated by sampling with seines to determine if restored (i.e., former salt hay farms restored in 1996) and reference (i.e., natural or relatively undisturbed) salt marshes were utilized by intertidal nekton in a similar manner. The overall nekton assemblage during June-October 2004-2005 was generally comprised of the same species in both the restored and reference marshes. Intertidal creek catches in both marsh types consisted primarily of Fundulus heteroclitus and Menidia menidia, with varying numbers of less abundant transient species present. Transient nekton were more abundant at restored marshes than reference marshes, but in insufficient numbers to cause differences in nekton assemblages. In both marsh types, low tide stages were characterized by resident nekton, dominated by F. heteroclitus, while high tide stages were characterized by a variable mix of transient and resident nekton. Assemblage level analyses indicated that intertidal creeks in restored and reference marshes were generally utilized in a similar manner by a similar nekton assemblage, so restoration efforts were deemed successful. This is in agreement with multiple comparative studies from the same marshes examining fish, invertebrates, and vegetation in different marsh habitats.

Intertidal creeks provide an extensive and direct interface with the marsh surface during periods of tidal inundation, and as such they represent a critically important corridor between the marsh surface and subtidal habitats. However, invasion by Phragmites can potentially alter this intertidal creek function. Habitat restoration was conducted in the oligohaline Alloway Creek watershed of Delaware Bay, USA, to ameliorate the deleterious effects of Phragmites invasion and restore marshes to pre-invasion form and function. Intertidal creeks in three marsh habitat types (natural Spartina-dominated, sites treated for Phragmites removal and now dominated by Spartina, and invasive Phragmites-dominated) were sampled during summer 2004 with seines during ebb and flood tides to determine juvenile nekton habitat and tidal utilization patterns and identify possible effects of marsh restoration efforts on intertidal nekton. Total nekton abundance was greater at Spartina and Treated marshes than Phragmites marshes. The overall nekton assemblage did not vary between habitat types, but the nekton assemblage did vary between tide stages, with low tide stages dominated by resident nekton (primarily Fundulus heteroclitus) and high tide stages consisting of a mix of transient and resident species (e.g., Anchoa mitchilli, Morone americana, Anguilla rostrata, Morone saxatilis). The effect of marsh restoration efforts on intertidal creek nekton was inconsistent, but most metrics examined indicated that restoration efforts had little effect in intertidal creek habitats, likely because the intertidal assemblage in all creek types was greatly influenced by many species moving from subtidal habitats and primarily a single (but abundant) species, F. heteroclitus, moving from the marsh surface.

This synthesis brings together published and unpublished data in an evaluation of restoration of former salt hay farms to functioning salt marshes. We compared nine years of field measurements between three restored marshes (Dennis, Commercial, and Maurice River Townships) and a reference marsh (Moores Beach) in the mesohaline portion of Delaware Bay. In the process, we compared channel morphology, geomorphology, vegetation, sediment organic matter, fish assemblages, blue crabs, horseshoe crabs, benthic infauna, and diamondback terrapins. For fishes we compared structural (distribution, abundance) and functional (feeding, growth, survival, reproduction, production) aspects to evaluate the restored marshes in an Essential Fish Habitat context. Marsh vegetation and drainage density responded gradually and positively with restored marshes approximating the state of the reference marsh within the nine-year study period. The fauna responded more quickly and dramatically with most measures equal or greater in the restored marshes within the first one or two years after restoration. Differences in response time between the vegetation and the fauna imply that the faunal response was more dependent on access to the shallow intertidal marsh surface and intertidal and subtidal creeks than on characteristics of the vegetated marsh. The fishes in created subtidal creeks in restored marshes responded immediately and maintained fish assemblages similar to the reference marsh over the study period. The intertidal creek fish assemblages tended to become more like the reference marsh in the last years of the comparison. Overall, these results document the success of the restoration and how marshes function for both resident and transient fauna, especially fishes.

The occurrence of lionfish (Pterois volitans/miles) complex on the southeast United States shelf represents one of the first documented invasions of a Pacific marine fish species into the western Atlantic Ocean. Temperature has been proposed as a possible factor limiting the range of this introduction. To examine this hypothesis, temperature-tolerance studies were conducted follow- ing the chronic lethal minimum protocol, with death as the endpoint. Overall, the mean chronic lethal minimum was 10.0°C and mean temperature at feeding cessation was 16.1°C. Rate of temperature decrease and acclimation temperature did not have a significant effect on chronic lethal minimum or temperature at feeding cessation. When combined with mean February water temperatures, lionfish thermal tolerance data indicated that lionfish could overwinter on the southeast United States conti- nental shelf, with a northern limit of Cape Hatteras and an inshore limit coincident with the mean 12°C isotherm, which equates to a 10°C minimum water temperature. The mean 12°C bottom isotherm also runs along the continental shelf break (200 m isobath), marking the offshore limit for lionfish on the southeast United States continental shelf. The current southern limit of the invasion is not bound by temperature, as lionfish could survive (but have not yet been reported) on the Florida coast south of Miami, throughout the Gulf of Mexico and Caribbean Sea, extending into the southern hemisphere. Possible reasons for the constrained southern limit may include planktonic transport mechanisms, patterns of juvenile and adult movements, and the initial lionfish introduction site.

The Nassau River estuary is located in north- east Florida adjacent to the eutrophic St. Johns River. Historically, development has been sparse in the Nassau River's catchment; thus, the system may provide a rela- tively undisturbed aquatic environment. To monitor the condition of the Nassau River estuary and to discern spatial and temporal trends in water quality, nutrients and hydrographic variables were assessed throughout the estuary from 1997 to 2011. Hydrographic (tempera- ture, salinity, total suspended solids, and turbidity) and nutrient parameters (total phosphorus, ortho-PO4 3− ,t otal nitrogen, NH4 + , total Kjeldahl nitrogen, and NO3 − ) were monitored bimonthly at 12 sites in the mesohaline and polyhaline zones of the river. Nonparametric Kendall's Tau was implemented to analyze long-term water quality patterns. Salinity was found to increase with time, par- ticularly in the mesohaline sampling sites. Dissolved oxygen decreased over time in the estuary and hypoxic conditions became increasingly frequent in the final years of the study. Nutrients increased in the estuary, ranging from 149 to 401 %. Rainfall data collected in adjacent conservation areas did not correlate well with nutrients as compared with stream discharge data col- lected in the basin headwaters, outside of the conserva- tion lands, attributed here to expanding urbanization. During the study period, the Nassau basin underwent rapid human population growth and land development resulting in commensurate impacts to water quality. Nu- trient and physical data collected during this study indi- cate that the Nassau River estuary is becoming more eutrophic with time.

We couple a species range limit hypothesis with the output of an ensemble of general circulation models to project the poleward range limit of gray snapper. Using laboratory-derived thermal limits and statistical downscaling from IPCC AR4 general circulation models, we project that gray snapper will shift northwards; the magnitude of this shift is dependent on the magnitude of climate change. We also evaluate the uncertainty in our projection and find that statistical uncertainty associated with the experimentally-derived thermal limits is the largest contributor (∼ 65%) to overall quantified uncertainty. This finding argues for more experimental work aimed at understanding and parameterizing the effects of climate change and variability on marine species.