Population Genetic Structure of the New Zealand Estuarine Clam <Emphasis Type="Italic">Austrovenus stutchburyi</Emphasis> (Bivalvia: Veneridae) Reveals Population Subdivision and Partial Congruence with Biogeographic Boundaries

We examined the population genetic structure of the New Zealand endemic clam, Austrovenus stutchburyi, to determine (1) whether populations of this estuarine taxon are genetically subdivided and (2) if the locations of genetic boundaries were congruent with known biogeographic break points. We obtained sequences of the mitochondrial gene cytochrome c oxidase I for 372 A. stutchburyi from 29 New Zealand estuaries and conducted analyses to identify population genetic structure. We detected a pattern of genetic isolation by distance and identified six A. stutchburyi subpopulations, a greater number of subpopulations than reported for much of New Zealand’s open coast benthos. Although these data indicate that long distance dispersal may be less frequent in estuarine than in open coast taxa, partial congruence between genetic and biogeographic boundaries suggests that historical events and natural selection may also contribute to the observed population genetic structure.     

Spatial and temporal differences of Atlantic menhaden (Brevoortia tyrannus) recruitment across major drainages (1966–2004) of the Chesapeake Bay watershed

Atlantic menhaden (Brevoortia tyrannus) is well known for its commercial and ecological importance and has been historically declining in the Chesapeake Bay (Maryland), one of its principal nursery habitats along the eastern coast. Using data from the Striped Bass Seine Survey of the Maryland Department of Natural Resources (2003), we evaluated how the distribution of Atlantic menhaden has changed from 1966 to 2004 for 12 river drainages. We observed significant or marginally significant declines in 42% of the drainages, with drainages of the northern Bay showing the majority of those declines. Continued recruitment to several drainages of the Bay may partly explain why the adult spawning population is not declining. We determined if temporal changes in abundance were related to changes in salinity or water quality for five major drainages of the watershed. For one of these drainages, the Patuxent River, differences in productivity across sites largely explained differences in abundance. For the four remaining drainages, differences in recruitment could not be explained by productivity or salinity gradients. While reducing nitrogen loading and enhancing water clarity may improve Atlantic menhaden production, we suggest that the role of offshore processes on large-scale declines has been largely neglected and studies on larval ingression are necessary for further elucidation of spatial and temporal patterns of juvenile distribution in the Chesapeake Bay.     

Pedo‐Geochemical Signatures of Archeological Sites in the Tapirapé‐Aquiri National Forest in Marabá, Amazonia,Brazil

The present study aims to interpret the occupation of terra firme (nonflooded uplands) archeological sites located at Tapirapé‐Aquiri National Forest in the Brazilian state of Pará, through an integrated analysis of pedological, archeological, and geochemical data. We focus on seven archaeological sites, selected among 22 identified in the region. Radiocarbon and thermoluminescence dating indicate distinct periods of occupation over the past ∼6000 years, and the pedo‐geochemical data identify intra‐ and inter‐site differences in soil. Archaeological, chronometric, and pedo‐geochemical data provide a basis for the functional classification of archeological sites found in the region and help to identify specific human activity areas. The results lead us to infer that many of the archeological sites were the result of multiple occupations that left a persistent pedological signature on the landscape.     

<Emphasis Type="Italic">Phragmites australis</Emphasis> (Common Reed) Invasion in the Rhode River Subestuary of the Chesapeake Bay: Disentangling the Effects of Foliar Nutrients,Genetic Diversity,Patch Size,and Seed Viability

The invasion and expansion of the introduced haplotype of Phragmites australis across North America is of growing concern. Previous studies in the Chesapeake Bay region found that Phragmites was more abundant, had higher foliar nitrogen, and produced more viable seeds in brackish wetland subestuaries with more anthropogenic development of the watershed. Here, we focus on a different scale and address issues related to the invasion of Phragmites within a single subestuary, the Rhode River. We evaluated patterns in seed viability, foliar nutrient concentrations, patch size, and genetic variation in ten Phragmites patches in wetlands that occur in the side of the subestuary that is surrounded by forest and 10 patches in wetlands that are in the side of the subestuary that has extensive anthropogenic development. Seed viability varied from 0–60% among the 20 patches but did not differ significantly between patches on the developed vs. forested sides of the Rhode River. Foliar nutrients also did not differ between patches on the two sides of the Rhode River. Seed viability, however, was negatively related to foliar nutrients. Most Phragmites patches consisted of >1 genotype. Larger patches had multiple genotypes, and patches with more genotypes produced more viable seeds. Our study indicates that the Rhode River subestuary behaves as one system with no differences in the measured Phragmites variables between the forested vs. developed sides of the watershed. Our findings also suggest a cyclical process by which Phragmites can spread: larger patches contain more genetic diversity, which increases the chances for cross-fertilization. The subsequent increased production of viable seeds can increase local levels of genetic diversity, which can further facilitate the spread of Phragmites by seed.     

Population maintenance of the scyphozoan<Emphasis Type="Italic">Cyanea</Emphasis> sp. Settled planulae and the distribution of medusae in the Niantic River,Connecticut, USA

Scyphozoan jellyfish are seasonally conspicuous in coastal waters, but relatively little is known about the factors that control their distribution and population dynamics.Cyanea sp is a seasonally abundant medusa in the Niantic River, Connecticut, U.S. and appears to maintain a population entirely within the estuary. To better understand the factors controlling their occurrence, we examined the temporal and spatial distribution of settled scyphistomae in relation to that of the medusae. Planula settlement patterns mirrored the presence of mature female medusae. The planulae settled primarily near the bottom. After settlement, planulacysts and polyps on the settlement plates were out competed by large barnacle and ascidian larvae, resulting in a sharp decline in cyst and polyp abundance. This stage-specific mortality may represent a population bottleneck in the life cycle of scyphozoans.     

The First Hop: Use of Beaufort Sea Deltas by Hatch-Year Semipalmated Sandpipers

River deltas along Alaska’s Beaufort Sea coast are used by hatch-year semipalmated sandpipers (Calidris pusilla) after leaving their terrestrial natal sites, but the drivers of their use of these stopover sites on the first “hop” of fall migration are unknown. We quantified sandpiper temporal distribution and abundance as related to food resources at three river deltas during the beginning of their fall migration (post-breeding period) to compare the habitat quality among these deltas. We conducted population counts, sampled invertebrates, and captured birds to collect blood samples from individuals for triglyceride and stable isotope analyses to determine fattening rates and diet. Patterns of sandpiper and invertebrate abundance were complex and varied among deltas and within seasons. River deltas were used by sandpipers from late July to late August, and peak sandpiper counts ranged from 1000 to 4000 individuals, of which 98% were hatch-year semipalmated sandpipers. Isotopic signatures from blood plasma samples indicated that birds switched from a diet of upland tundra to delta invertebrate taxa as the migration season progressed, suggesting a dependence on delta invertebrates. Despite differences in diet among deltas, we found no differences in fattening rates of juvenile sandpipers as indicated by triglyceride levels. The number of sandpipers was positively associated with abundance of Amphipoda and Oligochaeta at the Jago and Okpilak-Hulahula deltas; an isotopic mixing model indicated that sandpipers consumed Amphipoda and Oligochaeta at Jago, mostly Chironomidae at Okpilak-Hulahula and Spionidae at Canning. Regardless of the difference in sandpiper diets at the Beaufort Sea deltas, their similar fattening rates throughout the season indicate that all of these stopover sites provide a critical food resource for hatch-year sandpipers beginning their first migration.     

Post-settlement alteration of spatial patterns of soft shell clam (<Emphasis Type="Italic">Mya arenaria</Emphasis>) recruits

To examine the roles of settlement and early post-settlement processes in patterns of recruitment of the soft shell clamMya arenaria, abundance of juvenileMya at three intertidal sites in Barnstable Harbor, Massachusetts, was monitored over two settlement seasons. Two peaks of settlement occurred in 1998 (July and September) and one peak was recorded in June 1999, indicating that a late season settlement event is not a consistent feature at this site. Abundance of recent settlers (i.e., early recruits, < 1 week past settlement) varied significantly among the tidal flats (sites) that were separated by hundreds of meters to kilometers, but not among plots meters apart. Differences in abundance of settlers likely resulted in these differences in early-recruit abundance among sites. Settlement was greatest at the site with the greatest variability in flow speed. Sites also differed to some extent in their sediment characteristics and macrofaunal assemblages, which may influence larval substrate choice. Between-site differences in abundance ofMya decreased after settlement. The rate of decline of abundance varied among cohorts and sites. Comparison of abundance of recent settlers (up to 145,000 m⁻²) to that of juveniles > 3-mm shell length at the end of the settlement season (up to 60 m⁻²) indicated large losses of individuals during the early post-settlement period. This study demonstrates that spatial patterns inMya abundance can change substantially during the early post-settlement period, and that high mortality rates can result in cohorts contributing little to the population size even when rates of settlement are high.     

Phenotypic Variation Among Invasive <Emphasis Type="Italic">Phragmites australis</Emphasis> Populations Does Not Influence Salinity Tolerance

Phenotypic variation within species can have community- and ecosystem-level effects. Such variation may be particularly important in ecosystem engineers, including many invasive species, because of the strong influence of these species on their surrounding communities and environment. We combined field surveys and glasshouse experiments to investigate phenotypic variation within the invasive common reed, Phragmites australis, among four estuarine source sites along the east coast of North America. Field surveys revealed variation in P. australis height and stem density among source sites. In a glasshouse environment, percent germination of P. australis seeds also varied across source sites. To test the degree to which phenotypic variation in P. australis reflected genetic or environmental differences, we conducted a glasshouse common garden experiment assessing the performance of P. australis seedlings from the four source sites across a salinity gradient. Populations maintained differences in morphology and growth in a common glasshouse environment, indicating a genetic component to the observed phenotypic variation. Despite this variation, experimentally increased porewater salinity consistently reduced P. australis stem density, height, and biomass. Differences in these morphological metrics are important because they are correlated with the impacts of invasive P. australis on the ecological communities it invades. Our results indicate that both colonization and spread of invasive P. australis will be dependent on the environmental and genetic context. Additional research on intraspecific variation in invasive species, particularly ecosystem engineers, will improve assessments of invasion impacts and guide management decisions in estuarine ecosystems.     

Factors contributing to the removal of a marine grass invader (<Emphasis Type="Italic">Spartina anglica</Emphasis>) and subsequent potential for habitat restoration

Our goal is to understand how removal regime and habitat type interact to influence removal success of a marine plant invader and the subsequent potential for restoration. In particular, we investigate the management program designed to eradicate the English cordgrass,Spartina anglica C. E. Hubbard, in marine intertidal habitats of Puget Sound, Washington, United States. Observational and manipulative experiments were used to measure the regrowth (vegetative growth), reinvasion (seedling recruitment), and restoration potential (return to native condition) of invaded habitats. Removal regime (consistent: yearly removal; interrupted: yearly removal with the last year missed) and habitat type (low salinity marsh, mudflat, cobble beach, and high salinity marsh sites) were considered. The response to removal regime was dramatic. Under consistent removal, cordgrass slowly declined but under interrupted removal, there was substantial regrowth of the invader. This pattern results from the resiliency of belowground biomass and the subsequent high aboveground productivity and seedling growth ofS. anglica. We also found that removal success depended on differences among sites that represent different habitat types. Cordgrass regrowth and reinvasion were substantially higher in the low salinity marsh sites where soils have lower salinity. We also found that at the low salinity marsh sites, some restoration of native plants and soil conditions was evident. At mudflat, cobble beach, and high salinity marsh sites, colonization of native vascular plants and algae not normally present, in the absence of the invasion, occurred. Whether these habitats will eventually revert back to the pre-invasion conditions over a longer period of time is unknown.     

Spatial and temporal patterns of spawning and larval hatching by the horseshoe crab,<Emphasis Type="Italic">Limulus polyphemus</Emphasis>, in a microtidal coastal lagoon

Estuarine species with wide geographic distributions often experience tidal regimes that vary significantly throughout their range. Plasticity in behaviors associated with the tide is expected to enable synchronization with local tides. The American horseshoe crabLimulus polyphemus typically inhabits estuaries and coastal areas with pronounced semi-diurnal tides that play a role in synchronizing the timing of spawning and larval hatching, but also lives in areas that lack significant tides and associated synchronization cues. We investigated the spatial and temporal pattern of adult spawning and larval hatching ofL. polyphemus in a microtidal coastal lagoon (Indian River Lagoon, Florida, USA). Spawning activity and larval abundance were monitored weekly February 1998–August 2000 at sites spanning 100 km of the lagoon. To identify possible synchronization cues for spawning and hatching success, the presence of adult and larvalL. polyphemus were related to environmental and hydrologic variables using logistic regression. The presence of spawning adults varied significantly among the sub-basins of the lagoon, with the highest densities occurring in the Banana River. Large spawning aggregations were not observed and densities never exceeded 6 m⁻². Spawning occurred year-round but varied seasonally with episodes of increased mating activity in the early spring. The occurrence of mating pairs was episodic and was not synchronized among sites. Larval densities were low (4 m⁻³) and larvae were present at only 12 of the 21 sites. Hatching success was decoupled temporally from spawning activity, with peaks in larval abundance occurring approximately 8 wk after peaks in spawning. Larval abundance was associated with periods of high water. Reproductive activity of horseshoe crabs in the lagoon differs significantly from populations inhabiting areas with semi-diurnal and diurnal tides. These differences are likely due to the lack of periodic tidally-related synchronization cues and regular beach inundation.     

Winter Flounder Larval Genetic Population Structure in Narragansett Bay,RI: Recruitment to Juvenile Young-of-the-Year

The genetic population structure of winter flounder larvae was examined in Narragansett Bay, RI. Winter flounder larvae collected from 20 stations within Narragansett Bay and one station outside of the Bay were analyzed for six microsatellite loci. When analyzed by geographic collection sites, there were 16 distinct genetic populations of winter flounder larvae (R _ST values from 0.1 to 0.6). The presence of distinct genetic populations was supported by assignment of individual larvae to populations by Bayesian analysis. Bayesian analysis resulted in 14 distinct genetic populations that overlapped with the geographically distributed populations (R _ST values from 0.1 to 0.6). Young-of-the-year juveniles collected in the same year as the larvae were also analyzed at the same six microsatellite loci. Juveniles were assigned to larvae populations by both a Bayesian approach and a neural network approach. Juveniles collected from within Narragansett Bay were found to arise from geographically adjacent Narragansett Bay winter flounder larval populations (>99%), suggesting no widespread movement of juveniles away from spawning grounds. These results are discussed in the context of winter flounder population biology in Narragansett Bay, RI.     

Lichenometric dating using Rhizocarpon subgenus Rhizocarpon in the Patagonian Andes, Argentina

This study represents the first attempt to develop and apply lichenometric dating curves of Rhizocarpon subgenus Rhizocarpon for dating glacier fluctuations in the Patagonian Andes. Six glaciers were studied along the Patagonian Andes. Surfaces of known ages (historical evidences and tree-ring analyses) were used as control sites to develop indirect lichenometric dating curves. Dating curves developed for the studied glaciers show the same general logarithmic form, indicating that growth rate of subgenus Rhizocarpon decreases over time. The strong west–east precipitation gradient across the Andean Cordillera introduces statistically significant differences in the growth curves, with faster growth rates in the moist west sites than the drier eastern sites. Latitudinal difference among the studied glaciers does not appear to be a major factor regulating lichen growth rates. Therefore, we developed two lichenometric curves for dating glacier fluctuations in wetter and drier sites in the Patagonian Andes during the past 450 yrs. Application of the developed curves to moraine dating allowed us to complement glacial chronologies previously obtained by tree-ring analyses. A first chronosequence for moraine formation in the Torrecillas Glacier (42°S) is presented. Our findings confirm the utility of lichenometry to date deglaciated surfaces in the Patagonian Andes.     

Late Quaternary vegetation and fire history in the northernmost Nothofagus forest region: Mallín Vaca Lauquen,Neuquén Province,Argentina

The last 16 000 cal. a of vegetation, fire and limnological history are described from the steppe‐forest ecotone in the northernmost Nothofagus forest region east of the Andes (Mallín Vaca Lauquen, Neuquén Province, Argentina, latitude 36° 51.336′ S, longitude 71° 02.538′ W). Between 16 000 and 14 800 cal. a BP, scrub steppe with substantial open ground expanded in formerly glaciated valleys, whereas Nothofagus–Prumnopitys andina woodland covered mountain slopes. The site was a relatively deep and unproductive small lake at this time. After 14 800 cal. a BP, both steppe and woodland vegetation became denser, indicating increased moisture and temperatures, although not to present levels. The lake was still relatively deep and dystrophic, but became more alkaline by 10 000 cal. a BP. Between 8900 and 5500 cal. a BP, conditions were markedly drier than before; a Cyperaceae marsh developed and disturbance taxa increased. After 5500 cal. a BP, moisture increased but varied greatly, as evidenced by fluctuating water levels and high fire activity from 5500 to 4400 cal. a BP and from 2300 to 1000 cal. a BP. Human activity, in terms of forest clearance and livestock grazing, is documented in the uppermost levels. The evidence of high environmental variability in the middle and late Holocene is consistent with the onset or strengthening of the El Niño–Southern Oscillation, but differences in the timing of fire activity among sites on the west and east sides of the Andes suggest that fuel conditions were important in determining the local occurrence of fire. Copyright © 2008 John Wiley & Sons, Ltd.     

Horseshoe crabs (Limulus polyphemus) in an urban estuary (Jamaica Bay, New York) and the potential for ecological restoration

We assessed the suitability of intertidal habitats for spawning by horseshoe crabs (Limulus polyphemus) at 12 proposed restoration sites identified by the United States Army Corps of Engineers along the shore of Jamaica Bay, a highly developed estuary in New York City. Based on beach geomorphology, we chose to quantify horseshoe crab activity at five of the sites during the May–July 2000 breeding season. Horseshoe crabs spawned intensively on small patches of suitable sand within larger areas of eroding shoreline with bulkheads and rubble fill. Small areas of sand behind grounded barges at Brant Point and Dubos Point had densities of over 100,000 eggs m⁻², which was equal to or greater than the egg densities on longer, more natural appearing beaches at Spring Creek and Dead Horse Bay, or at a sand spit at Bayswater State Park. There were no significant differences in the percentage of Jamaica Bay horseshoe crab eggs that completed development when cultured using water from Jamaica Bay or lower Delaware Bay, a less polluted location. Only 1% of the embryos from Jamaica Bay exhibited developmental anomalies, a frequency comparable to a previously studied population from Delaware Bay. We suggest that the distribution and abundance of horseshoe crabs at our study areas in Jamaica Bay is presently limited by the availability of suitable shoreline for breeding, rather than by water quality. Restoration efforts that increase the amount of sandy beach in this urban estuary have a good likelihood of benefiting horseshoe crabs and providing additional value to migrating shorebirds that use horseshoe crab eggs as food.     

Low incidence and limited effect of the oyster pathogen dermo (<Emphasis Type="Italic">Perkinsus marinus</Emphasis>) on an artificial reef in Delaware's Inland Bays

Delaware's Inland Bays comprise a large estuarine system with a restricted access to the Atlantic Ocean (Indian River Inlet). As part of a local oyster stock enhancement and restoration effort, we conducted a survey for the protozoan pathogenPerkinsus marinus (Dermo) in oysters from a newly established reef. Using standardized methods for the polymerase chain reaction (PCR) amplification of the non-transcribed spacer (NTS) region, we were surprised to find no detectable titers of this pathogen in the 30 oysters sampled in the first year of the project. The detection threshold of the PCR coupled with chemiluminescent detection was 30 fgP. marinus NTS DNA. We were able to detect a trace presence of this pathogen in a few hard clams (Mercenaria mercenaria) from the same locale, indicating that aPerkinsus sp. was present in the Inland Bay system. Subsequent monitoring of the reef system using a fluid thioglycollate assay over 3 yr revealed no epizootic outbreaks of this pathogen within the planted oyster population. Two large mortality episodes that did appear in the oyster population were attributable to abiotic conditions and not pathogen exposure. This study emphasizes that all potential sources of mortality in the environment are important to consider when designing oyster seeding projects. In the Delaware Inland Bays,P. marinus does not appear to have a large enough oyster host population to become a significant disease threat at present. Because of the low parasite incidence levels in the Inland Bay system in 2000, the James Farm oyster reef restoration project presents an ideal model system to follow the population dynamics between an oyster-host population and a latent or reservoir pathogen population.     

How Population Decline Can Impact Genetic Diversity: a Case Study of Eelgrass (<Emphasis Type="Italic">Zostera marina</Emphasis>) in Morro Bay,California

Seagrass populations are in decline worldwide. Eelgrass (Zostera marina L.), one of California’s native seagrasses, is no exception to this trend. In the last 8 years, the estuary in Morro Bay, California, has lost 95% of its eelgrass. Population bottlenecks like this one often result in severe reductions in genetic diversity; however, this is not always the case. The decline of eelgrass in Morro Bay provides an opportunity to better understand the effects of population decline on population genetics. Furthermore, the failure of recent restoration efforts necessitates a better understanding of the genetic underpinnings of the population. Previous research on eelgrass in California has demonstrated a link between population genetic diversity and eelgrass bed health, ecosystem functioning, and resilience to disturbance and extreme climatic events. The genetic diversity and population structure of Morro Bay eelgrass have not been assessed until this study. We also compare Morro Bay eelgrass to Bodega Bay eelgrass in Northern California. We conducted fragment length analysis of nine microsatellite loci on 133 Morro Bay samples, and 20 Bodega Bay samples. We found no population differentiation between the remaining beds in Morro Bay and no difference among samples growing at different tidal depths. Comparisons with Bodega Bay revealed that Morro Bay eelgrass contains three first-generation migrants from the north, but Morro Bay remains considerably genetically differentiated from Bodega Bay. Despite the precipitous loss of eelgrass in Morro Bay between 2008 and 2017, genetic diversity remains relatively high and comparable to other populations on the west coast.     

Plasticity,Not Adaptation to Salt Level,Explains Variation Along a Salinity Gradient in a Salt Marsh Perennial

Evolutionary ecologists have long been intrigued by the fact that many plant species can inhabit a broad range of environmental conditions and that plants often exhibit dramatic differences in phenotype across environmental gradients. We investigated responses to salinity treatments in the salt marsh plant Borrichia frutescens to determine if the species is responding to variation in edaphic salt content through phenotypic plasticity or specialized trait response. We grew seedlings from fruits collected in high- and low-salt microhabitats, assigned seedlings to high- and low-salt treatments in a greenhouse, and measured traits related to salt tolerance. All traits were highly plastic in response to salinity. Plants from the two microhabitats did not differ in trait means or respond differently to the treatments. These results suggest that environmental differences between the two microhabitats are not creating genotypes adapted to high and low salt levels. In addition, despite evidence for variation in allozyme markers in this population, there was no significant genotypic variation (family effect) in any of the trait means measured across microhabitats. There was variation in plasticity for only leaf Na and leaf B concentration. The high degree of plasticity for all traits and the lack of differences among microhabitats across the salinity gradient suggest plasticity in many traits may be fixed for this species.     

Population structure and reproductive characteristics of the gulf pipefish,Syngnathus scovelli, in Mobile Bay, Alabama

The gulf pipefish,Syngnathus scovelli, is the dominant syngnathid found in coastal regions of the Gulf of Mexico and is the only species in this region known to occur in both freshwater and saltwater habitats. Relatively little is known about the population and reproductive cycles ofS. scovelli, particularly for those found in low salinity environments. The focus of the current study was to collect population structure and reproductive data forS. scovelli from a low salinity habitat, Meaher Park, located at the mouth of Mobile Bay, Alabama. Sampling was conducted twice a month from January 2003 to January 2004. Environmental parameters, as well as population and reproductive parameters, were collected. Water temperature was the primary abiotic factor associated with both the appearance ofS. scovelli and their breeding cycle. Based on gonadosomatic (GSI) and brood pouch somatic indices (BPSI), females and males were reproductively active throughout the summer. Peaks in male GSI and BPSI were consistent with the subsequent appearance of a large number of juveniles in early fall. These event coincided with the higher temperatures seen during late summer and early fall. Sex ratios (male : female 1 : 1.64) and operational sex ratios (1 : 4.09) indicated that this was a female biased population. Although there was no difference in the average size of males and females in this population, the largest individuals collected were female. The female-biased sex ratio supports previous genetic analyses suggesting thatS. scovelli exhibits true sex-role reversal and that operational sex ratios are a reliable indicator of the intensity of mating competition and sex roles.     

Variability in habitat use by young-of-the-year winter flounder,<Emphasis Type="Italic">Pseudopleuronectes americanus</Emphasis>, in three northeastern U.S. estuaries

We compared distribution and abundance by habitat for age-0, young-of-the-year (YOY) winter flounder,Pseudopleuronectes americanus, in three estuaries (Hammonasset River, Navesink River, and Great Bay-Little Egg Harbor) in the northeastern United States to better define essential fish habitat (EFH). Two replicates of five representative habitats were sampled in most estuaries: eelgrass (Zostera marina), unvegetated areas adjacent to eelgrass, macroalgae, (primarilyUlva lactuca), unvegetated areas adjacent to macroalgae, and tidal marsh creeks. Fish were sampled every two weeks, May through October 1995 and 1996, with a beam-trawl (1-m width, 3-mm mesh net). Abundance of YOY winter flounder was highest in the Navesink River estuary and similar between years, but was significantly lower and differed between years in the Great Bay-Little Egg Harbor and Hammonasset River estuaries. Annual temperature differences appear to influence estuary use by YOY. In the years and estuaries studied, where habitat-related differences in abundance were significant, YOY were found in higher densities in unvegetated areas adjacent to eelgrass. The exception was in the Hammonasset River in 1995 when densities were higher in eelgrass. We conclude that the type of habitat most important to YOY winter flounder varies among estuaries and as a result, care should be taken in defining EFH, based only on limited spatial and temporal sampling.     

Blue crab,<Emphasis Type="Italic">Callinectes sapidus</Emphasis>, response to the invasive common reed,<Emphasis Type="Italic">Phragmites australis</Emphasis>: Abundance,size, sex ratio,and molting frequency

Much effort has been directed recently at restoring marshes, by the removal of the invasive common reed,Phragmites australis, yet it is not clear how fish and invertebrates have responded either to the invasion ofPhragmites or to marsh restoration. The blue crab,Callinectes sapidus, uses marsh habitats during much of its benthic life. We investigated the response of blue crabs toPhragmites invasion and restoration efforts by comparing crab abundance (catch per unit effort), mean size and size frequency distribution, sex ratio, and molting of crabs in three physically similar areas differing in marsh vegetation;Spartina-dominated,Phragmites-dominated, and a treated area (Phragmites removed and now dominated bySpartina) in one marsh in the upper portion of Delaware Bay. Field sampling occurred monthly (April to November) from 1999 to 2001 using replicate daytime otter trawls in large marsh creeks. Crabs were categorized by carapace width into recruits (<30 mm), juveniles (30–115 mm), and adults (>115 mm). Juveniles dominated the system, representing 69.4% of all crabs. Similar monthly increases in mean size and molting patterns during the growing season (May–August) occurred inSpartina (natural and treated sites) andPhragmites sites suggesting that, subtidal habitats, used for molting, in these areas do not differ. More juveniles in the feeding molt stage (i.e., intermolt) than in other molt stages and more recruits predominantly in the feeding molt stage than adults were inSpartina, suggesting differences in the marsh surfaces used as feeding habitats withSpartina being preferred. Sex ratios of each life history stage were skewed towards males, but this was related to the low salinity of Alloway Creek, rather than marsh surface vegetation. Our results suggest that marsh surface vegetation influences the way blue crabs use marsh surface habitats, thus restoration efforts focusing on changing vegetation type may have a positive influence on blue crabs.