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1.
Knowledge of resource-use and movement patterns is a missing component in the development of horseshoe crab (Limulus polyphemus) management strategies. Available evidence indicates the potential for a variety of possible migratory behaviors, but the
lack of high-resolution, spatial-temporal data has hindered development of a year-round profile of ranging behavior. This
need was addressed in the present study by using acoustic telemetry to track the movements of adult horseshoe crabs in two
subembayments (Egypt and Hog Bays) of the Taunton Bay Estuary, Maine, from June 2003 to June 2005. Estimated mean total home
range sizes were 64.1 and 61.4 ha for breeding crabs tagged in Egypt and Hog Bays, respectively. We observed no horseshoe
crab dispersal to areas outside of the subembayments where they were tagged, so no mixing was observed between Egypt and Hog
Bay individuals despite a < 4-km separation. Observed shifts in movement patterns, resource use (subtidal versus intertidal),
and vagility facilitated a profile of seasonally partitioned horseshoe crab activity, which included late April to early May
post-wintering, June–July breeding, August–September pre-wintering, and October–April wintering, where space usage represented
about 10% of the mean total home range size. The apparent isolation of these resident populations implies a heightened vulnerability
to overexploitation and large-scale habitat alteration that might be more easily sustained by larger, more vagile populations.
This work underscores the need to apply horseshoe crab conservation, research, and management efforts at scales that are appropriate
to the ranging patterns of crabs, which first requires application of high-resolution methods to identify those patterns. 相似文献
2.
Mark L. Botton Robert E. Loveland John T. Tanacredi Tomio Itow 《Estuaries and Coasts》2006,29(5):820-830
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. 相似文献
3.
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. 相似文献
4.
Populations of the American horseshoe crab (Limulus polyphemus) differ in broad areas of their biology. We observed a non-harvested, marked Florida Gulf coast population during their spring
spawning (March–May) in 11 years across a 17-year period (1992–2009). Long-term changes occurred in the number of spawning
pairs: the population was stable from 1992 to 2000 but increased markedly after 2000. Short-term variation in numbers of spawning
pairs, unpaired females, unpaired males, and operational sex ratios was explained by changes over the season and during each
week of spring tides and by differences in actual (not predicted) maximum high tide height. Wind direction strongly affected
tidal inundation and the number of spawning horseshoe crabs. Tagging individuals revealed that females returned to the nesting
beach less often than males and most females were re-sighted only within 1 week of spring tides. No animals were seen across
more than 6 years. Implications for management are discussed. 相似文献
5.
Atlantic horseshoe crabs,Limulus polyphemus, are currently harvested for biomedical, scientific, and bait purposes. In recent years, changes in population abundance
and magnitude of harvesting have raised concerns about the status of this resource. We found horseshoe crab harvest in Pleasant
Bay, Massachusetts, was selective by sex and size. Biomedical harvest preferred larger individuals and females, the scientific
harvest preferred smaller individuals and males, and the bait harvest preferred females. Total 2001 harvest for all purposes
accounted for the mortality of ∼1–2% the adult population. Biomedical harvest accounted for the greatest loss of horseshoe
crabs from Pleasant Bay, ∼1–1.6% of the total population. Although biomedical harvest had the lowest associated mortality
rate (∼10–15%), many more crabs were harvested from Pleasant Bay for biomedical purposes than for other uses. The scientific
harvest accounted for the mortality of ∼0.4% of the population, and bait harvest accounted for the smallest mortality at ∼0.06%
of the population. Harvest mortality rate was estimated to be lower in Pleasant Bay than in other Cape Cod areas and may be
lower than natural mortality in the population. This study is the first qualitative investigation of commercial harvest on
horseshoe crab populations and emphasizes that harvest pressures on different populations need to be individually evaluated. 相似文献
6.
This study investigates the influence ofPhragmites australis (common reed) invasion on the habitat of the resident marsh fish,Fundulus heteroclitus (mummichog) in the Hackensack Meadowlands, New Jersey. These abundant fish play an important role in the transfer of energy
from the marsh surface to adjacent subtidal waters and thus estuarine food webs. The objectives of this 2-yr study (1999 and
2000) were to compare the distribution and abundance of the eggs, larvae, juveniles, and adults of mummichog and their invertebrate
prey inhabitingSpartina alterniflora-dominated marshes withPhragmites-dominated marshes, and to experimentally investigate the influence of marsh surface microtoprography on larval fish abundance
withinPhragmites-dominated marshes. In 2000, we verified that egg deposition does occur inPhragmites-dominated marshes. In both years, the abundance of larvae and small juveniles (4–20 mm TL) inS. alterniflora was significantly greater than inPhragmites-dominated marshes, while larger juveniles and adults (>20 mm TL) were similarly abundant in both habitat types. The overall
abundance of larvae and small juveniles was significantly greater in experimentalPhragmites plots in which microtopography was manipulated to resemble that ofSpartina marshes than inPhragmites control plots. Major groups of invertebrate taxa differed between marsh types with potential prey for larval fish being significantly
more abundant inS. alterniflora marshes.Phragmites-dominated marshes may not provide the most suitable habitat for the early life-history stages of the mummichog. The low abundance
of larvae and small juveniles inPhragmites marshes is likely due to inadequate larval habitat and perhaps decreased prey availability for these early life history stages. 相似文献
7.
David R. Smith 《Estuaries and Coasts》2007,30(2):287-295
Because the Delaware Bay horseshoe crab (Limulus polyphemus) population is managed to provide for dependent species, such as migratory shorebirds, there is a need to understand the
process of egg exhumation and to predict eggs available to foraging shorebirds. A simple spatial model was used to simulate
horseshoe crab spawning that would occur on a typical Delaware Bay beach during spring tide cycles to quantify density-dependent
nest disturbance. At least 20% of nests and eggs were disturbed for levels of spawning greater than one third of the average
density in Delaware Bay during 2004. Nest disturbance increased approximately linearly as spawning density increased from
one half to twice the 2004 level. As spawning density increased further, the percentage of eggs that were disturbed reached
an asymptote of 70% for densities up to 10 times the density in 2004. Nest disturbance was heaviest in the mid beach zone.
Nest disturbance precedes entrainment and begins the process of exhumation of eggs to surface sediments. Model predictions
were combined with observations from egg surveys to estimate a snap-shot exhumation rate of 5–9% of disturbed eggs. Because
an unknown quantity of eggs were exhumed and removed from the beach prior to the survey, cumulative exhumation rate was likely
to have been higher than the snap-shot estimate. Because egg exhumation is density-dependent, in addition to managing for
a high population size, identification and conservation of beaches where spawning horseshoe crabs concentrate in high densities
(i.e., hot spots) are important steps toward providing a reliable food supply for migratory shorebirds. 相似文献
8.
As part of the Microbial Exchanges and Coupling in Coastal Atlantic Systems (MECCAS) Project, crab larvae were collected in the shelf waters off Chesapeake Bay in June and August 1985 and April 1986. We conducted hydrographic (temperature, salinity, nutrients) and biological (chlorophyll, copepods) mapping in conjunction with Eulerian and Lagrangian time studies of the vertical distribution of crab larvae in the Chesapeake Bay plume. These abundance estimates are used with current meter records and drifter trajectories to infer mechanisms of larval crab dispersion to the shelf waters and recruitment back into Chesapeake Bay. The highest numbers of crab larvae were usually associated with the Chesapeake Bay plume, suggesting that it was the dominant source of crab larvae to shelf waters. Patches of crab larvae also were found in the higher salinity shelf waters, and possibly were remnants of previous plume discharge events. The distribution of crab larvae in the shelf waters changed on 1–2 d time scales as a consequence of both variations in the discharge rate of the Chesapeake Bay plume and local wind-driven currents. Downwelling-favorable winds (NW) intensified the coastal jet and confined the plume and crab larvae along the coast. In April during a downwelling event (when northwesterly winds predominated), crab zoeae were transported southward along the coast at speeds that at times exceeded 168 km d−1. During June and August the upwelling-favorable winds (S, SW) opposed the anticyclonic turn of the plume and, via Ekman circulation, forced the plume and crab larvae to spread seaward. Plume velocities during these conditions generally were less than 48 km d−1. The recruitment of crab larvae to Chesapeake Bay is facilitated in late summer by the dominance of southerly winds, which can reverse the southward flow of shelf waters. Periodic downwelling-favorable winds can result in surface waters and crab larvae moving toward the entrance of Chesapeake Bay. Approximately 27% of the larval crabs spend at least part of the day in bottom waters, which have a residual drift toward the bay mouth. There appears to be a variety of physical transport mechanisms that can enhance the recruitment of crab larvae into Chesapeake Bay. 相似文献
9.
Habitat use,temporal abundance variability,and diet of blue crabs from a New Jersey estuarine system
In a long-term, spatially comprehensive beam trawl survey of the Navesink River-Sandy Hook Bay estuary, the blue crabCallinectes sapidus was one of the most abundant species. Seasonal changes in abundance were evident, with low abundances in summer followed
by peak abundances in the fall, after juveniles recruited to the estuary. We saw no long-term trends in abundance during the
5 yr study. Location in the navesink River or Sandy Hook Bay explained most of the variance in abundance within any one survey.
In diet analyses, we found evidence of cannibalism in all seasons, but in the size range of crabs caught in this study (10–180
mm), we did not find a relationship between cannibalism and juvenile crab abundance. Within surveys, crabs divided into 20
mm size categories showed no sizerelated differences in location within the estuary or among 7 habitat types examined (algae
bed, amphipod bed, beach, channel, marsh edge, mid-depth, and sandbar). Channels and sandbars tended to exhibit lower crab
abundance than other habitats. Shallow habitats with and without cover were equally preferred by juvenile blue crabs, implying
that the presence of structure was not critical. Spatial models of crab abundance (<- 80 mm carapace width) to environmental
data were fit from several seasons of intensive sampling in the Navesink River-Sandy Hook Bay estuary between summer 1996
and spring 1998. These models indicated that fine-grained sediments, tmmperature, depth, and salinity were good indicators
of crab abundance in spring, summer, and fall. Using these spatial models and environmental data collected in subsequent seasons
(summer 1998−fall 1999), we were able to predict blue crab abundance in the river as evidenced by significant correlations
between predicted and observed abundances. For the size range of crabs examined here, physical conditions may be as important
as structural habitat types or cannibalism in determining habitat use in northerly estuaries. 相似文献
10.
An ichthyoplankton survey (18 stations in seven sampling sectors) was conducted in Narragansett Bay in 1990 to provide information on abundance, distribution, and seasonal occurrence of eggs and larvae of estuarine fishes, including seasonal migrants. An additional goal was to examine changes in species composition, abundance, and distribution occurring since the last baywide survey in 1972–73. The taxonomic composition of eggs and larvae in 1990 (41 species in 25 families from 684 plankton samples) and in 1972–73 (43 species in 28 families from 6900 samples) was similar. Maximum abundance of fish eggs occurred in June and larvae in July, minimum abundance in September to February. Species diversity was greatest in May–July and lowest during January in both surveys. However, egg and larval densities in 1990 were considerably lower than in 1972–73. Bay anchovy, tautog, and cunner accounted for 86% of the eggs and 87% of the larvae in the bay in 1990. These three species accounted for only 55% of the eggs and 51% of the larvae in 1972–73, with menhaden accounting for another 18% of the eggs and 34% of the larvae. Searobins, scup, and butterfish eggs were common in 1973 (19%) but rare in 1990 (2%). Ichthyoplankton abundance for several of the most abundant species was significantly lower (p<0.05) in the Providence River, upper bay, and Greenwich Bay in 1990 than in 1972–73. Density of fish eggs and larvae in the lower portions of the bay was lower in 1990 for some species but not others. Distribution data suggested a general down-bay shift in density in 1990. *** DIRECT SUPPORT *** A01BY085 00015 相似文献
11.
B. L. Swan 《Estuaries and Coasts》2005,28(1):28-40
Adult horseshoe crabs,Limulus polyphemus, were tagged in the Middle Atlantic Bight area, from New York to Virginia on the continental shelf and within bays, to determine
their migratory patterns and longevity. Of 30,432 horreshoe crabs that were tagged during the years 1986–2002, 1,122 were
recovered alive, and 1,027 were dead. Many of the live recoveries were observed within 30 d (54.4%) and after years (37.53%)
with one tagged animal surviving up to 10 yr. In 9 locations from Great Kills Harbor, New York, to Chesapeake Bay, Maryland,
the horseshoe crabs return to their release beach within days during the spawning season. Of the 762 (100%) recoveries from
crabs released along the Delaware Bay shoreline, 75.07% traveled 0–20 km, 21.0% traveled 20–50 km, 2.36% traveled 50–100 km,
and 1.57% traveled over 100 km. Within Delaware Bay, 327 tagged animals (43.6%) had moved away from the release points to
other locations, and 59 of these had moved out of the bay onto the continental shelf along the Mid-Atlantic Bight coastline.
Horseshoe crabs migrate into Delaware Bay from waters off Ocean City, Maryland, and adjacent coastal bays. In addition to
defining the range of the Delaware Bay spawning populations, 2 neighboring populations were identified by the tagging program.
In one, animals tagged in southern New York mingled with those in the Sandy, Hook, New Jersey area, comprising a population
that ranged from Raritan Bay across New York Harbor to Jamaica Bay. The second confirmed that a discrete population existed
in northern Chesapeake Bay in the general vicinity of the Annapolis Bay Bridge. 相似文献
12.
The blue crab, Callinectes sapidus, is an ecologically and economically valuable species in Chesapeake Bay. Field surveys and laboratory experiments indicate
that blue crab mortality is significant during severe winters. We applied a temperature and salinity-dependent survival model
to empirical temperature and salinity data to explore spatial and interannual patterns in overwintering mortality. Harmonic
regression analysis and geostatistical techniques were used to create spatially explicit maps of estimated winter duration,
average temperature, average salinity, and resulting crab survival probability for the winters of 1990–2004. Predicted survival
was highest in the warmer, saline waters of the lower Bay and decreased with increasing latitude up bay. There was also significant
interannual variation with survival being lowest after the severe winters of 1996 and 2003. We combine the survival probability
maps with maps of blue crab abundance to show how winter mortality may reduce blue crab abundance prior to the start of the
harvesting season. 相似文献
13.
Martin T. O’Connell Travis D. Shepherd Ann M. U. O’Connell Ransom A. Myers 《Estuaries and Coasts》2007,30(4):567-574
We analyzed historic and current fishery independent data to determine if the abundance of two apex predators, bull sharks
(Carcharhinus leucas) and alligator gar (Atractosteus spatula), in Lake Pontchartrain had changed significantly over the last half century. Lake Pontchartrain is an environmentally degraded
oligohaline estuary in southeastern Louisiana that has experienced considerable changes in fish assemblage composition over
this interval. Using gillnet, beach seine, and trawl data collected during three time periods (1953–1955, 1977–1978, and 1996–2005),
we analyzed trends in abundance forC. leucas andA. spatula using generalized linear models with a negative binomial error structure and a log link. Lake Pontchartrain data were divided
into four spatial locations (northwest, northeast, southwest, southeast) since each region represents a unique combination
of anthropogenic and natural influences that could affect catches. For each species and gear type, we produced log-likelihood
profiles for the instantaneous rate of change in relative abundance through time. Raw catches were generally lower for both
species in the later surveys.C. leucas were not captured in beach seines since the 1950s andA. spatula were rarely captured in trawls or seines since the 1970s. Likelihood profiles of changes in abundance forC. leucas andA. spatula showed very large declines in both species since 1953.C. leucas declined by 98.6% (95% CI: 73.4–99.9%) in gillnets and became functionally extirpated in beach seines with a decline of 99.9%
(95% CI: 23–99.9%). Among all gears,C. leucas declined by the same rate as in gillnets. The decline inA. spatula was also large with a decrease of 98.6% (95% CI: 73.4–99.9%) in beach seines and a decline of 99.2% (95% CI: 54.8–99.9%)
in trawls since 1953. Catches ofA. spatula in gillnets did not show a significant change over the study period. The continued decline of these two apex predators could
seriously affect efforts to restore this degraded estuarine ecosystem. 相似文献
14.
Mark L. Botton Christina P. Colón John Rowden Susan Elbin Debra Kriensky Kim McKown Matthew Sclafani Robert Madden 《Estuaries and Coasts》2018,41(4):974-987
Restoration of horseshoe crab spawning habitats through beach nourishment may be considered as a potential strategy to enhance reproductive success in areas where estuarine beaches have been lost to coastal erosion and development. The US Army Corps of Engineers performed a beach nourishment project at Plumb Beach (Jamaica Bay, Brooklyn, NY) in 2012 to stabilize the shoreline. While the addition of sand was done to protect infrastructure, it created an opportunity to examine the responses of American horseshoe crabs (Limulus polyphemus) to beach nourishment using a BACI (before-after control impact) design. During Spring 2012, before beach nourishment, horseshoe crabs made minimal use of the highly degraded western section of Plumb Beach in comparison to a nearby reference site, as quantified by numbers of spawning adults at high tide and densities of horseshoe crab eggs in core samples. In the first post-nourishment field season (Spring 2013), there was no detectable increase in horseshoe crab spawning activity on the newly restored beach. In 2014 and 2015, the density of spawning females began to increase at the nourished beach, although their numbers and especially the density of horseshoe crab eggs remained much lower than at the reference site. Three years after beach nourishment, differences in sediments texture (mean grain diameter, percent gravel, sorting, skewness, and hardness) were still evident between the nourishment and reference sites. Our results suggest that (1) at this site, beach nourishment appeared to bring about only slow increases in horseshoe crab spawning density after several seasons and (2) subtle differences in beach geomorphology over relatively short distances can be detected by horseshoe crabs and may underlie their selection of specific nesting sites. 相似文献
15.
Dreissena larval fluxes were studied in the lower stretch of the Seine River in 1996–1998. Fluxes reached 150×1012 ind d−1, representing a larval concentration of 5,000 ind l−1 in the Seine estuary. We showed that a sampling frequency with a 3-d interval allowed us to adequately estimate the annual production of larvae. The water residence time in the Seine River and estuary is sufficient for theDreissena larvae to complete their cycle and settlement. High abundance of the larvae in the plankton samples from the Seine River and its estuary showed the existence of a large community of benthic adults, known to be powerful filter-feeders. The progenitor population and the geographical extent of the adultDreissena were estimated from cohort analyses of the planktonic larvae. The maximum density ofDreissena was found in the highly channelized part of the estuary (up to 4,500 ind m−2). Estimated values were compared with concentration of mussels in the benthic traps and samples. Calculated filtration rates of benthic mussels were compared with those of larvae at different stages and with filtration of the zooplankton community. The impact of theDreissena was much higher than that of zooplankton; the filtration of the larvae exceeded that of adults during short periods of maximum larval emission. 相似文献
16.
The Delaware Bay contains the world’s largest population of horseshoe crabs, which constitute an ecologically significant component of this estuarine ecosystem. The North Atlantic speciesLimulus polyphemus has an extensive geographical distribution, ranging from New England to the Gulf of Mexico. Recent assessments of the Delaware Bay population based on beach spawning and trawling data have suggested a considerable decrease in the number of adult animals since 1990. Considerable debate has centered on the accuracy of these estimates and their impact on marine fisheries management planning. Compounding this problem is the lack of information concerning the genetic structure of Atlantic horseshoe crab populations. This study assessed patterns of genetic variation within and between the horseshoe crab populations of Delaware Bay and Chesapeake Bay, using both Random Amplification of Polymorphic DNA (RAPD) and DNA sequence analysis of the mitochondrial cytochrome oxidase I gene (COI). We examined 41 animals from Delaware Bay and 14 animals from the eastern shore of Chesapeake Bay. To provide high quality, uncontaminated genomic DNA for RAPD analysis, DNA was isolated from hemocytes by direct cardiac puncture, purified by spin column chromatography, and quantified by agarose gel electrophoresis. RAPD fingerprints revealed a relative paucity of polymorphic fragments, with generally homogeneous banding patterns both within and between populations. DNA sequence analysis of 515 bases of the 5′ portion of the mitochondrial COI gene showed haplotype diversity in the Chesapeake Bay sample to be significantly higher than in the Delaware Bay sample, despite the larger size of the latter. Haplotype analysis indicates minimal contemporary gene flow between Delaware Bay and Chesapeake Bay crab populations, and further suggests that the Delaware Bay population is recovering from a recent population decline. 相似文献
17.
The European green crab (Carcinus maenas) is invasive on the U.S. West Coast. This study uses a high-resolution circulation model to determine the likelihood that
green crab larvae spawned in Willapa Bay, Washington could be retained by circulation and behavior long enough to reach maturity
and resettle within the bay. A particle-tracking method (the “diffusive Lagrangian return map”) is presented that makes it
possible to track the dispersion of hundreds of thousands of model larvae—each subject to three-dimensional advection, vertical
turbulent diffusion, and imposed vertical migration behavior—over their full 30–50 days development time with modest computational
resources. Larvae spawned in summer show significant retention (5–40%) in the southern and western portions of the bay, including
the Stackpole shoals near the mouth, the area most likely to be colonized by late-stage megalopae arriving from the coastal
ocean. Larvae spawned in spring show much less retention throughout the bay because of (1) increased flushing caused by increased
river input relative to summer conditions and (2) longer development times caused by lower water temperatures. The role of
larval swimming behavior is secondary to hydrodynamics in setting these spatial and seasonal patterns of retention. 相似文献
18.
Marshes are important habitats for various life history stages of many fish and invertebrates. Much effort has been directed at restoring marshes, yet it is not clear how fish and invertebrates have responded to marsh restoration. The blue crab,Callinectes sapidus, uses marsh habitats during much of its benthic life. We investigated the response of blue crabs to marsh restoration by comparing crab abundance (catch per unit effort), mean size and size frequency distribution, sex ratio, and molt stages of crabs in recently restored marshes that were former salt hay farms to that of adjacent reference marshes with similar physical characteristics in the mesohaline portion of Delaware Bay. Field sampling occurred monthly (April–November) in 1997 and 1998 using replicate daytime otter trawls in large marsh creeks and weirs in smaller intertidal marsh creeks. Blue crabs were either equal or more abundant, the incidence of molting was in most months similar, and population sex ratios were indistinguishable in restored and reference marshes, suggesting that the restored areas attract crabs and support their growth. Site location had a greater effect on the sex ratio of crabs such that marshes closer to the mouth of the bay contained a higher percentage of adult female crabs. In each annual growing season (April–July), the monthly increase in crab size and, in some months (June–July), the incidence of molting at the restored sites was greater than the reference sites, suggesting that the restored sites may provide areas for enhanced growth of crabs. These results suggest that blue crabs have responded positively to restoration of former salt hay farms in the mesohaline portion of Delaware Bay. 相似文献
19.
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. 相似文献
20.
Spring and Summer Larval Fish Assemblages in the Surf Zone and Nearshore off Northern New Jersey,USA
Kenneth W. Able Dara H. Wilber Angela Muzeni-Corino Douglas G. Clarke 《Estuaries and Coasts》2010,33(1):211-222
Larval fish use of surf zone and nearshore habitats at northern latitudes has received little attention. Consequently, potential
impacts of beach nourishment and other forms of disturbance are not well understood. This study, on a northwestern Atlantic
coastline spanning May through July over 4 years, demonstrates that recently hatched larvae are common in both surf zone and
nearshore habitats. Taxonomic compositions of surf zone and nearshore assemblages were similar to each other and those from
an adjacent estuary. An influence of upwelling events was apparent in coincident changes in abundance and/or size of several
species in the surf zone. Other changes over the late spring–summer transition, including buoyancy-driven flows from the Hudson
River plume, demonstrate the dynamic nature of larval fish assemblages in the New York Bight area. 相似文献