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1.
Jessica M. Reichmuth Ross Roudez Terry Glover Judith S. Weis 《Estuaries and Coasts》2009,32(2):298-308
Populations living in contaminated environments may exhibit behavioral changes that can alter predator–prey interactions.
Blue crabs from the contaminated Hackensack Meadowlands (HM) had reduced ability to capture juvenile blue crabs and adult
mummichogs (both active prey) compared with crabs from a reference site (Tuckerton (TK)). However, they consumed equivalent
amounts of ribbed mussels and fiddler crabs, which are less active prey. Crabs may have reduced coordination rather than appetite
or motivation. The lab data are supported by stomach analysis of field-caught crabs. HM crab stomachs contained ∼60% algae,
plant material, detritus, and sediment and much lower weights of crab, fish, and other live food than TK crabs. However, the
relative absence of bivalves in their diet may reflect reduced amounts available. When TK crabs were caged in HM or fed food
from HM in the lab for 8 weeks, their prey capture ability declined significantly, and mercury in their muscle tissue increased
significantly, indicating that environmental factors were responsible for the behavioral differences. When HM crabs were caged
in TK or fed fish from TK in the lab for 8 weeks, their prey capture ability improved significantly. Mercury levels were variable
and did not show a significant decrease. 相似文献
2.
Florencia Botto Gabriela Palomo Oscar Iribarne Mariano M. Martinez 《Estuaries and Coasts》2000,23(2):208-215
Southwestern Atlantic estuaries (Southern Brazil to Northern Patagonia, Argentina) are characterized by the presence of an intertidal burrowing crab Chasmagnathus granulata. This crab species is an important bioturbator which lives in large assemblages and excavates semi-permanent burrows that affect sediment characteristics. Our observations showed that distribution of the crabs in the Mar Chiquita coastal lagoon, Argentina (37°45′S, 57°26′W) affected habitat use and feeding success of migratory shorebirds. During the migratory season the two-banded plover (Charadrius falklandicus) foraged more frequently inside crab beds, and yellowlegs (Tringa flavipes and T. melanoleuca) fed more freqeuntly outside crab beds. Focal observations on the feeding behavior of the white-rumped sandpiper (Calidris fuscicollis) and the two-banded plover inside and outside crab beds showed that the plover was a visual searcher and captured more prey inside crab beds, and the white-rumped sandpiper was a tactile feeder. Although consumption rates (prey min?1) did not differ between sites, their efficiency (prey probe?1) inside crab beds was less. These differences were probably related to changes in sediment characteristics and prey behavior, which vary with crab activity. Burrowing crabs alter the suitability of intertidal habitats used by shorebirds in southwestern Atlantic estuaries. We believe that the same process could be occurring with other burrowing curstaceans such as thalassinidean shrimps in other estuaries of the world and could have important implications for management of flats for shorebirds. *** DIRECT SUPPORT *** A01BY090 00007 相似文献
3.
Average summer densities of the xanthid crab,Eurytium limosum, in an intertidal salt marsh on Sapelo Island, Georgia were in the range of 7.5 to 80.0 individuals m?2. Crab densities were lowest in wet, lowlying marsh and highest in well-drained creekbank and mussel mound habitats. An analysis of crab stomach contents indicated that feeding occurred mostly around high tide, especially at night. Although the diet included some plant material,Eurytium limosum is primarily predatory and consumed crabs, polychaetes, ostracods, bivalves, and snails. In the laboratory, under simulated low-tide field conditions, both small (11–15 mm carapace width) and large (20–37 mm CW)Eurytium could capture and consume young killifish (Fundulus heteroclitus). Large crabs consumed the entire size range (7–19 mm total length) of larval/juvenile fish offered, but small crabs did not prey upon fish >11.5 mm TL. The potential importance ofE. limosum as a predator on young killifish may not be realized in the field because alternative prey are available and the crabs feed primarily at high tide, when young killifish are dispersed in the water column and are less vulnerable to benthic predators. 相似文献
4.
Feeding habits, seasonal diet variation, and predator size-prey size relationships of red drum (Sciaenops ocellatus) were investigated in Galveston Bay, Texas through stomach contents analysis. A total of 598 red drum ranging from 291–763 mm total length were collected and their stomach contents analyzed during fall 1997 and spring 1998. The diet of red drum showed significant seasonal patterns, and was dominated by white shrimp (Penaeus setiferus) during fall and gulf menhaden (Brevoortia patronus) during spring. Blue crab (Callinectes sapidus) was an important component of red drum diets during both seasons. Significant differences existed between prey types consumed during fall and spring as red drum diet reflected seasonal variation in prey availability. Predictive regression equations were generated to estimate original carapace width of blue crabs from several measurements taken from carapace fragments recovered in red drum stomachs. Regressions were highly significant (r2>0.97) and increased the number of blue crabs with size information nearly three fold. Predator size-prey size relationships were determined for red drum feeding on white shrimp, gulf menhaden, and blue crab. Although regression slopes were statistically significant, prey sizes increased only slightly with increasing red drum size. Comparisons of prey sizes consumed by red drum with sizes occurring in the field indicate that red drum feed in nearshore shallow water habitats, which serve as nursery areas for many juvenile fishes and crustaceans. Our findings demonstrate that red drum feed on several prey species of commercial and recreational value and may have important effects on estuarine community structure. 相似文献
5.
Atlantic croaker is one of the most abundant demersal fish in Chesapeake Bay. Until recently, when substantial declines in
abundance have occurred, high biomass supported elevated fisheries landings. Therefore, study of the diet of Atlantic croaker
is important to understand its own dynamics and its role in the Chesapeake Bay ecosystem. Patterns in the diet of croaker
varied annually, seasonally, and spatially, but were not strongly correlated with any measured environmental variables. Although
the majority of the diet of croaker consisted of polychaetes and other benthic items, about 20% of the croaker diet by weight
consisted of anchovy and other fishes. Croaker consumption of anchovy is likely a result of crepuscular feeding that has not
been captured in previous studies that sampled during the day and with bottom trawls. Thus, croaker influences both the benthic
and pelagic components of the Chesapeake Bay food web and incorporating such diel patterns in diet may increase the reliability
of fishery ecosystem models. 相似文献
6.
Kirstin K. Holsman David A. Armstrong David A. Beauchamp Jennifer L. Ruesink 《Estuaries and Coasts》2003,26(4):1155-1173
Complex intertidal habitats characteristic of northeastern Pacific coastal estuaries provide critical nursery environments for young-of-the-year Dungeness crab,Cancer magister, yet their role in supporting subsequent year classes remains unclear. SubadultC. magister (40–130 mm; 1+ and >1+ year classes), which reach densities as high as 4,300 crabs ha?1 in subtidal channels during low tides, migrate during flood tides from subtidal refuges into intertidal habitats to forage. As with other brachyuran species that undertake extensive tidally-driven migrations, intertidal foraging may contribute significantly to the energy budget of subadultC. magister. In order to explore the energetic incentive for intertidal migrations by subadult crabs, we developed an ontogenetically-based bioenergetics model for crabs within Willapa Bay, Washington. The model showed that energetic demand varied spatially across the bay, with the highest average energetic demand of a population of subadult crabs (2.13×106 kJ ha?1) occurring in a habitat stratum termed lower side channel (LSC) and characterized by relatively little subtidal area and extensive intertidal flats. Comparison of model results with subtidal prey production revealed that the latter could not satisfy subadultC. magister energetic demands, especially in LSC where modeled crab predation depleted subtidal prey biomass within 17 simulation days. We estimate that 1 ha of subtidal crabs from LSC would minimally require an additional 1.6 ha of intertidal area to satisfy energetic demands without depleting prey biomass. Our model results support the assertion thatC. magister make regular migrations to forage on productive intertidal flats, and suggest that intertidal foraging may contribute significantly to the diet of subadult crabs in coastal estuaries. 相似文献
7.
An increasing number of examples suggest that interactions among introduced species are ecologically important and relevant to the management of invaded systems. We investigated the potential for the introduced cephalaspidean sea slug Philine orientalis to interfere with the feeding of the introduced European green crab (Carcinus maenas) and the native Dungeness crab (Cancer magister). We observed co-occurrence of crab species and P. orientalis at field sites in Bodega Harbor and Tomales, San Pablo, and San Francisco Bays. In laboratory and field experiments, we determined whether crab feeding was suppressed by P. orientalis and the duration of this suppression for individual crabs. We also used foraging response models to explore changes in the feeding rate of crabs with varying densities of P. orientalis and small bivalve prey. We found that P. orientalis deterred predation by green and Dungeness crabs on small clams in laboratory feeding trials, but not in field experiments with green crabs and P. orientalis. Foraging models predicted that P. orientalis would only affect crab feeding in the field under specific conditions of crab, P. orientalis, and prey densities. These foraging models bridged an important gap between lab and field experiments and allowed us to predict how changes in species abundances at two trophic levels might alter the importance of crab suppression by P. orientalis. 相似文献
8.
Diane J. Brousseau Anna E. Murphy Nicole P. Enriquez Kara Gibbons 《Estuaries and Coasts》2008,31(1):144-151
The Asian shore crab, Hemigrapsus sanguineus, is a recent and particularly successful introduction to the east coast of the USA. Little research has been done on the
utilization of Asian shore crabs for food by native species, a potential form of biocontrol. Over a 4-year period, we examined
the gut contents of cogeners, Fundulus heteroclitus and Fundulus majalis, collected from two embayments in western Long Island Sound for the presence of juvenile H. sanguineus. Frequency (percent) of occurrence of food items in the guts of both species varied over year and study site. Asian shore
crabs were consumed more often by F. heteroclitus than by F. majalis, but predation pressure by both species was low. Only 13% of F. heteroclitus and 7.7% of F. majalis found with food in their guts had ingested Asian shore crab remains. Of those, 1/3 had consumed whole crabs; the rest had
only autotomized appendages in their guts. The mean carapace width of juvenile Asian shore crabs ingested by F. heteroclitus was 3.59 ± 2.22 mm (N = 33). Results of our study on killifish predation support the hypothesis that H. sanguienus abundance is partly explained by reduced impact of native predators (i.e., the “enemy release hypothesis”). Predation pressure
of other potential enemies on both planktonic and benthic stages of the Asian shore crab must be investigated, however, to
understand the full impact of predation on H. sanguineus population dynamics. 相似文献
9.
Rhythmic movements in response to tidal cycles are characteristic of infaunal inhabitant of intertidal soft-bottoms, allowing
them to remain in the area with best living conditions. The effect of bioturbators as modifier of local environmental conditions
and thus of gradients in intertidal habitats, has not been investigated yet. The Atlantic estuarine intertidal areas are dominated
by the burrowing crabChasmagnathus granulatus that generates strong environmental heterogeneity by affecting the physical-chemical characteristics of the sediment. The
comparison between intertidal areas with and without crab shows that sediments in the crab beds remain more humid, softer,
and homogeneous across the intertidal and along the tidal cycle than areas without crabs. The densities of infauna were higher
at high intertidal zones in crab beds than in similar areas without crabs. Infaunal organisms performed vertical movements
into the sediment following the tidal cycle that were always of higher magnitude in habitats without crabs. Infaunal species
tend to spend most of the time buried into the sediment in the crab bed. Migratory shorebirds use the Atlantic estuarine environments
as stopover or wintering sites. They feed (mainly on polychaetes) in the low intertidal zones of both habitats (with and without
crabs), but they also feed in the upper intertidal of the crab bed; polychaete per capita mortality rate is higher in the
upper part of the crab bed. Environmental heterogeneity produced by crab disturbance has an effect on the infaunal behavior,
risk of mortality, and the zonation pattern. This is another example of the ecosystem engineering ability of a burrowing intertidal
species. 相似文献
10.
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
11.
Kirt E. Moody 《Estuaries and Coasts》2003,26(3):759-764
Blue crabsCallinectes sapidus in lower Chesapeake Bay are subject to high rates of predation during the late summer of their first year of growth as they
migrate out of vegetated nursery habitats. Predators, potentially contributing to this pattern, were identified in video-recorded
field observations of tethered juvenile crabs (20–25 mm carapace width). Predators were also tested in large laboratory tanks
containing similarly-sized untethered crabs as prey. Seven different predators attacked tethered crabs in the field. Only
two predators, larger blue crabs and northern puffers,Sphoeroides maculatus, consistently succeeded in preying on crabs in both field and laboratory settings. These results confirm the importance of
cannibalism on juvenile blue crabs and identify puffers as a potentially overlooked source of predation pressure. 相似文献
12.
Scott Zengel Steven C. Pennings Brian Silliman Clay Montague Jennifer Weaver Donald R. Deis Michelle O. Krasnec Nicolle Rutherford Zachary Nixon 《Estuaries and Coasts》2016,39(4):1154-1163
The Deepwater Horizon oil spill was the largest marine oil spill in US waters to date and one of the largest worldwide. Impacts of this spill on salt marsh vegetation have been well documented, although impacts on marsh macroinvertebrates have received less attention. To examine impacts of the oil spill on an important marsh invertebrate and ecosystem engineer, we conducted a meta-analysis on fiddler crabs (Uca spp.) using published sources and newly available Natural Resources Damage Assessment (NRDA) and Gulf of Mexico Research Initiative (GoMRI) data. Fiddler crabs influence marsh ecosystem structure and function through their burrowing and feeding activities and are key prey for a number of marsh and estuarine predators. We tested the hypothesis that the spill affected fiddler crab burrow density (crab abundance), burrow diameter (crab size), and crab species composition. Averaged across multiple studies, sites, and years, our synthesis revealed a negative effect of oiling on all three metrics. Burrow densities were reduced by 39 % in oiled sites, with impacts and incomplete recovery observed over 2010–2014. Burrow diameters were reduced from 2010 to 2011, but appeared to have recovered by 2012. Fiddler crab species composition was altered through at least 2013 and only returned to reference conditions where marsh vegetation recovered, via restoration planting in one case. Given the spatial and temporal extent of data analyzed, this synthesis provides compelling evidence that the Deepwater Horizon spill suppressed populations of fiddler crabs in oiled marshes, likely affecting other ecosystem attributes, including marsh productivity, marsh soil characteristics, and associated predators. 相似文献
13.
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
14.
Beach-cast wrack of marine origin is considered a spatial subsidy to the marine-terrestrial transition zone. We found that
the wrack line on sand and gravel beaches of Vancouver Island was frequented by intertidal purple shore crabs,Hemigrapsus nudus (Dana 1851) and densely colonized by detritivorous talitrid amphipods. Amphipods spend the day buried in sand and forage
on beach wrack during the night.H. nudus were found in supratidal wrack putches immediately after nightly high tides in field censuses, but spent most of the day
and ebb tides either submerged subtidally or hidden underneath intertidal rocks and boulders. In feeding trials, intertidal
shore crabs were capable of preying on talitrid amphipods. We considerH. nudus an omnivore feeding on both fresh and decaying macroalgae as well as animal prey. Although living supratidally, amphipods
were significantly preferred over intertidal littorine snails by foraging shore crabs. Handling time of amphipods was significantly
shorter than for littorine snails. While amphipods had a reduced risk of predation byH. nudus when buried in the sand, foraging undern eath wrack patches did not reduce predation pressure on amphipods by shore crabs.
Rates of amphipod consumption by shore crabs were higher at darkness than daylight. In addition to an apparent day-night rhythm,
tidal height and time elapsed since previous high tide had a significant influence on shore crab density wrack. We conclude
that beach-cast wrack acts as a spatial subsidy by virtue of providing a valuable food source to talitrid amphipods, which
are in turn consumed by shore crabs that ride the nightly high tide into supratidal wrack patches to reduce the risk of passing
bare sand on theiry way to a feeding habitat rich in valuable prey. 相似文献
15.
Benthic resource utilization by, red drum (Sciaenops ocellatus) and spotted seatrout (Cynoscion nebulosus) was studied in a restored, mangrove-rimmed impoundment (Cabbagehead Bayou) of Upper Tampa Bay, Florida, and in a nearby, natural site of unaltered tidal regime (Double Branch Bay). Diets of fish captured from August 1990 to May 1992 were determined from stomach content analysis. Simultaneously, food availability was evaluated by sampling benthic macroinvertebrates, mobile decapods, and small fish. Red drum and spotted seatrout utilized the restored habitat 1 yr after it was opened to tidal influence. Both species also were collected in the natural mangrove. Although there were noted differences in benthic assemblages between the two sites, red drum and spotted seatrout exhibited flexibility in diet, feeding on abundant and accessible prey. The high abundance of microcrustacea, such as amphipods, on detritus accumulated in the restored habitat constituted a main food resource for both fish species. Major food items in the diet of small (<200 mm) red drum were amphipods, mysids, and nereid and arenicolid polychaetes. Large (200–590 mm) red drum fed on polychaetes, xanthid crabs, palaemonid shrimp, and small fishes. Spotted seatrout preyed primarily upon mysids, shrimp, and small fishes, and to a lesser extent, upon a nereid polychaete. Our findings on fish feeding in a restored mangrove impoundment indicated that the detrital-associated benthic community is utilized by reinvading fish within a short time period, suggesting that not only habitat but food resources were augmented by the reopening of this wetland. 相似文献
16.
Amanda W. J. Demopoulos Nicole Cormier Katherine C. Ewel Brian Fry 《Estuaries and Coasts》2008,31(2):371-381
The mangrove or mud crab, Scylla serrata, is an important component of mangrove fisheries throughout the Indo-Pacific. Understanding crab diets and habitat use should
assist in managing these fisheries and could provide additional justification for conservation of the mangrove ecosystem itself.
We used multiple chemical tracers to test whether crab movements were restricted to local mangrove forests, or extended to
include adjacent seagrass beds and reef flats. We sampled three mangrove forests on the island of Kosrae in the Federated
States of Micronesia at Lelu Harbor, Okat River, and Utwe tidal channel. Samples of S. serrata and likely food sources were analyzed for stable carbon (δ13C), nitrogen (δ15N), and sulfur (δ34S) isotopes. Scylla serrata tissues also were analyzed for phosphorus (P), cations (K, Ca, Mg, Na), and trace elements (Mn, Fe, Cu, Zn, and B). Discriminant
analysis indicated that at least 87% of the crabs remain in each site as distinct populations. Crab stable isotope values
indicated potential differences in habitat use within estuaries. Values for δ13C and δ34S in crabs from Okat and Utwe were low and similar to values expected from animals feeding within mangrove forests, e.g.,
feeding on infauna that had average δ13C values near −26.5‰. In contrast, crabs from Lelu had higher δ13C and δ34S values, with average values of −21.8 and 7.8‰, respectively. These higher isotope values are consistent with increased crab
foraging on reef flats and seagrasses. Given that S. serrata have been observed feeding on adjacent reef and seagrass environments on Kosrae, it is likely that they move in and out of
the mangroves for feeding. Isotope mixing model results support these conclusions, with the greatest mangrove ecosystem contribution
to S. serrata diet occurring in the largest mangrove forests. Conserving larger island mangrove forests (> 1 km deep) appears to support
crab foraging activities. 相似文献
17.
Seasonal variation in aquatic food web structure at Mad Island Marsh, Matagorda Bay, Texas, was examined using dietary information
obtained from the analysis of gut contents from large samples of fish and crustacean specimens. Unique aspects of this study
include the use of large samples of consumer gut contents (n=6,452), long-term sampling (bimonthly surveys over 18 mo), and
standard methods of data collection and analysis facilitating comparisons with other aquatic food webs. Dietary data were
partitioned for analysis into warm (summer) and cold (winter) seasons. Most consumers fed low in the food web, with trophic
levels ranging from about 2 to 3.5 during both summer and winter. Vegetative detritus was more important in macroconsumer
diets than live algae and macrophytes. Low trophic levels of consumers reflected the important role of abundant detritivores
(e.g., striped mulletMugil cephalus, Gulf menhadenBrevortia patronum, and macroinvertebrates) in linking detritus to top predators via short food chains, a finding consistent with many other
estuarine food web studies. Despite changes in community composition and population size structure of certain species, most
food web properties revealed comparatively little seasonal variation. The summer food web had more nodes (86), more links
(562), a higher density of links as indicated by connectance (0.08), and a slightly higher predator: prey ratio (0.51) compared
to the winter food web (75 nodes, 394 links, connectance = 0.07, predator: prey ratio = 0.47). Proportions of top (0.06–0.07),
intermediate (0.75–0.76), and basal (0.19) species did not vary significantly between seasons, but mean trophic level was
higher during summer. Addition of feeding links based on information from the literature increased connectance to 0.13 during
both seasons; other web parameters had values similar to those obtained for our directly estimated food webs. Seasonal variation
in food web structure was influenced by changes in community composition (e.g., influxes of postlarval estuarine-dependent
marine fishes during winter), availability of resources (e.g., more submerged macrophytes and amphipods during summer), and
size structure and ontogenetic diet shifts of dominant consumer taxa. Our findings suggest that some basic properties of estuarine
food web are resilient to seasonal changes in population and community structures and food web architecture. 相似文献
18.
Florencia Botto Agustina Mendez-Casariego Macarena Valiñas Oscar Iribarne 《Estuaries and Coasts》2008,31(1):134-143
We show that, as previously described, there are conflicts between areas used by people and shorebirds. However, we propose
that burrowing organisms add complexity to the shorebird–human interaction that should be taken into account for management
and conservation. This is because SW Atlantic mudflats are dominated by high densities (up to 60 crabs m−2) of a strong bioturbator, the burrowing crab Neohelice granulata (=Chasmagnathus granulatus). These crabs affect the habitat use and foraging performance of shorebird species. The two-banded plover Charadrius falklandicus feed more in burrow areas whereas the yellowlegs Tringa spp. and the white-rumped sandpiper Calidris fuscicollis tend to avoid burrow areas. We evaluated the effect of human recreational activities on shorebirds, taking into account shorebird–crab
interaction, during shorebird migratory periods (November to April) of 2001, 2002, and 2003. This study was performed at the
Mar Chiquita coastal lagoon (37° 40′ S, Argentina). Results showed that people only rarely used the extensive soft bottom
intertidals dominated by burrowing assemblages of N. granulata because the soft sediments make walking difficult. Therefore, human impact is reduced for the two-banded plover. However,
for several migratory shorebirds that also avoid burrow areas, these areas act as suboptimal alternative areas when human
impact is important in their preferred habitats. When human activity is low, shorebirds remain foraging in the area but they
decrease their feeding intakes. The extensions of burrow areas differ among estuaries and are likely to generate between-estuaries
differences as stopover sites for shorebirds. Also, other species that form large burrowing assemblages can have a similar
impact on shorebird–human interactions. 相似文献
19.
Stable Isotopes Reveal Complex Changes in Trophic Relationships Following Nutrient Addition in a Coastal Marine Ecosystem 总被引:1,自引:0,他引:1
Complex links between the top-down and bottom-up forces that structure communities can be disrupted by anthropogenic alterations
of natural habitats. We used relative abundance and stable isotopes to examine changes in epifaunal food webs in seagrass
(Thalassia testudinum) beds following 6 months of experimental nutrient addition at two sites in Florida Bay (USA) with different ambient fertility.
At a eutrophic site, nutrient addition did not strongly affect food web structure, but at a nutrient-poor site, enrichment
increased the abundances of crustacean epiphyte grazers, and the diets of these grazers became more varied. Benthic grazers
did not change in abundance but shifted their diet away from green macroalgae + associated epiphytes and towards an opportunistic
seagrass (Halodule wrightii) that occurred only in nutrient addition treatments. Benthic predators did not change in abundance, but their diets were
more varied in enriched plots. Food chain length was short and unaffected by site or nutrient treatment, but increased food
web complexity in enriched plots was suggested by increasingly mixed diets. Strong bottom-up modifications of food web structure
in the nutrient-limited site and the limited top-down influences of grazers on seagrass epiphyte biomass suggest that, in
this system, the bottom-up role of nutrient enrichment can have substantial impacts on community structure, trophic relationships,
and, ultimately, the productivity values of the ecosystem. 相似文献
20.
We evaluated nekton habitat quality at 5 shallow-water sites in 2 Rhode Island systems by comparing nekton densities and biomass,
number of species, prey availability and feeding, and abundance of winter flounderPseudopleuronectes americanus. Nekton density and biomass were compared with a 1.75-m2 drop ring at 3 sites (marsh, intertidal, and subtidal) in Coggeshall Cove in Narragansett Bay and two subtidal sites (eelgrass
and macroalgae) in Ninigret Pond, a coastal lagoon. We collected benthic core samples and examined nekton stomach contents
in Coggeshall Cove. We identified 16 species of fish, 16 species of crabs, and 3 species of shrimp in our drop ring samples.
A multivariate analysis of variance indicated differences in total nekton, invertebrates, fish, and winter flounder across
the five sites. Relative abundance of benthic invertebrate taxa did not match relative abundance of prey taxa identified in
the stomachs. Nonmetric multidimensional scaling plots showed groupings in nekton and benthic invertebrate prey assemblages
among subtidal, intertidal, and marsh sites in Coggeshall Cove. Stepwise multiple regression indicated that biomass of macroalgae
was the most important variable predicting abundance of nekton in Coggeshall Cove, followed by elevation and depth. In Rhode
Island systems that do not experience chronic hypoxia, macroalgae adds structure to unvegetated areas and provides refuge
for small nekton. All sites sampled were characterized by high abundance and diversity of nekton pointing to the importance
of shallow inshore areas for production of fishes and decapods. Measurements of habitat quality should include assessment
of the functional significance of a habitat (this can be done by comparing nekton numbers and biomass), some measure of habitat
diversity, and a consideration of how habitat quality varies in time and space. 相似文献