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1.
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   

2.
Fundulus luciae was collected for a year at Fox Creek Marsh and, occasionally, at other salt marshes along the York River, Virginia. It occurred in high intertidal areas in brackish, sometimes oxygen deficient shallow ditches, mudholes and tidal rivulets located in stands ofSpartina alterniflora. Preserved specimens were examined to determine the reproductive season, fecundity, diet and associated metazoan parasites of the species. Developing ova were present from mid-April to mid-August and exhibited a broad size range; the number of large ova (>1.6 mm diameter) never exceeded 16 per female. Stomach contents consisted mainly of detritus, diatoms, ostracods, dipterans and copepods. All major metazoan parasite groups except Cestoda were represented onF. luciae; Monogenea were most numerous, with 57.2% incidence. Eggs and larvae were described. Preserved larvae ofF. luciae were distinguished from those ofF. heteroclitus by their dorsal pigmentation pattern. It was concluded thatF. luciae, a purportedly rare species, is not rare, but probably restricted to high intertidal salt marshes where it may have been previously overlooked.  相似文献   

3.
The objective of this study was to determine if exploitative competition between between juvenile Chinook salmon (Oncorhynchus tshawytscha) and threespine stickleback (Gasterosteus aculeatus) reduces the foraging opportunity of juvenile Chinook salmon in tidal channels of the Columbia River estuary. We sampled Chinook salmon and stickleback diets monthly and over a diel cycle in spatially distinct emergent marshes of the Columbia River estuary. Diets of the two fish species did not differ among marsh systems, but both fish species exhibited diel and seasonal differences in diet composition. Diet overlap between the two fish species was greatest in March and June. Exploitative competition was unlikely based on a comparison between consumption rates and estimated invertebrate production.  相似文献   

4.
Food habits of the dominant fishes collected from 1974 to 1980 at eight locations in Elkhorn Slough, California, and the adjacent ocean were investigated. Epifaunal crustacea was the major prey group identified from stomach contents of more than 2,000 fishes, followed by epifaunal and infaunal worms, and molluscs. Overall, 18 fish species consumed 263 different prey taxa, ranging from 10 taxa to 125 taxa per fish species and including 99 crustacean, 56 polychaete, and 39 molluscan taxa. Mean prey richness was greatest at stations near the ocean and lowest at inshore stations. Detailed dietary data for all prey taxa were summarized as trophic spectra for each fish species. Trophic spectra represented functional groups of prey and were used for comparisons of dietary similarity. Cluster analyses, based on trophic spectra, resulted in four feeding guilds of fishes. Of 18 fish species, seven (Amphistichus argenteus, Leptocottus armatus, Embiotoca jacksoni, Clevelandia ios, Gillichthys mirabilis, Cymatogaster aggregata, andCitharichthys stimaeus) fed principally on epifaunal crustacea. Four species (Pleuronectes vetulus, Platichthys stellatus, Phanerodon furcatus, andMyliobatus californica) consumed mostly molluscs and infaunal worms. Two species (Psettichthys melanostictus andTriakis semifasciata) fed on mobile crustacea, and five species (Hyperprosopon anale, Engraulis mordax, Clupea pallasi, Atherinopsis californiensis, andAtherinops affinis) fed largely on zooplankton and plant material. Our results suggest that high food availability enhances the nursery function of imshore habitats, and emphasize the importance of invertebrate prey populations and the indirect linkage of plant production to the ichthyofaunal assemblarly marine immigrant species that are likely ‘estuarine dependent’.  相似文献   

5.
Quantifying the trophic dynamics of mesopredators in coastal habitats is an essential precursor to understanding their role in linking multiple trophic levels. Traditional dietary analyses may miss key aspects of a species’ feeding ecology and may thus fail to identify trophic linkages between predators and economically important prey populations. We applied stomach content and stable isotope analyses to estimate diet and trophic dynamics and investigated intraspecific dietary diversity of bonnetheads (Sphyrna tiburo) and red drum (Sciaenops ocellatus). Both juvenile and adult bonnetheads and juvenile red drum had diets comprised mainly of crustaceans, notably portunid crabs and penaeid shrimp, with varying degrees of dietary and isotopic niche overlap. Juvenile and adult bonnetheads had high dietary and isotopic niche overlap, whereas the degree of overlap between bonnetheads and red drum varied. Our findings indicate that bonnetheads are dietary specialists whereas red drum are dietary generalists. Further analysis identified intraspecific variability in the diet of each species; adult bonnetheads had the highest prey diversity whereas red drum had the lowest. We show that dietary and isotopic niche overlap and intraspecific variation in diet exist among juvenile and adult bonnetheads and juvenile red drum, though to varying degrees. Our findings demonstrate the importance of fully examining the trophic ecology of species that share habitats and resources, both at individual and population levels.  相似文献   

6.
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   

7.
The temperature tolerance and resistance times of postlarval (<25 mm SL) and small juvenile spot,Leiostomus xanthurus, from the Cape Fear Estuary, North Carolina were tested in the laboratory. Critical thermal maximum techniques were used to determine first equilibrium loss (FEL) and critical thermal maximum (CTM) end points and thermal shock methods were used to determine 96-h upper incipient lethal temperatures (LT50). Acclimation temperatures ranged from 10 to 35°C and acclimation salinities were 10, 20 and 30‰. A quadratics model was fit to the CTM and FEL data; r2 values were 0.924 and 0.928 respectively. Acclimation salinity, estimated weight, acclimation salinity by acclimation temperature interaction and acclimation temperature by estimated weight interaction were the significant components of the CTM model. Predicted CTM values ranged from 30°C at 10 °C and 30‰ acclimation to just over 40°C at 30 °C and 30‰ acclimation. Acclimation temperature, acclimation temperature squared, estimated weight and acclimation temperatures by estimated weight interaction were the significant components of the FEL model. Predicted FEL values ranged from around 28°C at 10°C and 10‰ acclimation to about 39°C at 30°C and 30‰ acclimation. The 96-h LT50 values of spot acclimated to 20‰ increased linearly with acclimation temperature to 25°C. From about 25 to 35°C, LT50 values increased very little with acclimation temperature. The ultimate upper incipient lethal temperature of postlarval and small juvenile spot was estimated at 35.2°C. Increased salinity increased resistance time but decreased LT50 estimates. Thermal shock tests were better for predicting the effects of thermal addition than were CTM tests.  相似文献   

8.
The habitats utilized by small juvenile (<40 mm carapace length, CL) lobsters (Homarus americanus) are poorly known. We discovered and studied an undescribed juvenile lobster habitat in Nauset Marsh, Cape Cod. Juvenile lobsters (X=26.7 mm carapace length, 6 to 72 mm, n=38) were collected from suction samples primarily 0144 01 in “peat reef” habitats during the period from August 1985 through October 1986. The reefs consisted of large blocks ofSpartina alterniflora peat that had separated from the marsh surface and fallen into adjacent subtidal marsh channels. The smallest lobsters (6 to 7 mm CL) were collected from peat reefs in October 1985, and April and July 1986. In these habitats, juvenile lobster density averaged 2.5 individuals m?2 (range 0–5.7) in suction samples. Peat reef habitats occur in other salt marshes in the northeastern United States and may be an important nursery habitat for small juvenile lobsters.  相似文献   

9.
Measurements of surface sediment accretion have been obtained for Hut Marsh, Scolt Head Island, Norfolk, England, using sand marker horizons. More than eighty 1-m2 marker sites were deployed in October 1983, and vertical accretion measured at them in April and October 1986 and April 1987. Elevations relative to Ordnance Datum were established by levelling each site at the time of deployment. Data collected by Steers between 1935 and 1957 on the same marsh show a clear relationship between marsh elevation and sedimentation. The results of the current more detailed study, presented as mean annual accretion rates, indicate a complex pattern of sediment distribution at this macrotidal location. These data, together with the results of tidal flow monitoring in the creeks on Hut Marsh, show the importance of spatial and temporal patterns of sediment delivery and variations in depositional processes in determining the distribution of sedimentation across the marsh surface.  相似文献   

10.
Patterns in seasonal abundance (no. per m2 surface area), growth and biomass (g per m2 surface area) of an annual fish, the Atlantic silverside, Menidia menidia (L.) were investigated in a marsh and more seaward bay region of Essex Bay, Massachusetts from August 1976 to May 1978 using a quantitative beach seining technique. Silverside abundance varied greatly by season and year class during the study period. Abundance was high in 1976 but winter mortality (99%) left an adult density of only .01 per m2 surface area in the marsh during spring 1977. Resultant 1977 year class density in the marsh was 1.88 per m2 by late fall 1977 but winter mortality again produced an adult density of .01 per m2 in spring 1978. Abundance was generally higher in the marsh than in the bay region especially during spring and late fall when catches in the bay were negligible. Based on catch rate comparisons, the summer and fall juvenile abundance of the 1976 year class was much higher than the juvenile abundance of the 1977 year class. Coincidentally, mean lengths and condition of the abundant 1976 year class in the late fall were significantly lower than those of the 1977 year class, suggesting density dependent population regulation. In both years, juveniles grew rapidly and reached full adult size by November when an offshore movement to deeper waters outside Essex Bay occurred. Biomass peaked in the marsh region in late fall 1977 at 7.8 g per m2 wet weight. Winter mortality was size selective, favoring larger individuals. The annual life history design of M. menidia including an offshore winter movement and high winter mortality suggests that silversides represent an important pathway of energy flow from marsh to offshore trophic systems.  相似文献   

11.
Juvenile spot,Leiostomus xanthurus (Pisces), were collected at 2-h intervals over two 48-h periods in a tidal creek in North Inlet, South Carolina, during July 1986. Gut fullness, dry gut contents weight as a percentage of fish wet weight, was measured to test the hypothesis that feeding intensity is randomly distributed through time. Spot were also collected and serially sacrificed from a holding tank to estimate their gut evacuation rate. Gut fullness was greatest during periods of ebb and high tides and was little affected by the amount of light available. Gut contents were evacuated at a rate of about 15% per hour in the laboratory, in close agreement with field emptying times of about 6 h from peak fullness to empty guts. A conservative estimate of daily ration for juvenile spot (19–42 mm standard length) was 4.5% of their live body weight per day. Studies of spot feeding ecology can be greatly affected by when fish are collected during the tidal cycle.  相似文献   

12.
The foraging ecology and diet of the green turtle, Chelonia mydas, remain understudied, particularly in peripheral areas of its distribution. We assessed the diet of an aggregation of juvenile green turtles at the northern edge of its range during winter months using two approaches. Stomach content analyses provide a single time sample, and stable isotope analyses integrate diet over a several-month period. We evaluated diet consistency in prey choice over time by comparing the results of these two approaches. We examined stomach contents from 43 juvenile green turtles that died during cold stunning events in St. Joseph Bay, Florida, in 2008 and 2011. Stomach contents were evaluated for volume, dry mass, percent frequency of occurrence, and index of relative importance of individual diet items. Juvenile green turtles were omnivorous, feeding primarily on seagrasses and tunicates. Diet characterizations from stomach contents differed from those based on stable isotope analyses, indicating the turtles are not feeding consistently during winter months. Evaluation of diets during warm months is needed.  相似文献   

13.
Invertebrate predation has been cited as the major factor determining post-settling survival of the soft-shell clam, Mya arenaria. Feeding studies on common mummichogs, Fundulus heteroclitus, in Essex Bay, Massachusetts, from July 1976 to June 1978 showed soft-shell clams to be an important diet item in fish greater than 55 mm TL. Biweekly quantitative seining from 16 April to 24 September 1977 revealed predation peaks in the spring and fall corresponding to March–April and June–July spawning periods for M. arenaria. In spring and fall 1977 and spring 1978, 38.5% of the male and 52.8% of the female mummichogs sampled over 55 mm TL averaged 6.77 and 7.32 clams per stomach respectively. The maximum number of clams per stomach was 49 (108 mm female), and 47 (100 mm male). Quantitative seining at low tide yielded mummichog densities from 0.35 to 6.04 fish/m2. Combining mummichog density estimates with soft-shell clam predation data gave a possible consumption of 546,000 M. arenaria per km low tide shoreline per day during peak predation periods. Results indicate mummichog predation may equal or exceed invertebrate predation as a major cause of small (<12 mm) soft-shell clam mortality in the Gulf of Maine.  相似文献   

14.
Over 968,000 adult Atlantic menhaden,Brevoortia tyrannus, were tagged from 1967 to 1969 and over 85,000 juvenile menhaden were tagged from 1969 to 1973. Recoveries of these tagged fish through 1975 provide direct evidence that Atlantic menhaden consist of a single population that over-winters in offshore waters off the southeastern coast of the United States, moves northward in spring and stratifies along the coast by age and size during summer, and moves southward in late autumn.  相似文献   

15.
Artificial fertilizers are contributing to the replacement of eelgrass (Zostera marina) by sea lettuce (Ulva lactuca) in estuaries of Prince Edward Island (PEI), Canada. In this study, we found that the nearshore fish community differed between areas dominated by these two vegetations within an estuary in every month sampled (April–August). Adult northern pipefish (Syngnathus fuscus), threespine stickleback (Gasterosteus aculeatus), blackspotted stickleback (Gasterosteus wheatlandi), and Atlantic silverside (Menidia menidia) were most strongly associated with eelgrass, while mummichog (Fundulus heteroclitus), ninespine stickleback (Pungitius pungitius), and American eel (Anguilla rostrata) were often more numerous in sea lettuce. Sea lettuce stations tended to have more young-of-the-year mummichog, fourspine stickleback (Apeltes quadracus), and Gasterosteus sp. than eelgrass stations but fewer young-of-the-year northern pipefish and Atlantic silverside. Fish richness and abundance were significantly lower in the sea lettuce than eelgrass habitat during August when benthic hypoxia occurred. We conclude that the loss of eelgrass from PEI estuaries will result in significant declines in fish biodiversity.  相似文献   

16.
The distribution of Fe3+ and Ga3+ between the two tetrahedral sites in three synthetic melilites has been studied by using 57Fe Mössbauer spectroscopy. In the melilite, (Ca2Ga2SiO7)50 (Ca2Fe3+GaSiO7)50 (mol %), the distribution of Fe3+ and Ga3+ in T1 and T2 sites is apparently random, which can be explained in terms of the electrostatic valence rule. However in the melilites, (Ca2MgSi2O7)52 (Ca2Fe3+GaSiO7)42 (Ca2Ga2SiO7)6 and (Ca2MgSi2O7)62 (Ca2Fe3+GaSiO7)36 (Ca2Ga2SiO7)2 (mol %), Fe3+ shows preference for the more ionic T1 site and Ga3+ for the more covalent T2 site. If the electronegativity of Ga3+ is assumed to be larger than that of Fe3+, the mode of distribution of Fe3+ and Ga3+ can be explained in terms of our previous hypothesis that a large electronegativity induces a stronger preference for the more covalent T2 site.  相似文献   

17.
Feeding habits ofMenidia peninsulae were analyzed monthly over a one year period and compared to planktonic prey available at the capture site. Three feeding stages were found: (1) In early spring, young-of-the-year fed on tychoplankton and detritus. (2) From late spring through winter,M. peninsulae preyed selectively on calanoid copepods and cypris larvae. (3) GravidM. peninsulae fed primarily on amphipods and larval silversides. In the Crystal River area,M. peninsulae reproduce in early spring. Silversides apparently migrate from the higher salinity bays to the lower salinity marshes in the summer, and then move back into the bays in fall.  相似文献   

18.
Currently, the species list of the macroalgae (excluding Charales) inhabiting the southern seas of Russia includes 388 species, specifically, 362 species in the Black Sea, 46 species in the Sea of Azov, and 70 species in the Caspian Sea. The species list has been increased by approximately 30% (96 species, most of them are registered in the Black Sea), compared to the data obtained 30 years ago. The green and red macroalgae of warm-water Mediterranean and tropical origin (Ceramium, Polysiphonia, Laurencia, Ulva, and Chaetomorpha) and brown algae (Sargassum and Cytoseira) were the key invaders. Nowadays the maximal species diversity is found on the Crimean coast and the Turkish coast of the Black Sea; and the species list of the Turkish coast differs significantly from all the other studied sites of the Black Sea. The number of the algae of the warm-water complex increased the most in 1990s–2000s in the Black Sea; species of boreal-tropical and subtropical origin dominate. However, such a tendency was not observed in the Sea of Azov and in the Caspian Sea, but expansion of the habitats of the brackish green algae has been registered.  相似文献   

19.
Neomysis americana, a common prey item in the diet of estuarine fish, is seasonally abundant in saltmarsh tidal creeks of North Inlet, South Carolina. Visual examination of mysids collected in winter revealed only diatom tests in their guts, with nearly all of the ingesta unidentifiable. Immunological diet analysis provided strong evidence that proteins fromSpartina alterniflora detritus were present in the guts of field-collected mysids. Laboratory determinations of weight-specific ingestion rates for male and female mysids fed particulateS. alterniflora were best described by a curvilinear quadratic function. Ingestion rates ranged from zero to 0.116 mg C ingested per mg C body weight per hr, or greater than 200% of body carbon per day if continuous feeding is assumed. These high ingestion rates may indicate low assimilation efficiency, but ifN. americana’s assimilation efficiency is similar to that of other mysid species, then this mysid may represent an efficient trophic link between saltmarsh macrophyte production and higher trophic levels. The occurrence ofSpartina detritus in the guts of winter mysids suggests that detritivory may be important during periods of scarce food.  相似文献   

20.
We examined the diets of Gulf killifish,Fundulus grandis Baird and Girard, collected monthly from March through July 1988 with unbaited minnow traps during two sampling periods: (1) on flood tides before they reached the marsh surface, and (2) on ebb tides as they left the marsh. Thirty-five prey taxa, plant parts, and detritus were identified from the stomach contents of 110 Gulf killifish (mean SL = 55 mm, range = 30?82 mm). Fiddler crabs,Uca longisignalis Salmon and Atsaides; amphipods, mostlyCorophium louisianum Shoemaker; tanaidaceans,Hargeria rapax (Harger); and hydrobiids,Littoridinops palustris Thompson, were their most important prey. Killifish diets differed both quantitatively and qualitatively relative to the habitat in which they were feeding. Fiddler crabs and polychaetes were consumed more frequently and in greater numbers in the intertidal zone, whereas more amphipods were eaten by killifish feeding in subtidal and low intertidal areas. Gulf killifish consumed a greater volume of food when they had access to the marsh surface than when they were confined to subtidal areas.  相似文献   

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