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1.
Seven species of mojarras (Gerreidae) were collected from three stations in the Indian River lagoon near the Sebastian Inlet, Florida over an eighteen month period to study spatial and temporal variations in occurrence and feeding habits. Two major habitats common to this area were represented in the study; a sandy beach and a seagrass flat. Of the 2,899 gerreids collected,Eucinostomus gula represented 67% and was found primarily in theHalodule seagrass site. The next most abundant species,E. argenteus (11%),E. jonesi andE. lefroyi (each 10%), were found most frequently at the inlet site.Diapterus auratus, E. melanopterus, andGerres cinereus were captured infrequently and were considered incidental. Prey items found included amphipods, bivalves, copepods, fish eggs, foraminifera, isopods, nematodes, ostracods, polychaetes and crustacean parts. Significant amounts of sand and unidentifiable amorphous debris were also included in the gut content analysis. Little interspecific variation in diet was found among the four major species examined. The general shift seen from a diet composed primarily of copepods and other crustaceans to one of polychaetes suggests an intraspecific ontogenetic progression. Spatial variations in diet composition were also indicated between the two major habitats. Feeding analyses showed gerreids to be diurnal feeders with the greatest consumption (total gut content weight) occurring at dusk.  相似文献   

2.
Habitat-related densities of natant macrofauna were compared between vegetated and nonvegetated areas in aSpartina alterniflora marsh on Galveston Island, Texas. The most abundant macrofauna were crustaceans,Palaemonetes pugio, Penaeus aztecus, Penaeus setiferus, andCallinectes sapidus, and small fish,Gobiosoma bosci, Lagodon rhomboides, Leiostomus xanthurus, Fundulus similis andMicropogonias undulatus. Excluding residentsP. pugio, G. bosci andF. similis, most of the macrofauna were transient juveniles of estuarine-dependent species. Among crustaceans,P. pugio, P. aztecus, andC. sapidus were significantly more dense in vegetated habitat, butP. setiferus was not consistently more abundant in either vegetated or nonvegetated habitat. Of 29 species of fishes, 14 were usually in vegetation, 11 were more often on nonvegetated bottom, and 5 were indifferent to either habitat. Much seasonal variability in abundances ofP. aztecus, P. setiferus, andC. sapidus, but notP. pugio, could be attributed to changes in temperature, salinity and water-level. Strong selection for vegetated habitat byP. aztecus was related to the historical water-level pattern coinciding with seasonal periods of marsh flooding. Apparently, high seasonal tides during the spring and fall facilitated access to vegetated habitat in the marsh and exploitation by transientP. aztecus. In contrast, strong selection for vegetation byP. pugio, abundant year-around in the marsh, was not similarly influenced by seasonal changes in water-level. Overall, habitat-related densities and physical interactions suggest that marsh physiography together with differences in tides may greatly determine the extent to which certain estuarine macrofauna utilize marsh habitats.  相似文献   

3.
The tidally inundated marsh surface is an importnat site for energy exchanges for many resident and transient species. In many areas along the East Coast of the U.S. the dominant vegetation,Spartina alterniflora, has been replaced by the common reed (Phragmites australis). This shift has caused concern about the impact ofPhragmites on marsh fauna but research in this area has been limited. During 1997 and 1998, we examined the effect ofPhragmites on fish and decapod crustacean use of the marsh surface in the brackish water reaches of the Mullica River, in southern New Jersey, U.S. Fish and decapod crustaceans were sampled with an array of shallow pit traps (rectangular glass dishes, 27.5×17.5×3.7 cm) and with flumes (1.3 m wide×10 m long of 3.2-mm mesh). Fish (2–60 mm TL) dominated pit trap collections withFundulus heteroclitus andFundulus luciae significantly more abundant atSpartina sites.Fundulus heteroclitus was also the dominant fish (15–275 mm TL) collected in flumes but collections with this gear, including a number of species not collected in pit traps, showed no distinct preferences for different marsh vegetation types. Decapod crustaceans (1–48 mm CW) collected in pit traps were generally less abundant than fishes withCallinectes sapidus andPalaemonetes spp. most abundant inSpartina, whileRhithropanopeus harrisii was most abundant inPhragmites. The same decapod crustacean species (2–186 mm CW) dominanted the flume collections and, similar to the pattern of fish collected by the flumes, there were no distinct habitat preferences for different marsh vegetation types. As a result of these observations, with different sampling techniques, it appears there is an overall negative effect ofPhragmites on larval and small juvenile fish but less or no effect on larger fish and decapods crustaceans.  相似文献   

4.
Molluscs were collected monthly for a year from two low salinity (0–9‰) intertidal marshes dominated by the macrophytesJuncus roemerianus orSpartina cynosuroides in St. Louis Bay, Mississippi. TheJuncus marsh had lower soil organic matter, higher pH and was more frequently inundated than theSpartina marsh. Eight species of gastropods were abundant and dominated in the higherSpartina marsh, while three bivalve species were dominant in theJuncus marsh. Of the common species,Succinea ovalis, Vertigo ovata andDeroceras laeve are gastropods of terrestrial origins;Geukensia demissa granosissima (bivalve) andMelampus bidentatus (gastropod) are euryhaline estuarine species and the remaining gastropods (Detracia floridana, Littoridinops palustris, Onobops jacksoni) and bivalves (Polymesoda caroliniana, Cyrenoida floridana) are brackish species. Most species were capable of continuous recruitment (based on size class analysis), but exhibited peak activity in particular seasons. Bivalve abundance correlated to temperature, and gastropod abundance was negatively correlated to soil pH. These correlations reflect the influence of flooding regime at the two sites. Biomass was greater in theJuncus marsh because of the increased presence of the large-bodiedPolymesoda. Polymesoda represented >90% and >50% of the total biomass in theJuncus andSpartina (except summer) marshes respectively but always <-5% of the individuals collected. Gastropod biomass was the same in both marshes. Species diversity (H′) was greater inSpartina except for summer months. TheJuncus marsh always exhibited greater species richness. Evenness (J′) determined seasonal changes in diversity (H′). Similarity values (Cz) were always quite low, with highest values in spring In contrast to faunal studies from Gulf and East Coast salt marshes, we found 1) fewer species, 2) communities comprised of unique species combinations, 3) greatest mean densities in summer, and 4) potentially less productivity by the molluscs of our sites. These mollusc communities exhibit structural characteristics that emphasize the unique ecotonal nature of the oligohaline marshes within which they are found.  相似文献   

5.
Since 1965 large areas of lower Connecticut River tidelands have been converted from high diversity brackish meadow andTypha angustifolia marsh to near monocultures ofPhragmites australis. This study addresses the impact ofPhragmites invasion on fish and crustacean use of oligohaline high marsh. During spring tides from early June through early September 2000, fishes and crustaceans leaving flooded marsh along 3 km of the Lieutenant River, a lower Connecticut River tributary, were captured with Breder traps at 90 sites, equally distributed amongPhragmites, Typha, and treated (herbicide and mowing)Phragmites areas. Pit traps, 18 per vegetation type in 2000 and 30 each inPhragmites andTypha in 2001, caught larvae and juveniles at distances of up to 30 m into the marsh interior. There were no significant differences in fish species compositions or abundances among the vegetation types. Size distributions, size specific biomasses, and diets ofFundulus heteroclitus, the numerically dominant fish, were also similar. The shrimpPalaemonetes pugio was more abundant inPhragmites than in other types of vegetation, whereas the fiddler crabUca minax was least numerous inPhragmites. Mean numbers ofF. heteroclitus andP. pugio caught per site event were positively correlated with increasing site hydroperiod. Significantly moreF. heteroclitus were captured along the upper reach of the river where marsh elevations were lower than farther downstream. MoreF. heteroclitus and fewerP. pugio andU. minax were captured during the day than at night. A relatively small number of larval and juvenileFundulus sp. were captured in pit traps, but consistently fewer inPhragmites than inTypha, suggesting thatTypha and brackish meadow marshes may provide better nursery habitat. Vegetation was sampled along a 30 m transect at each trap site in 2000. Plant species diversity was greatest in treatedPhragmites areas and lowest inPhragmites sites.  相似文献   

6.
This study presents both qualitative and quantitative data regarding marine mollusk (gastropods and bivalves) shell bioerosion and encrustation based on death assemblages obtained from a recent supratidal environment in Playa Norte, Veracruz State. The objectives of this study were to assess the nature of bioerosion and encrustation processes and to investigate the role of these taphonomic features contributing to the deterioration of natural shell accumulations within a tropical siliciclastic tidal environment. The assemblage comprises 31 species: 13 gastropods and 18 bivalves. The bioerosion and encrustation degrees were low to moderate for both types. The most abundant traces were predatory gastropod structures (Oichnus paraboloides and O. simplex), whereas sponge borings (Entobia isp.), polychaete dwellings (Caulostrepsis taeniola), and echinoid raspings (Gnatichnus isp.) were less frequent. The encrusting organisms include polychaete serpulids, bryozoans, and rare foraminifers (Homotrema rubrum). Because of the low bioerosion and encrustation degrees occurring in this area, accumulation is expected to predominate over biotic destruction. As deposition conditions (richly fossiliferous carbonate sandstone beds) were similar to those prevailing in the Tuxpan Formation during the Miocene (Langhian), it is suggested that this study provides an equivalent reference to interpret mollusk fossil assemblages located in this site.  相似文献   

7.
Hurricane Sandy was an extraordinarily large storm that affected most of the eastern coast of the USA in October 2012. To assess this storm’s impact, the benthic invertebrate community structure and sediment properties were compared in samples collected 3.5 months prior to (July 2012) and 8 months after (July 2013) the hurricane at 97 locations in Barnegat Bay, New Jersey, USA. Barnegat Bay is a shallow back-barrier estuary just north of where Sandy made landfall. For all locations taken together, sediment total nitrogen concentration was lower afterwards, while total organic carbon and total phosphorus concentrations were similar. Sediment median particle size was the same before and after, but the sediment was better sorted after the storm. There were no differences in total abundance of invertebrates, species richness, species diversity, or the abundance of polychaetes, bivalves, or gastropods. Malacostracan crustaceans were more abundant after Sandy (average 82 (0.04 m2)?1) than they were before (average 64), due almost entirely to increased abundance of ampeliscid amphipods, which showed a shift toward smaller sizes in 2013. Annelids in the order Clitellata were on average less abundant after the hurricane (17) than before (53). The apparent minimal effect of Sandy on the benthic community in Barnegat Bay was probably because the passage of the hurricane had no detectable effects on salinity or dissolved oxygen concentrations throughout the bay.  相似文献   

8.
The effect of predation by blue crabs and fishes on all species of infaunal macrobenthos of a subtidal sandy bottom in the York River, Virginia, was investigated by manipulative field experiments. Wire mesh cages were used both to exclude all large predators from and to confine different predators to small areas of the natural bottom. After 2 months, many species showed significant differences between the various treatments. There were similar patterns of species responses in three separate years. Species tended to fit one of two categories. Those species which had tough tubes, which lived deep in the sediment, or which could quickly retract deep into the sediment were shown experimentally not to change much in abundance regardless of whether predators were excluded or included. These species were generally the numerical dominants in the natural community—e.g.Peloscolex gabriellae, Heteromastus filiformis, Spiochaetopterus oculatus, andPhoronis psammophila. Other species which lived near the surface or exposed on the surface responded to experimentally altered predation intensity with large changes in density. These species were either uncommon or only sporadically abundant in the natural community—e.g.Polydora ligni, Streblospio benedicti, Mulinia lateralis, andLyonsia hyalina. This evidence indicates that the abundant species in the natural community are abundant because they avoid predators.  相似文献   

9.
New brachiopods (Dimerelloidea, Rhynchonellida) from Lower Jurassic (?lower Hettangian) hemipelagic sediments of the Swiss National Park in south-eastern Engadine are described: Sulcirostra doesseggeri sp. nov. and Carapezzia engadinensis sp. nov. Sulcirostra doesseggeri is externally similar to S. fuggeri (Frauscher 1883), a dubious species, that could not be included in a comparative study, because relevant samples no longer exist. A single specimen was tentatively assigned to Sulcirostra ?zitteli (Böse 1894) by comparison of its external morphology with S. zitteli from the type locality. The partly silicified brachiopods are associated with sponge spicules, radiolarians and crinoid ossicles. Macrofossils are rare: dictyid sponges, gastropods, bivalves, crustaceans, shark teeth and scales of an actinopterygian fish. The Lower Jurassic sediments (Alpisella beds, a basal member of the Allgäu Formation) preserving the brachiopods belong to the Ortler nappe (Upper Austroalpine nappes). The exact age of the Alpisella beds is not known, as index fossils are lacking. Their stratigraphic position above the Rhaetian Kössen Formation and below the ammonite-dated Trupchun beds suggests a very Early Jurassic, probably early Hettangian age for the new brachiopod fauna. The new species of Sulcirostra and Carapezzia are confined to a very small geographic area, a peculiarity also observed in other Early Jurassic dimerelloid brachiopods. These brachiopods presumably adapted to current-dominated submarine highs, where their shells could not accumulate, except when trapped in submarine cavities or re-deposited in submarine fans. Transport by turbidity currents is suggested for the Early Jurassic dimerelloids from the Engadine. Problems with the generic definition of Sulcirostra and the higher rank classification of Carapezzia are discussed.  相似文献   

10.
A study of contamination of the biological compartment of the Seine estuary was carried out by measuring the concentrations of cadmium (Cd), copper (Cu), lead (Pb), and zinc (Zn) in 29 estuarine and marine species belonging to 6 phyla. Species came from three main biological zones of the estuary: the Seine channel (copepods, mysids, shrimps, and fish), the intertidal mudflats (Macoma balthica community), and the subtidal mudflats (Abra alba community). Two fish species, the bass (Dicentrarchus labrax) and the flounder (Platichthys flesus), were also selected for analyses. A comparison of metal concentrations in estuarine species of the Seine with those found in the same species collected on contaminated and non-contaminated sites showed a contamination of the estuary by Cu, Zn, and Pb. For Cd, the contamination is mainly observed in bivalves, although the concentrations observed were low and less than 2 μg g?1 d.w. High concentrations of Cu were found in copepods, shrimps, and fish. Pb contamination was mainly found in species living in the Seine channel where the copepodEurytemora affinis shows an average concentration of 22 μg g?1 d.w. High concentrations of Pb (>10 μg g?1 d.w.) were found in deposit-feeders benthic invertebrates. Elevated levels of Zn were seen in all species collected in the Seine estuary, including fish and in particular small flounder. The concentrations of Cd, Cu, Pb, and Zn found in edible estuarine species (shrimp and fish) were in the same order of magnitude than those found in fish and shrimps fished along the French coast.  相似文献   

11.
A two-year trawl study of Laguna Joyuda, Puerto Rico, a small, polyhaline lagoon with restricted oceanic exchange, yielded 803 crabs belonging to sixCallinectes species.Callinectes danae was the most abundant (35.7%), followed byC. sapidus (21%),C. ornatus (12.6%),C. bocourti (12.1%),C. exasperatus (1.2%), andC. larvatus (0.4%). Abundances of different species differed more spatially than temporally despite very homogeneous salinities.Callinectes bocourti andC. sapidus were most abundant furthest from the lagoon’s inlet, whileC. danae andC. ornatus were most abundant near the inlet and in the center of lagoon. Juveniles were least abundant in the center of the lagoon. Size frequencies of most species showed common trends with high percentages of small crabs furthest from the inlet, and high percentages of larger crabs near the inlet and central parts of the lagoon. Distributional patterns appear to be a result of complex interactions of habitat preferences and intra- and interspecific interactions among the crabs.  相似文献   

12.
Small, abundant elasmobranchs use shallow marine areas (<20 m depth) of the US Middle Atlantic coast as nurseries and adult foraging habitat, an area also used by a diverse assemblage of economically important juvenile and adult teleost species. Specimens of three small elasmobranch species (smooth dogfish Mustelus canis, clearnose skate Raja eglanteria, and bullnose ray Myliobatis freminvillii) were collected in August 2007 and 2008 from a study area of ∼150 km2, extending 22 km south from Ocean City, Maryland, USA (38° 19′ N) and offshore from 5- to 20-m depth. Stomach contents indicated that fish were part of the diets of smooth dogfish and clearnose skate at a level comparable with sympatric piscivorous teleosts. However, stable isotope data suggest that piscivory is likely an opportunistic foraging behavior in this habitat. Studied elasmobranchs were secondary-tertiary consumers with diets composed primarily of decapod crustaceans, fish, and mollusks. There was significant overlap in diet composition, spatial distribution, and diel stomach fullness patterns between clearnose skate, southern kingfish Menticirrhus americanus (teleost) and, to a lesser extent, smooth dogfish. Despite this evidence for piscivory, their relatively low densities suggest that predation by these elasmobranchs is unlikely to affect teleost populations in shallow coastal ocean habitats. If shared prey were to become scarce, then competitive interactions are possible.  相似文献   

13.
Fossil biota and detailed biostratigraphy of the Permian northeastern Okhotsk and Ayan-Yuryakh sedimentary basins located in the northern Okhotsk region are characterized. The biota core is represented by bivalves associated with gastropods, brachiopods, and other faunal groups. It is shown that a new regional stratigraphic scale of northeastern Russia based on brachiopods and bivalves may be used for subdivision of Permian sections in these basins. Fossil assemblages have many features in common with their counterparts from the Verkhoyansk region; at the same time, there are endemic species and the big group of species characteristic of the Omolon basin. The upper part of the Khivach regional horizon is subdivided into subzones based on the evolutionary lineages of the Maitaia and Intomodesma genera. Changes in the taxonomic composition of coeval communities in different basins are shown to be largely controlled by the basin depths and facies environments. Impoverished fauna of the Ayan-Yuryakh basin was less diverse in taxonomic aspect, represented almost entirely by bivalves (mostly Inoceramus-like) accompanied by rare gastropods. The discovered taxa are figured in majority, and table of their stratigraphic distribution is presented.  相似文献   

14.
Dietary studies of fish can enhance our understanding of predator-prey interactions and provide important insights into complex marine food webs. In this study, we performed dietary analyses of three commercially important fish species in South China: Acanthopagrus latus, Pampus argenteus, and Scomberomorus commerson. Two distinct fragments of the mitochondrial cytochrome c oxidase I (mtCOI) gene, a small (130 bp) and large (300 bp) amplicon, were amplified from the DNA extracted from the gut contents in the presence of blocking primers designed to inhibit the amplification of predator-specific DNA. The amplicons from each predator species were tagged with a unique indexing bar code and sequenced using the Illumina MiSeq platform. Our results showed that the three fish species consumed a wide variety of prey, including jellyfish, copepods, crustaceans, and fish. Seasonal variations in prey composition and species-selective predation were observed. Our approach of combining next-generation sequencing with blocking primers greatly enhanced the speed and resolution of the dietary analyses in marine fishes and could provide novel insights into marine ecosystems.  相似文献   

15.
The use of the Tejo estuary, Portugal, salt marsh creeks by nekton was examined based on sampling surveys with a fyke net from September 1998 until August 2001. From the 20 taxa (14 fish species, 5 decapod crustacean species, and 1 cephalopod species) identified in the studied creeks, 16 were regularly caught throughout the sampling period. The shrimpPalaemonetes varians was the most numerically abundant species in the creeks, while the biomass was dominated by the mulletLiza ramada. The nekton assemblage was mainly represented by marine-estuarine opportunist species, comprising 85% of the total. A high seasonality was detected on the species abundance patterns: the most abundant species (P. varians, Crangon crangon, L. ramada, Pomatoschistus microps, Syngnathus sp., andAnguilla anguilla) occurred throughout the sampling period,Sardina pilchardus, Dicentrarchus, labrax, andAtherina boyeri were particularly abundant in spring and summer, andEngraulis encrasicholus, Liza aurata, Gambusia holbrooki, Palaemon longirostris, andPalaemon serratus were most abundant in autumn and winter.L. ramada occurred in the tidal creeks in high numbers during neap tides, while the majority of the remaining taxa were most abundant during spring tides, suggesting a differential pattern of habitat use occording to species.  相似文献   

16.
We examined the community structure of fish and selected decapod crustaceans and tested for within estuary differences among habitats at depths of 0.6 m to 7.9 m, in Great Bay and Little Egg Harbor in southern New Jersey. Several habitat types were identified a priori (e.g., eelgrass, sea lettuce, and marsh creeks) and sampled by trawl (4.9 m headrope, 19-mm mesh wings, 6.3-mm mesh liner), monthly, from June 1988 through October 1989. Repetitive (n=4) 2-min trawl tows were taken at each habitat type from 13 locations. The fishes and decapod crustaceans collected were typical of other Mid-Atlantic Bight estuaries but varied greatly inseasonal abundance and species. In the years sampled, bay anchovy (Anchoa mitchilli) was the dominant species (50.5% of the total number), followed by spot (Leiostomus xanthurus) (10.7%), Atlantic silverside (Menidia menidia) (9.7%), fourspine stickleback (Apeltes quadracus) (5.9%), blue crab (Callinectes sapidus) (4.6%), and northern pipefish (Syngnathus fuscus) (4.2%). The biota were examined by multi-dimensional scaling (MDS) for habitat associations and “best abiotic predictor” of community structure. Percent silt combined with salinity was the most important abiotic determinant of the faunal distributions among habitats. Temperature was a major factor influencing seasonal occurrence of the biota but had less effect on habitat comparisons. The analysis confirmed the distinct nature of the assemblages associated with the habitats, that is, eelgrass, upper estuary subtidal creeks, channels, and open bay areas. Several species were associated with specific habitats: for example,A. quadracus andS. fuscus with eelgrass, clupeids with subtidal creek stations,L. xanthurus with marsh channels, and black sea bass (Centropristis striata) and spotted hake (Urophycis regia) with sponge-peat habitat. Species richness appeared to be positively related to habitat structural heterogeneity. Thus, the best predictors for these estuarine fish and decapod crustacean assemblages were seasonal temperature, percent silt and salinity combined, and the physical heterogeneity of the habitat.  相似文献   

17.
Little is known about the importance of salmarshes to juvenile and adult fishes in temperate Australia. We assessed diel and feeding patterns of fish inhabiting saltmarsh in a sheltered embayment along the coast of Victoria, Australia, between October 2002 and May 2003. The saltmarsh flat was generally only inundated during low-pressure weather systems (barometric pressure <1,013 hP). Fish were sampled over the saltmarsh flats using fyke and seine nets. A total of 2,047 individuals (10 species, including juveniles and adults) were caught.Atherinasoma microstoma was most abundant (fyke [F], μ=1.6 fish h−1; seine [S], μ=28.2 fish shot−1), followed byFavonigobius, lateralis (F: 0.5; S: 0.6),Galaxias maculatus (F: 0.1),Heteroclinus adelaide (F:<0.1),Kestratherina esox (F: <0.1; S: 1.6),Leptatherina presbyteroides (F: <0.1; S: 7.1) andTetractenos glaber (F: 1). Commercial species, includingAldrichetta forsteri (F: <0.1; S: 3.2),Sillaginodes punctata (F: <0.1; S: 0.9), andRhombosolea tapirina (F: 0.4), were commonly sampled. Variability in species richness or fish abundance was not explained by water temperature, salinity, depth, or barometric pressure. Significantly more species were sampled with the seine during nocturnal periods (p=0.002); fish abundance did not vary between diel periods, nor did fish abundance and species richness in fyke net samples. Diets of the most abundant species (A. microstoma, A. forsteri, andF. lateralis) were primarily composed of gammaridean amphipods and hemipteran insects. There was no correlation between fish diets and the composition of benthic invertebrates as sampled at 3 different regions of the saltmarsh flat. The saltmarsh flats in our study region are inhabited by several species normally associated with alternative habitat types such as seagrass, and the patterns of habitat use observed appear to be partially attributed to foraging behavior.  相似文献   

18.
A total of over 32,000 demersal fish and epibenthic crustaceans belonging to 62 species were caught in 42 biweekly trawls from 10 stations in Yaquina Bay, Oregon, during 1967 and 1968. English sole,Parophrys vetulus, was the most abundant species. Seventeen species (13 fishes and 4 crustaceans) constituted 95% of the catch. Total numerical abundances of both individuals (mainly juvenile fishes) and species were greatest in the lower 12 km of the estuary during summer and early fall, a period of water mass stability and increased water temperature and salinity. This section of the estuary is used by many immature fishes and crustaceans as a “nursery area”. These fishes generally emigrate from the estuary as subadults in the fall around the onset of the rainy season. The fewest species were taken in January 1968 from the central, upper-estuarine, and riverine areas of the bay, this being a time when high rainfall and river discharge result in low salinity and temperature. Crustaceans (shrimp and subadult crabs) were generally most abundant in late winter and early spring throughout the estuary. Changes in diversity indices reflected variations in community structure, the influence of migratory species and juvenile fishes, and seasonal changes in dominance. Year-to-year fluctuations in abundance may be due, in part, to local hydrographic and meteorological conditions along the central Oregon coast.  相似文献   

19.
While most studies of the utilisation of food resources in aquatic ecosystems have focused on comparing the diets of closely related taxa, the present study was aimed at elucidating whether the diets of five species, representing two distant taxa, were correlated and overlapped. We have thus compared the diets of a fish species (the flathead, Platycephalus speculator) with those of two small species of cormorant (little pied, Phalocrocorax melanoleucos, and little black, P. sulcirostris) and two larger species of cormorant (pied, P. varius, and black, P. carbo) in a temperate southwestern Australian estuary. The flathead and the two smaller cormorants consumed predominantly shrimp and small, short-lived teleosts, whereas the two larger cormorants fed almost exclusively on larger species of teleost. Although the diet of flathead were correlated with and overlapped those of the two smaller cormorant species, there was no correlation or overlap between the diets of these three species and those of either of the larger species of cormorant. Our observations of P. speculator are consistent with the results of previous studies which have shown that platycephalids are ambush predators, whereas cormorants are pursuit surface plungers, with the little pied cormorant feeding solitarily and the little black cormorant feeding communally. Flathead preyed on both demersal and mid-water teleosts. The little pied cormorant fed almost exclusively on demersal teleosts and the little black cormorant exploited predominantly mid-water schooling fish. Thus, differences in the fish components of the diets of these three predators can be related to differences in the mode of foraging and the level in the water column in which feeding takes place. The respective daily consumption of shrimp and teleosts in the estuary was estimated as 1,000 kg and 450 kg by flathead and as 180 kg and 150kg by the four species of cormorants combined. The results of this study show that, in estuaries, the degree to which diets were correlated and overlapped amongst predatory vertebrates can be greater between representatives of distant taxa than between species within the same genus.  相似文献   

20.
The stratigraphy of the Farasan Islands (Pliocene?CPleistocene deposits) is established on the basis of a detailed study of six stratigraphic sections described and sampled in the field. Detailed examinations involve the microfacies analyses and identification of macrofossils makes it possible to determine two new informal formations, namely, from the base to the top: Esbah formation of Pliocene age and Farasan formation of Pleistocene age. The detected microfacies types of the studied samples are only carbonate facies and include five major types: mudstone, wackestone, packstone, floatstone and boundstone. No grains of quartz sand or igneous mineral were found in the islands. The nomenclature of the biostratigraphic units established in the present work is not intended to define world-wide zonal standards. It is only used to subdivide the sequence into biostratigraphic zones according to 137 macrofaunal species (78 bivalves, 56 gastropods and three echinoids). These biozones, namely: Lithophaga teres zone (Early Pliocene), Clypeaster reticulates?CLaganum depressum zone and Chesapecten madisonius?CNoetia limula interval zone are assigned to the Late Pliocene; meanwhile, Noetia limuli?CAnadara ovalis interval zone and A. ovalis range zone are assigned to the Pleistocene age. The affinity of the Pliocene?CPleistocene fauna recorded from the Farasan Islands increase with time towards the Indo-Pacific realm. The identified bivalves and gastropods are dominated by the Indo-Pacific forms suggesting the connection of the Red Sea rift with the open Indian Ocean via the Gulf of Aden and Bab El Mandab in the latest Miocene and Early Pliocene.  相似文献   

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