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1.
Six species of skates were trawled commonly on the continental shelf off the Southern Cape during routine surveys of demersal fish between 1986 and 1990. Raja miraletus is a small skate found principally in shallow (<50 m) water that feeds mainly on small crustaceans, such as mysids and macrurans. The large Raja alba occurs over most of the continental shelf, is a piscivore throughout its life and preys heavily on flatfish, especially Cynoglossus zanzibarensis. R. cf. clavata is ubiquitous on the shelf but most abundant between 50 and 150 m deep. Feeding predominantly on crustaceans, this skate switches from carids, penaeids and mysids when small to brachyurans and small benthic fish when larger. R. pullopunctata is found over a similar depth range but attains a much larger size. It eats small mysids and macrurans when small, but brachyurans and fish become more important in the diet with increasing size of the predator. R. wallacei is most commonly taken at depths of 80–>200 m, feeds initially on small crustaceans, but switches to fish, including eels, as it grows. The small Cruriraja parcomaculata is found at the edge of the continental shelf and over the upper slope; it preys on small crustaceans, including mysids, isopods and macrurans. The distribution pattern of the skates and their prey suggest overlap in prey taken, the overlap being greatest in those species which feed on crustaceans. The large biomass of skates in the area suggests that they are an important component of the demersal faunal assemblage of the continental shelf there, and also that they may have a significant impact on the benthic fauna.  相似文献   

2.
Although continental shelf and slope environments typically exhibit high epifaunal biomass and have been subjected to increasing fishing pressure, ecological information on assemblages of non‐commercial invertebrate species from subtidal and bathyal areas remains limited. Sea stars (Echinodermata: Asteroidea), which are known to influence communities through their feeding habits, have received less attention than structural taxa such as corals and sponges. To better understand the ecological roles of asteroids on continental shelves, we investigated ~30 species and assessed their distributions and co‐occurrence with other benthic invertebrates on the shelf and slope of Eastern Canada. Using fisheries data and in situ video footage, we compiled a large dataset covering ~600,000 km2 that included over 350,000 individual asteroid records (37–2243 m depth). Multivariate analyses revealed geographically distinct asteroid assemblages, with a maximal overall density at 400–500 m and the highest diversity at 500–700 m. The most abundant and densely occurring species was Ctenodiscus crispatus. We found that asteroids associate with corals, sponges, bivalves, and other echinoderms, and that depth and substrate influence these assemblages. We identified species likely to affect coexisting organisms by their burrowing behavior that can disrupt epi‐ and infauna (C. crispatus) and through predation on ecologically important corals (Hippasteria phrygiana). In addition to providing baseline distribution and ecological information for many bathyal asteroid species in the Northwest Atlantic, this work highlights the abundance and diversified roles of asteroids within continental shelf and slope ecosystems.  相似文献   

3.
Megafaunal assemblages were studied in August–September 1992 using a towed camera sled along seven cross-isobath transects on the continental slope off Cape Hatteras. A total of 20,722 megafaunal organisms were observed on 10,918 m2 of the sea floor between the depths of 157 and 1 924 m. These data were compared with data previously collected off Cape Hatteras in 1985 and at other locations along the eastern U.S. coast between 1981 and 1987. Megafaunal populations on the upper and lower slopes off Cape Hatteras were fouond to be similar, in terms of density and species composition, to those observed at the other locations.In contrast, megafaunal abundances were found to be elevated (0.88 and 2.65 individuals per m2 during 1985 and 1992, respectively) on the middle slope off Cape Hatteras when compared to most other slope locations (<0.5individuals per m2). These elevated abundances mainly reflect dense populations of three demersal fish, two eel pouts (Lysenchelys verrilli andLycodes atlanticus) and the witch flounderGlyptocephalus cynoglossus, and a large anemone (Actinauge verrilli). These four species dominated the megafauna off Cape Hatteras, whereas they represented only a minor component of megafaunal populations found at other slope locations. Additionally, numerous tubes of the foraminiferanBathysiphon filiformis were observed off Cape Hatteras, but not elsewhere. The high density of demersal fish found off Cape Hatteras appears to be related to the high densities of infaunal prey reported from this area. The high densities ofA. verrilli andB. fuliformis may be related to the same factors responsible for the high infaunal densities, namely enhanced nutrient inputs in the form of fine particles. Extreme patchiness also was observed in the distributions of the middle slope taxa off Cape Hatteras. This patchiness may reflect the habitat heterogeneity of this exceptionally rugged slope and the sedentary nature of the organisms inhabiting it.  相似文献   

4.
The food habits of five species of eels and one species of spiny eel collected from the upper continental slope off the Cape west coast and Agulhas Bank, South Africa, are described. All a re embers of a defined demersal micro- or mesocarnivore feeding guild except Simenchelys parasitica, a scavenger. Two congrids, Bassanago albescens and Gnathophis capensis and the spiny eel Notacanthus sexspinis usually employ the demersal grazer feeding method and infrequently switch to picking nekton in the water column. Two synaphobranchids, Diastobranchus capensis and Synaphobranchus kaupii, are chiefly demersal mesocarnivores that stalk prey, but also pick nekton and scavenge. A significant amount of the prey ofthe three large eels, B. albescens and the two synaphobranchids, consisted mainly of mesopelagic stomiiform, myctophid and juvenile gadiform fish, penaeid and caridean shrimps and various squid taken at the bathyal/deep-pelagic interface, as was found previously with some grnadiers (Macrouridae. Five categories of fleshy remains are documented for the scavenging Simenchelys parasitica for the first time.  相似文献   

5.
In 2004, we surveyed demersal fishes and habitats on the continental shelf off central California (65–110 m depth) using the occupied submersible Delta. Our objectives were to estimate the relative abundance of habitats and to examine demersal fish species composition, diversity, density, and sizes relative to these habitats. A total of 112 transects were completed covering 32 km of seafloor. A higher density of fishes was estimated in boulder and cobble habitats than in mud and brachiopod beds. More than 80% of the fishes were small, measuring 20 cm or less in total length. Species with small maximum size (primarily pygmy rockfish, Sebastes wilsoni, and blackeye gobies, Rhinogobiops nicholsii) accounted for nearly half (49%) of the total number of 12,441 fishes. Most fishes were immature, with only 4 of 20 harvested species having more than 50% of the individuals larger than the size at first maturity. Our study area on the continental shelf may be an ontogenetic transition zone for immature fishes before they move to their adult habitat on the slope. Alternatively, historical fishing pressure may have contributed to the lack of large, mature fishes in the survey area. Understanding the importance of these habitats to fishes at various life stages will improve our ability to assess these deepwater fish stocks and effectively manage these living resources on an ecosystem basis.  相似文献   

6.
Demersal fish communities were studied on the lower continental shelf and the upper continental slope along the Pacific coast of northeastern Japan. Species composition, number and weight of each species were examined based on otter trawl samples at 45 stations. Mean density and biomass of demersal fishes were 131 ha–1 and 21 kg ha–1, respectively. The ten most abundant species comprised of about 95% of total number and weight of overall catch indicating simple species composition. Gadiform fishesTheragra chalcogramma, Gadus macrocephalus andPhysiculus maximowiczi were the most important species by number, weight and frequency of occurrences, and three main community types represented by the three key species were recognized.Theragra-dominant community showed higher density and biomass, and lower diversity thanPhysiculus-dominant community did. Species diversity of demersal fish community was negatively correlated to density and biomass. Density and biomass of demersal fish community were high on the uppermost slope, and the high abundance resulted from low-diversity communities dominated byT. chalcogramma andG. macrocephalus.  相似文献   

7.
To describe demersal communities off the west coast of South Africa, collections of all species of fish, cephalopods and crustaceans made during four cruises in the area during January and July have been analysed. Hierarchical classification methods were employed to determine species and sample associations. The results showed that the species could be split into two main groups, the first containing Merluccius paradoxus (the dominant species both in abundance and frequency of occurrence) and other species normally found in deep (> 380 m) water. The second group is represented by species that live on the continental shelf, M. capensis being the most abundant. The boundary separating the deep-sea community from that of the shelf follows approximately the 385-m isobath. Seasonal variations in the number of main associations as well as in their spatial location are documented.  相似文献   

8.
The food habits of 10 species of grenadier collected from the upper continental slope off South Africa's west coast and Agulhas Bank are described. Three feeding strategies were identified. Members of the demersal micro- or mesocarnivore feeding guild and grazer feeding method include Caelorinchus braueri, C. simorhynchus, juvenile Coryphaenoides striaturus, Lucigadus ori, Malacocephalus laevis, Nezumia brevibarbata, N. micronychodon and N. umbracincta. A second strategy, that of Caelorinchus matamua and adult Coryphaenoides striaturus, involved switching approximately equally from demersal grazing to midwater picking or stalking. The deep-pelagic Mesobius antipodum displayed a third strategy, that of a midwater mesocarnivore picking or stalking. Ontogenetic dietary shifts were noted for the primarily demersal grazers Caelorinchus braueri, C. simorhynchus, Coryphaenoides striaturus and Malacocephalus laevis. Mesopelagic fish, shrimps and squid formed part of the diet of all species. These prey, taken at the bathyal/deep-pelagic interface, are an important source of energy transport from productive surface waters to the deep benthos.  相似文献   

9.
We have compared the distribution of mesopelagic, benthopelagic and benthic fauna between two areas: one on the continental side of the Catalan Sea (cCS: northwestern Mediterranean) and one to the SW of the Balearic Islands (SWB: southwestern Mediterranean) at depths between 147 and 2266 m. Based on 88 bathyal fish and crustaceans (Decapoda and Peracarida) dominant in these communities, we compared the maximum depth of occurrence (MDO) of (upper) middle-slope species and the minimum depth of occurrence (mDO) of lower-slope dwelling species. Mid-slope fish, decapods, peracarids and, within the latter, amphipods and cumaceans had a deeper MDO in the cCS than in the SWB. Depth differences between MDO of species were significant for all taxa, except isopods. In the same way, lower slope fish and decapods had a shallower mDO in the SWB than in the cCS. Within peracarids, the dominant taxon (amphipods) also followed this trend. Depth differences in mDO of species between the areas were significant for decapods and for amphipods (not for fish, nor all peracarids nor cumaceans). In summary, most taxa showed a deeper depth distribution of middle-slope species in the cCS, and a shallower depth distribution of lower-slope dwelling species in the SWB. This suggests that the whole community, from small detritus-feeders (peracarids) to top predators (fish) have a similar response to a common signal. Much basic information on the biology and possible environmental factors affecting deep-sea species distribution is not available, so causes of the trends demonstrated here cannot be fully evaluated. In spite of these obvious limitations, we have shown that (1) mesopelagic decapods (e.g., Gennadas elegans and Sergia robusta), with a higher dependence upon primary sources of food close to the surface primary production, showed greater differences in their mDO between the areas than benthopelagic (e.g., Acanthephyra eximia, Nematocarcinus exilis) and benthic (e.g., Stereomastis sculpta, Munida tenuimana, Geryon longipes) species, and (2) fish at lower trophic levels, deduced from fractional trophic levels, showed higher differences in the MDO than fish at higher trophic levels. Trophic position of species in food webs seems the most important factor affecting the distributional differences between contrasting areas.  相似文献   

10.
This study analyzed the factors structuring demersal fish community in a tropical bay in southeastern Brazil. The results were used to quantify the partitioning of ecological variation among the environmental, spatial and temporal components molding the fish community. Three bay zones (inner, middle and outer) were defined according to depth and salinity gradient. Monthly samplings were conducted by bottom trawl tows during daylight hours, between October 1998 and September 1999. In each zone, three replicate samples were taken. Ninety-three fish species from 73 genera and 37 families were recorded in the 108 samples. Two demersal fish assemblages were evidenced, one in the inner and the other in the outer zone. These assemblages were characterized by changes in species composition and relative abundance. Depth, followed by transparency and salinity, influenced spatial pattern of fish assemblages. The largest part of the explained variation occurred as a result of the spatial structure of environmental variables, which means that both species and environmental variables presented similar spatial structure. The spatial effect, not the seasonal, explained the highest part of species variations. The amount of unexplained variation was relatively high (76%), even assuming that part of it is due to nondeterministic fluctuation, which could be due to local effects of unmeasured (biotic and abiotic) controlling variables. Knowing the relative importance of these factors can be of decisive importance when applying casual hypotheses in the framework of some precise ecological theory and should facilitate management, planning, and usage of bay resources.  相似文献   

11.
The demersal fish and megafaunal assemblages in the area of Heraklion Bay, Crete, were sampled during four research cruises from September 1994 to September 1995 within the framework of the CINCS project, using a stratified trawl survey at depths ranging from 50 to 1000 m. The sampling at 1000 m depth was the deepest ever made in Greek waters, using a bottom otter trawl. Species density and biomass were found to vary between depths and seasons, with higher values occurring at the shallow stations. Species distribution and communities are also reported. A total of 127 species of osteichthyes, chondrichthyes, crustaceans, and cephalopods were recorded, four of which were found for the first time in Greek waters. Percent similarity index (PSI) was used to assess the differences in the relative abundance of species pairs between depth zones and seasons. Principal component analysis (PCA) was applied to examine station variability statistically.  相似文献   

12.
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13.
The timing and location of settlement of two cohorts (spring and fall) of windowpane (Scophthalmus aquosus) were identified based on collections from 64 sampling locations along a corridor from the lower estuary, through the inlet, and on to the adjacent inner continental shelf in southern New Jersey. Spatio-temporal patterns of settlement during 1989–1998 were determined based on capture location and timing, and eye migration stage. Spring-spawned windowpanes were collected in estuarine, inlet and ocean habitats as larvae, during settlement, and after settlement. Densities of spring-spawned larvae (∼2–10 mm standard length (SL)) peaked in May in all habitats (estuary, inlet, and ocean). Initial settlement of spring-spawned windowpane occurred during May in the inlet and ocean when fish had grown to ∼7–8 mm SL (mid-point of eye migration), but fish did not appear in demersal estuarine collections until June when they were larger and more developmentally advanced (∼24–32 mm SL; post-eye migration). A transitional settlement period, comprised of a progressive habitat shift from pelagic to demersal habitats, is proposed for the spring cohort to explain the observed patterns. Fall-spawned fish of all developmental stages and sizes were virtually absent from estuarine collections. Fall-spawned larval (∼2–10 mm SL) densities peaked in October in inlet and ocean habitats and fish began settling there during the same month at sizes similar to the spring cohort (∼7–8 mm SL). This research confirms that there are important cohort-specific and life-stage dependent differences in young-of-the-year (YOY) windowpane habitat use in southern New Jersey and perhaps in other east coast US estuaries. These differences may affect the overall contribution that each cohort makes to a given year class and thus, may have an important role in determining the recruitment dynamics of this species.  相似文献   

14.
Although the organization patterns of fauna in the deep sea have been broadly documented, most studies have focused on the megafauna. Bivalves represent about 10% of the deep-sea macrobenthic fauna, being the third taxon in abundance after polychaetes and peracarid crustaceans. This study, based on a large data set, examined the bathymetric distribution, patterns of zonation and diversity–depth trends of bivalves from the Porcupine Seabight and adjacent Abyssal Plain (NE Atlantic). A total of 131,334 individuals belonging to 76 species were collected between 500 and 4866 m. Most of the species showed broad depth ranges with some ranges extending over more than 3000 m. Furthermore, many species overlapped in their depth distributions. Patterns of zonation were not very strong and faunal change was gradual. Nevertheless, four bathymetric discontinuities, more or less clearly delimited, occurred at about 750, 1900, 2900 and 4100 m. These boundaries indicated five faunistic zones: (1) a zone above ∼750 m marking the change from shelf species to bathyal species; (2) a zone from ∼750 to 1900 m that corresponds to the upper and mid-bathyal zones taken together; (3) a lower bathyal zone from ∼1900 to 2900 m; (4) a transition zone from ∼2900 to 4100 m where the bathyal fauna meets and overlaps with the abyssal fauna and (5) a truly abyssal zone from approximately 4100–4900 m (the lower depth limit of this study), characterized by the presence of abyssal species with restricted depth ranges and a few specimens of some bathyal species with very broad distributions. The ∼4100 m boundary marked the lower limit of distribution of many bathyal species. There was a pattern of increasing diversity downslope from ∼500 to 1600 m, followed by a decrease to minimum values at about 2700 m. This drop in diversity was followed by an increase up to maximum values at ∼4100 m and then again, a fall to ∼4900 m (the lower depth limit in this study).  相似文献   

15.
O. N. Zezina 《Oceanology》2008,48(6):832-836
Of particular interest in the vertical biological zoning of the continental slope in seas and oceans are the substantial differences in the composition, diversity, and abundance (biomass and production) of benthic faunal communities populating the upper and lower subzones of the bathyal zone. The upper bathyal subzone (down to depths of 1500 ± 500 m) resembles the neritic (shelf) one, while its lower subzone is characterized by both reduced diversity and biomass, being similar in its biological parameters to the near-slope abyssal zone (>3000 m). The study of the bottom contour currents and related sediments (contourites) made the geological prerequisites for such differences understandable. Based on a comparative analysis of the bionomical boundaries and core depths of the contour currents in the North Atlantic and Gulf of Alaska, a changing of trophic zones, as well as quantitative and production characteristics of benthic communities, are established. It is shown that the differences between the biological parameters of the upper and lower bathyal subzones (the benthic biomass, the feeding mode of invertebrates, the growth rate, and the maximal sizes of adult specimens) are related to geological agents such as roiling and redeposition of the sediments.  相似文献   

16.
Demersal fish surveys carried out off Namibia from 1990 to 2000 were used to study the dynamics of demersal fish assemblages on the shelf and upper slope. The study was performed on each major assemblage, i.e. over the shelf (100–300 m deep) and the slope (300–600 m). Changes in size spectrum, diversity, species composition and trends in abundance of the dominating species were analysed. The most evident changes were those related to overall abundance and diversity of the slope assemblage.  相似文献   

17.
Drowned reefs, fossil reefs or paleo-reefs, are important ecologically as areas of high biodiversity, foraging, shelter environment, and as areas supporting the spawning aggregations of economically important reef fish species. This is particularly significant when the structures are situated in a wide soft-bottom continental shelf. The presence of limestone structures, fossil reefs and pinnacles dating from circa 8 to 9 ka, to the north of the Paria Peninsula in north-eastern Venezuela, has been known to local fishermen for decades. Using echograms obtained during acoustic fisheries evaluations and the scarce previously available information, an improved location map of hard-bottom structures was made. Benthic samples to study macromolluscs were taken at depths between 54 and 93 m using an unmodified 2-m beam trawl. Four trawl samples were located over fossil reef areas while another four were situated in soft-bottom valleys between limestone structures. Fossil reefs in the area showed a highly patchy distribution. A total of 91 species from 43 Bivalvia, Gastropoda and Scaphopoda families were found, Gastropoda being the dominant class with 49 species. Paleo-reef-covered areas showed higher species richness and only 21% of the species found were common to both substrates. Gastropods Tonna maculosa and Polystira albida were the most abundant species and occurred in both substrate types. Bivalve life habits, a mixture of organism–substrate relationships, shell fixation, mobility and feeding type, differed significantly according to bottom type. Six species are recorded for the first time for eastern Venezuelan waters. Bottom heterogeneity plays an important role in marine ecosystems, providing shelter to fish populations and may be significant as breeding and nursery areas. Its presence in a region with biogeographical interest, situated in the confluence of three major provinces and with oceanographic conditions varying seasonally from upwelling dominated to Orinoco River discharges, makes this the area of interest and it should be evaluated as a possible Marine Protected Area.  相似文献   

18.
The seasonal, spatial and bathymetric changes in the distribution of chloroplastic pigments (Chl a, phaeopigments and CPE), TOC, TON, ATP, bottom water nutrient content and the main biochemical classes of organic compounds (lipids, proteins and carbohydrates) were recorded from May 1994 to September 1995 over the continental margin of northern Crete. The concentration of chloroplastic pigment equivalents (CPE) was always low, dropping dramatically along the shelf-slope gradient. Microbial activity (ATP) also dropped sharply beyond the continental shelf following a distribution pattern similar to TOC and TON. Lipid, protein and carbohydrate concentrations, as well as biopolymeric carbon were comparable to those reported for other more productive areas, however, the quality of the organic matter itself was rather poor. Thus, carbohydrates, the dominant biochemical class, were characterised by being highly (80–99%) refractory, as soluble carbohydrates represented (on annual average) only 6% of the total carbohydrate pool. Protein and lipid concentrations strongly decreased with depth, indicating depletion of trophic resources in the bathyal zone. Proteins appeared to be the more degradable compounds and indeed the protein to carbohydrate ratios were found to decrease strongly in the deeper stations. Organic matter content and quality decreased both with increasing distance from the coast and within the sediment. All sedimentary organic compounds were found to vary between sampling periods, with the changes being more pronounced over the continental shelf. The different temporal patterns of the various components suggest a different composition and/or origin of the OM inputs during the different sampling periods. The amount of material reaching the sediments below 540 m is extremely low, suggesting that most of the organic material is decomposed and/or utilised before reaching the sea floor. In conclusion, the continental shelf and bathyal sediments of the Cretan Sea can be considered, from a trophic point of view, as two different subsystems.  相似文献   

19.
Analyses of six years of bottom trawl data collected from Northumberland Strait, southern Gulf of St. Lawrence revealed four major fish assemblages, two of which occurred in the same two geographic areas each year. One of the two persistent assemblages occurred in deeper water off northwestern Prince Edward Island and consisted mostly of demersal fishes. The other persistent assemblage contained a mixture of demersal and pelagic fishes and occurred primarily in shallow water of central Northumberland Strait. Analyses of abiotic (depth, bottom temperature, substratum type) and biotic (presence of American lobster Homarus americanus, northern lady crab Ovalipes ocellatus) factors revealed bottom temperature and catches of lady crab correlate best with the fish assemblage structure each year, but correlation values were low (ρw ≤ 0.48). Combinations of all abiotic and biotic variables only marginally improved the strength of the correlations in four of six years (2002, 2003, 2005, 2006). Changes observed in the Northumberland Strait ecosystem over the six years included an increase in the ratio of pelagic to demersal fishes, disappearance of one of the four assemblages, and increased spatial overlap between the two persistent assemblages, which coincided with an increase in bottom temperature. The increasing importance of pelagic fishes, relative to demersal fishes, suggests a shift in food web structure may be occurring in Northumberland Strait.  相似文献   

20.
The Arabian Sea oxygen minimum zone (OMZ) impinges upon the Indian continental margin at bathyal depths (150-1500 m) producing changes in ambient oxygen availability and sediment geochemistry across the seafloor. The influence of these environmental changes upon the epi-benthic megafaunal assemblage was investigated by video survey at six stations spanning the OMZ core (540 m), lower boundary (800-1100 m) and below the OMZ (2000 m), between September and November 2008. Structural changes in the megafaunal assemblage were observed across the six stations, through changes in both megafaunal abundance and lebensspuren (biogenic traces). Most megafauna were absent in the OMZ core (540 m), where the assemblage was characterised by low densities of fishes (0.02-0.03 m−2). In the lower OMZ boundary, megafaunal abundance peaked at 800 m, where higher densities of ophiuroids (0.20-0.44 m−2) and decapods (0.11-0.15 m−2) were present. Total abundance declined with depth between 800 and 2000 m, as the number of taxa increased. Changes in the megafaunal assemblage were predicted by changes in abundance of seven taxonomic groups, correlated to both oxygen availability and sediment organic matter quality. Lebensspuren densities were highest in the OMZ boundary (800-1100 m) but traces of large infauna (e.g., echiurans and enteropneusts) were only observed between 1100 and 2000 m station, where the influence of the OMZ was reduced. Thus, changes in the megafaunal assemblage across the Indian margin OMZ reflect the responses of specific taxa to food availability and oxygen limitation.  相似文献   

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