Hyperbenthic crustacean fauna of the Gullmarfjord area (western Sweden): Species richness,seasonal variation and long-term changes

Distribution of 118 species of Amphipoda, Mysidacea and Decapoda, sampled in 1984 and 1985 with an epibenthic sledge along a transect from the Skagerrak to the inner Gullmarfjord (Sweden), is described. Amphipods were richest in species in the Skagerrak, while most mysid species were taken at the sill. Deca-impoverished and the Lilljeborgidae, earlier represented by three species, had disappeared since the 1930s. The changes are most likely caused by eutrophication of the fjord. and deep-basin samples; (III) sill samples; (IV) Skagerrak samples. Characteristic species of the groups were identified with a pseudoF-test. Detrended Correspondence Analysis indicated seasonal faunal changes at 42 and 72 m depths. At both depths a shift in numerical dominance from amphipods to mysids was found in winter. The most pronounced changes seemed to occur at 42 m. Changes in composition and abundance of species during a renewal of the bottom water indicated that mysids were influenced by presumed near-bottom currents, while amphipods and decapods were not. Comparison of the present amphipod fauna with the fauna in 1933–37 revealed significant differences. The fauna in the deep basin was impoverished and the Lilljeborgidae, earlier represented by three species, had disappeared since the 1930s. The changes are most likely caused by eutrophication of the fjord.     

Composition of the near-reef zooplankton at Heron Reef,Great Barrier Reef

Using a light trap, zooplankton was sampled at three stations at Heron Reef, Great Barrier Reef: (a) a typical patch reef in the Heron lagoon, (b) a site in 8 m water on the southern slope of Heron reef, and (c) a station approximately 300 m south of (b), in the open water of the channel between Heron and Wistari reefs. Samples were taken at the surface and on the substratum at the lagoon and reef-slope stations, and at 3 to 6 m depth at the open-water station. A total of 114 taxa, many recognized as species, were distinguished in the samples. Pronounced differences existed in abundance, diversity, and taxonomic composition of the samples obtained at different stations. Less pronounced differences existed between surface and substratum samples from the same station. Near-reef samples were more similar to one another than to open-water samples. Decapod larvae, amphipods, and cumaceans were all abundant in near-reef samples and very rare in open-water samples. Forams, isopods, mysids and polychaetes were common in near-reef samples, and rare or absent in open-water samples. Copepods were abundant in all samples but the near-reef samples contained predominantly different species than did samples from the open water. The near-reef fauna included 66 taxa which did not occur in open-water samples. Many of these were epibenthic rather than strictly planktonic in behaviour.     

Does the composition of the demersal fish assemblages in temperate coastal waters change with depth and undergo consistent seasonal changes?

The aim of this study was to determine whether the composition of the demersal fish fauna in coastal marine waters in temperate Australia changes markedly with increasing water depth and distance from the shore and whether the composition of the fish fauna in water depths of 5 to 35 m undergoes cyclic, seasonal changes. Samples of demersal fishes were therefore collected by trawling over the predominantly sandy substrate at nine sites located in water depths of 5 to 15 m or 20 to 35 m and within 20 km of the shore in four regions along ∼200 km on the lower west coast of Australia. The sampling regime involved trawling for fishes at each site at night in seven consecutive seasons between the summer of 1990/1991 and winter of 1992. A total of 72 435 fishes, representing 77 families, 143 genera and 172 species was caught. The compositions of the fish faunas in offshore waters with depths of 5 to 35 m were shown to differ markedly from those previously recorded for nearshore marine waters in the same regions. However, as some species, such as Sillago burrus, S. vittata, S. bassensis and Rhabdosargus sarba, increase in size, they move out from their nursery areas in nearshore waters into deeper and more offshore waters, where spawning occurs. Ordination showed that, in each of the four regions, the composition of the fish fauna in depths of 5 to 15 m differs from that in depths of 20 to 35 m. This difference is attributable to the fact that some species, such as  S. burrus, S. vittata and Upeneichthys lineatus, are far more abundant in depths of 5 to 15 m, whereas other species, such as S. robusta, U. stotti and Lepidotrigla modesta, occur predominantly in depths of 20 to 35 m. However, the samples collected from the single site that was inshore but in deeper water demonstrate that the composition of the fish fauna is influenced by distance from shore as well as by water depth. The compositions of the fish faunas differed with latitude, largely due to the fact that some subtropical species, such as Polyspina piosae, S. burrus and  S. robusta, did not extend down into the more southern regions. Ordination also showed that the composition of the fish faunas at all but one of the nine sites underwent pronounced and consistent cyclic, seasonal changes. This seasonal cyclicity at the different sites was attributable to sequential patterns of immigrations and emigrations by a number of fish species during the course of the year. These seasonal migrations involved, inter alia (1) movements of certain species from their nursery areas into these deeper waters, e.g.  S. bassensis and Scobinichthys granulatus; (2) migrations into and off the sandy areas of the inner continental shelf, e.g. Arnoglossus muelleri; (3) migrations to spawning areas, e.g. Sillago robusta; and (4) movements into areas where detached macrophytes accumulate in winter, e.g. Cnidoglanis macrocephalus and Apogon rueppellii. Received: 21 August 1998 / Accepted: 9 February 1999     

Species diversity and faunal affinities of meiobenthic Copepoda in the deep sea

This first attempt at measuring species diversity of the numerically abundant marine meiobenthos on a vertical gradient into the deep sea supports the stability-time hypothesis developed with the macrofauna. Diversity, as measured by rarefaction, indicated highly evolved, stable and unique assemblages in the deep sea. Shelf samples were consistently dominated by a few species; below 1000 m many of the species were new and few were duplicated from sample to sample. Rarefaction curves are clearly separable for the three environments, with the vertical component of diversity increasing to abyssal depths. Rarefaction analysis of shelf samples above and below the Cape Hatteras zoogeographical boundary further revealed distinct spilits in the faunal assemblages. Faunal affinity analyses indicate that the deep-sea fauna is not homogenously distributed over wide expanses of the ocean floor and are contrary to previously reported macrofaunal findings.     

Responses of fish assemblage structures to sandy beach types in Kyushu Island, southern Japan

To determine differences in fish assemblage structures between beach morphodynamic types on an exposed sandy shore, three beach types (reflective, intermediate, and dissipative) were sampled at Fukiagehama Beach, Kyushu Island, southern Japan, in May, August, and November 2006 and 2007. Distinct differences in physical conditions and the amount of major prey invertebrates, such as copepods, mysids, and amphipods, were recognized between the three beach types. The reflective beach was characterized mainly by turbulent swashes, coarse sediment, and a low abundance of major prey invertebrates. In contrast, the dissipative beach was characterized mostly by benign swashes, fine sediment, and a high abundance of prey invertebrates. The intermediate beach tended toward an intermediate condition between the reflective and dissipative beaches. The fish assemblage structures also differed clearly between the three beach types, with species and individual numbers being greatest on the dissipative beach and lowest on the reflective beach. A similarity index indicated differences in species composition of the assemblages between the beach types. Such differences arose primarily from the differential distributions of two dominant trophic groups, zooplankton (mostly copepods) and epibenthic crustacean (mainly mysids and amphipods) feeders, between the beach types, both groups tending to increase in species and individual numbers from the reflective beach to the dissipative beach. In addition, the mean standard length of all fish collected in each month tended to decrease toward the dissipative beach. These results suggested that beach types strongly influence sandy beach fish assemblage structures.     

Local changes in the composition and community structure of suprabenthic peracarid crustaceans on the bathyal Mediterranean: influence of environmental factors

Deep-water assemblages of suprabenthic peracarids were analyzed in the SW Balearic Islands (Algerian Basin, southwestern Mediterranean) between 249 and 1,622 m depth; the patterns of species composition, possible zonation, and trophic structure found in this area were compared with those exhibited by peracarids in the mainland side of the Catalan Sea slope (northwestern Mediterranean). One hundred and four peracarid species (plus one leptostracan) were identified on the Balearic Islands slope, amphipods being the most diversified taxon (45 species). On the Balearic slope, two distinct depth assemblages were distinguished: one at the upper slope (US), between 249 and 402 m depth and the second at the deep slope, between 543 and 1,620 m depth. A remarkable species substitution occurred at depths between 402 and 638 m. In the Catalan Sea, in addition to the US assemblage occupying depths between 208 and 408 m, a second boundary of faunal change was found around 1,250 m. Suprabenthos biomass increased from 242 to approximately 500 m. Suprabenthos attained the highest biomass values (100 g wet weight/10,000 m²) at intermediate depths between 504 and 1,211 m, as also occurred with the associated zooplankton collected with suprabenthos (peak biomass between 502 m and 898 m). Suprabenthos biomass did not show any significant correlation with any environmental water-column variable. In contrast, zooplankton (especially small fish and decapod crustaceans) showed a significant positive correlation with fluorometry and turbidity at different levels of the water column. The feeding guilds of species showed important differences between the two areas only on the US, with a higher abundance of deposit feeders in the Catalan Sea (20.4%) than in the Balearic Islands (4.2%). The low contribution of deposit feeders in the SW Balearic Islands may ultimately be a consequence of the lack of river discharges in this area.Communicated by S.A. Poulet, Roscoff     

Diets of clupeoid,stomiatoid and salmonoid fish of the Rockall Trough,northeastern Atlantic Ocean

The trophic interactions of species of fish of the continental slopes have not been investigated previously in detail. The present study examines the diets of the clupeoid, stomiatoid and salmonoid species occurring demersally and pelagically in the Rockall Trough to the west of Scotland and Ireland. Pelagic fish were collected between the surface and about 2 500-m depth between 1973 and 1978. Demersal fish were sampled at 250-m intervals of depths between 500- and 2 900-m depth during the years 1975 and 1981. Of the 28 species caught, 18 were strictly pelagic and dominated by the stomiatoids while five were strictly demersal. The remaining five species occurred in both the pelagic and demersal environment. The commonest clupeoid was Alepocephalus bairdii, which is a dominant species within the demersal fish associations at depths of 750 to 1 250m. This species, along with the deeper-living A. agassizi, and 3 other alepocephalid species feed primarily on benthopelagic prey but also exploit the epibenthos. The stomiatoid species, such as Cyclothone microdon, C. braueri, Maurolicus muelleri and Argyropelecus hemigymnus, dominate the associations of pelagic fish in the Trough. They feed on different proportions of ostracods, copepods and amphipods. Of the salmonoids, only Argentina silus and Bathylagus euryops occurred commonly and both feed on benthopelagic fauna, the latter at much greater depths than the former. The principal factor acting to prevent direct competition between species is the modal centres of bathymetric distribution of the species. Other contributing factors are briefly discussed.     

Parasitism and ecological relationships among deep-sea benthic fishes

We have studied the metazoan parasite fauna of 52 species of deep-living benthic fishes from depths of 53 to 5000m off the New York Bight (39–49°N; 70–72°W). 17144 parasites were recovered from 1712 fishes. The infestation rate was 80%, with an average of 12.5 worms per host. Percentage occurrence by group among all fishes was Monogenea 12.9%, Digenea 48%, Cestoda 22.1%, Nematoda 54.5%, Acanthocephala 3.8%, and Copepoda 4.5%. Differing composition of the parasite fauna in different fish species reflects differences in diet. Specialized feeders are rather distinct; generalized feeders, which predominate, show overlaps in parasite fauna. In individual species, changes in diet with growth are reflected in changes in the parasite fauna. Infestation rate is directly related to abundance of the free-living fauna; hence, fish from within the submarine canyon are more heavily infested than those living without. Although it contains fewer families and genera than shallow faunas, the deep-sea parasite fauna is not extremely unusual in terms of its abundance, diversity, or host specificity. At the greatest depths, parasite abundance and diversity dramatically decline.     

Deep-water decapod crustacean communities in the Northwestern Mediterranean: influence of submarine canyons and season

The specific composition and abundance of bathyal decapods in the Catalan Sea were investigated. A total of 109 bottom trawls were effected at depths ranging from 141 to 730 m on the continental slope in the Catalan Sea (northwestern Mediterranean) during two sampling cruises in spring and autumn 1991. Multivariate analysis of the samples revealed four groups of the decapod crustacean communities: (1) A shelf-slope transition-zone group at depths between 146 and 296 m, primarily characterized by the presence of Plesionika heterocarpus; (2) an upper-slope community between 245 and 485 m, characterized by the presence of the mesopelagic species Pasiphaea sivado and Sergestes arcticus, with Processa nouveli, Solenocera membranacea and Nephrops norvegicus as secondary species; (3) a middle-slope community below 514 m, with Aristeus antennatus and Calocaris macandreae as the most abundant species; (4) a group at 430 to 515 m, comprising all samples collected exclusively within or in the vicinity of submarine canyons. Mesopelagic decapods were predominant on the slope, while benthopelagic fishes (Merluccius merluccius, Micromesistius poutassou, Gadiculus argenteus) replaced mesopelagic decapods on the shelf. There were seasonal variations, with higher densities of mesopelagic species in spring, which were probably related, among other factors, to variations in the photoperiod. Our surveys also revealed higher species richness in the canyons together with seasonal changes in the megafaunal biomass. Generally, the upper and middle-slope communities both displayed seasonal changes in the composition and abundance of megabenthos.     

Faunal relationships among the near-reef zooplankton at three locations on heron reef,great barrier reef,and seasonal changes in this fauna

Samples of zooplankton were collected using a light trap at 5 sites in 3 locations on Heron Reef: (a) near the surface of open water 300 m south of the reef crest; (b) near the surface and at the substratum on the upper reef slope; (c) near the surface and at the substratum on a patch reef in the Heron lagoon. The collections made were analysed with respect to: (a) distribution and abundance of the taxa present; (b) faunistic relationships among samples from the 5 sites; (c) seasonal changes in both of these factors. A total of 181 taxa were recognised, many of which are identified to species, and many of which are demersal or epi-benthic in habits. At all sites, the abundance of animals increases from May to November, and faunal similarity between sites also changes. In May, reef collections are generally similar to one another and, with the exception of the slope surface collection, distinct from the open water collection. In September this pattern is enhanced, but in November slope collections more closely resemble the open water collection, while the lagoon collections are quite distinct from slope and open water collections. Lagoon surface and substratum collections also differ considerably from each other at this time. A MULTCLAS cluster analysis of the samples confirms the pattern of change in faunal relationships seen from examination of the collections. Dark-trap samples were used to assess the bias introduced by using a light to attract the animals, as well as to estimate the density of the fauna sampled. Lighttrap samples over-represent calanoid and harpacticoid copepods and gammarid amphipods, but the bias is minor and does not prevent use of a light trap as an efficient sampling tool for near-reef plankton. The density of the fauna is approximately 700 animals m^-3 at all sites. This may be a lower density than in more tropical regions. Pronounced seasonal changes occur in faunal composition of collections from open water and from surface sites. The substratum collections show more constant faunas throughout the year. Major changes are primarily in the proportions of copepods and cumaceans present. Changes in amphipod numbers are also important at lagoon sites.     

Resident mysids: community structure,abundance and small-scale distributions in a coral reef lagoon

Seasonal and diel variations in community structure and abundance of coral-reef lagoon mysids were examined at Davies Reef in the central region of the Great Barrier Reef (GBR) between June 1980 and May 1981. Twenty-five mysid species belonging to three subfamilies of the family Mysidae were captured during the study, with six new records for the GBR. The epibenthic mysid community differed from that in the overlying water, was faunistically uniform, but formed characteristic seasonal and diel groupings. The dominant epibenthic species were Erythrops sp., Anisomysis pelewensis, Doxomysis littoralis, A. laticauda, Prionomysis stenolepis, A. lamellicauda, and A. australis, five of which formed schools. Total mysid abundances ranged between 110 and 790 m^-3 with peak abundance in October. Schooling species occurred at local densities of up to 500 000 m^-3. Mysids were absent from shallow and midwater depths during the day, but were distributed throughout all depths at night with peak abundances in mid-water and deep layers. The dominant species in the water column at night were Pseudanchialina inermis, A. laticauda and Gastrosaccus indicus, in descending order of abundance. Lagoonal mysids contribute little to the food of sessile reef planktivores, as all but three species remain concentrated near or on the lagoon floor both day and night. The contribution of resident lagoon mysids to reef trophodynamics is probably through remineralization of lagoon detritus. Given the vast reef areas comprised of sandy lagoons, the large populations and relatively large size of lagoon mysids, this trophodynamic role may be of considerable importance.A.I.M.S. Contribution No. 477     

Observation and collection of deep-reef fishes off the coasts of Jamaica and British Honduras (Belize)

Over 60 species of reef fishes were observed from submersibles between 50 and 305 m depth, and 25 species were collected from the same depth range using fish traps and submersibles. Short transects gave relative abundance of some species with depth. Many shallow-water coral-reef fishes reach depths far below the lower growth limits of reef-building corals. A true “deep-reef” fauna exists, but the juveniles of some of these species are found at depths of less than 50 m.     

Ecological overlap between macrourids in the western mediterranean sea

Stomachs from over 323 specimens of Hymenocephalus italicus, 168 Nezumia aequalis, 160 Coelorhynchus coelorhynchus and 1670 Trachyrhynchus trachyrhynchus were collected from September 1976 to September 1978 from the West Mediterranean continental slope at depths between 200 and 800 m. Copepods, amphipods and other pelagic crustanceans form the main fraction of the diet of H. italicus. The diets of N. aequalis and C. coelorhynchus consist largely of polychaetes, isopods, amphipods, mysids and decapod crustaceans. T. trachyrhynchus feed heavily on decapods. Decreasing fractions of small crustaceans are found in diets of all species as fish size increases. The mean size of prey increases with the body size of the fish. A positive size-depth correlation has been observed in macrourids. Juveniles and intermediates of N. aequalis, C. coelorhynchus and T. trachyrhynchus were found in shallow-water zones (<400 m), while adults were more common in deeper areas. Niche breadth and niche overlap were calculated between size groups. Niches are relatively broader with respect to habitat and narrower for prey size and prey type. The food overlaps between N. aequalis C. coelorhynchus and between C. coelorhynchus and T. trachyrhynchus are notably the greatest. Overlap in relation to habitat is high, while the correlation between niche parameters is very poor, indicating a certain degree of independence between these factors. Alpha matrices were estimated using both multiplicative ( product) and additive ( summation) multidimensional estimates for niche overlaps. Rates of competitive exclusion are low.     

Habitat associations and diet of young-of-the-year Pacific cod (<Emphasis Type="Italic">Gadus macrocephalus</Emphasis>) near Kodiak,Alaska

The influence of environmental variables and habitat on growth and survival of juvenile gadoid species in the Atlantic has been clearly demonstrated; conversely, in the North Pacific little is known about the habitat and ecology of juvenile Pacific cod (Gadus macrocephalus Tilesius). The hypothesis that density of young-of-the-year (YOY) Pacific cod in nearshore habitats is predicted by shallow depth and the presence of eelgrass and macroalgae was tested in a variety of nearshore habitats adjacent to commercial fishing grounds near Kodiak Island, AK. From 10 to 22 August 2002, a beach seine and small-meshed beam trawl were used to capture YOY Pacific cod (n = 254) ranging from 42 to 110 mm fork length. Depth, water temperature, salinity, sediment grain size, and percent cover by emergent structure (i.e. tube-dwelling polychaetes, sea cucumber mounds, macroalgae) were measured prior to fishing. Density of YOY Pacific cod was highest in areas of moderate depth (15–20 m) and positively and linearly related to percent cover by sea cucumber mounds and to salinity. No previous studies have documented fish utilizing sea cucumber mounds as habitat. Furthermore, eelgrass and macroalgae were inconsequential to cod distribution. Diets consisted mainly of small calanoid copepods, mysids, and gammarid amphipods and were significantly related to cod length and depth. This work provides important information on previously undocumented factors that affect distribution and feeding of YOY Pacific cod, which ultimately influence growth and survival in this species.     

塔里木河中游水盐梯度下的物种多样性研究

根据塔里木河中游5个断面30眼地下水监测井和30个植物样地2006—2008年调查监测的数据,分析了输水堤防修建后地下水埋深、地下水质以及物种多样性的变化及其相互关系。结果表明：地下水埋深的空间变化表现为沿河道方向先增加后减小的趋势,在时间上则表现为,从2006年到2008年埋深呈逐渐增加的特点;地下水化学类型的变化,在空间上表现出沿着河道方向有由Cl-—SO42-—Na＋—Mg2＋向Cl-—Na＋类型转变的趋势,在时间上,地下水矿化度逐渐增加。物种多样性总体上呈现增加变化,地下水位和水质对塔里木河中游物种多样性变化有着密切的关系,地下水埋深2.8~3.7 m,矿化度1.8~2.4 g·L-1水平下的多样性较高,随着地下水埋深的增大和矿化度的升高,物种多样性水平降低。     

Biomass of the invertebrate megabenthos from 500 to 4100 m in the northeast Atlantic Ocean

Data are presented on the biomass of the invertebrate megafauna at 22 stations on the continental slope in the Porcupine Seabight (PSB) (northeast Atlantic Ocean). Samples were collected between 1980 and 1982. Several units of biomass are used, all of which illustrate a decrease by a factor of about 30 from 500 to 4100 m. Lognormal curves were fitted to the data, the gradients of which were very similar for all biomass units and similar to the value for a transect down the continental slope in the western Atlantic. Biomass levels in the PSB are compared with those from other deep-sea environments. Some published values are more than ten times higher than the values reported here, while others are less than a tenth. The reasons for these differences and trends are discussed in terms of food supply. Sampling variability was examined at two stations, but by chance one (at 1300 m) appeared to encompass a sharp faunal discontinuity of the dominant fauna and the other (at 4000 m) contained very small numbers of large animals. For these reasons, sample variability was high at the repeat stations. Suspension-feeders and crustaceans dominated the biomass at upper-slope depths, while echinoderms were dominant on the middle and lower slope. As a result of this phyletic change, there was a small but insignificant decrease in mean body weight with increasing depth. Within phyla there was also a small but insignificant decrease with depth. If large species are excluded from the biomass/depth regression, the gradient changes considerably, demonstrating the increasing importance of small species at greater depths. The size distribution of megafaunal biomass was examined at several stations. This indicated that the megafauna form a functional group distinct from the macrofauna, just as the macrofauna are distinct from the meiofauna.     

Density surface modelling with line transect sampling as a tool for abundance estimation of marine benthic species: the <Emphasis Type="Italic">Pinna nobilis</Emphasis> example in a marine lake

Density estimation of marine benthic fauna is most often conducted with fishery surveys using dredges or trawls. These estimates are often unreliable due to low and variable efficiency and are inappropriate when dealing with rare or endangered species. In the marine Lake Vouliagmeni, a density surface modelling (DSM) approach using survey data from line transects, integrated with a Geographic Information System (GIS), was used to estimate the population density of the endangered fan mussel Pinna nobilis. This is the first time that such an approach has been applied for a marine benthic species. DSM was beneficial in relation to traditional distance sampling. Apart from providing a more precise total abundance estimate, it related the density of the species to spatial covariates of interest, gave a depiction of the species dispersion in the study area, and provided abundance estimates in any sub-region of the study area. In Lake Vouliagmeni, a marked zonation of P. nobilis distribution was revealed, with the species being restricted in the shallow peripheral zone at depths <22 m. Two density peaks were observed, a major peak at depths between 12 and 13 m and a secondary peak at ∼4 m. A main hotspot of high density was also observed in the northeastern part of the lake. Total abundance of the species was estimated to be 6,770 individuals with a 95% confidence interval of 5,460–8,393 individuals.     

In situ beziehungen zwischen nahrungsangebot und aufgenommener Nahrung bei 5 Blennius-Arten (Pisces) des Mittelmeeres

Eight epiphytal samples were taken from the upper littoral at Banyuls-sur-Mer (French Mediterranean coast) and the fauna living on the thalli of algae or between bivalves was examined. Intestinal food contents of 67 specimens of 5 Blennius species (B. trigloides, B. canevae, B. sphinx, B. incognitus, and B. dalmatinus) occurring in the same biotope were also investigated. The epiphytal samples consisted of a rich supply of amphipods, bivalves, and algae. Amphipods are the preferred food of the Blennius species examined. These fishes also consume large amounts of copepods and algae, and small quantities of halacarids, bivalves, and ostracods. In addition to serving as a substrate for the main food-animals of the fishes, the algae themselves constitute an important food source. Presumably, for these reasons, the fishes remain close to the area inhabited by the algae on rocky substrates.     

Zooplankton community structure and water flow in the lee of Helix Reef (Great Barrier Reef, Australia)

To investigate which physical processes contribute most in moulding zooplankton community structure in the waters close to coral reefs, light traps moored in a grid pattern were used to collect zooplankton from the sea surface at 16 stations on the downstream side of Helix Reef during three time periods (2100-2200, 2400-0100, and 0300-0400 hours) over three consecutive nights covering the new moon period in January 1992. Two distinct zooplankton communities were present: a community composed primarily of reef-resident, demersal plankton immediately to the south of the reef in an area of reduced flushing, and a community containing coastal and shelf-seas taxa at the more exposed sites in the open flow field. The fauna composition at a number of exposed stations was as rich as that at sheltered stations both in terms of number of taxa and diversity indices but was almost an order of magnitude less abundant. The reef-resident, demersal plankton community was dominated by gammarid amphipods, mysids, and polychaetes, whereas only transient, meroplanktonic forms such as echinoderm and echinopluteus larvae and shelf-seas, holoplanktonic forms such as doliolids and larvaceans were significantly more abundant in the exposed community. Zooplankton associations were apparently formed by a combination of hydrodynamic processes, spatial and temporal distribution patterns of individual taxa, specific behaviours of certain taxa, and the interactions among taxa at different trophic levels.     

Relationship between sediment texture,species richness and volume of sediment sampled by a grab

This paper discusses the problems involved in obtaining grab samples for direct comparison of the respective benthic fauna, using information from a survey conducted across the South African Continental Shelf below the Benguela Current. Many factors influence the depth of grab penetration into the sediment and, hence, the grab sample volume. One of the most important of these factors is sediment texture. While this fact has been long recognised, most workers have attached little significance to it. It is shown here that an exponential relationship exists between the grab sample volume and sediment texture, until the minimum percentage of silt plus clay that will give a maximum grab sample volume is reached. This relationship only extends to a certain depth, in this case to 280 m. There are more species per unit number of specimens (“species richness”) in association with sand or muddy-sand than with mud. A linear relationship is given between the grab sample volume and species richness between the depths of 280 and 440 m, inclusive.