Paleoceanographic interpretations of coccoliths and oxygen-isotopes from the sediment surface of the southwest Indian Ocean

The distribution of forty-four coccolithophore species in one hundred deep-sea core-tops from the southwest Indian Ocean is described. Three coccolith assemblages have been recognised (Maputo, Agulhas Current and deep water) by the relative abundances of four ecologically significant coccolithophore species (Gephyrocapsa oceanica, Emiliania huxleyi, Calcidiscus leptoporus and Umbilicosphaera sibogae). Their biogeographical distribution appears to be related to water temperature, nutrient concentration and dissolution.The degree of preservation of coccoliths and foraminifera indicates that the carbonate lysocline lies somewhere between 3500 and 4000 m, resulting in the concentration of dissolution-resistant microfossils below this depth.Stable oxygen isotope ratios of the planktonic foraminiferal species Globigerinoides sacculifer range between −1.5 to −1.0‰ PDB (equal to 22.8–25.1°C) and occur in a narrow band on the sea floor beneath the “A” route of the Agulhas Current.These values are about 0.5 per mil PDB lighter than samples analyzed on either side of this band and can be explained by the Agulhas Current's elevated temperature at the ocean surface of 2–3°C. Thus an oxygen isotope imprint of the Agulhas Current exists beneath it on the sea floor.The Agulhas Current is probably the major factor influencing sedimentation, sediment-distribution patterns and geological features in the study area. At present it is voluminous and fast flowing, possibly eroding sediments up to 2500 m below the surface.The oxygen-isotope ratios and nannoplankton counts obtained in this study indicate, however, that the majority of samples are most probably recent or at least not older than 85,000 years. This implies that sediments are accumulating on the ocean floor and that the Agulhas Current does not have a pronounced erosional influence, at least in areas from which cores were retrieved for this study.     

Meiobenthic stocks and benthic activity on the NE-Svalbard shelf and in the Nansen Basin

Summary High Arctic meiofaunal distribution, standing stock, sediment chemistry and benthic respiratory activity (determined by sediment oxygen consumption using a shipboard technique) were studied in summer 1980 on the NE Svalbard shelf (northern Barents Sea) and along a transect into the Nansen Basin, over a depth range of 240–3920 m. Particulate sediment proteins, carbohydrates and adenylates were measured as additional measures of benthic biomass. To estimate the sedimentation potential of primary organic matter, sediment bound chloroplastic pigments (chlorophylls, pheopigments) were assayed. Pigment concentrations were found comparable to values in sediments from the boreal and temperate N-Atlantic. Meiofauna, which was abundant on the shelf, decreased in numbers and biomasses with increasing depth, as did sediment proteins, carbohydrates, adenylates and sediment oxygen consumption. Meiofaunal abundances and biomasses within the Nansen Basin were comparable with those observed in abyssal sediments of the North Atlantic. Nematodes clearly dominated in metazoan meiofauna. Protozoans were abundant in shelf sediments. Probably in response to the sedimentation of the plankton bloom, meiofauna abundance and biomass as well as sediment proteins, carbohydrates and adenylates were significantly correlated to the amount of sediment bound chloroplastic pigments, stressing the importance of food quantity to determine benthic stocks. Ninety-four percent of the variance in sediment oxygen consumption were caused by chloroplastic pigments. Benthic respiration, calculated per unit biomass, was 3–10 times lower than in the East Atlantic, suggesting low turnover rates in combination with a high standing stocks for the high Arctic benthos.     

Biodiversity of peracarid crustaceans(Malacostraca) from the shelf downto the deep Arctic Ocean

During three expeditions with the RVs Meteor and Polarstern more than sixty thousand peracarids were sampled from the deep Arctic Ocean (northern North Atlantic) by means of an epibenthic sledge. Sampling areas were the Kolbeinsey Ridge north of Iceland (800–1100 m), the Northeast Water Polynya, off Greenland (45–517m), and 75°N east of Greenland (197–2681m). Until now 288 species of Peracarida have been identified to species level. These 288 species comprise 152 genera and 59 families of Amphipoda, Cumacea, Isopoda, Mysidacea and Tanaidacea. Thirty-eight genera were very frequent and were sampled at each expedition (these were 22 species of Isopoda, seven species of Cumacea, three species of Amphipoda and Mysidacea, each, and two species of Tanaidacea). Sixty genera are eurybathic, occurring at least over a depth range of 1000m, some even from the shelf up to 2681m depth. Only 10 genera are stenobathic, occurring only in the deep sea. No significant decrease in species number with depth or latitude could be observed. The influencing factors probably causing different community structures are diverse, ranging from food availability over substrate or hydrographical qualities to interspecific competition.     

Trophic structure of macrobenthos in the Tagus estuary and adjacent coastal shelf

The trophic structure of benthic communities in the Tagus estuary and adjacent coastal shelf was characterized according to a functional guild approach, based on sampling surveys conducted between 1987 and 2000. Macrobenthic organisms were assigned to seven distinct trophic groups (herbivorous, filter feeders, surface deposit feeders, subsurface deposit feeders, carnivores, filter feeders/detritivores, carnivores/detritivores) and the dominance of these groups was related to environmental variables using multivariate ordination techniques. Surface-deposit feeders were numerically dominant in the Tagus estuary, making up 52% of the benthic communities, while in the adjacent coastal shelf the assemblage was dominated by both surface-deposit feeders and filter feeders (37% and 33%, respectively). When biomass was considered, filter feeders and filter feeders/detritivores were the dominant groups in the estuary, while for the adjacent coastal shelf filter feeders represented 83% of the total biomass. Salinity, depth and sediment composition were the main factors structuring spatial distribution. Surface-deposit feeders were the most abundant macrobenthos of the upper estuary. Surface deposit feeders also dominated the middle and the lower estuary but the proportion of filter feeders as well as other trophic groups increased with salinity. Generally, a more even distribution of trophic structure was found at stations with high salinity. In the adjacent coastal shelf, the trophic diversity decreased with depth. The trophic structure revealed that filter feeders dominated in abundance and biomass in shallow sandy sediments (<25 m), while in deeper sandy mud and muddy habitats (>50 m to 260 m), deposit feeders and carnivores were the most important groups in abundance and biomass, respectively.     

Diversity and structure of shrew communities in montane forests of southeast Kenya

As a step towards setting conservation priorities for declining moist forests in southeast Kenya, we assessed for small mammal diversity and distribution. These habitats are under severe pressure due to increased demand an forests products and arable land, yet there is a dearth of information an impacts an biodiversity. Over an eight-month period, we used a combination of box and pitfall traps with drift fences to study 13 forest fragments in five geographic areas ranging between 3°28′−4°10′ S and 38°28′−39°2b′ E. We recorded 12 species including 10 soricids and two macroscelids in 31440 trap nights. Diversity estimates using rarefaction method indicate a species richness of 12, consistent with our collection. There were six unique species, each limited in distribution to one forest fragment. Our record of Crocidura cf. selina in Kyulu Hills is the first outside Mabira forest in Uganda where it is considered endemic and endangered. We also report the first record of C. fuscomurina in Kenya, white those of C. Luna and Suncus megalura are first in the southeast of the country. By providing new ranges to four species, our study is of significance to the biogeography and conservation of forest small mammals in the region.     

Polychaete distribution on the southwestern Atlantic continental shelf

Diversity and distribution of polychaetes on the southeastern Brazilian Shelf (SBS) adjacent to the city of Santos were studied. The study area is situated in the vicinity of Santos Bay with its estuarine complex and other small rivers along the coast. A total of 16,274 specimens belonging to 214 polychaete species were found at 21 sampling stations during two different periods. Two communities occur along the shelf and were related firstly to sediment characteristics. Prionospio dayi (Spionidae) was dominant in the inner shelf community that was characterized by well-sorted, very fine sand. The outer shelf community was found in muddy sediments with high organic matter content and was dominated by subsurface deposit feeders, like Petersenaspis capillata (Sternaspidae) and Leitoscoloplos kerguelensis (Orbiniidae), and by large carnivores such as Aglaophamus sp. (Nephtyidae) and Sigambra sp. (Pilargidae). A transition zone of mixed sediments presenting high diversity and richness was found between these communities. The characteristics of bottom water and food quality in the sediment were important to divide the inner shelf into two sub-areas. Nearshore sampling stations (A group) were more influenced by freshwater input, mainly during summer. This influence is not conspicuous at stations close to 30?m depth (B group). However the effect of South Atlantic Central Water mass (SACW) intrusion on the benthic system was observed on the inner shelf – B group during the summer. The summer intrusion of SACW onto the inner shelf may explain the higher quality of organic matter that resulted in an increase in polychaete abundance and richness.     

Seasonal variation of macrobenthic infauna in the Johor Strait,Singapore

Sediment samples were collected every three months from December 2001 to December 2002 to study the seasonal variation of soft-bottom macrobenthic community at a site (1°25′30′′N, 103°52′00′′E; depth: 6.5 m) in the Johor Strait, Singapore. Seasonal changes in species number, abundance and diversity of macrobenthic infauna significantly differed, the lowest values for the three parameters were recorded in December, the highest values for species number and species diversity in March and the highest abundance in September. Species composition and community structure also varied gradually over time. The differences in dominant species and community structure between December 2001 and December 2002 suggest an interannual variation of macrobenthic infauna.     

The distribution of the Euchaetidae (Copepoda: Calanoida) around South Georgia

Summary Fourteen species of the genus Euchaeta (Copepoda: Calanoida) were encountered during two cruises undertaken around South Georgia during November–December 1981 (Summer) and July–August 1983 (Winter). All 14 species were present in summer but only nine in winter. The distribution of the majority of species centered on the mesopelagic (500–1000 m) and bathypelagic (1000–2000 m) depth horizons. During both cruises, four species, Euchaeta Antarctica, E. biloba, E. rasa and E. farrani were numerically dominant. Although all four species had a wide depth distribution, E. Antarctica and E. biloba had distributions centered around the 250–500 m (epi-mesopelagic) and mesopelagic depth horizons. E. rasa was most abundant in the mesopelagic whereas E. farrani, the largest species encountered, was centered on the mesopelagic and bathypelagic depth horizons. Two species, E. Antarctica and E. biloba commonly occurred in the surface 250 m, the former being far more abundant especially over the shelf and shelf break areas, with a high abundance of copepodite stages IV and V being present in summer and adults in winter.     

Distribution of recent benthic foraminifera on the Sunda Shelf (South China Sea)

In this study we investigate the species composition and spatial distribution patterns of Rose Bengal stained and unstained benthic foraminifera from the central part of the Sunda Shelf in the south-western South China Sea in relation to environmental factors. The uppermost centimetre of the surface sediments (> 150 μm) from 45 sites from inner (60 m) to outer shelf (226 m) water depths revealed 584 species including 443 stained species.The univariate analyses of individual species abundances and community parameters and next canonical correspondence analysis were used to relate the faunal data to a set of measured environmental parameters. Four biofacies recognised on the Sunda Shelf are most strongly correlated to water depth, primary production and sediment type of the habitat. The inner shelf biofacies (CCA cluster A), defined by Ammomassilina alveoliniformis and Asterorotalia pulchella, occurs in fine grained sediments classified as modern terrigenous mud in the region with the highest primary production values. The high-energy inner shelf biofacies (CCA cluster B), defined by Heterolepa dutemplei and Textularia lythostrota, occurs in modern terrigenous sand and silt dominated sediments, northeast from the Natuna Island. The high-energy outer shelf biofacies (CCA cluster C), defined by Cibicidoides pachyderma and Textularia bocki, is sandwiched between assemblages of biofacies D. It occurs in the region characterised by neritic relict sand. In the shallow-waters on the Sunda Shelf the relationship of benthic foraminiferal faunal composition to grain size of sediments indirectly signals the prevailing bottom hydrodynamic conditions. The dominance of the epibenthic foraminifera attached to bigger particles (e.g. Cibicides lobatulus, Planulina arimiensis) and much higher abundances of empty tests suggest greater current velocities northeast of Natuna Island. The outer shelf biofacies (CCA cluster D) is defined by Facetocochlea pulchra and Bulimina marginata. It occurs in an area covered with modern terrigenous silt and mud and is characterised by lower annual primary production, but seasonally influenced by weak upwelling.     

Submerged reefs and terraces on the shelf edge of the Great Barrier Reef,Australia

The morphology and distribution of seabed features on the shelf edge and upper slope adjacent to the Great Barrier Reef, Australia, has been examined using shallow seismic profiling, side-scan sonar and precision echo sounding data, supplemented by submersible investigations. The data reveal a submerged barrier reef system at different locations between 15° 45 S and 21° 00 S. At two locations, an extensive offshore platform rising above the 50 m isobath and extending for over 20 km parallel to the shelf edge is backed by a relict lagoon at an average depth of 75 m. In addition, outer shelf and upper slope terraces are found at many depths; however, only some occur consistently throughout the region while most others occur only locally. Frequency distributions indicate the greatest occurrence of features at depths of 44–46, 60–66, 72–78, 80–84, 102–106 and 146–148 m. Caution should be exercised when interpreting these features with respect to specific lower sea level stands.     

Methane Content in the Bottom Sediments and Water Column of the Black Sea

The methane content in the bottom sediments and water column of the Black Sea was determined using various methods of desorption and analysis of gases and various methods of calculating their concentrations. The head-space method with the use of salting out and calculation by an internal standard proved to be the most accurate procedure for the analysis of methane concentration in bottom sediments. The methane content in bottom sediments increased downward along the sediment thickness. In the upper 50–70 cm of shelf sediments, two minimums of methane concentration were revealed; in deep-sea sediments, only one minimum was recorded (in the 20–50 cm horizons). In the water column, methane concentrations slowly grew from the surface to a depth of 150–200 m and abruptly increased to a depth of 700–1200 m, remaining virtually constant in underlying layers. In certain deep-sea regions, peaks of methane content in the 1000–1200 m horizons of the water column were revealed, which were most probably due to local influx of abyssal waters enriched with this gas.     

Water mass and bathymetric characteristics of polar cod habitat along the continental shelf and slope of the Beaufort and Chukchi seas

Relatively little is known about the distribution of fish in deep water (>200 m) in the Beaufort Sea. Data collected by an Acoustic Doppler Current Profiler operated in the Chukchi and Beaufort seas in summer were examined for evidence of fish biomass detections between 18 and 400 m. The presence of fish in waters between 1 and 30 m was explored opportunistically with a non-scientific echo sounder. Evaluation of findings was enhanced by measurements of water column properties (temperature, salinity, fluorescence and transmissivity). Relatively small shoals of fish were detected on the Chukchi shelf and eastern Chukchi shelf break, and also on the Alaskan and Canadian Beaufort shelves in the upper 20 m (T = 2–5°C). Much larger shoals (putative polar cod) were detected within Atlantic Water along the Beaufort continental slope (250–350 m) and near the bottom of Barrow and Mackenzie canyons, where temperatures were above 0°C. A warm-water plume of Alaska Coastal Current water with high concentrations of phytoplankton, zooplankton, and fish was found extending along the shelf 300 km eastward of Barrow Canyon. In contrast to the warm surface and Atlantic Water layers, very few fish were found in colder, intermediate depth Pacific-origin water between them. The large biomass of fish in the Atlantic Water along the continental slope of the Chukchi and Beaufort seas represents previously undescribed polar cod habitat. It has important implications with regard to considerations of resource development in this area as well as understanding impacts of climate change.     

Mesophotic communities of the insular shelf at Tutuila, American Samoa

An investigation into the insular shelf and submerged banks surrounding Tutuila, American Samoa, was conducted using a towed camera system. Surveys confirmed the presence of zooxanthellate scleractinian coral communities at mesophotic depths (30–110 m). Quantification of video data, separated into 10-m-depth intervals, yielded a vertical, landward-to-seaward and horizontal distribution of benthic assemblages. Hard substrata composed a majority of bottom cover in shallow water, whereas unconsolidated sediments dominated the deep insular shelf and outer reef slopes. Scleractinian coral cover was highest atop mid-shelf patch reefs and on the submerged bank tops in depths of 30–50 m. Macroalgal cover was highest near shore and on reef slopes approaching the bank tops at 50–60 m. Percent cover of scleractinian coral colony morphology revealed a number of trends. Encrusting corals belonging to the genus Montipora were most abundant at shallow depths with cover gradually decreasing as depth increased. Massive corals, such as Porites spp., displayed a similar trend. Percent cover values of plate-like corals formed a normal distribution, with the highest cover observed in the 60–70 m depth range. Shallow plate-like corals belonged mostly to the genus Acropora and appeared to be significantly prevalent on the northeastern and eastern banks. Deeper plate-like corals on the reef slopes were dominated by Leptoseris, Pachyseris, or Montipora genera. Branching coral cover was high in the 80–110 m depth range. Columnar and free-living corals were also occasionally observed from 40–70 m.     

Estimating denitrification in North Atlantic continental shelf sediments

A model of coupled nitrification/denitrification was developed for continental shelf sediments to estimate the spatial distribution of denitrification throughout shelf regions in the North Atlantic basin. Using data from a wide range of continental shelf regions, we found a linear relationship between denitrification and sediment oxygen uptake. This relationship was applied to specific continental shelf regions by combining it with a second regression relating sediment oxygen uptake to primary production in the overlying water. The combined equation was: denitrification (mmol N m^–2 d^–1)=0.019^* phytoplankton production (mmol C m^–2 d^–1). This relationship suggests that approximately 13% of the N incorporated into phytoplankton in shelf waters is eventually denitrified in the sediments via coupled nitrification/denitrification, assuming a C:N ratio of 6.625:1 for phytoplankton. The model calculated denitrification rates compare favorably with rates reported for several shelf regions in the North Atlantic.The model-predicted average denitrification rate for continental shelf sediments in the North Atlantic Basin is 0.69 mmol N m^{– 2} d^–1. Denitrification rates (per unit area) predicted by the model are highest for the continental shelf region in the western North Atlantic between Cape Hatteras and South Florida and lowest for Hudson Bay, the Baffin Island region, and Greenland. Within latitudinal belts, average denitrification rates were lowest in the high latitudes, intermediate in the tropics and highest in the mid-latitudes. Although denitrification rates per unit area are lowest in the high latitudes, the total N removal by denitrification (53 × 10¹⁰ mol N y^–1) is similar to that in the mid-latitudes (60 × 10¹⁰ mol N y^–1) due to the large area of continental shelf in the high latitudes. The Gulf of St. Lawrence/Grand Banks area and the North Sea are responsible for seventy-five percent of the denitrification in the high latitude region. N removal by denitrification in the western North Atlantic (96 × 10¹⁰ mol N y^–1) is two times greater than in the eastern North Atlantic (47 × 10¹⁰ mol N y^–1). This is primarily due to differences in the area of continental shelf in the two regions, as the average denitrification rate per unit area is similar in the western and eastern North Atlantic.We calculate that a total of 143 × 10¹⁰ mol N y^–1 is removed via coupled nitrification/denitrification on the North Atlantic continental shelf. This estimate is expected to underestimate total sediment denitrification because it does not include direct denitrification of nitrate from the overlying water. The rate of coupled nitrification/denitrification calculated is greater than the nitrogen inputs from atmospheric deposition and river sources combined, and suggests that onwelling of nutrient rich slope water is a major source of N for denitrification in shelf regions. For the two regions where N inputs to a shelf region from onwelling have been measured, onwelling appears to be able to balance the denitrification loss.     

Habitat specialization in tropical continental shelf demersal fish assemblages

The implications of shallow water impacts such as fishing and climate change on fish assemblages are generally considered in isolation from the distribution and abundance of these fish assemblages in adjacent deeper waters. We investigate the abundance and length of demersal fish assemblages across a section of tropical continental shelf at Ningaloo Reef, Western Australia, to identify fish and fish habitat relationships across steep gradients in depth and in different benthic habitat types. The assemblage composition of demersal fish were assessed from baited remote underwater stereo-video samples (n = 304) collected from 16 depth and habitat combinations. Samples were collected across a depth range poorly represented in the literature from the fringing reef lagoon (1-10 m depth), down the fore reef slope to the reef base (10-30 m depth) then across the adjacent continental shelf (30-110 m depth). Multivariate analyses showed that there were distinctive fish assemblages and different sized fish were associated with each habitat/depth category. Species richness, MaxN and diversity declined with depth, while average length and trophic level increased. The assemblage structure, diversity, size and trophic structure of demersal fishes changes from shallow inshore habitats to deeper water habitats. More habitat specialists (unique species per habitat/depth category) were associated with the reef slope and reef base than other habitats, but offshore sponge-dominated habitats and inshore coral-dominated reef also supported unique species. This suggests that marine protected areas in shallow coral-dominated reef habitats may not adequately protect those species whose depth distribution extends beyond shallow habitats, or other significant elements of demersal fish biodiversity. The ontogenetic habitat partitioning which is characteristic of many species, suggests that to maintain entire species life histories it is necessary to protect corridors of connected habitats through which fish can migrate.     

Community structure of deep-sea demersal fish in the North Aegean Sea (northeastern Mediterranean)

The spatial structure and seasonal changes of the demersal fish assemblages on the continental shelf (100–200 m) and upper slope (200–500 m) in the North Aegean Sea (Northern Aegean and Thracian Seas, northeastern Mediterranean, Greece) were analysed. Seasonal experimental trawl surveys, carried out from summer 1990 to autumn 1993, provided a total of 151 demersal fish species. Analysis of 259 bottom trawls showed the existence of four groups associated with the continental shelf and the upper slope; each group was dominated by a small number of species. The bathymetric distribution of the species, established using measures of the centre of gravity and habitat width, revealed that most of the species had a wide distributional range within the study area, although a few were restricted to the greatest depths. Density, biomass, species richness and diversity decreased significantly with depth, and were also indicative of distinctive characteristics between these fish assemblages. Mean fish weight exhibited two different trends: a bigger-deeper phenomenon at the continental shelf and a smaller-deeper phenomenon at the upper slope. The variability in assemblage structure was determined mainly by depth and, to a lesser extent, by season and geographical location. For some species, results suggest a pattern of gradual species replacement along the depth gradient coupled with ontogenetic habitat shifts.     

The trawlfauna of the Mauritanian shelf (Northwest Africa): density,species composition,and biomass

In May 1988, epifaunal trawlsamples were collected at 17 stations on the Mauritanian shelf off the Banc d'Arguin. The species composition and biomass of the invertebrates and demersal fish were analysed. On the basis of species abundances, three station groups could be distinguished each corresponding to a subregion of the shelf: an inner shelf, a midshelf and an outer shelf station group. The average depth increased from 20 m for the inner to more than 100 m for the outer shelf stations. The biomass of mobile epifauna and fish was lowest on the inner shelf stations where the trawlfauna was dominated by large sessile filterfeeders. The trawlfaunas of the mid- and outer shelf were more similar in species composition. Demersal fish and crustaceans appeared to be more abundant on the outer shelf. The increase in density and biomass from inner to outer shelf is discussed in relation to the distribution of the infauna and the hydrographical conditions on the Mauritanian shelf. Being a demersal fishing area, density and biomass of the epifauna on the shelf are compared with that of the demersal fishing grounds in the southern North Sea. The result of this comparison shows that, except for echinoderms, all taxa attain higher densities and biomasses at the Mauritanian shelf.     

Intraspecific morphological variation with biometry of Distephanus speculum (Silicoflagellata)

Living specimens of Distephanus speculum (Silicoflagellata) were collected in waters of <150 m depth in the Pacific Sector of the Southern Ocean (57°31.6′S, 150°02.9′E), South of Tasman Island, and a biometric study has been conducted. The skeleton of D. speculum has a simple morphology, which can be readily expressed quantitatively. Using a new methodology, repeated measurements were obtained and converted to numerical indices. The circumference of the basal rings was the most useful character for subdivision into groups, and using this parameter we recognized two populations in the 620 studied specimens: (1) 500 individuals were placed in Group A, with a basal ring circumference of 53 to 67 µm, and a difference in length of spine axes from 2 to 6 μm; and (2) 120 individuals were placed in Group B (basal ring circumference 80 to 105 µm, difference in length of spine axes 3 to 6 µm). The circumference of the basal ring in Group B is approximately 10 µm smaller than in Distephanus speculum giganteus [Bukry, D., 1979. Comments on opal phytoliths and stratigraphy of Neogene Silicoflagellates and Coccoliths at Deep Sea Drilling Project Site 397 off Northwest Africa. Initial report of the DSDP, Washington, 49:977–1009.], and Distephanus boliviensis [Bukry, D., 1976a. Silicoflagellate and coccolith stratigraphy, Norwegian–Greenland Sea. Initial Report of DSDP LEG 38. Initial report of the DSDP, Washington, 38:843–855.; Bukry, D., 1976b. Silicoflagellate and coccolith stratigraphy, southeastern Pacific Ocean, Deep Sea Drilling Project Leg 34. Initial report of the DSDP, Washington, 34:715–735].     

The measurement of marine species diversity, with an application to the benthic fauna of the Norwegian continental shelf

Species diversity includes two aspects, the number of species (species richness) and the proportional abundances of the species (heterogeneity diversity). Species richness and heterogeneity diversity can be measured over different scales; a single point, samples, large scales, biogeographical provinces and in assemblages and habitats. In the literature, the terminology of these scales is confused. Here, scales are given a uniform notation. Scales of species richness and heterogeneity diversity are distinguished from turnover (beta) diversity, which is the degree of change in species composition along a gradient. Methods of measurement of the scales of species richness, heterogeneity diversity, turnover diversity and for estimating total species richness are reviewed. Two methods for measuring heterogeneity diversity are recommended Exp H′ (where H′ is the Shannon-Wiener index) and 1/Simpson’s index, together with an equitability index J′. The reviewed methods are then applied to a data set from the Norwegian continental shelf to illustrate the advantages of the recommended methods. Finally, the application of the methods to assessment of effects of disturbance, to studies of gradients of species richness and to conservation issues are discussed.