The macrobenthic invertebrates in the shallow (<0·5 m), medium-depth (0·75–1·0 m) and deep (2·0–2·5 m) waters of the lower and upper regions of the large basin of the seasonally closed Wilson Inlet were sampled, using corers, in each season between the winters of 1989 and 1990. The fauna was dominated by capitellid, spionid and nereid polychaetes and mytilid, venerid and tellinid molluscs. Almost 75% of the total numbers were contributed by the polychaetes Heteromastus filiformis (Claparède) (30·2%), Capitella capitata (Fabricius) (17·4%), Prionospio cirrifera (Wirén) (7·9%) and Boccardia chilensis (Blake & Woodwick) (5·4%), and the gastropod Hydrococcus brazieri (Tenison Woods) (12·4%). The numbers of species recorded in Wilson Inlet (41) were relatively very low for an estuary. This presumably reflects (i) the low salinities, which would restrict colonization by stenohaline marine species, (ii) the prevention of recruitment from the sea by the closure of the estuary mouth during the summer, at which time many macrobenthic species are producing pelagic larvae, (iii) the very limited tidal movements, and thus mechanisms for transporting larvae from the sea, when the estuary mouth is open, and (iv) the lack of a pronounced salinity gradient and the small variation in sediment composition along the estuary. Characteristics (ii–iv), together with the dispersal of pelagic larvae within the basin by wind mixing, would also account for the fact that faunal composition was influenced less by the region within the basin than by water depth. The densities of species, such as Ceratonereis aequisetis (Augener), Capitella capitata and H. brazieri, were greater in the shallow and medium depths than in deeper water, while the reverse pertained with P. cirrifera. Since densities of the first three species are correlated with the biomass of Ruppia megacarpa Mason, the greater amounts of this aquatic macrophyte in the shallow and medium-depth waters may thereby provide more food and/or protection from predators in those waters than would be the case in deep water. In contrast, P. cirrifera, which is a detritivore, would benefit from the greater proportion of particulate organic material in the deep waters. The greater habitat complexity in the shallow and medium-depths, that is provided by the greater amounts of R. megacarpa and shell debris in those waters, was associated with a greater species richness, diversity, density and biomass of benthic invertebrates. The composition of the fauna underwent cyclical changes, which were related, in part, to the patterns of recruitment of certain major taxa following spawning.

In the Bay of Seine (English Channel) the polychaete Pectinaria koreni exhibits interannual stability in its abundance, despite its isolated distribution and its bentho-planktonic life cycle. To test the hypothesis of a high level of recruitment related to high survival rate of the post-larvae due to metamorphosis in the water column (transformation of metatrochophore into aulophore), we undertook a study of the morphology and the dynamics of the aulophore stage during May and June 1987. The morphological study snowed that aulophore larvae do not possess all the morphological features needed for benthic life on their first contact with the substratum. Fifteen days are needed to complete this development, and during this time the mortality rate is high. The possible role of this delayed metamorphosis on the transport of aulophore larvae towards sites favourable to adults is also discussed.

Pectenogammarus planicrurus Reid (Crustacea: Amphipoda) is an inhabitant of unstable gravel beaches. The reproductive output of females of this species was studied at Aberystwyth, on the west coast of Wales. There was marked seasonal variation in the size of eggs: the mean volume of eggs at an early stage of embryonic development ranged from 0·023 mm3 in summer to 0·030 mm3 in winter. Egg size was negatively related to brood size, but seasonal variation in brood size was greater than could be accounted for by egg size alone. Mean brood size ranged from 1·4 eggs in winter to 5·9 eggs in summer. Brood size was also strongly related to female body size, ranging up to 14 eggs in a large female. These findings are discussed in relation to adaptation to interstitial living in coarse intertidal gravels. A model of seasonal variation in reproductive output is suggested in which the importance of point reproductive output is related to the probability of females surviving to produce subsequent broods.

Bivalve spat were grown in an on-shore upwelling nursery using a landlocked heliothermic marine basin (Norwegian oyster-poll) as a food production system and thermal source. Several manipulations, involving artificial fertilization (N, P and Si), were performed in order to enhance the production capacity. Based on data from a monitoring programme (May-August) on physical, chemical and biological variables in the system, main paths of nitrogen flow and dynamics of bivalve production and nitrogen conversion efficiency were described. The conversion efficiency of the system, bivalve N production over estimated new N, of which 86% was fertilizer nitrogen, was 16·2% for the experimental period of 93 days. During this period the decrease in efficiency from levels of 22–25% to 8% was probably due to the transition from nitrate-limited to light- and grazing-limited phytoplankton production. The food utilization efficiency, bivalve N production over available particulate N in the nursery, was 19·8% for the experimental period. The efficiency increased in July from 19·4% for the first two weeks to 27·0% during late July. This was probably due to a higher food value of the phytoplankton community in late July, dominated by Skeletonema costatum (Bacillariophyceae) and Nitzschia sp., than the phytoplankton community in early July, dominated by Fragilaria sp.

The natural feeding of the two most abundant ommastrephid squid (Cephalopoda: Ommastrephidae) in Galician waters was studied and compared. A sample of 334 stomach contents of Todaropsis eblanae (34–222 mm ML) and 267 stomach contents of Illex coindetii (50–379 mm ML) caught by commercial trawlers was examined. A total of 21 (T. eblanae) and 23 (I. coindetii) different prey items, belonging to three zoological groups (Teleostei, Crustacea and Cephalopoda), were taken by these cephalopods. However, 43% of the T. eblanae diet comprised only one fish species, Micromesistius poutassou. The diet of these squid species was significantly influenced by the geographical area (both species), size (T. eblanae) and maturation (I. coindetii). Feeding rate of both species decreased with size, but the percentage of stomachs with food remains increased in maturing and mature females. Weight of prey captured was dependent on available prey sizes and, in small individuals, maximum prey weight was very close to the squid weight. Both squid species are mainly neritic nekto-benthic predators, but I. coindetii seems to have a broader and more pelagic diet.

The stomach contents of ten species of elasmobranch from the north-eastern Atlantic indicate that most are generalist predators, eating a variety of polychaetes, molluscs, crustaceans and teleosts. Two species, Mustelus asterias and Squatina scjuatina were found to be specialist feeders, consuming portunid crabs and pleuronectids, respectively. Measures for both dietary breadth and dietary overlap are given and the implications of elasmobranch predation on the prey communities and on commercial species are discussed.

Morphometric data on bass, Dicentrarchus labrax L. (Pisces: Percoidei), sampled around the coasts of England and Wales between 1982 and 1990, have been analysed to elucidate seasonal patterns of feeding, body condition and gonad maturity. The somatic condition and fat reserves of bass in the Irish Sea and southern North Sea improved more rapidly during the spring and summer than in bass further to the south. In winter, however, fat reserves were higher and there was more food in the stomachs of bass caught in the western English Channel. The onset of maturity was related to fish length. Male bass became mature for the first time at 32–36 cm total length, but though many females showed signs of gonad growth at this size, no female <42 cm was found with mature (ripe or spent) gonads. Gonad development in adult bass of both sexes began in October and, from January until June, most males >36 cm had ripe testes. The period during which ripe eggs could be expressed from the ovaries of female bass was briefer, with spawning apparently peaking in April. It is concluded that the migration of adult bass to the north in spring and southwards and westwards in autumn has both growth and reproductive benefits related to sea temperature, and that the more limited movements of bass <42 cm, which remain in relatively cold, inshore waters in winter, results in an inhibition of gonad maturity in females.

The olfactory epithelium of developmental stages from yolk sac larvae to adults of plaice, Pleuronectes platessa L. (Pisces: Pleuronectidae) and Dover sole, Solea solea (L.) (Pisces: Soleidae) was examined using scanning electron microscopy (SEM). Two ciliated cell types and a microvillar cell are present in both species soon after hatching and persist into adulthood. In juveniles and adults of plaice, there were significantly higher densities of ciliated sensory cells in the eyed side of the fish than in the blind side over all regions of the olfactory lamellae. Densities of microvillar cells were an order of magnitude less than those of ciliated cells in regions on the wider part of the lamellae, with no significant difference between organs in most of these regions. On the narrow part of the lamellae, densities of microvillar cells were significantly higher than on the wide part, and significantly higher in the eyed side organ. In sole, ciliated cells were significantly more dense in the blind side organ in three of the four regions examined in this species. In contrast, microvillar cells showed a similar pattern to that in plaice, being significantly more dense in the eyed side organ in two of the four regions. Comparisons between the species showed significantly higher densities of both cell types in sole, microvillar cells being an order of magnitude denser in comparable regions on the lamellae. In addition, the total area of the olfactory lamellae is around three times greater in sole. These data point to a possible morphological basis for the enhanced olfactory capabilities of sole apparent from behavioural studies.

Dispersion of Lepeophtheirus salmonis Kreyer 1838 (Crustacea: Caligidae) larvae from a single cage and also from a farm system was investigated in Ardmore Bay, west coast of Ireland. Surface plankton tows were taken from within a cage and also at various distances from the farm. Highest densities of larvae (maximum, 66·1 m−3) were consistently recorded within the cage. Less than 10% of the larval density recorded inside the cage was found outside at any one time, indicating a high retention of larvae within the cage throughout the sampling period. This was due to a reduction of water movement inside the cage caused by the physical barrier of the net which was fouled during the sampling period. Highest densities of larvae were consistently found in samples taken at 10 m (maximum, 4·8 m−3) from the last cage on the farm in comparison to those taken further away from it (maximum, at 1 km; 0·4 m−3). Regression analysis of the data from each of the sampling dates showed a significant inverse relationship (P=0·001) between distance and larval numbers. The models produced suggest that few louse larvae would have been recovered in samples (i.e. 100 m plankton surface tows) taken more than 2 km from the last cage on the farm. Although the ratio of copepodids to nauplii increased with distance from the farm, the densities of the copepodids did not increase.

A meeting on Marine biodiversity: causes and consequences was held in York on 30 August – 2 September 1994, organized by the Marine Biological Association and the Scottish Association for Marine Science and supported by the World Wildlife Fund for Nature, the Natural History Museum and the Marine Conservation Society. The following 16 papers were first presented at this meeting.

A description is provided of the large-scale spatial distribution of the diversity of the benthic macrofauna in the eastern English Channel. Data from the oceanographic cruises of the RCP (Recherche Coopérative sur Programme) Benthos de la Manche Research Programme were obtained during the summers of 1971 to 1975. A total of 707 samples were analysed.

Diversity of each sample was measured by means of the species richness (i.e. the total number of species present), the Shannon-Weaver diversity index and Pielou's evenness index. Diversity values were plotted for all 707 oceanographic stations in the area, following a smoothing procedure. Large-scale spatial trends of diversity of the benthic macrofauna were analysed in relation to sediment and species assemblage distribution, but no spatial correlation was found between the two factors. These results indicate that mechanisms affecting large-scale spatial distribution of the diversity are different from those acting on a smaller scale. The role of the hydro-sedimentary processes acting at the geographic scale of the eastern English Channel as presumptive causes of this large-scale pattern of the macrobenthic diversity is discussed.

From 1989–1992, at quarterly intervals, the National Rivers Authority (NRA) (Thames Region) Thames Estuary Benthic Programme sampled 28 sites within the estuary for benthic macroinvertebrates; meiofauna samples were also taken for the first year. At one subtidal site, situated off Canvey Island, over 200 invertebrate species over the survey period from a sample area of 4·4 m2 were recorded. This species richness was far higher than surrounding sites, including those further out into the North Sea. The most important groups at this site were Nematoda (77 spp.), Crustacea (46 spp.) and Polychaeta (40 spp.) and a species capture curve for macroinvertebrates continued to rise after 44 day grabs. The mean biomass of the site (248 g wet weight /m2) was 20 times that of any other site in the outer estuary. The substratum at the site was highly heterogeneous, yet comparatively stable due to its situation at the base (>20 m depth) of a man-made shipping channel, the provision of a large number of niches perhaps explaining the high biodiversity. The anthropogenic influence on a naturally low biodiversity area emphasises the importance of these ecosystems when considering the conservation of global biodiversity. Methods to determine the relative importance of ecosystems are discussed.

A global study of latitudinal gradients in biodiversity of marine shallow-water, motile epifauna of hard substrata has been initiated by Plymouth Marine Laboratory and the International Association of Meiobenthologists. It is based on the use of artificial substratum units (ASUs) consisting of four pan-scourers and emphasizes the standardization of habitat type and complexity, sample area, sampling strategies, sample processing and analysis. Non-comparability of these factors has invalidated some of the few previous studies on global patterns in biodiversity of marine benthic communities which are reported in the literature. A list of sampling locations and participating research organizations is given along with some preliminary results from one location (south-west England).

Determination of fossil echinoid diversities is an important aspect of detailed palaeon- tological studies. The comparison of recent and fossil associations can be used to elucidate the problems of determination of fossil echinoid distributions. Actuopalaeontological studies of echinoids from the Red Sea (northern Bay of Safaga, Egypt) have shown that the study of fragments within bulk sediment samples greatly increased the possibilities for determining echinoid presence and distribution. The results show the restricted distribution as well as the differential preservation potential of the various echinoids.

The distribution of echinoids is primarily controlled by grain size, food availability, exposure to current activity, and predation pressure. Regular and irregular sea-urchins show the expected disjunct distributions with the former showing a more undifferentiated distribution to various hard substrates. Irregular echinoids are tightly restricted to particular types of soft substrates reflecting their adaptation to the specific grain size of the sediments. Co-occurring irregular sea-urchins show a spatial differentiation into shallow (clypeasteroids) and deeper burrowers (spatangoids). This investigation shows that important echinoid species known to occur in the Red Sea are lacking or are very rare within the study area, although a large number of different facies types are present. Patchy distributions are present for both regular and irregular sea-urchins. The determination of biodiversity is therefore seen to be largely dependent on the scale of investigation.

An important implication for fossil echinoid presence are the differential effects of taphonomic agents on the various test architectures. Some species are well represented due to their common occurrences, and their comparatively robust tests or test fragments.

Major hotspots of amphipod species richness and of species and generic endemicity can be recognized in shallow seas. Recognition of ‘hotspots’ for amphipods must take account of the species-area relationship but not of latitude. The richness and endemicity of amphipods in the Mediterranean Sea is shown to be high when compared with other shallow seas This indicates a long in situ evolutionary history and is therefore not compatible with the hypothesis that the Mediterranean fauna was extirpated in the late Miocene.

Marine mussels are widely distributed and have been used extensively as environmental biomonitors. Communities associated with mussel patches have a high species richness but are typically dominated by a few very abundant species. These communities exhibit significant temporal and small-scale spatial variations in abundance and diversity which should be recognized when considering global patterns of marine biodiversity. Many of the species associated with tropical mussel beds are also represented by taxonomically and functionally equivalent species in mussel communities from temperate waters. The phenomenon of ‘parallel communities’ on rocky shores is thus apparently replicated on a finer spatial scale within mussel patches.

There is a greater diversity of spectrally distinct chlorophyll(ide) pigments in individuals of many of the large number of higher taxa of marine oxygen-evolvers which contain only small organisms than in those few higher taxa which also (or only) have large-sized organisms. The occurrence of more types of pigment in smaller organisms can be mechanistically related to the lesser degree of self-shading in smaller organisms, thus allowing spectral diversity to be reflected in enhanced photon absorption from a given light field as a result of multiple spectral forms of chlorophyll(ide)s. This provides a mechanistic basis with ecological significance for the greater chlorophyll(ide) diversity in small marine O2-evolvers which show greater biodiversity at the level of higher taxa than do classes or divisions which are comprised only, or predominantly, of macrophytes (Ulvophyceae, Rhodophyta, Phaetophyta, seagrasses).

Studies of the interplay of immigration, emigration and extinction in shaping the fauna of islands (McArthur & Wilson, 1967) have influenced the terrestrial ecologists view of the creation and maintenance of diversity. Although in the deep ocean, hydrothermal vents have been the subject of a number of biogeographic studies (Tunnicliffe, 1991), there have been few attempts to validate theories of island biogeography in the shallow marine environment. To rectify this situation, a study comparing the fauna of the mainland of Cornwall, with that of the Isles of Scilly, which lie 45 km from the mainland and were separated from it ~0·3 my BP has been undertaken.

Evidence for some comparative impoverishment of the Isles of Scilly fauna was provided by Crisp & Southward (1958) who noted that a small number of cirripedes and molluscs with planktonic larvae, living close to their geographic limits of distribution in Cornwall, were unable to bridge the gap to the islands. They suggested that although species with long-lived planktonic larvae can be widely dispersed, excessive dispersal can lead to their loss from the fauna of small islands. This is clearly demonstrated on the remote island of Rockall where both Crisp (1956) and Moore (1977) noted that only animals with direct development occur. On the Island of Lundy, four species of gastropod were estimated to be less abundant than on the mainland which lies only 18 km away (Hawkins & Hiscock, 1983). However, such studies only deal with a small number of conspicuous intertidal species, and there is a requirement to expand observations to the community level. The present study attempts to question the following hypotheses: (1) α - diversity (that of single samples) is lower on the islands than the mainland; (2) the diversity of species with planktotrophic larvae is lower on the islands than on the mainland.

Patterns of variation in the assemblage structure of butterflyfishes (Chaetodontidae) of the Red Sea and western Indian Ocean have been compared. There is a lower number of species in the Red Sea, a high proportion of which are endemic to the region, both features that have been attributed to the relatively recent origin of the Red Sea. In the Red Sea overall mean abundance of butterflyfish is greatest in the central part, decreasing both to north and south. Several species present in the southern Red Sea are absent from the north. By contrast, most western Indian Ocean species are widely distributed within the Indo-West Pacific. Comparative field studies in the northern Red Sea (Egypt) and western Indian Ocean (Kenya) showed that mean number of species was higher in the western Indian Ocean, but mean density of butterflyfishes was higher in the Red Sea. In both areas diversity of butterflyfish was related to mean substrate diversity (the number of coral growth forms). Mean spatial niche breadth of butterflyfish species was much higher in the Red Sea than in the western Indian Ocean, whereas the extent of microhabitat use was higher in the western Indian Ocean. It is suggested that these differences may be related to the more recent evolution of the Red Sea fauna.

The effect of artisanal fishing on the abundance and diversity of coral reef fish assemblages was investigated in the Kisite Marine National Park and Mpunguti Marine National Reserve at Shimoni, Kenya. Fishing is prohibited within the Park whereas in the Reserve artisanal fishing using traditional methods is practised. Visual censuses of six representative reef fish families (Chaetodontidae, Lethrinidae, Lutjanidae and Serranidae in 1992 and 1994, and Labridae and Pomacentridae in 1994 only) were undertaken along 250×10 m band transects on two similar pairs of reefs subject to differing fishing pressure. The abundance of commercial species (Lethrinidae, Lutjanidae and Serranidae) was depressed in the Reserve. The unfished butterflyfishes (Chaetodontidae) and damselfishes (Pomacentridae) also showed a greater abundance in the Park than in the Reserve. However, neither species number nor Shannon diversity (H′) of any of these families was affected by fishing pressure. Possible reasons for these findings are discussed. The abundance of commercial species, though not of non-commercial unfished species, increased significantly in the Reserve between 1992 and 1994, suggesting that the unfished Park may be acting as a source of larvae or supply of emigrating adults for the depleted Reserve. The results are comparable with other recent studies describing the effects of fishing pressure and also with those studies detailing the effects of habitat refugia in coral reef areas.