The current interest in diversity as one of the major parameters describing a community has led to an increasing number of published results and theoretical discussions during the last years. Diversity has variously been related to other attributes of the community or properties of the environment, among which time, spatial heterogeneity, stability, primary production, productivity, competition, predation, niche structure and evolution. Although this rather overwhelming amount of possible relations seems somehow too much of a good thing, the importance of diversity remains well established in current ecological theory. One of the most important applications of diversity indices is their usage in the biological assessment of pollution. This immediately raises the problem of comparing diversity indices within habitats in time or between habitats in communi-ties. These comparisons are frequently made, yet the statistical significance of the observed differences or similarities is seldom mentioned. A test for these differences was formulated by Hutcheson (1970) but it apparently failed to attract the attention it deserves. In this study it was our purpose to investigate the distributions of the more important diversity indices and their evenness components in a low-diversity community of meiobenthic copepods of a shallow brackish water pond in northern Belgium. In this habitat the number of species is rather low, which greatly simplifies the analysis, and we hope that the statistical behaviour of the indices we find will hold for other, especially other low diversity communities as in polluted environments, as well. We chose copepods because they are taxonomically well known, the benthos because it is approximately two-dimensional and a shallow environment because of the possibility of accurate sampling.

It is well known that towards the limits of an animal's geographical range both its abundance and exact boundaries may fluctuate from time to time. These fluctuations can sometimes be correlated with environmental changes, and thus may help to assess the relative importance of the factors that control distribution. For example the distribution of the common intertidal barnacles Chthamalus stellatus (Poli) and Balanus balanoides (Linnaeus) underwent changes which were attributed to a general rise in temperature over several years (Southward & Crisp, 1954a). The abundance of these barnacles has fluctuated further since 1951–52, and we are now able to analyse more closely the relation between the population changes and environmental variations.

The assemblages of attached and freeliving epibenthic species in the North Sea are described, based on analysis of samples collected with a small beam trawl. Clustering of survey sites based on the presence or absence of attached species indicated that three regions had characteristic assemblages: the northern North Sea, the central North Sea from 55 to 57°N and the southern North Sea. Clustering of sites based on counts of free-living epibenthic species also revealed that the sites formed three major groups but these corresponded to regions in the north-east North Sea, the northern and western central North Sea and the southern and eastern central North Sea. Species which contributed most to the similarity within and dissimilarity between groups were identified. The environmental factors which best accounted for the grouping of sites were depth, winter temperature and the temperature difference between winter and summer for attached species and depth and the temperature difference between winter and summer for free-living species. The species richness of attached and free-living epibenthic species was higher in the central and northern North Sea than in the south. The number of abundant (Hill's N1) and very abundant (Hill's N2) free-living species also increased from south to north.

It is well established that the lipid content of the herring Clupea harengus from the waters around the British Isles and Ireland undergoes a marked seasonal cycle, being highest during the summer months of active feeding and lowest after a winter fast (Wood, 1958; lies & Wood, 1965; Lovern & Wood, 1937; Molloy & Cullen, 1981; Wallace, 1986). In the case of spring-spawning herring, the minimum lipid content coincides with the spawning period and the depletion of lipid over winter corresponds with the development of gonads (Lovern & Wood, 1937).

Structural parameters of periphytic ciliate communities on a modified substrate were studied in Korean coastal waters during the period August–November 2007. In order to reduce the strong disturbances from tidal current and circulation in marine ecosystems, a modified slide method, named the polyurethane foam enveloped slide (PFES) system, was used to host ciliate communities. A total of 37 ciliate species, about half of which belong to the orders Hypotrichida and Cyrtophorida, were identified using living observation and silver impregnation method with this system. The sessile ciliates belonged to the orders Peritrichida and Suctorida, while the motile forms were represented primarily by the species of the orders Hypotrichida, Cyrtophorida and Pleurostomatida. The species diversity and evenness were significantly higher in the PFES system than those on the conventional slides (paired t-test: t = 2.384, 2.415; P < 0.05). Multivariate analysis revealed that the ciliate communities from both sampling systems had similar species composition, but represented significant differences in species distribution and temporal dynamics mainly due to the most dominant peritrich Zoothaminium duplicatum, which overly colonized the conventional slides. Results suggest that the PFES system is more effective than the conventional slide method for periphytic ciliate colonization with high species diversity, evenness and sensitive temporal dynamics mainly due to the reduction of disturbances from tidal current and circulation in marine ecosystems.

1. Simultaneous observations are recorded of some biological, physical, and chemical changes in the Clyde Sea Area in 1924, 1925, and 1926.

2. A close relation between diatom increases and changes in pH value, dissolved oxygen saturation and dissolved phosphate has been found.

3. It appears that the more numerous diatom increases in Loch Strivan as compared with the open sea are due to the more frequent mixing.

4. Confirmation of the fact that diatom increases begin at the surface and gradually spread into deeper water has been obtained.

5. The occurrence of Peridinians is apparently related to high temperature and low salinity.

6. The amount of sunshine in the early part of the year does not exert any apparent influence on the date of the spring diatom increase in the Clyde Sea Area.

7. The regeneration of phosphate in the deep water of Loch Strivan has been described.

The salinity of the water retained within the mantle cavity of mussels after the shell valves have closed in response to falling environmental salinities is influenced by the rate of external salinity change. At high rates of salinity change the retained water salinity is significantly higher than in animals exposed to slowly changing salinities. However, the mantle fluid salinity is not primarily determined by the timing ofx shell valve adduction, but by closure of the exhalant siphon.

Details are given of the breeding biology, including the fecundity, of the Long Rough Dab deduced from samples taken in the Clyde Sea area from October 1953 to April 1955. Where possible breeding is related to the condition of the fish; the index of condition is based on the length-weight relation.

The weight of Long Rough Dabs of each sex and stage in maturity increases as a power, slightly greater than the cube, of the length. An annual cycle of fluctuations of this power is seen in the immature females, and indicates how changes in condition at different seasons affect the different size-groups. The measure of condition is taken as the expected weight of a 20 cm Long Rough Dab, and the changes in this weight are followed through the sampling period for males and for immature, maturing and spent females. All groups tend to be in best condition during November and December followed by a decline to the spawning time, in March and April, after which there is a slow recovery.

During three consecutive years of observation 23 Atlantic cod (Gadus morhua) were tagged with ultrasonic transmitters as part of two experiments to determine the movement patterns of adult cod in the genetically distinctive population inhabiting Gilbert Bay, Labrador. Individual cod were relocated for periods up to 15 months, indicating year-round residency within the bay despite unimpeded access to the open ocean. The tracking data show that individual cod have a strong homing tendency. In experiment 1 displaced cod returned (homed) to their place of capture in a small arm separated from the rest of the bay by a shallow sill while non-displaced fish remained at their capture site. In experiment 2 some cod remained within 2 km of their capture/release site, a spawning area, while others ranged widely in Gilbert Bay before returning to this site. Whether an individual ranged widely or had more restricted movements was not related to size. Cod exhibited wider ranging movements in the spring and early summer, following spawning, than in the late summer and early autumn. The return of Gilbert Bay cod to specific locations in the inner part of the bay to overwinter and spawn is evidence of one mechanism that could have led to their genetic distinctiveness.

Since the introduction of the Manila clam Ruditapes philippinarum (Mollusca: Bivalvia) to aquaculture clam beds, this species has spread to several sites. As a result, an extensive fishery has developed around this species. Its reproductive cycle and that of a native clam species, Ruditapes decussatus (Mollusca: Bivalvia) from two Brittany sites are examined here and the seasonal variations in the condition index, the scale of maturation stages, the histology and the oocyte size-frequencies of both species are compared. The differences observed between the species and between sites were attributed to environmental conditions. Ruditapes philippinarum showed a more extended breeding period and a greater number of spawning events than R. decussatus. In the Morbihan Gulf, the reproductive activity of R. philippinarum appeared particularly great in terms of number of spawning events, and speed of maturation. For both species, synchronism was more apparent during the first maturation, while spawning, and particularly partial spawning, tended to decrease the level of synchronization.

The responses to light and temperature variations of the gametophytes and early sporophytes of Laminaria hyperborean were compared in culture with those of its main competitors in Britain, namely L. digitata, L. saccharina and Saccorhiza polyschides. Some undeveloped gametophytes of all species are able to survive in the dark for at least 80 days.

Tagging data for 5959 bass, Dicentrarchus labrax L., released around England and Wales between 1970 and 1984 have been compiled and analysed to show seasonal distribution patterns and implied movements of populations in the southern North Sea, the central English Channel and the south-west and west coasts. Juvenile bass appear to remain near their nursery areas throughout the year, whilst adults show extensive migrations between summer feeding areas and winter pre-spawning areas, which are specific to local populations. Straying occasionally occurs between populations, but only at the ‘adolescent’ phase, and for management purposes local populations may be considered discrete.

A radical change in the abundance of invertebrate megafauna has occurred over a vast area of the Porcupine Abyssal Plain, north-east Atlantic, in recent years. In particular, the holothurian Amperima rosea has increased in abundance by three orders of magnitude. The sudden increase in abundance of A. rosea appears to be the result of environmental forcing rather than localized stochastic population variations. Amperima rosea produces small eggs ([les ]200 μm) indicating (1) planktotrophic larval development or (2) lecithotrophic larval development with an abbreviated larval stage. It also reaches maturity at a very small size. The reproductive biology of A. rosea indicates that it can increase rapidly in population size and can colonize large areas quickly. It has high fecundity, as predicted by gonad indices and observed in histological studies. Fecundity was greater in winter than in summer months, but there was no clear evidence of seasonal or episodic reproductive events. All males, irrespective of sample season or year, were mature with spermatozoa. Most oocytes were of an intermediate size (70 to 120 μm), either at the late previtellogenic (70–90 μm) or early vitellogenic (100–120 μm) stage of development. It is postulated that development of full vitellogenesis, leading to episodic spawning, might be dependent on certain environmental stimuli. The most likely stimulus is food supply. Amperima rosea has been shown to feed preferentially on phytodetritus and to have a requirement for certain sterols in its diet. Qualitative changes in the flux of organic matter to the sea-floor may control vitellogenesis and fecundity, and hence have an effect on the population dynamics of the species.

Considerable differences were found in the size compositions of populations of Asterias rubens off Plymouth. These differences were not correlated with age.

Laboratory observations on rate of growth showed that well fed starfishes grow fast during summer and autumn and somewhat slower in winter. Poorly fed starfishes did not increase in size, but were able to survive for long periods with a minimum of food.

The inter-tidal habitats of the common limpet, Patella vulgata L,, have been investigated in relation to constant lunar tidal levels and tidal zones. The habitats of some common shore organisms which occur at approximately definite tidal levels or zones—and can therefore be used with discretion for zoning the habitats of Patella—are shown in a chart.

A study of the distribution of the common limpet on the shores of Devon and Cornwall has shown that limpets are absent or rare on those parts of the foreshore above high-water neaps which are subjected to prolonged periods of direct insolation. In the same locality limpets may be totally absent from the high-water region on cliff-faces or rocks facing southerly, but present on adjacent ones facing northerly or north-westerly. Strongly insolated habitats appear to be unviable as a result of the direct effect of the insolation on the animal, but the apparent deficiency of food in such habitats is probably also a limiting factor of importance.

The importance of the splash-line of any tidal level is emphasised. It is shown that in Devon and Cornwall the occurrence of low-water spring tides at about midday (and midnight) results in exposing to strong sunshine (and correlated factors) those regions of the shore above high-water neaps which face in a southerly direction. In other localities where high-water spring tides occur about midday, equivalent regions of the foreshore are not so strongly nor so persistently insolated as in the former.

Viable habitats may therefore occur in different regions on the shore in different localities or at different latitudes according to the local orientation of the substratum and local tidal phenomena.

The combustion of fossil fuels and the resultant impacts on climate may now represent one of the largest environmental threats. In the Mediterranean Sea, changes in bio-chemical and physical seawater properties resulting from global warming are likely to alter marine biodiversity and productivity, trigger trophic web mismatches and encourage diseases, toxic algal bloom and propagation of thermophilic species. This review highlights the current and potential threats of climate change to the Mediterranean marine ecosystems, including cetaceans, and stresses the emergent necessity for more integrated regulations and policies for the protection of marine biodiversity. For instance, in the Mediterranean Sea, the distribution and abundance of the small euphausid species Meganyctiphanes norvegica is correlated with specific hydrobiological parameters including seawater temperature, salinity and current patterns. Situated at the northern limit of its ecological tolerance, this species, which constitutes the only known food supply of the fin whales (Balaenoptera physalus) in this region, might be affected by climate change-induced alteration of ocean circulation.

The Periwinkle, Littorina littorea (L.), is one of the most abundant gastropods on the shore, and can live under widely varying conditions. It is found on clean, alga-covered rocks, among small stones, on gravel, on soft mud, and rarely even on sand. It ranges from about high water of neap tides to extreme low water of spring tides, and in some places even slightly below this, although in most localities it is restricted to a much smaller part of the tidal zone. It occurs also from shores with high wave-exposure to sheltered and even polluted estuaries, where it is tolerant of considerable lowering of the salinity. The material for the present study was collected at intervals throughout 1934—1936 from three localities near Plymouth, the details of which are as follows.

Photosynthesis in the open sea is due mainly to two groups of organisms, the diatoms and the dinoflagellates. In British seas the diatoms are so much more numerous that the chemical changes which are due to photosynthetic activity can be almost entirely ascribed to their influence. Recent work on these chemical changes has shown that they do not extend deeper than about 30 metres. Of the external limiting factors light is among the most important and the depth to which photosynthesis can go on must, of course, depend on the light intensity. In the study of the phytoplankton under natural conditions the results are complicated by the interaction of many other factors such as temperature, viscosity, or lack of food salts, so that it is difficult to come to definite conclusions on the effect of light alone.

The reproductive cycles of the two cockles Cerastoderma edule (L.) and C.glaucum (Poiret) (= Cardium lamarcki Reeve) from a mixed population in the Crouch estuary, Essex, have been investigated. Reproductive maturity was estimated by assessment of gonad condition. A difference in maturity related to shore level was noted. The reproductive cycles of the two cockles were found to be essentially similar. Rapid gametogenesis occurred in both cockles in spring, C. edule then spawned in May, whereas C. glaucum did not spawn until July. The difference in time of spawning appears to be responsible for the maintenance of the two genotypes in a sympatric association, as hybridization experiments showed an absence of isolation at the gamete level. The relationship between C. edule and C. glaucum is discussed.

SOND Cruise 1965 aboard the R.R.S. ‘Discovery’ afforded the opportunity for short-term estimation of the penetration of daylight at midday into three regions of the eastern North Atlantic, evaluation of the fluctuations in the character of noonday light at depth in a restricted area over a 2-month period, and a determination of the penetration of moonlight in this area at the full of the moon.