This is the first comprehensive check-list of the diatoms of the British Isles to cover all currently reported taxa from freshwater, brackish and marine habitats. It contains a classification of the genera in order of families, followed by a complete list of species and lower taxa set out in alphabetical order within each genus.

The two main orders of the British Diatomaceae are represented in:- 5 sub-orders, 20 families, 3 sub-families, 152 genera, 1798 species, 6 sub-species, 745 varieties and 73 forms.

The check-list also includes 2048 synonyms formerly in common use, together with 512 cross references to the names of taxa in current use.

Some marine endolithic algae grow well and are restricted to the strongly lit littoral and uppermost sublittoral environments. The wide depth ranging boring algae must however adapt to different light intensities. Whereas Eugomontia sacculata Kornmann is considered as a form adapted to high light intensity (Akpan, 1981), Ostreobium quekettii Bornet & Flahault and Conchocelis - a boring phase in the life cycle of red algae in the Porphyra and Bangia genera - are able to survive under low light conditions even though they thrive at depths with strong illuminations (Rooney & Perkins, 1972; Clokie & Boney, 1980). Sheath, Hellebust & Sawa (1977) have demonstrated that the Conchocelis of a Porphyra sp. can survive prolonged very dim light condition and probably remain in a ‘steady state’ without growth in the dark for a long time. This adaptation is important for those algae in the lower part of the photic zone because during winter, deep light penetration is hampered.

Numerous studies have shown that only a small percentage of the organic carbon produced by photosynthesis in the upper layers of the oceans reaches the underlying sediments (see review by Angel, 1984). During intense phytoplankton blooms, plant cells could account for most of the organic carbon contributed to sediments in certain shallow inshore areas (Smetacek, 1980). Examination of the sediments from open ocean environments, however, indicates that the main contribution of organic carbon to these is in the form of faecal material released by zooplankton, for example salps (Iseki, 1981) and larger species of copepod (Schrader, 1971; Krause, 1981).

The development of male characters, notably a penis and a vas deferens, on the female (the phenomenon of ‘imposex’) of the dog-whelk, Nucella lapillus, is described. Three stages are recognized: an ‘early’ stage involving the formation of a vas deferens and a small penis, an ‘intermediate’ stage characterized by the enlargement of the female penis to a size approaching that of the male and a ‘late’ stage during which the female opening (vulva) is occluded by overgrowth of vas deferens tissue. This blockage of the pallial oviduct prevents the release of egg capsules and renders the female sterile. The extent and cause of such reproductive failure is evident from the high incidence of females containing aborted capsules in declining populations close to sources of tributyltin (TBT) contamination. These same populations comprise fewer females than expected and it would appear that the accumulation of aborted capsules within the pallial oviduct eventually causes the premature death of the female.

A survey of the gastropod Nucella lapillus around the south-west peninsula of England has revealed that the incidence of ‘imposex’, the induction of male sex characters in the female, is widespread, that all populations are affected to some degree and that the phenomenon is most prevalent along the south (Channel) coast. Populations close to centres of boating and shipping activity show the highest degrees of imposex, especially those within the vicinities of the Helford, Fal, Salcombe and Dart estuaries and in Plymouth Sound and Tor Bay. Within Plymouth Sound the degree of imposex increased markedly between 1969 and 1985, coinciding with the introduction and increasing usage of antifouling paints containing tributyltin (TBT) compounds.

The stomach contents of 221 sperm whales were examined at the Icelandic whaling station between 1977 and 1981. Evidence of at least eight species of fish and 22 species of cephalopod was found, together with an assortment of foreign bodies including rock fragments and fishing nets. Fish remains were found in 87% and cephalopods in 68% of the sperm whale stomachs in this area, but quantification of dietary input is complicated by differential rates of digestion and variation in the retention of indigestible remains in the stomach. Prey species are benthic or pelagic in habit and are caught by the whale in waters from 400 m to at least 1200 m in depth. One fish, the lumpsucker Cyclopterus lumpus, forms a major part of the diet. Ninety-four per cent of cephalopods are oceanic and neutrally buoyant and 84 % of these are ammoniacal. Cranchiids contribute 57% by number and an estimated 25% of the weight, and histioteuthids 26% by number and 38 % of the weight of cephalopods eaten. Three species offish and two of cephalopod have not been previously recorded in sperm whale diets. Comparison with an earlier study shows that the diet is essentially stable over a 14-year period.

Yonge (1962) suggests a possible universal occurrence of byssal apparatus in the post-larval spat of bivalves. Subsequent studies have revealed that the byssus thread secreted by the post-larval byssal apparatus of many bivalves is involved in settlement as well as migration by means of bysso-pelagic drifting (Sigurdsson, Titman & Davis, 1976; Blok & Tan-Maas, 1977; Board, 1983). Recent studies on the byssus and other foot glands in the early stages of bivalves have included Ostrea edulis (Cranfield, 1973 a, b, c); Pecten maximus (Gruffydd, Lane & Beaumont, 1975); Mytilus edulis (Lane & Nott, 1975; Lane, Nott & Crisp, 1982); and Chlamys varia L. (Gruffydd, Budiman & Nott, 1979)

On the night of 4–5 August 1984 an unusual fish was captured in a trammel net set in Elbery Cove, Torquay, South Devon, by Mr W. Blackmore. Its captor realizing it was an unusual species forwarded it to Mr A. D. (Tony) Mattacola for identification. Tony Mattacola recognized it as a member of the genus Seriola, and using the works of Berry & Burch (1979) and Randall (1968) tentatively identified it as Seriola rivoliana Valenciennes, 1833, a species which had never hitherto been recognized in northern European seas. The identification of the specimen was confirmed when the specimen was sent to the author at the British Museum (Natural History); register number 1984.10.22.1.

Colonization of the littoral zone presents many problems to both sessile and relatively sessile invertebrates. These may be especially acute for inhabitants of the upper reaches of this zone, since suitable niches are usually sparsely distributed there, and are often ephemeral in nature. Consequently, both intraand inter-specific competition for space is likely to be particularly intense.

The widely distributed and abundant, beadlet anemone, Actinia equina L., in common with a number of other littoral anthozoans, is apparently capable of both asexual (apomixis or somatic embryogenesis; Polteva, 1963; Gashout & Ormond, 1979; Orr, Thorpe & Carter, 1982) and sexual (Carter & Thorp, 1979) reproduction. The former results in the production of young, which are brooded within the coelenteron and which appear most suited to local dispersal, whilst the latter, if it occurs, is assumed to involve either ovipary or larvipary followed by a planktonic phase. Study of this species therefore affords an opportunity to investigate the dynamics of colonization and dispersal in an heterogeneous environment, in relation to flexibility in reproductive tactics.

A number of nematodes are known to develop in decapod crustaceans. These parasite nematodes are present in the coelom of the host either free or surrounded by different types of host cells. All belong to the order Ascaridida or Spirurida and most of them develop only to the third larval stage in the decapod host; further development takes place in a predator of the crustacean which is generally a teleost or elasmobranch (Berland, 1961; Ouspenskaia, 1960; Petter, 1970; Poinar & Kuris, 1975;Uspenskaja, 1953; Yamaguti, 1961). The life-cycle in most cases is not fully understood. Ouspenskaia (1960) and Uspenskaja (1953, 1963) deduced the life-cycle for Ascarophis morrhuae van Beneden and A. filiformis Poljanski in the Barents Sea by relating the larvae found in decapod crustaceans through affinity of characters to the adults present in cod (Gadus morhua L.) and haddock (Melanogrammus aeglefinus L.). Similarly, the life-cycle of the spirurid Proleptus obtusus was described by Lloyd (1928); the larvae occur in a decapod crustacean, usually the hermit crab Pagurus bernhardus L. and in some cases the shore crab Carcinus maenas L. and the adults are found in the lesser spotted dogfish (Scyliorhinus canicula L.). A more complex life-cycle has been proposed for some anisakids such as Anisakis, Contracaecum and Hysterothylacium (Berland, 1961; Norris & Overstreet, 1976; Wootten, 1978) in which more than one intermediate host is required.

Surveys of the plankton at a depth of 10 m in the western English Channel have been carried out at monthly intervals from 1958 onwards using Continuous Plankton Recorders to provide data on annual fluctuations in abundance of the plankton. Interpretation of these results has been attempted by empirical associations with environmental factors (salinity, sea-surface temperature, radiation, atmospheric pressure patterns, wind speed and current strength). Principal component analysis has been used to extract the main patterns of change and correlation analysis for assessing the relationship between the plankton and the environmental factors. There are complex relationships between the plankton and all environmental factors, supporting previous conclusions that the long-term changes are mediated through interaction between the plankton and the climate. Spectral analysis showed long-term trends and shorter cycles of six and three to four years in both the biological and physical elements, indicating that changes in the western Channel are responding to changes in climate over a much wider area

The long-term monitoring of two stations, 55 and 80 m depth, from 1971 to 1985 shows clear evidence of periods of stability interspersed with periods of change. These periods were identified by several different multivariate methods and persistence stability was quantified by the use of a between years similarity index. A short period of change at the shallow station, 1972–3, was followed by a prolonged period of stability 1974–80. The period 1981–3 witnessed a second period of change with rising total numbers and biomass with some evidence of a downward reversal in 1984–5. The deep station exhibited an essentially similar response except that the stable period 1974–80 was broken into two sub-periods 1974–6 and 1978–80 due to sequential changes in the dominant species which were regarded as evidence of biological interaction with the activities of the polychaete Ophelina acuminata possibly playing a key role. The shallow station showed little evidence of biological interaction and the majority of the species have exhibited similar responses throughout. The general rise in numbers and biomass at both stations is regarded as evidence of intermittent changes in organic flux to the bottom from the water column. The winter temperature fluctuations were shown to have short-term, but significant, effects on the diversity of the communities, bringing about year to year changes in the equitability and dominance.

In the period 1973–80, the infauna at the standard 55 m station exhibited a high degree of persistence stability. The period was characterized by a stable biennial cycle in total numbers of individuals and substantial stability in species ranking. The biennial cycle was associated with density dependent mortality which appears as the principal controlling factor of the community. Evidence is discussed in support of the hypothesis that the density dependent mortality is due to interspecific and intraspecific competition, in a food limiting environment, between species with rather broad niche overlaps.

Although intraspecific aggression in the anemone, Actinia equina L. has been behaviourally well characterized in laboratory-based studies (Bonnin, 1964; Brace & Pavey, 1978; Brace, Pavey & Quicke, 1979), both its incidence and functional role on the shore have remained obscure. Since A. equina broods young, which are produced asexually (Carter & Thorp, 1979; Gashout & Ormond, 1979; Orr, Thorpe & Carter, 1982) and which appear best suited to local dispersal, we have previously postulated that aggression is likely to be primarily directed towards maintaining ‘territorial’ space for settling syngeneic offspring (Quicke & Brace, 1983; Brace & Quicke, 1985). As such, this postulated role is functionally analogous to that provided by aggression in the clonally reproducing anemone, Anthopleura elegantissima Brandt, in which it serves to maintain the integrity of clonal boundaries (Francis, 1973, 1976), thereby presumably also facilitating the competitive expansion of those boundaries. Work by Ayre (1983) on the Australian anemone, Actinia tenebrosa Farquhar appears to support this contention, for both local settlement and genotypic clustering were detected within aggregations.

The mysid fauna of the Rockall Trough consists of more than 35 species partitioned between the pelagic water column and the bentho-pelagic environment. The pelagic mysids are dominated by Eucopia grimaldii, E. unguiculata and Boreomysis microps. The benthopelagic mysids, in a transect from 400 to 2900 m depth, are divided into four faunal associations. Pseudomma affine dominates the 400–800 m depth range; the impinging bathypelagic Gnathophausia zoea and the benthopelagic Boreomysis widens dominate the 800–1300 m range;Michthyops parva and Paramblyops rostrata are co-dominants in the 1400–2300 m range; while Amblyopsoides ohlinii dominates the 2170–2965 m range. The benthopelagic mysid fauna is most diverse at depths below 1400 m. It is dominated by species whose geographical distribution is restricted to the North Atlantic, in contrast to the pelagic mysid fauna, which is dominated by cosmopolitan species. Notes on the breeding season, biology and population structure of several species are given.

Adults of the isopod genus Holophryxus (Dajidae) occur as ectoparasites on natant decapod crustaceans, but little is known of the ecology and life-history of most species. Species of Holophryxus are thought to have a typical dajid life cycle involving an intermediate host (copepod), a definitive host (prawn) and three larval stages (epicaridium, microniscus, cryptoniscus), and the one species for which details are available fits this pattern (Coyle & Mueller, 1981). The final host is infected by the cryptoniscus, a stage superficially resembling a cirolanid isopod, and the first cryptoniscus to settle loses its isopod-like appearance and develops through a juvenile stage into a rather inflated, highly modified female (Coyle & Mueller, 1981). Any subsequent settler becomes a male, retains the small cryptoniscus body form and lives within the marsupium of the female.

Based on analysis of videotape records, species of the genus Argyropelecus are capable of swimming diagonally downwards at considerable speeds without altering their body postures. Morphological evidence strongly suggests that they are able to swim diagonally upwards in a similar way. Their distinctive hatchetlike profile presents a streamlined airfoil in both diagonal and horizontal movements, even though the body is not tilted. Modifications of the caudal musculature probably enable all hatchetfishes (including members of the other two genera, Polyipnus and Sternoptyx) to use the tail for propulsion for both diagonal and horizontal movements. The dorsal fin probably aids in diagonally downward movements and the pelvic and anal fins in diagonally upward movements, whilst the pectoral fins serve as stabilizers for these movements, and as an axis of rotation for striking at prey. The seemingly ungainly shape of the hatchetfish is the result of achieving a streamlined, fish-like shape for horizontal and diagonal movements without tilting of the body, presumably in order to maintain an effective camouflage in midwater.

Measurements of gill dimensions in relation to body weight have been carried out in a mudskipper, Boleophthalmus boddarti. The data was analysed with respect to body weight using logarithmic transformations (log Y = log a + b log W). The slope (b) of the log/log regression lines for the gill area, total filament length, average number of secondary lamellae/mm, bilateral area of an average secondary lamella, and total gill area/g were 1·0496, 0·427, -0·229, 0·851 and 00496 respectively.

These results indicate variations in growth patterns for the different dimensions of the gills. The analysis shows that the increase in gill surface area with the body size is mainly due to an increase in the area of individual secondary lamellae and, to a lesser extent, an increase in filament length and total number of lamellae.

The average weight-specific area for 14 specimens measured (3·6–35·4 g) was 108–15 mm2/g. This value is consistent with results obtained with some other intertidal species.

Marked differences were found in the thickness of the water/blood barrier, which is thinner around the marginal channels. Morphometric diffusing capacity taking this heterogeneity into account was estimated as 0·0208 ml O2 min1 mmHg−1 kg−1.

INTRODUCTION

Morphological studies on the gills of many fish have shown adaptations of the basic structure which can be related to the particular mode of life. Among these adaptations, air-breathing species show many remarkable structural modifications (Munshi, 1976), which extend to the gills forming air sacs in species such as Heteropneustes fossilis (Hughes & Munshi, 1979). Fish which inhabit the intertidal zone, like other seashore animals, are subjected to periodic exposure to air, which may produce problems of water loss and reduction in support for the gills, with consequent collapse and restriction of gas exchange surfaces.

On the 16 June 1982 a thresher shark, Alopias vulpinus (Bonnaterre, 1788), became entangled in a gill net at Bigbury Bay, S. Devon. The stomach contents were found to consist solely of teleost otoliths. The soft tissues of prey taken by large marine predators are often macerated and digested very rapidly or, as in this case, regurgitated during capture or stranding. Identification of the prey is therefore only possible from the hard parts which often remain, e.g. teleost otoliths, bones and scales, and cephalopod beaks, statoliths and gladiuses. The regular seasonal occurrences in the waters off south-west England and south-west Ireland make the thresher the most common of the large sharks in this area. Their accidental capture or collisions with nets are not rare and they have been taken by rod and line on several occasions.

Brander & Dickson (1984) observed that fish production in the Irish Sea is low compared with fish production in the North Sea. They identified the lower number of recruiting fish as being the main reason for this difference. They presented circumstantial evidence suggesting that the low recruitment of fish is in turn linked to the shorter and later production cycle in the Irish Sea but the nature of this link is not understood. An example of the way that fish populations are affected by timing of events in the plankton production cycle is provided by the annual fat cycle of herring. Many workers have shown conclusively that the fat content of the herring is intimately connected with feeding and the time of spawning (e.g. Milroy, 1907; Johnstone, 1915; Bruce, 1924; Hansen, 1955).