Most current literature concerning moult control in crustaceans concludes that initiation of premoult is controlled by changes in the level of moult-inhibiting hormone (MIH) produced by the eyestalk neurosecretory organs. MIH is thought to act by repressing the secretory activity of the Y-organs, preventing increases in circulating ecdysteriod levels, necessary for moulting (see Kleinholz & Keller, 1979). This hypothesis is based upon the observation that eyestalk removal, by removing the source of MIH, leads to accelerated moulting (see Passano, 1960; Vernet-Cornubert, 1961; Sochasky, 1973, for reviews), and it survives despite many contrary reports indicating that moulting is unaffected by eyestalk removal (Sochasky, 1973). Perhaps the best known of the most contradictory data of this nature have been reported for Palaemon serratus for which Drach (1944, 1947), Panouse (1946, 1947) have shown that eyestalk removal generally accelerates moulting in this species. In contrast, Scheer & Scheer (1954) and Carlisle (1953) demonstrated no moult inhibition in this species following eyestalk removal.

Strontium was shown to occur in marine organisms in the early part of the nineteenth century (Moretti, 1813; Vogel, 1914). However, since early detection methods have relied upon chemical separation, accurate quantitative determination of small amounts of strontium, has presented many difficulties due to the chemical similarity of strontium and calcium. During the last 30 years a number of relatively sensitive methods have been developed (Smales, 1951; Thompson & Chow, 1955; Bowen, 1956; Hummel & Smales, 1956; Odum, 1957b; Sugawara & Kawasaki, 1958; Culkin & Cox, 1966; Riley & Segar, 1970; Gibbs & Bryan, 1972). Towards the beginning of this period, Vinogradov (1953) made an extensive review of the chemical data on the marine biota. Due to the limitations mentioned above there was relatively little information available on the occurrence of strontium.

Although the distribution of most coastal and oceanic fishes of the seas of northern Europe is relatively well-known extensions to known range are reported with moderate frequency as vagrant specimens are found or captured and recorded. Possibly it is partly because the fish fauna is well documented, with reliable literature to permit identification, that rare or unusual fishes are quickly recognized and attempts made to identify them. Most such specimens are housed in museum or other institutional collections and thus information about them can be retrieved long after their capture. However, the circumstances of the present report which records the stranding of a white marlin T. albidus Poey, 1860 on the Lancashire coast at Morecambe Bay are somewhat unusual in that the whole specimen was eaten and the only evidence remaining are two photographs and a small piece of skin. In view of the interest of this occurrence, which represents a northward extension of the range of the species by several hundred miles, as well as the first report of its occurrence in British seas, full documentation is given here and both available photographs are reproduced.

Members of the genus Phascolion Théel are probably the most familiar of sipunculans because most species inhabit the empty shells of molluscs and other similar structures and are therefore easily collected in dredge samples. Although the genus is represented in most seas and depths, few species have been investigated in detail and much of our knowledge is based on studies of the widespread Atlantic species P. strombi (see Åkesson, 1958; Hylleberg, 1975; Kristensen, 1970; Wesenberg-Lund, 1929). P. strombi is known to be remarkably plastic in many of its characters, particularly external, to the extent that Gerould (1913) was able to distinguish seven varieties in the western Atlantic region alone. Much of the variation in the size and colour of P. strombi, and in the form of the skin papillae, especially those generally termed ‘holdfasts’ or ‘adhesive papillae’, may be attributable to the size and type of shelter that is inhabited but experimental evidence is lacking. It follows that a similar degree of external plasticity to that recognised in P. strombi must be assumed for most, if not all, Phascolion, presently totalling around 45 species. Many Phascolion species have been erected on single or just a few specimens showing only slight differences of dubious systematic significance.

Taxonomically, the genus is very difficult and no satisfactory key to the species has yet been devised. As a first step, there is a need for definitions of subgenera, preferably based on internal characters which are not subject to environmental influences. To this end, the retractor systems of the north-east Atlantic species described below have been studied and compared with the type specimens of species from other areas.

The following three species of grey mullet (Mugilidae) are recorded by Wheeler (1978) for the waters of north-western Europe: thick-lipped mullet, Chelon labrosus (Risso, 1826); thin-lipped mullet, Liza ramada (Risso, 1826) and golden mullet, Liza aurata (Risso, 1810). Liza ramada was obtained in relatively large numbers during the course of extensive sampling of the material collected on the intake screens of power stations in the Bristol Channel and Severn Estuary (for details of other studies see e.g. Claridge & Gardner, 1977, 1978; Titmus, Claridge & Potter, 1978; Abou-Seedo & Potter, 1979; Claridge & Potter, 1983, 1984). Since there is apparently no detailed information on the biology of the thin-lipped mullet in the estuaries of north-western Europe based on regular frequent collections, the power station material was used to provide data on seasonal and annual abundance, size composition, growth and lip depth of this species in the Severn Estuary and Bristol Channel. Comparisons have been made between these data and those obtained for C. labrosus from the same environments and more particularly from outside the area at Pembroke where much larger collections of this latter species were taken.

A spermatophore is defined as a capsule of albuminous matter containing a number of sperm. Among opisthobranchs the families Retusidae, Philinoglossidae, Bullidae, Atydae and Runcinidae are all said to possess a copulatory apparatus which stores sperm and also forms spermatophores (Ghiselin, 1966). Relatively little information exists concerning the structure of the copulatory apparatus or the spermatophore in these groups and practically nothing is known about the copulatory behaviour of the animals and the fate of the spermatophore (Perrier & Fischer, 1914; Ghiselin, 1963, 1966; Thompson, 1976;Beeman, 1977). This paper will focus on the structure of the spermatophore of the cephalaspid Runcina (Kress, 1977). The formation of sperm occurs in the hermaphroditic glands, in a more central position than that of the eggs. These autosperm leave via the common genital aperture which is located laterally to the gills. They travel by means of strong ciliary action, through a seminal groove to the male copulatory apparatus on the right of the mouth. The sperm then moves through the penis and the prostate into a storage sac, the seminal vesicle. For copulation, these sperm are packed into a spermatophore which should presumably be introduced into the common genital aperture but which may be found attached to the mantle or foot, even to animals not yet sexually mature. We have taken this opportunity to study the spermatophore which otherwise might not be easily detected.

A comparative study of Chorda filum populations from the British Isles (S 34‰) and the Baltic coast of Finland (S 6‰) has revealed differences in response by live adult thalli to treatment for 2 h with sea water of different salinities. Water uptake and loss by thalli differed significantly in salinities of х o‚ х 1/6, х ⅓ and х 1 ( = 34‰). British material showed severe cell disruption in freshwater whereas Finnish material did not. Killed thalli also behaved differently, British material showing little response to salinity treatment but Finnish plants continuing to react much as live tissues.

Anatomical differences between populations were also observed, cortical cells in Finnish plants being significantly smaller than their British counterparts. Diaphragms traversing lumens of British material were simple, entire structures, but those in Finnish plants were deeply dissected and complex in organization.

It is postulated that Baltic Chorda may have undergone a process of evolutionary divergence in response to its changed saline environment.

INTRODUCTION

Chorda filum (L.) Stackh. is one of several species of north Atlantic Phaeophyceae to be found in the inner Baltic Sea and Gulf of Bothnia; its geographical limit being associated with sea water salinity of approximately 4‰, (Waern, 1952; Hällfors et al. 1981). This species has been studied by Norton & South (1969) and South (1966) who traced the development of gametophytes and early sporophytes in culture media of different salinites. Although their cultures had been established from British material only, they felt able to argue from their results that the Baltic population did not constitute ‘… a different physiological strain specially adapted to the extreme environmental conditions prevailing there’.

A major contribution to our understanding of the distribution and taxonomy of echinoids in British waters was made by Mortensen (1927, 1928–1951). Many earlier qualitative investigations (e.g. Süssbach & Breckner, 1911; Brattström, 1941) which dealt only with limited areas, were combined in Mortensen (1928–1951) to produce an overall assessment of the North Sea echinoid fauna.

In his discussion paper Ursin (1960) synthesized findings from his 20 year grab sample survey with the work of others to produce a valuable quantitative analysis of the echinoids of the central North Sea (54–5 8° N).

In recent years (1977–1983) participation on demersal fish surveys in the North Sea has enabled the distribution and population structure of the macroepibenthic component of the water column to be recorded (Dyer et al. 1982, 1983; Cranmer, Fry & Dyer, 1984).

Although this present study has added no new echinoid species to the fauna it has given a detailed picture of echinoid distribution in the area.

The common mussel inhabits an environment of fluctuating temperatures, salinities and water turbulence. To help cope with these stresses, mussels have evolved some extraordinary structural and biochemical adaptations. The production of the byssus is one such adaptation. The byssus is a complex array of threads and adhesive plaques that serves alternatively to attach the mussel to solid objects, to absorb shock, or to scale a vertical face (Waite, 1983 a; Price, 1983). Because of its location outside the animal's living tissues, the byssus cannot count on the same kind of repair and remodelling offered to structures within the animal. The byssus is thus confronted with two conflicting demands. One is to be a mechanically dynamic structure shielding the animal against the buffeting impact of waves; the other is to be chemically inert towards the hydrolytic action of sea water and microbial enzymes.

For centuries man has used lights to attract and concentrate fishes near the sea surface to aid their capture by nets or hooks (Ben-Yami, 1982). Underwater lights lowered into shallow seas are now regularly used to lure fish into set nets, large nets suspended beneath ships or into the vicinity of powerful pumps (Sidelnicov, 1981; Andreev, 1962; Nikonorov, 1969). Usually lights of more than 1 kw are used and such power requires a surface generator and strong insulated cable from the surface to the light. Although we know from these applications that some fish species are attracted by lights, the use of lights on trawls has not been developed for commercial exploitation or for research sampling. Perhaps such development has been discouraged by the safety problem and technical difficulties of providing electrical power on deck and handling heavily insulated conducting cable between the trawl and the generator. Lights have been used on commercial trawls with television in experiments to study fish reaction to trawls but such experiments were not concerned with finding the effect that lights might have on the quantity of fish caught and catches have not been analysed (A. Maclntyre, personal communication).

In some earlier papers we have discussed the distribution of water and the total amounts of the major inorganic solutes in the cells of Arenicola marina (L.) equilibrated to full-strength and to diluted sea water (Freeman & Shuttleworth 1977b, c). We concluded that adaptation to dilute media by this osmoconforming worm was dependent entirely upon the regulation of cell volume. In dilute media substantial amounts of water do enter the cells but down to about 30% sea water this is only 55% of that which would have entered if the osmotic equilibrium was accomplished by entry of water alone. The influx of water is restrained by simultaneous loss of solute, an increasing amount of solute being lost or rendered osmotically inactive as the dilution increases. For lugworms in 35% sea water, for example, the volume of cell water has doubled compared with worms in 100% sea water, but the increase would have been far greater if the intracellular solutes had not declined by 30%.

The Sr, Mg, and Ca chemistry and mineralogy of the shell, beaks, and inorganic compounds of the renal appendages of Nautilus pompilius Linné 1758 reveal a complex physiochemical system of biomineralization. The chemistry of the shell and septal aragonite is similar, and establish that N. pompilius discriminates against the concentration of Sr and Mg in sea water by 78% and more than 99% respectively. Beaks consist of high-Mg calcite (4.4% MgCO3). Renal appendages contain either aggregates of crystals (uroliths) of Mg-oxalate dihydrate with nuclei of hydroxyapatite or disassociated particles of hydroxyapatite or both. There is no evidence that uroliths or hydroxyapatite particles serve as temporary reservoirs of Ca during calcification of septa.

Studies concerned with the sub-lethal aspects of the toxicity of copper to the mussel have, in many cases, been compromised through the use of static experimental systems (see Davenport & Redpath (1984) for review). Manley, Gruffydd & Almada-Villela (1984), using a through flow system, reported a significant reduction in shell growth at a concentration of 10 μg I-1 added copper with recovery after metal addition had ceased. Strömgren (1982) investigated the effects of a series of concentrations of the metal (amongst others) on Mytilus, but there are discrepancies between his results and the work of others which have been fully discussed elsewhere by Davenport and Redpath.

The genus Fucus L. is widely distributed through the cool temperate waters of the north Atlantic and north Pacific oceans. The very large number of sub-generic taxa (> 100) previously recognized was reduced by Powell (1963) to only 6 species. In his revision, Powell recognized F. distichus L. emend. Powell as the most variable of these. He classified the intra-specific variation in this species into 4 sub-species: F. distichus distichus, F. distichus anceps (Harv. et Ward ex. Carruthers) Powell, F. distichus evanescens (C.Ag) Powell and F. distichus edentatus (Pyl.) Powell. Because of reports that intermediate forms existed in Iceland (Jonsson, 1903) and the Faeröes (Börgesen, 1902), Powell (1957 a,b) decided to use sub-specific status rather than specific designation for these 4 taxa. However, within North America the 4 sub-species of F. distichus were often assigned specific rank (e.g. Taylor, 1957).

Observations on the density of pelagic marine fish eggs have indicated that they are near neutral buoyancy for most of development and have a tendency to become denser towards hatching (see Russell, 1976). However, most of this information has been based on limited laboratory observations on the relative buoyancy of eggs; only a few experiments have given more precise estimates of the absolute density of eggs based on the salinity of water in which they are neutrally buoyant (e.g. Franz, 1910; Sundnes, Leivestad & Iversen, 1965). Recently, a new technique (Coombs, 1981), based on the use of a stable column of continuously graded sea-water concentration has allowed more precise and routine measurements of the density of fish eggs throughout development.

The morid fishes are important members of the deep-water associations of fish on the continental slope of the Rockall Trough. Three species, Lepidion eques, Halargyreus johnsonii and Mora moro, are distributed between about 500 and 1250 m while Antimora rostrata has its centre of abundance between about 1750 and 2200 m. Aspects of their biology including changes in abundance and length composition with depth, reproduction and fecundity and age composition are described.

INTRODUCTION

In a trawling survey of the bottom-living fish of the Rockall Trough at depths from about 400 to 2900 m, 4 species of the family Moridae were sampled. Three species, Lepidion eques, Halargyreus johnsonii and Mora moro were distributed on the upper and mid slopes while a fourth species Antimora rostrata occurred on the lower slope and continental rise. Several different trawls were used to sample the fish populations of the slope and Gordon & Duncan (in the Press) have discussed the relative selectivity of each of these nets for sampling different species of fish. In many of the bathymetric zones fished morids were important both in terms of biomass and abundance. Some preliminary observations on aspects of the biology of Lepidion eques have been published (Gordon, 1979 a, b) and Mauchline & Gordon (1980, 1984) have described the diets of the morid fish from the Rockall Trough in some detail. In this paper other aspects of their biology will be described.

Goldman, McCarthy & Peavey (1979b) argued that growth rates of phyto-plankton in apparently oligotrophic ocean waters may near maximal. Their hypothesis was succinctly restated by Goldman (1980): ‘…the chemical composition of phytoplankton is extremely variable under exacting laboratory conditions of nutrient limitation and approaches the ‘Redfield’ proportions (C:N:P of 106:16:1) when neither nitrogen nor phosphorus is limiting so that near maximal growth rates are attained. In marine surface waters the chemical composition of particular matter often is in the Redfield proportions, thus implying that natural phytoplankton growth rates may be close to maximal.’ We argue on theoretical, experimental and observational grounds that this implication may not necessarily be correct.

Crustacean cuticle consists essentially of chitin impregnated and coated with protein which is tanned with quinone (Dennell, 1947a). The outer surface is most heavily tanned, and the cuticle is further strengthened by calcification. The various theories as to the mechanism of calcification in crustacean and other biological material have been reviewed briefly by Digby (1967). Most appear unsatisfactory for various reasons, and evidence was outlined that calcification might arise from the formation of base by processes which are essentially electrochemical in origin. The quinone-tanned protein of the cuticle is electrically semiconducting and supports electrode action in suitable gradients of potential (Digby, 1965), and small potential differences may arise by diffusion or by active processes. Thus the deposition of calcareous salts might arise partly at least by action comparable to that which takes place at a metallic cathode. In support of this, the position of the initial calcareous deposits in Carcinus maenas (L.) was found to change with the gradient of sea-water salinity in the manner expected if some control were exercised by diffusion potentials, acting across a thin semiconducting layer to generate small changes of pH (Digby, 1968).

There are five common species of wrasse (Labridae) in British coastal waters, two of which are hermaphrodite, (Labrus bergylta Ascanius and Labrus mixtus L.) and three are gonochorists with discrete sexes (Ctenolabrus rupestris) (L.), Centrolabrus exolelus (L.) and (Crenilabrus melops (L)) (Dipper & Pullin, 1979; Dipper, 1981). L. bergylta (Sjolander, Larson & Engstrom, 1972; Potts, personal observation) and L. mixtus (Wilson, 1958; Potts, 1984) lay their eggs in shallow depressions excavated in coarse paniculate substrates often closely associated with sublittoral reefs. Ctenolabrus rupestris, the smallest of the species is most usually associated with sublittoral crevices, and is the only one to produce pelagic eggs despite showing territorial aggression in the spawning season, a behaviour mostly confined to species with demersal eggs. Little is known about Centrolabrus exoletus, but from the striking sexual dichromism at maturity and its association with rocky reefs it may be supposed that it exhibits some form of parental care for the demersal eggs (Potts, 1984). Crenilabrus melops shows parental care of its eggs which are laid in large and complex algal nests, a feature which is common to all this genus (Fiedler, 1964; Quignard, 1966; Potts, 1984). The corkwing wrasse is one of the commonest coastal species which at maturity show sexual dimorphism and dichromism, a feature which led to taxonomic confusion among earlier workers and which is discussed by Potts (1974).

Pelagic zooplankton and fish release faecal material which rapidly sinks through the water column and contributes various amounts and types of organic and other chemical constituents to bottom sediments. The major importance of this process in linking biological events in the water column with inputs to sediments has been well demonstrated in a number of sea areas through the use of field experiments with pumps or traps (Bishop et al. 1977; Gagosian, Volkman & Nigrelli, 1983; Honjo, 1978; Knauer, Martin & Bruland, 1979; Prahl, Bennett & Carpenter, 1980; Wakeham et al. 1980; Wakeham, Farrington & Volkman, 1983). In general, field studies have shown that the deposition of organic matter of pelagic origin occurs with considerable alterations both quantitative and qualitative (Gagosian, Nigrelli & Volkman, 1983; Prahl et al. 1980; Wakeham, 1982). Such studies, however, have not clearly defined how individual biological processes competing in the water column influence the overall composition of organic matter in vertically transported paniculate material.