The coastal prosobranch Hydrobia ulvae is known to occur in a wide range of marine and brackish habitats and to display great variation in its breeding and life-history characteristics. Several hypotheses have been advanced to account for the latter, including that the variation is environmentally induced and that the species can be divided into ecotypes. Comparison of two adjacent populations in Norfolk, U.K., one from the marine intertidal zone and the other from a non-tidal, landlocked, brackish coastal lagoon, however, disclosed that although shell form differed markedly (including a mean height ratio of 1:1.2), there was no difference in such otherwise variable features as numbers of eggs per capsule, size at hatching and larval type. In both, each capsule contained an average of 21-22 eggs, which hatched at a shell length of 152-154 μn to liberate relatyyively long-lived, free-swimming veligers. The two populations were also interfertile. In no respect had the isolated lagoonal population diverged away from the parent marine one towards the contrasting reproductive strategies characterizing the specifically lagoonal species of Hydrobia that occur nearby. The ‘displacement’ of shell size observed in the lagoon in the absence of sympatric hydrobiids is considered to cast further doubt on competitive character displacement in this genus.

The larval development of the parasitic barnacle, Sacculina carcini, has been closely followed. Size and volume measurements have been made for the four naupliar stages and cyprids of both male and female broods. Volume increases between naupliar stages are minimal (x 1.03–1.09) and in line with other barnacle species with lecithotrophic larvae. However, the large volume reduction between stage IV and cyprid for S. carcini, which is more acute for the female larvae, is a unique characteristic. The reduced setation formulae of the larval appendages of S. carcini and another rhizocephalan are compared to those of larvae, both lecithotrophic and planktotrophic, of a range of barnacles. Sex ratios and carapace length data for 184 S. carcini cypris populations are presented which reinforce the seasonal changes in sex ratios.

The haemolymph of balanomorph barnacles contained very few haemocytes. The hyaline cell was the main haemocyte type found and this cell is capable of phagocytosing foreign bodies. A few semi-granular cells were also found, but granulocytes never occurred. Haemocytes were not found within haemolymph clots.

Ostrea puelchana is a larviparous oyster from the S.W. Atlantic coasts. This species is not being commercially exploited at present. Because of its high food qualities, however, it may constitute a resource of economic interest in the future.

Until now larval development and characteristics of the incubation period have been poorly known. This study describes the characteristics of the mode of brooding under laboratory rearing conditions and, using scanning electron microscopy, the morphogenesis of the hinge until larval release from the parents.

The larva develops two anterior and two posterior denticles during brooding. A comparison with larvae of other species of the genus Ostrea reveals that the main differences among them do not lie so much in the pattern of hinge dentition as in the rate of evolution of the hinge components, which is faster in Ostrea puelchana. This species has fully developed denticles at the time of release, which places the larva of this oyster as particularly evolved within the genus Ostrea.

The hermit crab Clibanarius erythropus first reported from Britain in 1961 is no longer present. There appears to have been no further recruitment since the late 1950s when there was a favourable combination of climate and hydrographical factors that led to successful invasion of Devon and Cornwall.

The population appears to have succumbed to the combined effect of age and declining temperatures. Additional contributory factors in the decline could be the mortalities resulting from the ‘Torrey Canyon’ disaster; the reduction in numbers of the dog-whelk (whose empty shells are the favoured home of the crab in Britain) as a result of organotin antifouling paints; and increased public pressure on the habitat.

Gills are the typical respiratory organ of fish in their usual habitat of well-aerated water. The transition from water- to air-breathing required many modifications to the structural and physiological adaptations of the gas-exchange surfaces, i.e. gill, skin, swimbladder and other accessory organs of the alimentary canal. The skin is particularly important among air-breathing fish. This histological study showed varying degrees of adaptation of parts of the skin from different body regions, paying particular attention to the water/blood barrier. The results suggest a general importance in gas exchange in the following order: gill, inner operculum, nasal, body and outer opercular skin, as indicated by increasing thickness of the water/blood barrier.

Scientific data from the last 100 years are combined with primary and secondary historical information on the fisheries to summarize changes in the relative abundance of pilchards and herrings in the south-west in the last 400 years. The fluctuations in the two species are compared with recorded and inferred annual mean temperatures over the period. Pilchards are more abundant and extend farther to the east when the climate is warmer, as from 1590 to 1640 and from 1930 to 1960. In cooler times, as in the second half of the seventeenth century, herrings are more abundant while the pilchard fishery occurs later in the year and is restricted to west Cornwall. Lesser changes in the relative abundance of the two species and the timing of the fishery along the south coast of Devon and Cornwall in the intervening periods between these extremes accord fairly well with smaller fluctuations in climate. It is presumed that in addition to direct effects on reproduction and behaviour, changes in climate can indirectly influence the relative competitive advantage of the species through alterations in the associated ecosystem.

This work reports on the fine structure and histochemistry of several regions of the alimentary canal in Pholoe minuta (Fabricius, 1780). Particular emphasis is placed on the elaborate secretory cells (tryptophan-containing secretion) associated with the pharyngeal jaws. Mucus gland cells were located and described for the oesophagus (acid mucins), pharynx papillae (sulphated acid mucins), pharynx luminal lining (mixed acid mucins) and the intestine (mixed acid mucins). Enzymic gland cells (zymogen-like secretory granules) were identified in the luminal lining of the pharynx and in the intestine. Lysosome-containing cells (presumably absorptive) were described in the intestine. Glycogen reserves were observed along the coelomic peritoneum and a seasonal pattern for their deposition and utilization is briefly discussed.

Young vestimentiferans, ranging from 0.15 to 10 mm in length, were examined by light and electron microscopy (SEM and TEM). The newly settled stages have a functional gut and traces of larval ciliation, which suggests that they may have developed from a planktonic trochophore stage. The larval mouth becomes an elongated siphon and the ciliated gut persists for some time after the development of the bacterial symbiosis in the trophosome. The segmentation of the body in the earliest stages is similar to that in postlarval Pogonophora, and it is concluded that Vestimentifera and Pogonophora are closely related.

Relationships between respiratory area, oxygen consumption, and body mass have been examined during the development of water- and air-breathing fish. It is concluded that there is at least one stage at which the slope of the relationship between log gill area and log body weight changes during fish development. This usually occurs in the weight range 0.05–1.0 g and is often associated with a distinct metamorphosis, but no common functional significance can be attached to them. However, the change in slope does not appear to be associated with a comparable inflexion in the corresponding relationship between body mass and oxygen consumption (routine). It seems probable that other surfaces are important during these transitions and that the total gas-exchange surface of the fish shows a more constant change throughout the life history. Further analyses of a wider range of species is required to test this hypothesis.

The phenomenon of acid secretion has arisen independently many times, for feeding, for penetrating calcareous material to make a shelter or to pursue prey, or for defence. This last category contains examples from many groups of marine organisms, in which acidic allomones may serve to deter fouling by epibionts or predation by teleost fish. Histochemical and histophysical methods have increased the precision with which acidic allomones can be identified within acid vacuoles, cells, glands, sacs or capsules. Acidic allomones are produced in pleurobranch molluscs by unicellular epidermal glands, by multicellular subepidermal sacs, or by an arborescent internal acid gland, connected to the buccal mass by a thick medio-dorsal duct. Some species have all three types. In the case of the epidermis, discharge is probably triggered directly by the trauma of attack by a predator (effectively, holocrine discharge), but the other types of gland are discharged by contraction of a strong muscle sheath, without tissue damage. Cypraeid molluscs have extensive, mobile mantle lobes which can ensheath the massive shell temporarily. The epidermal acid glands are orientated within the mantle so as to discharge away from the shell. The lamellariid and philinid molluscs have internal shells, well protected from chemical attack, and the multicellular, subepidermal acid glands are situated over all the surfaces of the body. In the tunicates investigated, both blood and tunic were neutral in Ciona intestinalis, but they were both acid (pH 1) in Ascidiella aspersa. In Ascidiella scabra and Ascidia mentula the blood was neutral, and the tunic alone was acid. The acid tunics contained abundant blind lacunae. It is unlikely that these acid-filled lacunae correspond to the blind-ending arterial ampullae described by other workers. Discharge is probably brought about directly through the trauma of attack. The perennial species of the alga Desmarestia, D. aculeata, exhibited a pH near to neutrality. Two annual species, D. dresnayi and D. ligulata, contained acid of pH 1–2, and showed strong precipitation of BaSO4 after BaCl2 treatment. Sections confirmed that the acid is normally held within the swollen parenchymatous cells which pack the sporophyte frond. The cuticle is comparatively thin in the acidic species. In conclusion, it is argued that acid secretion may be the allelochemical analogue of warning or aposematic coloration.

Surface fluorescence measurements in June in the Bay of Biscay showed little correlation with chlorophyll a measurements due to the presence of a marked diurnal fluorescence rhythm although satisfactory correlations have been obtained at other times of year in the same region (see Fig. 10 of Pingree et al. 1982). By contrast, the beam attenuation coefficient values showed a good correlation with the chlorophyll a measurements and can be used to map the sea surface distribution of chlorophyll a when the diurnal rhythm is present, particularly when the phytoplankton is dominated by a single species. This conclusion may be of considerable practical significance when contemplating synoptic surveys in such situations. As Prezlin & Ley (1980) have observed there is growing awareness that fluorescence per unit chlorophyll a is not a constant that can be used reliably in mixed phytoplankton biomass estimates based on in vivo chlorophyll a fluorescence, and the problem is clearly compounded if some species exhibit a marked diurnal fluorescence rhythm. Furthermore, the present observations support the caveats of Falkowski & Kiefer (1985), that in situ moored fluorometers, the use of air-borne laser-induced fluorescence, or satellite-received passive, solar-induced fluorescence, only measure fluorescence, not chlorophyll per se.

The fluorescence response near the shelf-break over a 24 h period following a drogued dahn buoy showed a variation of about a factor of 5 between the day and night fluorescence levels. Beam attenuation coefficient measurements and Coulter Counter analyses showed that these results could not be attributed to the migration of the phytoplankton.

Twenty species, one of them represented by two ecologically different isolates, were grown at salinities from 0 to 60‰ at intervals of 5‰ or less. Growth was measured spectrophotometrically on a pigment extract, and formation of sexual organs was recorded. For each species the results are presented in a diagram, and compared with the salinity preference suggested by information in the literature and by the author's observations in nature.