Recent studies on the osmotic responses of marine invertebrates to dilution of the external medium have tended to emphasize the osmotic and ionic regulation at the intracellular level rather than at blood/body fluid level. Even in those invertebrates, principally euryhaline crustaceans, possessing osmoregulatory mechanisms which enable them to maintain concentrations of the blood above those of dilute media, the regulation is not perfect, and there is some lowering of the blood concentration below the level exhibited in full-strength sea water (Lockwood, 1962). This requires the establishment of a new osmotic equilibrium between the intracellular solutes and those of the blood. The nature of the intracellular osmotic constituents is, however, strikingly different from those of the blood, even in those invertebrates which are stenohaline and purely marine in their distribution (Robertson, 1961). The osmotic pressure of the blood is due almost entirely to the same inorganic electrolytes as are present in sea water, although the percentage contribution of the various ions may differ. On the other hand these inorganic ions account for only about one third to one half of the intracellular osmotic pressure. The remainder is accounted for by organic solutes, most particularly free amino acids.

Arenicola marina (L.) is one of the most common members of the outer estuarine sandy and muddy shores. A moderately euryhaline osmoconformer, this polychaete cannot survive in water of less than about 10‰ constant salinity and then only in the Baltic; however, in the outer portions of estuaries, it is not uncommon for the overlying water to be practically fresh at some stages of the tide. Wells (1949b) postulated that parts of the complex burrowing behaviour of the animal prevents irrigation of the burrow with noxious water, but the advantages to the lugworm of its periodic inactivity have never been fully investigated.

Off the coast of Cornwall from the Lizard Head to Padstow there has been, for many years, a small but locally important fishery for crawfish Palinurus elephas (Fabr.).

The fishermen had used pots and tangle nets up to the outbreak of the Second World War in 1939. From 1945 tangle nets had been little used and the fishery was pursued mainly by pot fishermen until the early 1960s when divers using self-contained under-water breathing apparatus began to collect crawfish. Tangle nets were re-introduced widely in the late 1960s.

Parathemisto gaudichaudi (Guerin) (= P. gracilipes, Sheader & Evans, 1974) is a species of planktonic hyperiid amphipod which occurs in temperate and subpolar regions in both hemispheres (Dunbar, 1964; Kane, 1966; McHardy, 1970, Ph.D. thesis, Edinburgh University).

Our previous studies have dealt with the taxonomy (Sheader & Evans, 1974), feeding and gut structure (Sheader & Evans, 1975), and morphological variation (Sheader, 1975) of P. gaudichaudi. These studies involved the routine maintenance of the species in laboratory conditions, allowing behavioural and developmental data to be gathered. The present paper deals with fertilization of the eggs and subsequent development up to the time of release from the marsupium. Animals were collected at a station 5 miles east of Blyth, Northumberland (55° 07′ N, 1° 22′ W). Laboratory culture is described in previous papers (Sheader & Evans, 1974, 1975).

Ampelisca tenuicornis Lilljeborg, 1855, is a member of a widely distributed genus of benthic tube-dwelling amphipods. Population studies of A. macrocephala Lilljeborg in the Øresund show it to have a generation length of 2 years (Kanneworff, 1965), and A. vadorum Mills off Massachusetts, U.S.A., produces two generations per year (Mills, 1967). A. brevicornis (Costa) in the Mediterranean breeds throughout the year with a generation time of 5–7 months (Kaim-Malka, 1969), but has only one generation per year in Helgoland Bight (Klein, Rachor & Gerlach, 1975).

Balanus balanoides (L.) is a cross-fertilizing hermaphrodite. The spermatozoa which are inseminated into the mantle cavity are initially inactive. Eggs are laid into the two elastic sacs of the oviducal glands (see Walley, 1965), which expand into the mantle cavity as more eggs are laid. The discharge of eggs into the elastic sacs also forces fluid out of the oviducal glands into the mantle cavity where the spermatozoa have been deposited. The fluid activates the inseminated spermatozoa (Walley, White & Brander, 1971; Walker, 1977).

In order to effect fertilization of the eggs activated spermatozoa must pass across the oviducal gland sac wall. How the spermatozoa accomplish this is the subject of the present investigation.

The pelagic environment can be divided into five gross regions. These are the intertidal and estuarine, the neritic and the oceanic epipelagic, mesopelagic and bathypelagic regions. Each of these regions has an endemic crustacean fauna but many species inhabit more than one region. The ranges and rates of fluctuations of environmental characteristics vary from the extremes encountered in the intertidal and estuarine region to the relative constancy of those in the bathypelagic region.

The occasional reports of butterflies sighted at sea or landing on ships many kilometres from the nearest land indicate the transport of insects by wind from terrestrial to marine environments. However, the frequency with which insects are blown out to sea, the abundances of airborne insects over and on the surface of the sea, the eventual fate of these insects and their possible ecological roles are rarely considered (Bowden & Johnson, 1976).

More than half of the species of British prosobranchs living intertidally have planktonic larvae. Settlement involves a positive response to certain factors which results in a speedy loss of structures fulfilling larval needs and the introduction of others associated with locomotion and feeding on the sea-bed (Fretter, 1972). Unless this response relates to the needs of the species, settlement could lead to mass mortality of larvae settling on unsuitable ground.

Several authors have shown that by feeding bivalve larvae on a mixed algal diet growth is often better than when each of the constituent species of the diet was fed individually (Davis & Guillard, 1958; Walne & Spencer, 1968; Calabrese & Davis, 1970). The criterion upon which the value of the diets has been assessed has almost invariably been larval growth and rarely have the larvae been grown to metamorphosis.

This paper reports the results of a series of trials with Ostrea edulis L. larvae which were fed with three diets. Two were single species diets of Isochrysis galbana Parke and Tetraselmis suecica (Kylin) Butch, while the third was a combination of these two species. Larvae were grown to metamorphosis on each of the diets and then for a further period with a common food to assess the value of the larval diet on the subsequent performance of the spat.

The possibility that marine invertebrates might obtain part of their nutritional requirements by direct absorption of dissolved molecules through the epidermis has recently received considerable attention. This revival of interest in a field which had been virtually abandoned since the early part of the century was led by the findings of Stephens & Schinske (1957, 1958, 1961). Modern analytical techniques have revealed that the amount of dissolved nutrients in coastal waters is much greater than was formerly realized; total amino acids have been recorded in concentrations of up to 10-4 mole/litre in south-east Alaskan waters (Schell, 1974) and 7 x 10-5 mole/litre off Helgoland (Bohling, 1970). Direct absorption of amino acids has been conclusively established in several phyla (see reviews by Stephens, 1968,1972), and one of the major aims of current research is to show that dissolved organic molecules taken up from available concentrations could be of nutritional significance. Recent developments concerning the possible roles of uptake in marine ecosystems have been reviewed by West, de Burgh & Jeal (1977).

Among the teleosts three basic modes of locomotion have been recognized; anguilli-form, carangiform and ostraciiform (Breder, 1926). During the past 50 years much attention has been paid to the anguilliform (Breder, 1926; Gray, 1933 a, b; Gadd, 1952; Taylor, 1952; Lighthill, 1960, 1969, 1970) and carangiform (Breder, 1926; Gray, 1933 c; Bainbridge, 1958, 1960, 1963; Lighthill, 1969, 1970) modes. In contrast little work has been done on the ostraciiform mode. Models have been made along mechanical (Breder, 1926; Gray, 1968, p. 35) and mathematical (Smith & Stone, 1961) lines. How-ever as Gray (1968) points out, ostraciiform locomotion has not been analysed in living fish.

The saithe, Pollachius virens (L.), makes substantial diel vertical migrations like many other teleost fish. Adulst saithe offshore are known to ascent at dusk from 100 to 10 m (Schmidt, 1955) during which they experience a pressure decrease from 11 to 2 atm. If the swimbladders of these fish were fully adapted to the daytime depth, the gas of the swimbladder (which ‘obeys’ Boyle's Law) would expand 4½ times and rupture the swimbladder wall (Tytler & Blaxter, 1973). Even if not fullly adapted it is likely that some increase in volume would be experienced, giving not only the danger of the swimbladder bursting, but also a serious equilibrium problem as the fish become more positively buyant during the ascent. Jones (1952) for example suggested that the physoclistous perch adapted to a particular pressure could only cope with a 33% decrease in pressure without rising to the surface out of control.

Temperature, salinity and nutrient structure at a station, E1, in the English Channel 22 miles from Plymouth have been described for many individual years (see Armstrong & Butler, 1968, for example). By averaging the results gathered over many years (1903–61) the mean seasonal changes in the vertical distributions have been obtained (Pingree & Pennycuick, 1975). In this paper these distributions have been extended to incorporate data to 1975 and as well as presenting up-to-date mean distributions for temperature, salinity and inorganic phosphate, the mean distributions for silicate and nitrate are included. The purpose of the present work is to interpret the observed mean seasonal changes in the inorganic nutrient distributions in the light of recent measurements giving continuous variations of chemical properties (Armstrong & Lafond, 1966), and in particular, from the knowledge gained from continuous vertical chlorophyll ‘a’ determinations (Lorenzen, 1966; Holligan & Harbour, 1977; Pingree, Holligan & Head, 1977).

The development of sensitive fluorimetric techniques for continuous in vivo measurements of chlorophyll ‘a’ (Lorenzen, 1966) has made it possible to study in detail the vertical distribution of phytoplankton in lakes and seas (e.g. Strickland, 1970; Berman & Pollingher, 1974; Lasker, 1975; Fasham & Pugh, 1976; Pingree et al. 1976). However, for marine environments there is little compatible data, such as given by Lasker (1977), on the species composition of localized phytoplankton populations. This is an important gap in our knowledge since the variations shown by different algal taxa in attributes such as nutrient requirements, growth rates, adaption to light, and palatability to zooplankton have wide ecological implications.

Considerable obscurity surrounds the mechanism of calcification in all biological material. The coralline algae, which lay down quantities of calcium salts in their tissues, are no exception. These forms are common in the littoral and sublittoral in exposed situations in northern waters and make up a large part of many of the reefs in tropical seas. This paper describes observations and experiments relating to growth and calcification in two northern corallines, Clathromorphum circumscriptum Foslie and Corallina officinalis Linn. Calcification is related to the production of an alkaline reaction by the cells when exposed to sunlight. The source of the base concerned will be considered in a following paper.

Study of the pH relations of the coralline algae has shown that there is good reason to believe that calcification may be brought about by the development of alkalinity by the cells of the thallus, while a slightly acid reaction may be detected on occasion on the outer surface (Digby, 1977). The mechanism of calcification is obscure, but in general two types of action might be involved, direct chemical action and active transport. In direct chemical action a chain of reactions may occur in which the laws of chemical equivalence must be obeyed. Active transport involves complex metabolic processes which may be much more efficient in moving ions from one place to another, the utilization of one chemical equivalent of oxygen providing the energy to transport more than one equivalent of a particular substance.

The taxonomic position of the golden-brown flagellate Diacronema vlkianum Prauser has hitherto been uncertain. It was first reported by Vlk (1938) from fresh water and a brief description given, particular interest being ascribed to the flagella which staining and light microscopy indicated to be without appendages. Because of this Vlk concluded that the organism, which he did not name, occupied a taxonomic niche somewhat apart from typical chrysophytes. In 1958, Prauser isolated, also from fresh water, a flagellate which he identified as Vlk's organism and he described it using both electron microscopy of shadow-cast cells and optical microscopy of living material. He confirmed the lack of flagellar hairs and discussed the taxonomy of Diacronema in relation to both the Ochromonadales with heterokont flagella and the genus Chrysochromulina Lackey with equal smooth flagella. He suggested that the genus could be thought of as representing a new family, the Diacronemataceae, arising from an ochromonad stock and possibly representing a unique line within the chrysomonads.

Two species of Gracilaria, G. foliifera (Forsk.) Børg. and G. verrucosa (Huds.) Papenf., have been recorded from the Maritime provinces of Canada (South & Cardinal, 1970), although in recent years only G. foliifera var. foliifera is listed (South, 1976). These species are also known from the British Isles (Parke & Dixon, 1976). Chromosome counts of G. foliifera (Greig-Smith, 1954: as G. multipartita) and of G. verrucosa (Magne, 1964) from the European flora suggest these are distinct species.