Many aspects of the food web in the sea are ill understood: none more than the quantitative aspects of the heterotrophic activity of micro-organisms. Heterotrophic utilization of dissolved organic material by micro-organisms was recognized and discussed in principle by such workers as ZoBell, Waksman and Rakestraw in the thirties. There has been very little subsequent progress in understanding the details of the process, principally because of the lack of a suitable approach. Parsons and Strickland (1961) revived interest in this field when they introduced a simple radiochemical technique to follow the uptake of individual soluble organic compounds; subsequently Williams & Askew (1968) developed a method to measure the respiration of such compounds in sea-water samples.

Two earlier papers (Wilson, 1968 a, b) have described the rearing of Sabellaria alveolata (L.) and the settlement behaviour of the larvae. It was thought that some of the questions remaining unanswered might be resolved for the cost of one more rearing to obtain the crawling stages needed. With this end in view adult worms were collected at Duckpool on 12 July 1968 during the lowest day-time spring tide of that month. The worms were found to be spawning and had already shed about half of their genital products. On returning to the laboratory a fertilization was made immediately, using a mixture of ova from many females and a mixture of sperms from several males. This fertilization, made at 8 p.m. a few hours after leaving the shore, is the basis of most of the work described in this paper.

Opisthobranchs are mostly unsuitable animals for detailed ecological work since it is unusual to come across an adequate population for quantitative analysis. This difficulty is reflected in the generalized surveys that may be found described in the literature and which deal with a large number of species, each in little detail (Garstang, 1889; Swennen, 1961; Miller, 1961; Thompson, 1964; Schmekel, 1968). Very few detailed works on a single species are found of the kind published by Thompson (1966) on Archidoris pseudoargus (Rapp). Most often ecological notes are available as a by-product of works involved chiefly with anatomy and taxonomy. The result is that, in the absence of facts, hypotheses are formed to cover portions of the life histories of nudibranchs about which little is known. The problematical migrations attributed to nudibranchs is a case in point and, as the summaries of Costello (1938) and Miller (1961) show, there would appear to be several ways of interpreting the scant data.

Because of the attention at present focused on the artificial rearing of plaice and other flat fish, there has been a revival of interest in the shallow sandy areas where the first bottom stages of these fish live. An additional interest in such areas derives from the growing threat of marine pollution. A need is being increasingly felt for more basic data on the structure of animal communities in unpolluted coastal waters, and on the range of natural variation within these communities so that base lines can be set, against which changes due to pollution may be assessed. With all these interests in mind, a detailed study is at present under way from the Marine Laboratory, Aberdeen, of the fauna of Scottish coastal waters. This paper, dealing with some of the preliminary results, describes the range of macrobenthic biomass of intertidal sand communities, and discusses the variations.

The growth of certain unicellular marine algae has been shown to occur in culture solutions whose total ionic content and chemical composition departs markedly from that of natural sea water. In fact, some of these algae apparently grow more rapidly in half-strength sea water media than in a medium of salinity equal to 35‰. This ability, on the part of the algae, to grow at widely different salinities suggests that the algal cells are able to maintain an internal ionic composition despite wide variation in the external composition of the surrounding culture medium in which they are growing. Droop (1958) has shown that the major cations present in sea water can be varied within wide limits and it was decided to concentrate on the cations, sodium, potassium, calcium and magnesium. A series of analyses of Phaeodactylum tricornutum has been carried out to determine the concentrations of the four cations present in the cells and also to determine whether these concentrations vary during the growth of cells in culture over a period of time. In addition the analyses have been carried out on cells which have been grown at two different salinities, to compare internal cellular concentrations at different salinity levels of the media.

Although a good deal of attention has been paid to the type of sediments found in the south-western English Channel as a whole (see, for example, Allen, 1899; Stride, 1959, 1963; Flemming & Stride, 1967) very little work has been done on the local distribution of sediments in the immediate coastal area. The only data on the sediments in St Austell and Mevagissey Bays appear to have been given by Holme (1961), but even he provides details for only three stations. Some information on sediments in these bays in less recent times can be obtained from early Admiralty surveys, although the accuracy of some of the very old data may be questioned.

In the Plymouth area Sabellaria spinulosa Leuckart is common on stones and shells below low tide mark in the Sound and on outside dredging and trawling grounds. It is often found on living Pecten maximus, much more rarely on Chlamys opercularis, and it is frequent on shells of Buccinum undatum, especially those inhabited by hermit crabs. Several tubes may be found close together, sometimes in contact, but it does not form massive colonies as it does on some shores bordering the North Sea and in deeper water of that region (McIntosh, 1922, pp. 14, 20). It is a smaller species than S. alveolata (L.) and its tubes, built mostly of mineral grains, are harder and stronger than those of the latter. At Plymouth the tubes attached to Pecten shells are usually larger, stronger, and include bigger grains, and are cleaner than are those on stones dredged in the Sound. Empty tubes are common, especially on stones and loose shells, and such tubes are sometimes tennanted by other worms.

In the sea, heterotrophic bacteria and other micro-organisms oxidize dissolved organic material. This process is important to the seasonal biological cycle of matter there because it is responsible for the return of an appreciable fraction of the inorganic nutrients (Andrews & Williams, 1971). It is also important in the process whereby the sea purifies itself of added dissolved organic pollutants: domestic and industrial wastes and spillages. These two processes, especially the latter, pose important and unanswered questions. One in particular is the behaviour of these heterotrophic populations when subjected to sudden increases in the concentration of an organic substrate. This will occur to some degree under natural conditions in sea water during or after a phytoplankton bloom and will occur to a considerable degree when pollutants are run into the sea.

Spirula spirula has stimulated considerable interest since it was first discovered.

It is a member of one of the two genera of sepioids to frequent oceanic water (the other being Heteroteuthis); it has a unique spiral shell which acts as a buoyancy mechanism and can withstand considerable pressure (Denton, Gilpin-Brown & Howarth, 1967); and, until the capture by the Danish Oceanographical expeditions it was considered very rare, only 12 specimens having been captured. The Dana expeditions caught 193 individuals from 1909 to 1931 and these were described by Kerr (1931) and Bruun (1943,1955). Most of these were caught in the waters around the Canary Islands of the North Atlantic. Bruun (1943) arranged the specimens according to month and size and claimed that two size groups could be distinguished. The specimens were taken over a wide geographical area, in several years and during the months of February (1 specimen), March (40), April (3), May (8), June (1), August (1) and October (23). His conclusion concerning growth depends entirely upon his decision to split the March sample into two year-groups; those above 1.9 cm in ventral mantle length he put in a separate year-class to those below 1.9 cm in ventral mantle length. This division was arbitrary and, one suspects, based on a belief that a one-year life-span was likely.

Clearly the growth of Spirula requires further study based on a larger collection and the present paper is an attempt to fulfil this need.

MATERIAL AND METHODS

This work is based upon 256 specimens collected to the south-east of Fuerteventura in the Canary Islands by R.R.S. ‘Discovery’ during 1965–68.

During the autumn of 1965 a detailed study was carried out by members of the National Institute of Oceanography and Scripps Institution of Oceanography into the vertical distribution of the micronekton, plankton and sonic scattering layers in the upper 1000 m at a position off Fuerteventura in the Canary Islands. This is one of a number of similar papers by various authors on the vertical distribution of the animal groups sampled (Angel, 1969; Clarke, 1969). A background to the investigation, including the hydrology of the area studied, has been given in an introductory paper by Currie, Boden & Kampa (1969).

In 1959 and 1960 eight surveys were made in an area about 54 x 83 km in the English Channel immediately south of Plymouth (Armstrong & Butler, 1962b). Measurements of temperature and salinity and of phosphate and silicate concentrations showed a good deal of variation from place to place so that it would be difficult to accept results from any one station as typical of the area. The density distributions suggested a general eastward movement in the winter and, in summer, a movement of surface water offshore from the English coast, with a corresponding onshore movement of deeper water.

This investigation of the bottom fauna of St Austell and Mevagissey Bays was prompted by the feeling among local fishermen that the increasing amount of china-clay waste being deposited in the bays was adversely affecting the local fishery. Physical pollution on a large scale can harm a fishery in a number of ways. The smothering of shellfish grounds is often to be expected, and where the pollutant contains a high proportion of very fine particles there is the danger that unstable clay banks will build up and constitute a purely mechanical hazard to trawling and potting. In this paper, however, we are concerned only with the effects of clay-waste pollution upon the bottom fauna, since it had been suggested that clay deposition might be impairing St Austell and Mevagissey Bays as feeding grounds for demersal fish.

Previous work on the biological effects of china-clay waste includes that of Miss N. Sproston (1945, unpublished), who examined the effects of suspended clay upon some species of pelagic fish. This worker was unable to demonstrate any recognizable effect of mica particles (present in clay waste) upon the gill tissues of fish taken from polluted water at Pentewan. However, Herbert et al. (1961) recorded cases of gill damage in Salmo trutta from china-clay-polluted reaches of the River Fal. These workers also showed that ‘the bottom fauna in the control streams was on average 3.3 times greater than in the polluted part of the Fal and 19 times greater than in the polluted part of the Par’.

Three species of grey mullet have been recognized in the English fauna, namely, Thick-lipped, Thin-lipped, and Golden. There have been several revisions of the Mugilidae, and the names preferred here are: Thick-lipped grey mullet, Crenimugil labrosus (Risso); Thin-lipped grey mullet, Liza ramada (Risso); Golden grey mullet, Liza aurata (Risso).

The degree of exposure of a beach to wave action largely determines particle size, sorting and beach gradient (King, 1959) and these, in turn, have a dominant effect on the animal communities within the sand (Swedmark, 1964; Mclntyre, 1969). It is likely, however, that the main turnover of energy, as indicated by the rapid removal of oxygen (Brafield, 1964; Hamilton & Greenfield, 1967), is due to bacteria and algae. On sheltered muddy beaches, motile diatoms can be of considerable importance (Aleem, 1950; Perkins, 1960) but for a relatively exposed beach at Firemore, Loch Ewe, on the west coast of Scotland, Fig. 1, there was negligible unattached plant material, living or dead, and the primary production by the diatoms attached to the sand grains was low (Steele & Baird, 1968). Further, these diatoms did not show evidence of heterotrophy (Munro & Brock, 1968; Mclntyre, Munro & Steele, 1970) yet, at low water mark on this beach, the populations of attached diatoms are relatively uniform to a depth of 20–30 cm in the sand and show no sign of pigment degradation or decreased photosynthetic ability. These conditions at low water mark differ from those at a water depth of 5–10 m where chlorophyll concentration in the upper 5 cm of the sand is higher but where pigment degradation and blackening of the sand, indicating reducing conditions, are usually found below 10 cm depth of sand.

One of the major advances made in the development of media for the culture of marine phytoplankton was the introduction of chelating agents as a means of controlling the concentrations of the trace metals necessary for plant growth; an excellent historical survey of this field has been provided by Provasoli, McLaughlin and Droop (1957). Much of the discussion concerning the role of the chelating agents has centred upon the maintenance of the iron in solution at concentrations adequate for plant nutrition (Droop, 1961; Provasoli, 1963; Johnston, 1964). In the absence of chelators, the pH of the culture media would result in almost complete precipitation of the iron.

Jørgensen (1944) showed that young specimens of the siliceous freshwater sponge Spongilla lacustris L. obtained their skeletal silica from the water and demonstrated that, under experimental conditions, a relationship existed between the size of the microscleric spicules produced and the concentration of dissolved silicate in the culture medium. The thickness of the microscleres increased with increasing concentration of dissolved silicate in the medium but no changes were detected in the lengths of the microscleres or in the size of the megascleres. Prior to this report Jewell (1935) showed that specimens of 5. lacustris with normal spiculation were rarely found in natural waters with a silicate content below 0.005 to 0.01 mm Si02. Hartman (1958) suggested that the greater thickness of siliceous spicules found in specimens of Haliclona caniculata Hartman collected in winter from New England shores, compared with spicules from summer-collected specimens, might reflect the increased concentration of dissolved silicate in the sea water during the winter months. Similar effects have been demonstrated experimentally in calcareous sponges: Maas (1906) showed that calcareous sponge larvae reared in calcium-free water produced no mineral spicules but organic ‘spiculoids’ of similar form. A relationship between spicule size and environmental silicate has not, in the past, been conclusively demonstrated for any siliceous sponge in field conditions.

Present knowledge of the nutritional requirements of fish is limited to certain species of salmon and trout (e.g. Halver, DeLong & Mertz, 1957; Shanks, Gahimer & Halver, 1962). In view of the current interest in the cultivation of marine flatfish (Shelbourne, 1964) information on their dietary needs is equally desirable. Experience with salmon (DeLong, Halver & Mertz, 1958) has indicated that protein is the largest and most expensive constituent of fish diets and studies on the nutritional value of different food proteins for fish are necessary if the fish are to be reared economically and successfully. A desirable prerequisite to such studies is a knowledge of those amino acids for which the fish has an absolute dietary requirement, i.e. which it cannot itself synthesize from other substances normally available. With most animals these requirements have been identified by growth trials using partially (or wholly) defined diets. The rearing of fish on defined diets is not easy and it seemed in the first instance that an indirect but valid approach might be utilized. If animals are given a radioactively labelled carbon source, such as uniformly labelled [U-14C]glucose a significant amount of the radioactive carbon will be incorporated only into those compounds which the animal can itself synthesize. By isolating the amino acids from the tissue proteins following such a dose the essential amino acids are identified as those which are not radioactive. The amino acids containing radioactivity correspond with the so-called non-essential amino acids.

Despite the widespread occurrence of Eurydice pulchra Leach on sand beaches along the Atlantic coasts of Europe and around Britain (Jones & Naylor, 1967), there has been no detailed work on growth and reproduction in this species until a recent account by Salvat (1966), who carried out investigations on breeding populations of this species and the closely allied E. affinis at Arcachon, south-west France. Apart from this there are some brief generalized observations on the reproductive cycle of E. pulchra in ecological studies upon the fauna of sandy beaches (Watkin, 1941, 1942; Scott, 1960; Lagardère, 1966), and some reference to reproduction in other species of the genus is given by Fage (1933), Bacesco (1948), and Soika (1955). In view of some contrasting accounts given by previous authors and the lack of detailed observations on British material, present investigations were carried out into the reproduction and life cycle of E. pulchra and E. affinis in South Wales. Estimates of the reproductive potential of each species are made and discussed in relation to actual population densities recorded on the beaches.

Oil pollution in marine waters has been a subject of growing concern and has stimulated a variety of pollution studies. Past methods of dealing with the problem have been mechanical, which are effective on land, and chemical which, in the past, have used highly toxic detergents, usually in open waters (Spooner, 1969).

When electro-osmosis is observed through a substance (or tissue) certain inferences can be made about the fine structure of the substance. These include the presence of a zeta potential whose sign is the same as that of the electrode towards which water moves, and the presence of interstices or channels large enough to allow ions to move through them and to sweep along more water molecules than those carried as hydration shells. Channels too large may permit both positive and negative ions to move or at least allow a counter flow of water to reduce the net (observable) movement of water molecules.