Many workers have considered the possibility of hydroids being potentially somatically immortal, largely because of the continued production of interstitial cells which can differentiate and migrate to replace cells in other parts of the hydroid (Schmid, Schmid & Tardent, 1974). In addition, many thecate hydroids show an orderly regression and replacement of their hydranths (see review by Toth, 1969) and this led Crowell (1953) to suggest that by this means hydroids might avoid senescence. Such considerations are undoubtedly fostered by the lack of evidence for senescence of hydroids which, although sometimes showing a cycle of degeneration followed by regrowth from a dormant stolon, may live for many years in the laboratory (Strehler, 1961; Brock, 1974). Only recently has the senescent death of a hydroid (Corymorpha nutants (L.)) been recorded (Svoboda, 1973).

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.

Mesodinium rubrum is a marine planktonic holotrich ciliate of extremely wide geographical distribution which has often been found to be associated with ‘red water’ phenomena (Taylor, Blackbourn & Blackbourn, 1971). It has mainly been recorded from extremely neritic locations such as bays and fjords; away from the coast it is usually associated with regions of upwelling and in such conditions the blooms have been recorded as extending over areas as large as 100 square miles (Ryther, 1967). Fifty instances of the occurrence of M. rubrum are usefully summarized by Taylor et al. (1971).

The results of experiments recorded by Bayne & Scullard (1977) confirmed earlier studies (Bayne, 1973) in describing a decline in the rate of oxygen uptake (Vo2) by Mytilus edulis during starvation, eventually reaching a steady-state value, called the standard rate of oxygen consumption. Earlier experiments had also shown that if such starved mussels were fed, oxygen uptake increased rapidly to a high level called the active rate of oxygen consumption (Thompson & Bayne, 1972; Bayne, Thompson & Widdows, 1973). Some of this increase in metabolic rate is undoubtedly due to an increased filtration rate that is stimulated by the presence of food (the ‘mechanical cost of feeding’ discussed by Bayne et al. 1976), and part is due to the ‘physiological costs of feeding’, which includes energy utilized in digestion and assimilation of the food, and energy that is lost during deamination and other catabolic processes that accompany digestion (Warren & Davis, 1967). Increases in metabolic rate associated with feeding have been called the specific dynamic action (SDA) of the ration (see Harper, 1971, for a discussion) or the apparent SDA (Beamish, 1974)5 and they have been related to aspects of protein metabolism (Krebs, 1964). This paper describes the results of some experiments designed to examine the relationships between SDA and ammonia excretion in Mytilus edulis L.

Species of Haliotis are of economic importance in several countries around the world and the ormer Haliotis tuberculata (L.) is of importance in the Channel Islands off the north coast of France.

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 study reported here stems from experiments performed upon cirripedes and bivalve molluscs exposed to fluctuating sea water concentrations. It is obvious that these two groups of benthic organisms are capable of shutting themselves off to a greater or lesser degree from the external environment by opercular or shell valve closure, thus avoiding the osmotic stresses associated with exposure to lowered salinity levels. With the development by Davenport, Gruffydd & Beaumont (1975) of an apparatus to deliver fluctuating salinity regimes to experimental animals in a repeatable, routine manner, it has become possible to establish the sea-water concentrations at which such mechanisms operate.

Idotea pelagica Leach is typically found on exposed shores among barnacles and stunted fucoid algae. It has been recorded from Norway to the coast of France, excluding the low salinity waters of the inner Baltic (Naylor, 1972). Studies have been made of its feeding (Naylor, 1955a), external morphology (Naylor, 1955 b) and ecological distribution (Naylor, 1955 c).

Wide-ranging surveys of the sea-bed and of its fauna may be made either from sledges or similar vehicles towed along the bottom, or from free-floating manned or unmanned submersibles. In general, towed sledges involve less sophisticated equipment because the needs for units for forward propulsion and for maintenance of a floating body at a specified distance above bottom are absent. However, sledges lack the manoeuvrability of submersibles, and are more likely to be fouled by obstructions on the sea-bed.

Studies of tissue metal concentrations in shellfish have progressed along two major lines: first, to record the range of concentrations within commercial species, a response to the need to identify potentially hazardous levels from a human nutritional standpoint; and second, to compare concentrations within a single species on a geographical basis as a framework for an environmental monitoring programme. Body size is a parameter which can influence tissue metal concentrations, and if significant variations due to size do occur, then clearly it is a factor which should be taken into consideration within these contexts.

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).

A map of the Looe Estuary in south-east Cornwall is shown in Fig. 1. As it flows to the western branch of the estuary, the West Looe River passes through the Herodsfoot mining area which lies about 5 km above Sowden's Bridge. By Cornish standards, this was a productive area for lead and Dewey (1921) gives the output of Herodsfoot mine as 13470 tons of metal between 1848 and 1884 and more than 17 tons of silver between 1853 and 1884.

Although anaesthetic techniques are well established for most of the vertebrates, methods for the invertebrates are generally not well documented. The decapod Crustacea are widely used for neurophysiological studies involving the implant of chronic electrodes and other techniques. With sluggish species such as Cancer pagurus some workers simply give the animal an object to grasp and perform their operations in the unanaesthetized condition. Others use hypothermia to immobilize their animals, although this may result in autotomy of appendages. Other methods include immersion in solutions of ethanol, magnesium salts (Pantin, 1946), or carbon dioxide. Conventional aquatic vertebrate anaesthetics such as MS-222 (Sandoz) are generally ineffective by immersion in decapods. This short investigation has set out to find out if a suitable anaesthetic drug is available for experimental work and for live dissections.

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.

The intertidal phyllodocid polychaete Eulalia viridis (O. F. Müller) is widely regarded as a predator as stated, for example, by Newell (1970). This assertion is based on statements made by several authors, e.g. Moore & Kitching (1939), Glynne-Williams & Hobart (1952), Connell (1961), and Kensler (1964, 1967), who have reported E. viridis foraging over rocky substrates at low tide in daylight and in some cases have observed the insertion of the proboscis between the opercular plates of a barnacle and the subsequent ingestion of the soft tissues. The capture of a large chironomid by E. viridis has been recorded by Connell (1961). This was considered sufficient evidence for stating that E. viridis is a predator attacking living barnacles and other intertidal animals. Moore & Kitching (1939) further suggested that E. viridis might be as important a predator on barnacles as Thais lapillus (L). On the other hand Michel (1970) regarded E. viridis as a scavenger feeding on dead and decaying animals. There is evident disagreement about the feeding habits of E. viridis and consequently of its role in the population ecology of the community of which it forms a part. Examination of its feeding behaviour has been undertaken to clarify the situation.

A number of species of ophiuroid are known to occur in dense clusters on the sea-bed. Aggregations of Ophiothrix fragilis (Abildgaard) have been recorded from the English Channel by Allen (1899), Vevers (1951, 1952), Barnes (1955), Ancellin (1957), Cabioch (1961, 1967, 1968), Holme (1966), Warner (1969, 1971), and by Allain (1974). Beds of the same species have been found in the Irish Sea by Jones (1951) and by Brun (1969), on the west coast of Ireland by Könnecker & Keegan (1973) and Keegan (1974), and on the west coast of Scotland, where it is widespread in sea lochs and elsewhere around the coast (McIntyre, 1956, and personal communication, 1975). Records of Ophiothrix fragilis from the North Sea have been summarized by Ursin (1960). In the Mediterranean, aggregations of Ophiothrix quinquemaculata (D.Ch.) have been described by Guille (1964, 1965) from off the south coast of France, and by Czihak (1959) from the Adriatic. Hurley (1959) gives underwater photographs of Ophiocomina bollonsi Farquhar from the Cook Strait, New Zealand. Further examples of aggregation in ophiuroids and other echinoderms are cited by Reese (1966), Mileykovskiy (1967) and by Warner (1978).

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 observations of Schlieper (1929) established the lugworm Arenicola marina (L.) as an osmoconformer which remains virtually isosmotic with the external medium over a wide range of salinities. In a recent comprehensive review of salt and water balance in lugworms, Oglesby (1973) describes ‘the extensive swelling associated with transfer of lugworms to lower salinities’, and ‘when maintained in salinities lower than about 50% s.w. in the laboratory, lugworms are rendered incapable of such vital physiological activities as burrowing and burrow ventilation’. Under these conditions, lugworms exhibit little or no ability to regulate their volume or water content.

Analyses of the relationship between the size and the number of eggs per female in various decapods, isopods, cumaceans and mysids were made by Jensen (1958) based upon personal research and information from available literature. Regression analyses indicated that the number of eggs per female is related to the cube of the body length.

The small hermit crabs of the genus Clibanarius are mainly found in tropical regions but one of them, C. erythropus (Latrielle), is common along Mediterranean shores (Holthuis & Gottlieb, 1958); this species was formerly known as C. misanthropus (Risso), but the name C. erythropus has priority (Forest, 1958) and is now in general use. Outside the Mediterranean the species ranges from Brittany to southern Morocco and the Azores (Holthuis & Gottlieb, 1958; Zariquiey Alvarez, 1968). In 1955–7 the extreme northern limit in Brittany was placed at Melon, between Brest and Trémazan (Crisp & Fischer-Piette, 1959); these workers, and also Carlisle & Tregenza (1961), were apparently unaware that the crab had been discovered at Roscoff, on the north coast of Brittany in 1955 (Rullier, 1959; Thiriot, 1965; Bourdon, 1965).