The embryos of Icelandic capelin (which spawn subtidally) tolerate as low temperatures, and are as euryhaline, as those of Balsfjord capelin which spawn intertidally. The median lethal lower temperature for Icelandic capelin eggs exposed for 6 h to low temperatures in frozen seawater films (34‰) is -6.3°C. The median lethal high salinity (6 h exposure) is 88.3‰. Eggs were reared and hatched successfully in all salinities from 1.5 to 34‰. When exposed to high salinities capelin eggs shrink in a matter of seconds (shrinkage being manifested in depressions of the chorion), but resume a normal shape in a few minutes as salts diffuse into the perivitelline fluid. Evidence is presented to show that mortality in frozen seawater films is due to osmotic dehydration, rather than to a final invasion by ice crystals. A model of freezing avoidance in capelin eggs is described.

The naked dinoflagellate Gymnodinium cf. nagasakiense is responsible for red tides frequently associated with mortality of marine organisms in North European waters during summer (see reviews by Tangen, 1977 and Partensky & Sournia, 1986). This species is currently referred to as Gyrodinium aureolum Hulburt in the literature, since its first occurrence in Norwegian waters in 1966 (Braarud & Heimdal, 1970). However, it was recently found to be morphologically closer to the Japanese bloom-forming species Gymnodinium nagasakiense Takayama & Adachi than to the original Gyrodinium aureolum (Partensky et al., 1988).

At Looe, Cornwall (south-west England), engineering problems have resulted in the Sewage Treatment Works operating on saline rather than the typical freshwater sewage input. Saline water enters the system at all stages of the tide, except low water, mainly through the open-jointed sewers embedded in the mud of the Looe River Estuary, and causes a cyclical salinity regime within the works (Jones & Johnson, in press). A consequence of this seawater intrusion is the replacement of the freshwater macroinvertebrate community commonly associated with biological filters by two species of euryhaline amphipods. In particular, Gammarus duebeni Liljeborg is permanently established at various sites in the works including the percolating filters and humus tanks (Jones & Wigham, 1988). The ability of G. duebeni to colonise and establish a breeding population at the works is probably a reflection of its wide tolerance to several environmental factors. This species is extremely euryhaline (Forsman, 1951; Sutcliffe, 1967; Pinkster, 1970) and can withstand marked hypoxic exposure (Bulnheim, 1979; Ritz, 1980). However, in addition to fluctuations in salinity and oxygen saturation, treatment works amphipods are exposed to relatively high levels of heavy metals associated with domestic and industrial inputs (Jones & Johnson, in press). Within the humus (secondary settlement) tanks, zinc concentrations are particularly elevated compared with the adjacent estuary, although there are considerable fluctuations in zinc levels experienced by animals due to the tidally based dilution of the incoming sewage (Jones & Johnson, in press).

I am pleased and honoured to have been asked to give the first of the lectures in memory of Dr Leslie Cooper. I was especially moved by the thought that the invitation was made knowing that I should almost certainly choose Gaia as the topic of my lecture. I know that many of you, especially biologists, think that the Gaia hypothesis is either trivial and untestable or else a mere reiteration of conventional wisdom in poetic terms. Hardly a topic with which to commemorate Leslie Cooper's memory.

You will be relieved to know that although Gaia is the theme of my talk, I shall try not to be overly partisan or dogmatic. My objective is to use Gaia theory to illustrate a top-down approach to earth and life science and try to contrast it with the bottom-up approach which is conventional in the earth and life sciences.

Previous work on barnacle biometry has mainly been concerned with the opercular valves, whose shape is often an important taxonomic character (Barnes & Healy, 1969; Henry & McLaughlin, 1975). The well-known change in shape whereby columnar individuals are produced as a result of crowding has also been described by many workers (e.g. Trusheim, 1932; Barnes & Powell, 1950; Subklew, 1969; Crisp & Bourget, 1985). The influence of environmental variables on the shape of the barnacle shell as a whole has been little studied.

Field data on the pelagic occurrence of Corophium volutator were obtained in 1981–82 in the Dollard (Ems estuary). The pelagic population density averaged over a tidal half cycle was in the range 0–15 m-3. The pelagic population represents about 0.06% of the benthic population. On most sampling days pelagic occurrence resulted in a net flood surplus transport.

The caridean prawn Palaemon longirostris (Milne-Edwards) (Palaemonidae) occurs predominantly in the upper regions of large river estuaries in Europe, and reaches its northern limit of geographical distribution along southern parts of Britain (Smaldon, 1979). All post-larval stages are thought to live under dilute and fluctuating salinity conditions, although there are conflicting reports as to whether ovigerous females need to migrate to the sea at times of egg hatching (Gurney, 1923; Fincham & Furlong, 1984). The species has been known to be extremely euryhaline for some considerable time (Gurney, 1923), yet the salinity tolerance limits of larval (Antonopoulou & Emson, 1989) and post-larval stages (Campbell & Jones, 1989) have been established only recently. Apart from studies on salinity tolerances, and some preliminary measurements of blood and urine osmolality (Parry, 1957), the osmoregulatory adaptations of P.longirostris to its dynamic habitat have not been investigated previously. The present paper describes the osmoregulatory responses of P.longirostris acclimated to a wide range of salinities, and also reports on the ability of individuals to compensate for sudden acute salinity change.

Many large-scale properties of the biosphere are affected or determined by the activities of living organisms and are maintained at remarkably constant values over long periods. For example, the oxygen content of the atmosphere appears to have been maintained near its present value for hundreds of millions of years, despite the rapid flux of oxygen between production by plants and consumption by animals and decomposing microorganisms. (In this article, I shall use 'biosphere' to denote the whole of the concentric shell of the planet Earth which holds life, and 'biota' to mean all living organisms. Others have sometimes used 'biosphere' to mean the latter.) Lovelock was the first to show clearly how the composition of the Earth's atmosphere, unlike that of Mars or Venus, was held well away from thermodynamic equilibrium by the activities of living organisms (Lovelock, 1983). Other biospheric properties, such as temperature and oceanic pH and salinity, have similarly remained fairly constant despite the existence of large perturbing influences (Lovelock, 1979).

Anemones of the genus Actinia exhibit a well documented, stereotyped aggressive sequence (Bonnin, 1964; Brace & Pavey, 1978; Brace et ah, 1979) involving specialized, nematocyst-bearing structures called acrorhagi, which can be directed against an opponent. Experiments on the Australian species, A. tenebrosa Farquhar, and on the clonal anemone, Anthopleura elegantissima (Brandt) (which similarly bears acrorhagi), indicate that aggression occurs principally between genetically dissimilar (allogeneic) opponents (Ayre, 1982; Francis, 1973a, b; Bigger, 1980). Once acrorhagial contact has been made with an allogeneic individual, massive discharges of nematocysts ensue, which can cause severe necrotic lesions.

The pinnate (feather-shaped) hydrocauli (stems) of Aglaophenia harpago are dish-shaped with the food catching hydranths borne on the convex side of the lateral branches, a morphology recognised as an adaptation to feeding from unidirectional currents. A. harpago experience unidirectional currents because the hydrocauli are able to rotate close to their bases on an articulation in the perisarc (the tubular exoskeleton) so that the concave surface always faces into the current and the hydranths face leeward. The structure of this articulation, revealed by light and electron microscopy, is described and its mechanism interpreted. The articulation consists of two oblique grooves of thin flexible perisarc which traverse around the hydrocaulus at an angle of 62–65°. The grooves terminate in areas of perisarc divided into longitudinal lamellae (probably of structural protein). The grooves and lamellae confer the flexibility which allows the hydrocaulus to ‘fold’ up to 90° clockwise or anticlockwise across each groove. The lamellae maintain the longitudinal support necessary to prevent the hydrocaulus collapsing.

Giesbrecht (1895) was the first to report that the luminescence produced by marine copepods was produced by certain ‘skin glands’. In Pleuromamma abdominalis he described specific sub-cuticular cells which were responsible for the production and secretion of luminous material; such cells always contained a greenish-yellow secretion whilst non-photogenic cells were colourless. The only published histological study of luminous cells in copepods is that by Clarke et al. (1962). These authors reported numerous paired cells in the head of Metridia longa, each pair opening through a common pore, the distribution of which was correlated with areas of fluorescence. Clarke et al. (1962) further showed that the cells in each pair had different staining characteristics, and suggested that each of the two cell types produced a different component of the luminescent system, proposed as ‘luciferin’ and ‘luciferase’ respectively. They hypothe-sized that when stimulated, each cell secreted its contents, generating light as the materials combined in the surrounding seawater. Although there has been much work carried out on the physical characteristics and kinetics of copepod luminescence (e.g. David & Conover, 1961; Clarke et al., 1962; Barnes & Case, 1972; Bityukov & Evstigneev, 1982; Herring, 1983, 1988; Evstigneev, 1983, 1984, 1986; Latz et al., 1988) there is still little known of the comparative distribution of luminous cells in a range of copepod species, and even less is known of their detailed structure.

Infestation of cage cultured Atlantic salmon by the external parasitic copepods Caligus elongatus (Nordmann) and Lepeophtheirus salmonis (Kröyer) is a serious cause of loss of production in the commercial sea water culture of this species. The copepods feed on the mucus, skin and blood of their hosts (Kabata, 1974; Brandal et al., 1976) causing irritation and lesions. Loss in production due to infestation by lice occurs directly by the mortality of fish from osmotic shock and indirectly from a probable reduction in growth, from secondary infections such as vibriosis (Wootten et al., 1982) or by increasing vulnerability to ultraviolet radiation damage (McArdle & Bullock, 1987).

The barnacle cypris larva possesses a pair of laterally placed compound eyes and a median nauplius eye which is tripartite in structure. Concomitant with the metamorphosis to the juvenile is the loss of compound eyes and the nauplius eye separates into its three constituent parts (Walley, 1969). The two dorsolateral components of the nauplius eye come to lie under the rostral shell plates, whereas the ventral component forms the median ocellus which underlies the mantle flaps of the scutal plates at the posterior margin of the adductor muscle (Figure 1).

A tide pool population of the brittle-star Amphipholis squamata in South Devon was monitored from July 1986 to July 1987 with respect to a number of population dynamical attributes. The population had a simple life history. Most individuals recruited into the population in the period June-September, were reproductively active in the following summer and died when 13-17 months old. The population differed from others studied in temperate latitudes in pattern of recruitment, survival and in duration of reproductive activity. We speculate that these differences are a consequence of tide-pool conditions.

The common goby Pomatoschistus microps (Krøyer), is a small and abundant brackish water fish, which becomes sexually mature after the first winter of life and usually survives for only a single breeding season (Miller, 1975). During a protracted breeding season from approximately mid-April to August or September, the goby can produce up to 9 or 10 separate batches of eggs. It is therefore considered to be an iteroparous species, but because of the short adult life-span during which spawning occurs, this species has been termed an abbreviate iteropare (Miller, 1984). The nest-building activities of the male fish, courtship behaviour and subsequent brood-care are well documented (Vestergaard, 1976).

Studies on the lateral lines of the sprat {Sprattus sprattus (L.); Clupeidae; Clupeiformes) have shown that the patterns of excitation of the neuromasts in the canals on the head changed dramatically with relatively small changes of position of the fish with respect to a source (Denton & Gray, 1983; Gray, 1984). It was concluded that, in the case of the sprat, this sensory system was capable of providing the information needed to maintain position in relation to other fish in a school; cf. the work of Partridge & Pitcher (1980) on saithe (Pollachius virens; Gadidae; Gadiformes). The structure of lateral lines varies greatly between fish of different species and even between different parts of the same fish. It seems likely that these differences have evolved to meet different behavioural needs. An attempt has been made to understand the mechanisms of lateral line excitation in general. This has led to the development of methods to calculate first approximations of likely excitation patterns from a knowledge of the morphology of particular systems (Denton & Gray, 1988).

The present investigation is a confirmation and extension of the idea that visual pigments adapted to the quality of their own bioluminescence have evolved in certain deep-water marine fishes. In this case a single fish (Malacosteus danae) of the family Malacosteidae, known to have red-emitting photophores, was trawled up in daylight from the Pacific off the coast of Southern California. Retinal extractions were found to contain two photopigments with absorbance maxima, one at 556 nm, the second at 514 nm. From the spectral positions of the oximes formed by bleaching in the presence of hydroxylamine it was inferred that the 556-pigment is an A2-pigment and the 514-pigment, an Aj-pigment. Evidence was also obtained from the effect of hydroxylamine on the unbleached extract of the possible presence of a photopigment that was bleached by the daylight when the fish was brought to the surface. This pigment, also identified as an A,-component from the oxime spectrum, could have been a moiety of the 514-photopigment but the possibility of a third visual pigment in the retina of this fish cannot be discounted. Except for this hydroxylamine effect the results are in agreement with published data from Aristostomias scintillans.

Narcomedusae are a small and mostly oceanic group of hydromedusae whose tentacle morphology and comportment sets them off behaviourally and perhaps ecologically from most other medusae. Their tentacles are relatively few in number (2–40), stiff, and noncontractile, with points of insertion located well above the bell margin. Eleven species representing eight narcomedusan genera (Aegina, Aeginura, an undescribed aeginid, Cunina, Pegantha, Solmaris, Solmissus, and Solmundella) were observed and collected in situ in the NW Atlantic, Arctic and Antarctic, using scuba and manned submersibles. In life, the tentacles of narcomedusae are nearly always held upwards over the bell or projected laterally. The major prey were other gelatinous zooplankton, especially salps and doliolids. In the laboratory, these relatively large prey were caught on the tentacles which bend inward and coil at the tips to bring food to the mouth. By extending the tentacles perpendicular to the swimming path, these medusae achieve a relatively large encounter area, thus increasing the probability of contact with prey, for the amount of protein invested in tentacles.

The importance of feeding pattern is well documented in fish (Jenkins & Green, 1977; Simenstad & Cailliet, 1986) but there are not many reported studies in cephalopods. Feeding patterns, as defined by Jenkins & Green (1977) have been studied, to our knowledge, only in Todarodes pacificus (Okiyama, 1965), Loligo pealei (Vovk, 1972), Loligo opalescens (Karpov & Cailliet, 1978), Illex illecebrosus (Amaratunga et ah, 1979; Amaratunga, 1980) and Nototodarus gouldi (O'Sullivan & Cullen, 1983). Boyle (1983) dealt with aspects of feeding in several cephalopod species but not specifically with feeding pattern. Aspects of feeding in Sepia officinalis have been reviewed by Nixon (1987). The present work describes the daily feeding pattern in Sepia officinalis from data collected in the field.