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.

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).

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 theposterior margin of the adductor muscle (Figure 1).

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.

Nephrops norvegicus (Linnaeus, 1758) is a valuable commercial shellfish species. UK landings in 1986 totalled 25,515 tonnes with a market value of over £39 million. It is difficult to estimate stock abundance using trawl surveys because of seasonal changes in the availability of females which tend to remain in their burrows whilst berried (ovigerous) (Chapman, 1980). An alternative method is to assess the number of mature adults in the stock using fecundity data and abundance estimates of larvae derived from plankton surveys (Thompson et al., 1986; Nichols et al., 1987). Estimates of the age of larvae are necessary to enable daily and seasonal production rates to be calculated from abundance data. Water temperature causes considerable variations in the development rate of planktonic Crustacea (Winberg, 1971; Thompson, 1982), and reliable estimates of larvae production therefore require knowledge of the relationship between stage duration and water temperature. This paper describes the results of laboratory experiments carried out from 1984 to 1986 to study this relationship in the three free-swimming stages referred to as zoea I-III by Farmer (1974). Stage IV is generally accepted as the first juvenile stage (Anger & Püschel, 1986). The morphology and general biology of Nephrops larvae are described by Farmer (1975) and Nichols et al. (1987); these authors comment on the scarcity of data concerning the effect of temperature on stage duration.

Many techniques have been devised to overcome certain problems encountered when narcotising actiniarians. From these a few have been selected as being at least partly successful. Further modifications to these narcotising methods have been introduced in order to block more effectively the nervous pathways responsible for secondary contraction reactions. Until now, perfectly expanded specimens have been achieved largely by chance. This paper records experimental results and arising problems as a contribution to a better understanding of the process and a more consistent rate of success.

The effects of nutrient enrichment of natural water bodies range from small increases in plant biomass and production, to gross deterioration of water quality. The input of nutrients (e.g. nitrogen and phosphorus) to the sea off NW Europe (especially the North Sea) has increased dramatically over the last three or four decades (Folkard & Jones, 1974; Bennekom et al., 1975; Postma, 1978; Cadee, 1986a) but there is uncertainty about the effects on the ecosystem. One possible effect might be to induce changes in the phytoplankton community. Such an effect has been reported for the North Sea, where increases in flagellate algae have been observed (Gieskes & Kraay, 1977; Postma, 1985; Cadee, 1986b; Batje & Michaelis, 1986). Phaeocystis is one such alga, and its purported involvement in the formation of large quantities of foam, observed on European beaches (Batje & Michaelis, 1986; Weisse et al, 1986), together with evidence that the alga is a source of atmospheric sulphur compounds (Barnard et al, 1984) (with implications for atmospheric acidity), has attracted particular attention and concern

The progress of the copepod Mytilicola intestinalis Steuer from obscurity in Mediterranean mussels, Mytilus galloprovincialis, to notoriety as the scourge of European blue mussels, M. edulis, has been well documented (e.g. Lauckner, 1983). However, a reputation as a pest in a commercially important species is not easily overturned and operators in the economic sphere must be expected to proceed with circumspection where their livelihoods are.at stake. In the UK, Parliamentary Orders still control the deposition and movements of seed shellfish in the attempt to contain the spread of the copepod.

It is now well established that there are several species in the group of rough periwinkles inhabiting European rocky shores. The usual consensus agrees on four, namely Littorina saxatilis (Olivi), Littorina arcana Ellis, Littorina nigrolineata Gray and Littorina neglecta Bean. The first two species are particularly difficult to distinguish in the field and have received much attention. Recent work indicates that the ovoviviparous L.saxatilis is a very variable species living in a wide range of habitats (e.g. Janson, 1985) and that, although it is close to the oviparous L. arcana in shell morphology and in genotype, the two are separate species (Ward & Warwick, 1980; Ward & Janson, 1985), and not reproductive morphs of the same species.

Many symbiotic organisms are narrowly distributed on one or a few host species. These associations are intriguing, as they invite the development of hypotheses regarding the pattern and process of speciation and serve as laboratories for the testing of methods of phylogenetic reconstruction (Kraus, 1978; Futuyma & Slatkin, 1983; Stone & Hawks worth, 1986). The evolution of host-specificity in the sea may be expected to be severely constrained by the difficulty of achieving reproductive isolation in taxa whose gametes are freely released into the water column and/or whose larvae are potentially widely distributed (Scheltema, 1977). Yet this difficulty may well be overestimated, given the recent demonstrations of limited gamete (Pennington, 1985; Yund, in press) and larval dispersal (Knight-Jones & Moyse, 1961; Ryland, 1981; Olsen, 1985; Jackson & Coates, 1986; Grosberg, 1987). Indeed, if gamete and larval dispersal are as limited as has recently been contended (Jackson, 1986), local isolation of populations may be a routine occurence, offering repeated opportunities for speciation.

Descriptions of the polychaete Nephtys hombergii Savigny, 1818 have encompassed a wide range of apparently intraspecific variation in taxonomic features such as the segment on which interramal cirri first occur, and the form and size of pre- and postsetal lamellae (Fauchald, 1963; Woolf, 1968; Hartmann-Schröder, 1971). During the examination of museum collections and of extensive ecological collections from the North Sea (Rainer, 1990) and from Danish waters, it was found that the name N. hombergii has been applied to three morphologically similar species, viz. N. hombergii (s.s.), N. assimilis Örsted and N. kersivalensis Mclntosh. Both are locally abundant species that may occur with N. hombergii. This paper designates a neotype of N. assimilis, provides a full description of N. assimilis and N. kersivalensis, and removes these species from synonymy with N. hombergii.

Feeding by marine invertebrates affects dietary lipids as they pass through the gut (Volkman et al, 1980s; Tanoue et al, 1982; Prahl et al, 1984a, b,1985; Neal et al, 1986; Harvey et ah, 1987,1989). Not only do animals appear to alter the dietary lipids but they also contribute their own lipids to the egested material. Faecal pellets are thus likely to have a lipid composition which has contributions from the ingested food material, the animal itself and the microbial populations residing in the animal's alimentary system.

Lincoln (1979) listed four species of Hyale Rathke from British and Irish waters. A fifth species Hyale grimaldii Chevreux has recently been collected from among goose barnacles, Lepas anatifera L., attached to drift timber washed ashore on a rocky beach in Co. Galway, west coast of Ireland. This record was referred to previously in an abstract by McGrath (1984) but no details of the occurrence or material collected was given. An earlier unconfirmed record of H. grimaldii from Scotland is listed among the Reid collection by Sanderson (1973). H. grimaldii was originally described by Chevreux (1891) from two males found among algae attached to drift timber at sea in the Atlantic, north east of the Azores. Subsequently, the species has been recorded on a number of occasions in the Mediterranean (Chevreux & de Guerne, 1893; Cecchini, 1928; Ruffo, 1946; Berner, 1976) and from the Azores, on a coconut cast ashore (Mateus & Afonso, 1974). All records of the species are from objects floating at sea or washed ashore.