This work was undertaken at the suggestion of Mr F. S. Russell that little was known about the natural history of even so familiar a species as Leander serratus, the common prawn of the English Channel, which may at times form a valuable natural resource to the inshore fishermen. Attention was therefore chiefly concentrated on its growth rate and breeding biology. In spite of the long breeding season the statistical method of studying growth was adopted when preliminary results appeared successful. By this method additional data could be obtained on distribution and migration. In the closely related genus Crangon, growth has been shown to be retarded under laboratory conditions (Nouvel & van Rysselberge, 1937), so that an experimental study could not be relied on to give a picture of the normal life history. Höglund's recent monograph (1943) has treated Leander squilla in great detail. However, this species differs considerably in size and distribution from L. serratus, and it was felt that a similar study in the Plymouth area would not be mere repetition; in fact the biology of L. squilla itself differs somewhat in the two districts.

The main objective of this study was to describe the reproductive cycle of the sea urchin Paracentrotus lividus on the Cantabrian coast (north of Spain), and assess its relationship with environmental factors. To achieve this, samples were taken monthly from three localities during 17 months in two different habitats. At least 15 individuals from each location and habitat were collected during each sampling occasion and used for assessments of gonad index and histological sections. The water temperature and the chlorophyll concentration were also measured. The breeding season of P. lividus in Cantabria started in March and continued until September with one or two main spawning periods per year (depending on year and population), the first one in the beginning of spring and the second one in the summer. The most important differences in the gonad cycle were observed among localities, and the smallest among habitats. Temperature, photoperiod and nutritive stage are important factors controlling the gonad cycle. The beginning of spawning in the Cantabrian populations coincides with the spring phytoplankton bloom and the rise in temperature, which may act as environmental triggers.

The rate of cirral beat of Balanus balanoides is related to the logarithm of the body weight as an exponential function. In any one animal, there is little effect of temperature on cirral activity between 7·5° and 10° C. Between 10° and 20° C, however, there is a rapid increase in cirral beat with temperature followed by a fall at temperatures above 20° C.

Balanus balanoides exhibits a fast, medium and zero rate of oxygen consumption. These rates of oxygen consumption correspond with (a) normal cirral beating, (b) ‘testing’ activity with no cirral movement, and (c) with the closure of the mantle cavity. Both of the possible levels of oxygen uptake are related to the logarithm of the body weight in a logarithmic fashion over the temperature range 7·5°–22·5° C. Temperature affects the two rates of oxygen consumption differently. In the slower rate (rate B) there is an increase in the rate of oxygen consumption between 7·5° and 14° C but there is no significant increase in the rate of oxygen consumption between 14° and 22·5 C°.

The various steps involved in experimental investigations of the causes of observed ecological patterns are examined. A sequence of different steps (observation, model, hypothesis, null hypothesis, test) is identifiable. The logical necessity for distinguishing and evaluating each of these steps is discussed. The potential usefulness of explicit recognition of the logical relationships between the various parts of the procedure is evaluated by reference to experimental studies to determine the causes of boundaries of vertical distribution of macro-algae in rocky intertidal habitats. Pitfalls of experimental procedures can sometimes be recognized as failures in the logical progress from one part to the next in the sequence of steps necessary in any study. Particularly important is the early recognition of the existence of many, potentially conflicting, but sometimes interactive, models to account for any observed pattern. Greater attention to the relation-ships between the components of the logical structure of an experimental study might aid in reduction of errors in the design, analysis and interpretation of ecological experimental data.

Available data on the size distribution of particles captured by Mytilus indicates that a somewhat leaky, but non-sticky, filter with a minimum mesh size of a little over 1.0 μm is present. The side branches of the latero-frontal cirri have such a mesh and are positioned so as to filter water passing between the gill filaments. Information on the pressure distribution within the water circulation, and calculations of the pressure required to pass watet ihrough the latero-frontal filter at observed speeds, suggest that a little more than half the pressure generated by the lateral ciliary pump is required to overcome resistance in the latero-frontal filter and the remainder is required to circulate water in through the inhalant opening and out in an exhalant jet. The lateral cilia appear theoretically capable of generating sufficient power to produce the required pressures. Calculations indicate that although hydro-mechanical shear forces are unlikely to provide a significant contribution to particle capture, they may provide a means of keeping particles within the frontal current without a need for mucus, after filtration and transfer of particles to the frontal surface by the latero-frontal cirri.

Previous field studies have recorded yearly variations in fecundity of 40–60% in similar sized plaice, and an experiment was conducted to investigate whether these changes could be generated, in the laboratory, by feeding plaice different levels of ration. One group of plaice was fed at a rate of about 2–2.3% of wet body weight per day, and a second group was fed initially 0.5% and later 1.8% per day. The experiment lasted for a period of 406 days.

Of those fed on the lower ration, 39% produced no granular oocytes, whereas all fish on the higher ration produced granular oocytes. A comparison between the two groups, of those which did produce granular oocytes, found that the better-fed fish had 59% more granular oocytes, but the differences were less pronounced for the smaller, mature fish. Numbers of resting oocytes are also recorded.

The results suggest that food level can significantly affect fecundity, and also revealed a new mechanism for regulation of fecundity in the plaice. The lack of granular oocytes was not due to atresia, but to an early decision not to proceed with gonad development; whether this is of practical significance for the population of plaice in the wild is not yet established.

Microphytobenthos are significant primary producers in many coastal systems. It is therefore important to quantify their biomass and productivity. Chlorophyll-a is often used as an index for microphytobenthic biomass. However, complications arise as most studies of sediment properties have been on a millimetre scale, whilst chemical and biological gradients in the surface layers of sediment occur over a microscale. The development of a new technique, the Cryolander (Wiltshire et al., 1997; Wiltshire, 2000), now allows microscale analysis of the sediment surface. Areas of high and low diatom biomass were compared using two coring techniques of different vertical resolution; the Cryolander method, with a vertical resolution of 0·2 mm and plastic core tubes (coarse coring), with a vertical resolution of 5 mm. Results indicated that, except at extreme biomass levels, coarse coring does not detect statistically significant differences in chlorophyll-a between obviously diverse sample sites. This may lead to misinterpretation of seasonal and spatial data when coarse coring is used. Furthermore microscale sectioning allows distinctions to be made between chlorophyll-a measured in the photic zone (photosynthetically active biomass (PAB)) and chlorophyll-a measured below the photic zone (photosynthetically inactive biomass (PIB)), allowing accurate determination of biomass specific primary production.

Hydroids can establish symbiotic relationships with most marine phyla. Almost entire genera or even families are associated with specific groups (e.g. Hydractiniidae and Cytaeididae with gastropods and hermit crabs, Zancleidae with bryozoans, Dipurena with sponges, Ralpharia with octocorals, Eugymnanthea with bivalves, Proboscidactyla and Teissiera with serpulids, Bythotiara with tunicates). Generally, the symbiotic groups belong to the Anthomedusae that, due to the absence of theca, are more plastic in establishing trophic relationships with the hosts. Nevertheless a number of scattered species, mainly Leptomedusae, are strictly associated to algae or sea grasses: in these cases no evident morphological or behavioural adaptations were observed. In animal symbiosis several unrelated symbiotic species show polymorphic colonies or a strong reduction in number and/or size of the tentacles, which are sometimes completely lost. Moreover, these symbiotic species may lack perisarc even in the hydrorhiza.

In this paper we summarize the morphological and behavioural adaptations of symbiotic species suggesting that the described aptitude of hydroids to establish relationships with other organisms is not only the result but also the source of the evolutionary radiation of this group.

Experiments with larvae of Ophelia bicornis Savigny have shown that they metamorphose most readily in sand from their natural habitat and with hesitancy or not at all in sands from other sources. Their natural sand consists largely of smooth rounded grains of quartz, very uniform in size; sands of smaller and more angular grains are unfavourable to settlement and metamorphosis. It appears that size and shape of the sand grains, or perhaps, more likely, the sizes and shapes of the interstices among the grains, perceived probably by the tactile sense, is the main stimulus to metamorphosis. Chemical substances dissolving out of the sands do not seem to be responsible for this.

There is a period of time, amounting under favourable conditions to several weeks, during which an Ophelia larva is able to settle and metamorphose as soon as it comes into contact with a substratum suitable for adult life.

The ability of the larvae to distinguish bottom deposits suitable for adult life from those which are unsuitable must be of great advantage to the species in maintaining normal distribution and in conserving larvae.

Local dive shop operators and fishermen report that rough-toothed dolphins (Steno bredanensis) are frequently encountered off the coast of Utila, Honduras, (16°05'46.5"N 86°55'47.8"W). Our observations suggest that at least some of these animals may constitute a resident population, although the extent of the resident group's home range has not been determined. Twenty-eight rough-toothed dolphins were identified using photo-identification techniques, 15 of which were re-sighted on two or more occasions. The 12 animals that were re-sighted four or more times were typically seen together, suggesting that they constitute a stable social group. At least one of these dolphins is an adult male, and his continued presence in this social group may reflect a social structure for rough-toothed dolphins that differs from that described for other dolphin species. Social interactions often involved tactile behaviours such as pectoral fin rubbing and side rubbing. The observed dolphins sometimes expressed interest in the research vessel and other boats by approaching, and on separate occasions examined a hydrophone and slow moving propeller visually and echoically. Overall, our behavioural observations suggest: (1) synchronous behaviours and ‘tight’ groupings are common while rough-toothed dolphins are travelling; (2) tactile contact is an important aspect of social interactions for rough-toothed dolphins; (3) cooperative behaviour occurs during play; and (4) rough-toothed dolphins are curious.

Here we report the first direct underwater observations of extensive human-caused impacts on two remote seamounts in the Corner Rise complex (north-western Atlantic). This note documents evidence of anthropogenic damage on the summits of Kükenthal peak (on Corner Seamount) and Yakutat Seamount, likely resulting from a limited Russian fishery from the mid-1970s to the mid-1990s, highlighting how bottom trawling can have long-term detrimental effects on deep-water benthic fauna.

Thin-layer chromatography has been used for the rapid separation of microgram amounts of pigments of marine phytoplankton, both from cultures and from the sea. The separation is carried out on plates coated with silica gel; the chromatogram is developed with a solvent consisting of petroleum ether (b.p. 60–80°), ethyl acetate and diethylamine in the ratio 58:30:12 by volume. The separated individual pigments may be eluted from the plate and characterized by their absorption spectra. The pigments of the following phytoplankton have been examined: Dunaliella primolecta, Phaeodactylum tricornutum, Isochrysis galbana, Dicrateria inornata, Coccolithus huxleyi, and Peridinium trochoidium.

Introduction

A knowledge of the component pigments of phytoplankton is of value in the systematic classification of these organisms and in the study of the mechanism of photosynthesis. Very little is known about the amounts of the lesser phyto-plankton pigments associated with the natural phytoplankton crop in the sea, but a considerable amount of work has been carried out on the measurement of chlorophylls a, b and c and of carotenoids for the estimation of the plant bio-mass in the sea. These determinations are usually carried out by modifications of the poly-chromatic spectrophotometric method originally described by Richards with Thompson (1952) and modified by Creitz & Richards (1955) (see also Parsons & Strickland, 1963). While these procedures give a satisfactory measure of chlorophylls a and b, their precision for chlorophyll c and carotenoids is poor; furthermore, no resolution of carotenes from xanthophylls can be attained; nor can any indication of the presence of unusual pigments be obtained.

The jelly-fish Aurelia aurita possesses external and internal ciliary currents that play a large part in food collection and in the transport of food, reproductive products and excretory matter.

Adults feed on relatively small organisms, which are collected in mucus on all external surfaces and eventually passed to the inner surfaces of the oral arms.

The inner surfaces of the oral arms bear two ciliated tracts which operate simultaneously in opposite directions. The lateral tract carries food materials proximally towards the gastric pouches, but is capable of rejecting inedible matter. The basal tract carries excretory matter distally, away from the gastric pouches and canals to the exterior.

Rejection reactions are also found in the gastric pouches and radial canals, parts of which have currents moving in opposite directions on the roof and on the floor. These opposing currents appear to be derived from the system in the ephyra stage, where the circulation in the wide gastric cavity and blind-ending canals is maintained partly by centripetal currents on the floor and centrifugal currents on the roof.

The directions of the main currents remain constant throughout the larval stages to the adult, although slight variations are introduced by morphological changes. The currents also remain the same during spawning, when the eggs and sperm leave the gastric pouches by the normal excretory path.

Many of the ciliary currents found in Aurelia are present in other semaeostome and rhizostome medusae, but only in Aurelia do the umbrella surfaces and currents play a large part in food collection.

The life history and taxonomic position of Rhodymenia palmata (Linnaeus) Greville, one of the commonest red algae in the northern hemisphere, have been a source of considerable speculation. Carpogonial plants and carposporangial plants are unknown although tetrasporangial plants are common and spermatangial plants have been reported on numerous occasions. A parallel situation occurs in the genus Halosaccion Kützing for which carpogonial and carposporangial plants have never been recorded and spermatangial plants are well known only in the species Halosaccion ramentaceum (Linnaeus) J. G. Agardh. It is proposed in this paper to consider the relationship of Rhodymenia palmata to the other genera of the Rhodymeniaceae (Rhodymeniales) particularly Halosaccion and Leptosarca Gepp & Gepp.

A population of the two species, Nephtys hombergii Savigny and N. caeca Fabricius, has been studied for a period of 3 years. Three separate but related aspects of the biology of these species have been investigated; gametogenesis (Olive, 1976a, and in preparation), reproductive endocrinology (Olive, 1976 a, b) and the life-history and population structure which is the subject of the present report. Nephtys species are particularly interesting for studies of this kind since Kirkegaard (1970) described rings in the teeth of N. hombergii which were thought to represent annual growth rings. Estcourt (1975) has found that these rings can be used to age the nephtyid species Aglaophamus verrilli in New Zealand which is a slow growing species living to at least 5 years of age. The degree of overlap between the successive generations, as indicated by the rings in the teeth, emphasizes how difficult age analysis of populations with this type of growth is without additional information of this kind. This problem is particularly acute in long lived polytelic (= iteroparous, Gadgil & Bossert, 1970) species. Olive (1975) has discussed the problem with reference to Eulalia viridis and other recently investigated polychaetes but it is not peculiar to Polychaeta as, for instance, Lewis & Bowman (1975) have shown in a particularly detailed study of populations of Patella vulgata.

Several authors have studied the rhythmic behaviour of amphipods, including Papi (1955) who demonstrated an endogenous solar time sense in Talitrus saltator which was used for navigation. Talitrids were also investigated by Featherston & Maclntyre (1957) who suggested that changes in light intensity triggered the nocturnal foraging activity. Enright (1961, 1962, 1963) tested the effects of pressure, temperature, light intensity, absence of sand and shaking on rhythmic behaviour of the intertidal and in-faunal amphipod Synchelidium. The activity rhythm of Corophium volutator has been reported by Morgan (1965) in which a peak occurred on the early ebb. Various rocky shore Peracarida including species of Gammarus also perform vertical migrations into the surf at night (Jansson & Källander, 1968); the inhibiting effect of light was proven by experiments with controlled illumination.

The objectives of this study were to describe the peracaridean fauna associated to the algae Corallina elongata from the Strait of Gibraltar, and explore possible biodiversity and biogeographical patterns of variation along the north–south and Atlantic–Mediterranean axes across the Strait of Gibraltar. Twenty-five stations were selected along the north and south coasts of the Strait to cover the broadest possible range of human pressure and environmental conditions, including both natural rocky shores and artificial breakwaters. The alga Corallina elongata was selected as substrate, and the peracaridean crustaceans were identified to species level and classified in geographical distribution groups. Univariate and multivariate analyses were conducted to explore and confirm patterns of variation. Forty peracarid species were collected, most of them with an Atlantic–Mediterranean distribution (67%) with only the gammarid Parhyale eburnea, being an endemic Mediterranean species. The most common species collected during the present study were the gammarids Hyale stebbingi, Jassa marmorata, Stenothoe monoculoides and Ampithoe spp., the caprellids Caprella grandimana and C. penantis, the isopod Ischyromene lacazei and the tanaid Tanais dulongi. The number of species per station and the diversity index were significantly higher in the stations located along the north side of the Strait of Gibraltar. However, the two-way ANOVA discarded differences between north and south due to the type of substrate (natural versus artificial) and degree of human pressure. Based on peracaridean assemblages, the Strait of Gibraltar behaves as a whole and homogeneous region, with a very similar faunal composition in all stations and there is not a clear gradient of species substitution from the Mediterranean to the Atlantic stations. Provided that we selected the same substrate in all stations, and that statistical analyses revealed that differences between north and south stations were not due to environmental factors such as anthropogenic stress or type of substrate, we should look to historical biogeographical reasons to explain the higher diversity in the north side of the Strait of Gibraltar.

This paper is the third of four dealing with the calanoid copepods taken with a modified Indian Ocean Standard Net (N113H) on the R.R.S. 'Discovery' SOND cruise of 1965. Details of the cruise are given by Currie, Boden & Kampa (1969) and the sampling methods used in the N113 H series are described by Foxton (1969) and by Angel (1969).

The energetics of leaping (porpoising) in aquatic animals is investigated employing two simple hydromechanical models. The first compares the energy required for swimming at different depths below the surface with that for leaping, the second is employed to calculate maximum cruising speeds in fish and cetaceans for the cases of laminar and turbulent boundary layer flow. Leaping is energetically less efficient than swimming close to the surface up to a certain speed (crossover speed) after which it is more efficient. It is shown that dolphins ought to be capable of reaching the required crossover speeds even if subject to a turbulent boundary layer. This is not so for the larger cetaceans that have been observed to porpoise (e.g. killer whales, Orcinus orca). However, crossover speeds for leaping are well within their scope for the case of a boundary layer that is half laminar and half turbulent. Crossover speeds in pelagic animals that do not undulate a substantial proportion of their body in swimming (e.g. baleen whales and penguins) are relatively high. The crossover speeds of the baleen whales are about four times their observed cruising speeds. It is suggested that these animals swim at speeds at which their filtration apparatus (baleen) operates most efficiently. Pelagic fish do not porpoise and reasons are suggested for this.

The stomach contents of 221 sperm whales were examined at the Icelandic whaling station between 1977 and 1981. Evidence of at least eight species of fish and 22 species of cephalopod was found, together with an assortment of foreign bodies including rock fragments and fishing nets. Fish remains were found in 87% and cephalopods in 68% of the sperm whale stomachs in this area, but quantification of dietary input is complicated by differential rates of digestion and variation in the retention of indigestible remains in the stomach. Prey species are benthic or pelagic in habit and are caught by the whale in waters from 400 m to at least 1200 m in depth. One fish, the lumpsucker Cyclopterus lumpus, forms a major part of the diet. Ninety-four per cent of cephalopods are oceanic and neutrally buoyant and 84 % of these are ammoniacal. Cranchiids contribute 57% by number and an estimated 25% of the weight, and histioteuthids 26% by number and 38 % of the weight of cephalopods eaten. Three species offish and two of cephalopod have not been previously recorded in sperm whale diets. Comparison with an earlier study shows that the diet is essentially stable over a 14-year period.