Chrysochromulina minor and C. kappa have been re-investigated by means of electron microscopy of thin sections to add details of the microanatomy of pyrenoids and haptonemata, and by anoptral contrast light microscopy to study pyrenoids in living cells. In both species the pyrenoid is in the form of a diverticulum projecting from the centre of the inner face of a plastid and, in C. minor, strongly flexed to lie along it. In C. kappa the pyrenoid is commonly enveloped by the nucleus which may conceal it entirely from view in life. Some details of the behaviour of the surface membranes of plastids and pyrenoids in relation to that of the nucleus are given. The haptonema structure in both species is shown to be comparable to that of others in which this appendage is much longer, though an occasional variant with eight instead of seven central fibres or tubes has been encountered in C. kappa and is demonstrated. The presence of ‘peculiar’ Golgi structure is reported for both species and demonstrated for C. kappa. Some direct evidence indicating an internal origin of scales from vesicles is demonstrated in C. minor. Finally a summary is given of salient structural criteria for all the described species attributed to this genus from the marine plankton, the closest agreement as regards pyrenoid structure in the two species under investigation being with C. chiton.

There are four important influences on the temperature tolerance displayed by infaunal bivalves, namely their position on the shore, the depth to which they burrow, their geographical distribution and the seasonal cycle.

The temperature tolerance of a species is closely related to shore position and burrowing depth, since these both modify the actual range of temperatures to which the organism is exposed and the tidal variation in temperature. As one might expect, southern populations of a species tend to be lower on the shore than equivalents in northern Europe, but at any one location it is difficult to detect a difference in tolerance between individuals from the top of the shore and those from the bottom. Southern populations do have a higher tolerance to high temperatures than northern, despite the shift in littoral distribution. A similar pattern of response and shift in tolerance is shown between summer- and winter-acclimated specimens.

However, the seasonal shift in response to temperature is not entirely as might be expected, as oxygen consumption measurements show reverse acclimation (i.e. winter respiration rates lower than summer). Reverse acclimation has been demonstrated in a number of bivalve species, and the degree of reverse acclimation is here suggested to be related to the degree of deposit- or filter-feeding habit.

There is evidence that bivalves are capable of regulating to some extent their metabolic rate, independent of temperature. Six groups of Macoma balthica were investigated, of which the four from relatively high temperature environments regulated from 20°C, while the other two did not, suggesting that this capability can be acquired.

Studies were made relating to the problem of how Calanus feeds during winter in the Clyde sea-area. Different diets were assessed in terms of sustaining the levels of body nitrogen and phosphorus in Calanus helgolandicus (Claus) over a period of several days. The test diets, all equivalent to the same level of particulate nitrogen in sea water, were: (1) suspended matter collected from the Clyde sea-area in winter; (2) particulate material produced in a foam-tower by bubbling sea water enriched with soluble extracts of plant cells; (3) living nauplii of the barnacle Elminius modestus Darwin; (4) dead nauplii of this species.

It was found that neither body nitrogen nor body phosphorus was sustained by diet 1; that body nitrogen, but not body phosphorus, was sustained by diet 2; that both were sustained by either of diets 3 and 4.

With living Elminius nauplii as the food, each Calanus captured the equivalent of 25 % of its body nitrogen and 47·3 % of its body phosphorus daily: with dead nauplii as the food the corresponding values were 34·4 and 44·5%. These rations are much higher than those found in an earlier study of Calanus grazing on a spring diatom increase in the Clyde (Butler, Corner & Marshall, 1970) and demonstrate that animal diets are readily captured.

In general, the results indicate that Calanus could survive the winter in the Clyde sea-area by feeding carnivorously.

It is necessary to monitor shell-associated polydorid worms owing to the risk that they pose to commercially important molluscs. This requires accurate identification, but is often hampered by morphological similarities among species, insufficient type specimens, and abridged species descriptions. Thus morphological characteristics and molecular sequences of the most harmful polydorid species, Polydora uncinata from Japan and Australia and Polydora hoplura from South Africa were compared to determine whether they represent two morphologically similar, but genetically distinct species, or a single species. A wide range of morphological variation (with respect to size, length of caruncle and pigmentation patterns) was observed in each species and population, and their variations largely overlapped and revealed them to be at the intraspecific level of a single species. This was confirmed by gene sequences of nuclear 18S and 28S rRNA that were completely identical for P. uncinata and P. hoplura. The mitochondrial 16S rRNA and cyt b gene analyses also showed no genetic differences between these two species. The tree topology of the mitochondrial cyt b gene did not reflect geographic differences but instead suggests artificial transportation of the species. We recommend the synonymization of P. uncinata with P. hoplura.

video observation of oral gastric eversion in a free-living caribbean reef shark (carcharhinus perezi) shows voluntary gastric eversion followed by retraction not only occurs, but is extremely rapid (lasting ∼0.3 s). eversion may occur by stomach relaxation–oesophageal contraction coupled with increased abdominal pressures to enable prolapse, and retraction by a mechanism analogous to suction feeding. this behaviour provides a ‘cleansing’ function for removing indigestible food particles, parasites or mucus from the stomach lining. sharks, and possibly other animals with similar gut morphologies, may use this technique to help maintain a healthy alimentary tract.

During 1951 Evadne nordmanni was present in the Clyde plankton from late February to the end of October and was most abundant during May and early June. The bulk of the population was always found in the top 30 m. Reproduction is mainly parthenogenetic; sexual individuals first appeared in May and sexual reproduction was most intense during October.

The relation between maternal size and stage of embryonic development is described. Sexual females showing the formation of a resting egg are large and have previously produced at least one brood by parthenogenesis.

Of the females with embryos at an early stage of development the primiparae have smaller broods than larger and older individuals. During the development of embryos some may be resorbed and in the primiparae this results in a decrease of embryo number with increase of size. Larger individuals tend to produce larger broods of young.

There was a considerable decrease of size from June to July and a partial recovery in August. These fluctuations follow similar fluctuations in embryo production.

The reproductive capacity of the parthenogenetic females and the intensity of sexual reproduction did not show any clear relationship, though there are indications that the latter is favoured by moderate rather than severe depression.

Food organisms are captured only during the hours of daylight. Evadne appears to be a selective feeder the diet of which consists mainly of tintinnids and peridinians.

Several aspects of the biology of the species are discussed with reference to the findings on the food and feeding habits.

The upper bathyal sea-pen Kophobelemnon stelliferum extends to depths of about 1600 m in the Porcupine Seabight, to the south-west of Ireland, but is rare below about 1150 m. Photographic data suggest that the species attains numerical abundances of more than 2 m−2and a wet weight biomass of at least 4 g m−2. The highest densities, however, do not necessarily correspond to the highest biomass values since there is a clear depth-related change in population structure. The largest sea-pens are restricted to the deeper parts of the bathymetric range of the species. There is also a marked change in the growth form at a total colony length of about 250 mm, with larger colonies having relatively more polyps than smaller ones. The sexes are separate in Kophobelemnon stelliferum and the sex ratio of colonies is about 1:1. The maximum oocyte diameter is about 800 μm, but there is no evidence of seasonal reproduction by this pennatulid in the Porcupine Seabight.

During the expedition EASIZ II with RV ‘POLARSTERN’ in 1998 a multibox corer yielded 151 quantitative samples from 26 stations between 120 and 2415 m water depth for benthic community analysis. From this material a total of 235 polychaete species out of 37 families was determined. Forty-seven species are new to science. The polychaete fraction contributed 41.9% to total benthic abundance and 6.5% to total benthic biomass at these stations. Overall mean polychaete abundance (ind m−2) and biomass (g wet weight m−2) at the stations were 1617 and 49, respectively.

Multidimensional scaling procedure clearly grouped the stations into south-eastern Weddell Sea shelf stations, deep-water stations, and stations mostly around the Antarctic Peninsula. Differences between these groups existed in terms of polychaete abundance and biomass as well as species composition, diversity, and evenness.

Whilst there have been a number of fundamental studies illustrating the effects of Earth's rotation on the flow around submerged obstacles (Hogg, 1973) and islands (Longuet-Higgins, 1969) there appear to be relatively few studies that include both non-linear advective and frictional effects (Huthnance, 1972), and few were found describing the stagnation region that develops in the lee of the flow due to the advection of vorticity generated by the frictional stress associated with a beach gradient (Pingree & Maddock, 1979). In this paper some rotational flow patterns that can develop around an island due to these effects are examined using a numerical model and an overall attempt has been made to illustrate the possible use of numerical models as a tool for theoretical investigations in areas of study that until recently have been exclusively analytical or experimental. An island is surrounded by a uniform beach gradient and the model illustrates how varying bottom topography modifies a steady flow due to both frictional and Earth's rotation effects. Only non-oscillating flows with steady wakes are considered here so that the vorticity sources and sinks can be examined as simply as possible. Stagnation regions due to frictional effects are known to be important in determining sediment deposition and the effects of the Earth's rotation may result in increasing asymmetry in sediment distributions (Johnson, Vogt & Schneider, 1971).

Coelenterazine chemiluminescence is now established as the most common chemistry responsible for bioluminescence in the sea, being found in seven phyla. However, the organisms which synthesize coelenterazine have yet to be identified. In order to deter-mine whether the luminous midwater shrimp Systellaspis debilis (A. Milne Edwards) (Arthropoda: Decapoda) is capable of luciferin biosynthesis, a developmental series of eggs was assayed for its luciferin, coelenterazine. The advantages of this system are that S. debilis eggs are autonomous and therefore have no external nutrient supply, the embryos can be ranked for developmental stage and the large egg size allows clutch numbers to be determined accurately. Recombinant apo-aequorin, which requires coelenterazine for luminescence, was used to quantify coelenterazine during the developmental sequence. An increase of almost two orders of magnitude was detected in coelenterazine content per egg between the first and final stage of development (mean values of 1 pmol and 71 pmol). This demonstrates de novo biosynthesis of coelenterazine for the first time.

The resident population of common bottlenose dolphins (Tursiops truncatus) in the Sado Estuary, Portugal, has been declining at least during the past three decades. A complete photographic census produced a current count of 24 animals—19 adults, three subadults and two calves. It appears to be phylopatric and essentially closed, but given the likely importance that exchanges with neighbouring coastal groups may play, even if rare, the most adequate term to define this dolphin should be community and not population. Large groups with all age-classes are common in the community, possibly as a calf and subadult protection strategy, and this may be related to the fact that these age-classes have had high mortality rates in the last decade. Maternity of two calves was determined, and we found that the two mothers adopted different parenting strategies. While one mother spent more time alone with her calf, the other mother spent more time with her calf in larger groups. The average coefficient of association for this community is 0.45, quite high for this species. Associations and typical group size are similar between all individuals, with no patterning according to age-class or sex, which constitutes an atypical trait for dolphin societies. There are also no clear divisions in this community according to cluster analysis. Associations are preferred and long term, lasting approximately 34 days and fitting a pattern of casual acquaintances, where individuals associate for a period of time, disassociate and may reassociate after that. This reflects the fission–fusion character of the community, but in a more stable manner. We think this is caused by a combination of demographic characteristics and a stable and productive environment, which led to a decrease in competition between individuals.

Studies in the Pacific have identified distinct killer whale ecotypes that are either specialized mammal- or fish-eaters. The different types have developed hunting strategies that would suggest specialization could be more advantageous than generalism. However, it has been suggested, based on long-term dietary markers of tooth wear and stable isotope values, that lineages in the North Atlantic are generalist, but with individual variation in the proportion of prey types consumed. Here, we present the results of ten years of observational and photo-identification data of a population of killer whales that follows the Norwegian spring-spawning stock of Atlantic herring. Although the whales were predominantly observed while feeding upon herring, one pod of herring-eating whales was also observed interacting with seals. This supports the hypothesis based on the long-term markers, of a degree of specialization, with a small number of groups persistently feeding upon mammals, but switching between herring and seals. We further investigated this prey switching by conducting playbacks of herring-eating killer whale sounds to harbour seals at haul-out sites on the herring spawning grounds. We recorded changes in behaviour consistent with an anti-predator response, suggesting the seals perceived the herring-eating killer whales as a potential predatory threat and had not habituated to their calls. This could be due to the risk of herring-eating killer whales switching to mammalian prey, or the difficulty of discriminating between killer whale pods due to the large population size and number of killer whale call dialects in this population, or a combination of both.

The present study was carried out during the summer of 1997 in three locations of the western Italian coast (La Spezia, Ligurian Sea; Ischia, central Tyrrhenian Sea; Ustica, southern Tyrrhenian Sea) to investigate variability in abundance and size structure of the labrid fish Thalassoma pavo along a latitudinal gradient and over different spatial scales. Fish abundance and size were estimated by visual census in shallow rocky reefs. Significant differences were detected in average abundances of T. pavo (with and without the contribution of juveniles) among locations (separated by a distance of hundreds of kilometres from each other) and over the smallest scale examined (i.e. among sites located tens of metres from each other). However, most variability was explained considering the largest spatial scale associated with the latitudinal gradient. Average abundances generally decreased from the southern Tyrrhenian to the Ligurian Sea. In terms of frequency, juveniles (<5 cm total length (TL)) increased from north to south, while the largest fish (16–20 cm) displayed an opposite trend. The intermediate size-classes (6–10 and 11–15 cm) did not show any distinct patterns. In terms of abundance, small T. pavo (0–5 cm) showed significantly higher densities at Ustica, followed by Ischia and La Spezia. Fish 6–10 and 11–15 cm long were significantly less abundant at La Spezia than at Ischia and Ustica, while those between 16 and 20 cm TL did not differ numerically among the three locations. The results of the present study provide suggestive evidence that factors acting on a geographical scale are likely to influence distribution patterns of the thermophilic fish T. pavo, although significant effects have been also observed at the smallest spatial scale examined. Climatic conditions (e.g. water temperature along the latitudinal gradient) and substrate features (e.g. macroalgal cover, physical complexity, slope) are thus likely to affect average abundances and size structures of T. pavo populations along the western Italian coast.

The size-frequency distributions of monthly collections of Aplysia punctata from a sublittoral population in Trearddur Bay, Anglesey, made during the period from July 1964 to October 1965, indicate that the animals live for one year and that the major recruitment to the population occurs in the autumn. The Aplysia in this area are restricted mainly to sublittoral beds of the red alga, Plocamium coccineum, and the majority of animals feed, copulate and deposit spawn on this seaweed. The animals spawn from May, when the sea temperature reaches a minimum of about 9–9·5° C, until about October, with a maximum output of spawn in the late summer when the animals are fully grown. Aplysia in Trearddur Bay do not migrate inshore; instead, they probably colonize the intertidal region after being accidentally washed inshore from the sublittoral habitat. Intertidal and shallow-water Aplysia are larger than those from deeper water possibly because of the greater abundance of food. Similarly, it is thought that Aplysia found in the intertidal zone are brown and olive-green because they eat a particular alga or combination of algae present in this habitat.

The seasonal development of the microbial food web in eastern McMurdo Sound, Antarctica, was investigated during and immediately after the 1990–1991 bloom of Phaeocystis sp. (Prymnesiophyceae: Prymnesiales). From 23 November to 7 December, which was before the appearance of macroscopic colonies of Phaeocystis, both phytoplankton and Protozoa were low in abundance. During the Phaeocystis bloom (~10 December to 7 January), phytoplankton biomass was high and was dominated by colonial and singlecelled Phaeocystis, but other phytoplankton taxa, including diatoms and photosynthetic dinoflagellates, co-occurred. Heterotrophic nanoplankton and protozoan microzooplankton increased dramatically in biomass during the bloom. Non-thecate heterotrophic dinoflagellates were the most abundant microzooplankters. There was no evidence for inhibition of the microbial food web by Phaeocystis. By the post-bloom period, macroscopic colonies were rare and phytoplankton biomass had declined markedly. Microzooplankton biomass continued to rise until the end of the sampling period (23 January). Microfaecal pellets (median size range, 10–30 μm) were abundant during the bloom and post-bloom periods. In the post-bloom period, the heterotrophic protistan assemblage became very diverse, with numerous trophic linkages within the microbial food web. The abundance and diversity of the heterotrophic protist assemblage suggests that there was little control of protists by metazoans and that the microbial food web, consisting of bacteria, algae and Protozoa, was poorly coupled to metazoan zooplankton.

INTRODUCTION

The caesium radionuclides, caesium-137 and caesium-134, are important constituents of aqueous radioactive effluents discharged to the environment of the United Kingdom from fuel re-processing plants and nuclear power stations (Howells, 1966; Mitchell, Harvey & Smith, 1968; Harvey, Baker & Mitchell, 1969). Their accumulation by marine fishes has been the subject of several previous studies, beginning with that of Chipman (1959) who noted that caesium-137 was accumulated in the flesh of the killifish (Fundulus heteroclitus) and that accumulation continued even after a period of 72 days. Similarly, Hiyama & Shimizu (1964) showed that the muscle of the common goby (Acanthobus flaviamus) continued to accumulate caesium-134 from sea water after periods of 30 days. Baptist & Price (1962) have examined the whole body uptake of caesium, by absorption from sea water, in two marine species, the flounder (Paralichthys dentatus) and the Atlantic croaker (Micropogon undulatus), and they also investigated the accumulation, tissue distribution and excretion of caesium-137 in the croaker, the little tuna (Euthynnus alleteratus) and the bluefish (Pomatomus saltatoux), following oral administration of single doses. These authors concluded that the heart, liver and spleen of the croaker absorbed caesium-137 from sea water at a faster rate than the muscle, and that orally administered caesium-137 was rapidly absorbed from the digestive tract. Tissue distributions were similar in the croaker, bluefish and tuna. The retention of caesium-137 in croaker tissue was described as a multiple rate process. In later experiments Hiyama & Shimizu (1969) compared turnover rates in various organs and tissues following uptake from sea water and from single injection experiments, and obtained good agreement between the values from the two methods.

The investigation of the food of larval and post-larval fish from Plymouth Sound and beyond for three years has brought out some interesting facts. For the first two years fresh material from the tow-nets was examined together with old material from the Young Fish Trawl (Lebour, 1918, 1919). During the present year, in addition to the tow-nettings, fresh material from the Young Fish Trawl was also available from July to the end of September, and several fish from outside the Sound examined which had not been obtainable for the last two years. We thus have a fair number of young Mackerel, Ling, Hake and Gurnard and several others.

Vance (1973a, b) argued that among the possible range of developmental strategies available to marine invertebrates, only the extremes of obligate planktotrophy and obligate lecithotrophy are evolutionarily stable. Vance's model, relating reproductive 'efficiency' to egg size (in terms of energetic content), predation rate, and prefeeding (lecithotrophic) vs feeding (planktotrophic) larval periods, has been a source of much discussion and debate since its inception (e.g. Underwood, 1974; Vance, 1974; Christiansen & Fenchel, 1979; Obrebski, 1979; Williams, 1980; Jablonski & Lutz, 1983; Strathmann, 1978, 1985; Todd, 1985). Subsequent publications have continued to dwell mainly on potential selective factors and the extremes of larval developmental type (i.e. obligate planktotrophy or obligate non-pelagic lecithotrophy). For the most part, these investigations have ignored questions concerning how a transition from one larval type to another would be accomplished in morphological and functional terms. Nonetheless, the consensus persists that small eggs and planktotrophy are the primitive (or ancestral) condition, and that lecithotrophy is the more advanced evolutionary derivative (see Strathmann, 1978,1985).

Six species of luminescent polynoids of the Plymouth fauna have been studied, namely Lagisca extenuata, Gattyana cirrosa, Harmothoë liinulata, Polynoë scolopendrina, Acholoë astericola and Malmgrenia castanea. Their scales are luminescent, and the light is produced by granular eosinophilic photocytes, which form a unicellular layer on the lower surface of the scale. The nervous supply of the elytrum is described, and the luminescent response is shown to be under nervous control. Luminescent responses from all six species have been recorded by the use of a photomultiplier cell and oscilloscope. The normal response has been found to consist of a series of rhythmic flashes, from 9 to 1 per sec, lasting up to 1 min. Some characteristics of the luminescent responses are given, and the part they may play in the normal life of the animal is discussed.

The production of larvae by Ostrea edulis L. was studied in collections made from brooding females obtained from oyster grounds on the east, south and south-west coasts of England and from the Menai Straits. The size of the brood was directly related to the size of the oyster, but considerable variation was found from oysters of the same size whether measured as diameter, volume between the shells or dry meat weight. Part of the scatter was due to variation in condition of the oyster at spawning; oysters in good condition at the time of spawning produced more eggs than those in poor condition. This cause of variation was also seen in different populations; those with a high average condition index had a higher average fertility than those in poor condition, although the correlation was not quite significant at the P = 0.05 level (r = 0.632). It is presumed that most of the remaining variation is of genetic origin.

Fertility was related to size rather than age, although it is suggested that in some old slow-growing oysters it may be reduced. No decline in fertility was found as the breeding season progressed, nor was there clear evidence that larvae are liberated at a smaller size late in the season.

A comparison of the average size of broods at an early stage of development with those that were nearly mature showed that there was no loss of larvae during brooding. Samples of shelled larvae from 204 broods were measured; less than 10 % exceeded 190 µ size.