Age-and sex-dependent patterns of aggregation in the tropical gastropod Strombus luhuanus

The spatial dispersion of the tropical coral sand-dwelling mesogastropod Strombus luhuanus Linné, 1758 was studied at several sites in two localities (Australian Great Barrier Reef and southern Papua New Guinea), from September 1980 to February 1983. S. luhuanus usually occurred in local aggregations, many of which were relatively dense with discrete boundaries: Four types of aggregation are described: mixed age-class, juvenile, mating, and clusters. The former two are termed colonies, because they persisted over time and exhibited some coordinated movements. Mixed age-class colonies contain individuals of all ages, but within them the different ageclasses are frequently spatially segregated from each other. This was sometimes due to the younger age-classes' preference for shallower areas, but also occurred in areas of constant depth. Juvenile colonies are relatively smaller in area but higher in density, and are dominated by a single size-class. Mating aggregations are concentrations of copulating individuals, in which competition between males for access to females occurs. Clusters are concentrations of inactive individuals (juvenile and adult) piled together in close contact. All types of aggregation were concentrated in only a part of what appeared to be the suitable habitat. Most aggregations' boundaries shifted over time within the habitat. We conclude that intraspecific attraction must be an important factor which maintains the spatial structure of all aggregations, although habitat specificity sets the larger area in which they move. Processes which may underlie this pattern, and some of its implications, are discussed.     

Unstable processes in the metabolic rate measurements in flow-through systems

Measurements of metabolic rate within a flow-through system generally begin only after the difference between input and output concentration has become constant. This limits the use of such a system to objects with high metabolic rates. The processes in the flow-through system were described mathematically and the differential equations obtained are analytically resolved for different situations. They can be used for the calculation of metabolic rates for any time after the onset of measurements. The flexibility of a flow-through system and its suitability for physiological and ecological measurements are significantly increased.     

The role of isopods and amphipods in the initial fragmentation of eelgrass detritus in Nova Scotia,Canada

Daytime observations on the isopods Idotea phosphorea and I. baltica and the amphipod Gammarus oceanicus held in laboratory microcosms showed that I. phosphorea and G. oceanicus spent 45% and 30% respectively, of their active time feeding on dead, intact eelgrass leaves which had been recently released from plants. I. baltica spent 41% of its active time consuming intact green leaves. The shredding of intact dead leaves by I. phosphorea and G. oceanicus resulted in production of small detrital particles which were liberated from the faeces of the invertebrates and this type of feeding led to the breakdown of whole leaves. Field experiments which separated the effects of shredding by invertebrates and grinding by waves and ice on the loss of weight from leaf packs showed that relative to controls isopods significantly increased weight loss from dead leaves. Loss of weight from leaf packs exposed to both biotic and physical shredding forces was not significantly different from that found on those exposed only to shredding by isopods. However, trends in the data indicated that fragmentation of whole, dead leaves in the field probably is a result of the synergistic effects of shredding by invertebrates and physical factors, particularly ice grinding. The role played by invertebrates in fragmenting intact, dead leaves is discussed in the light of energy flow and nutrient cycling within seagrass systems.     

Storage and depletion of lipid components in the pyloric caeca and ovaries of the seastarAsterias rubens during its annual reproductive cycle

Detailed information is presented on the changes in lipid-class profiles (polar lipids, total neutral lipids, free sterols, steryl esters, triacylglycerols, neutral ether lipids and free fatty acids), which are manifest during the annual reproductive cycle of the seastarAsterias rubens for both the storage organs (pyloric caeca) and utilizing organs (ovaries). The ovaries appear to accumulate all individual lipid components proportional to progression of vitellogenesis. Pyloric caeca, in contrast, show variable lipid-class levels, probably due to more complex processes in these organs, operating simultaneously: digestion of food, accumulation of storage lipids, mobilization of stored lipids and their release. The results are discussed in terms of current knowledge on the role of lipids in echinoderm reproduction.     

Effect of zinc on the settlement of the oyster Crassostrea gigas

The influence of zinc upon the pattern and success of settlement was examined in the oyster Crassostrea gigas. Late larvae were more tolerant of zinc than embryos. A delay in settlement was recorded in treatments containing zinc as low as 125 μg/l, and numbers of larvae settling was reduced in the presence of zinc. Larvae subjected to zinc immediately prior to settlement showed evidence of slowing in behavioural development. Those larvae which settled in the presence of zinc, however, when ongrown in clean water were as viable as controls. Zinc at concentrations of 250 and 500 μg/l suppressed spat growth, but recovery was rapid upon subsequent on-growing in clean water conditions.     

Concentration of lodine and bromine by plants in the seas of Japan and Okhotsk

Iodine and bromine content were measured in 24 species of red (Rhodophyta), brown (Phaeophyta) and green (Chlorophyta) seaweeds and 2 species of higher water plants (Embryophyta) from the Sea of Japan, as well as in 12 species of the abovecited taxa and 1 species of flowering plant from the Sea of Okhotsk. Iodine was determined by photometric extraction with brilliant green, and bromine by neutron activation of samples. Phaeophyta and Rhodophyta were richest in iodine and bromine content. Representatives of the order Ceramiales (Rhodophyta) had high iodine and bromine contents. Thus, iodine concentrations in Ptilota filicina, Campylaephora hypnaeoides and Myriogramme yezoensis, a new iodine concentrator discovered by us, amount to 0.42, 0.094 and 0.75%, respectively. Bromine content in representatives of the family Rhodomelaceae was 3.36 and 3.74% in Japan Sea and Okhotsk Sea Rhodomela larix, respectively. Polysiphonia japonica (Rhodomelaceae) is a newly discovered concentrator of bromine (3.20%). Many species of the order Laminariales (Phaeophyta) were characterized by high iodine contents: Laminaria japonica, L. cichoriodes, L. inclinatorhiza, Cymathaere japonica and Alaria marginata. The Br:I ratio for all the species except those that concentrated iodine, was more than 1. Seaweeds that grow at greater depths showed increased iodine and bromine contents. A tendency toward increased iodine content was observed in species growing further to the North. Iodine and bromine were accumulated selectively by various organs of Sargassum pallidum.     

On the introduction of the Kamchatka King crab Paralithodes camtschatica (Decapoda: Anomura: Lithodidae) into the Barents Sea

About 2,500 specimens of the Kamchatka king crab Paralithodes camtschatica (Tilesius), ca. 5 to 15 years old, and about 10,000 juveniles, ca. 1 to 3 years old, were released into the Barents Sea from 1961 to 1969. One large berried female was caught in 1974, and the number of records increased in 1976 (at least 100 records, including 6 reliable ones). The crab therefore seems to have become a permanent inhabitant of the Barents Sea. It will be important in future to continually record new occurrences of the crabs, especially of juveniles, in order to document the extent of their distributional range and to obtain evidence of successful reproduction of the species.     

Nutrients and biomass distribution in the Gulf of Aqaba (Elat), Red Sea

The distribution of phosphate, nitrate and silicate values obtained from 300 samples and of biomass determined by displacement volume in about 1,900 vertical plankton hauls (65, 200 and 330 m) collected from 8 oceanographic station during 1974–1975 in the Gulf of Aqaba (Elat) are summarized and illustrated by crosssections. Generally, the Gulf is poor in nutrients and the data indicate that it is filled with upper (150 m) Red Sea waters, flowing in over the sill of Tiran. Nutrient content of the upper and deep waters immediately outside the sill are well within the known range of those in the northern Red Sea. Biomass values are relatively low in the Gulf are generally similar to those reported from the northern Red Sea. Both nutrients and biomass values display seasonal and bathymetric variations in the Gulf and outside the sill.     

Interannual variation in the reproductive cycle and biochemical composition of the cockle Cerastoderma edule from Mundaca Estuary (Biscay,North Spain)

Seasonal determinants of body weight, biochemical composition and reproductive condition in the cockle Cerastoderma edule L. from the Mundaca Estuary, Spain, were performed from December 1983 to July 1985. Interannual differences in timing of gametogenesis and spawning between 1984 and 1985 were correlated with temporal variations in the cycles of storage and utilisation of carbohydrate reserves. Young individuals exhibited larger annual fluctuations in soft-body weight, displaying higher growth rates in spring and greater diminishment of energy reserves during autumn and winter than older individuals. Carbohydrate content displayed a similar tendency, levels being lower in young individuals throughout the year.