Effect of low salinity on the activity,feeding, growth and absorption efficiency of Luidia clathrata (Echinodermata: Asteroidea)

Exposure of Luidia clathrata (Say) to low salinity (17 S) results in a decrease in activity and rate of feeding, but has little effect on the absorption efficiency. Growth, as indicated by changes in body size and energy content of the body wall and pyloric caeca, is reduced in low salinity due to a decrease in feeding rate (energy consumption) and to a decrease in efficiency of utilization of material and energy absorbed. The low efficiency indicates that either additional energy is required for maintenance or energy is used inefficiently in low salinity. Thus, L. clathrata is limited energetically in low salinities, although it lives and reproduces there.     

Activité biologique en domaine profond: transformations biochimiquesin situ de composés organiques marqués au carbone-14 à l'interface eau-sédiment par 2000 m de profondeur dans le golfe de Gascogne

In June 1983,in situ water-sediment interface experiments were conducted with the submersible Cyana at 2 000 m depth in the Bay of Biscay. Dissolved or particulate¹⁴C-labelled organic compound was injected into a compartment of a box-corer specifically adapted for use with the submersible. After incubation, the biochemical reactions were stopped by addition of Formalin. In the laboratory, the pathways of the labelled molecules in the various extracts were followed by means of chemical and granulometric fractionation and isolation of meiofauna. Various experiments run at 1 atm and atin situ pressures, for incubation times of between 3 and 144 h, revealedin situ biochemical transformation. After recovery of the samples, activity at 1 atm was low, with only 4% of the radioactivity being recovered in the macromolecules against 84% for thein situ experiments. These results comprise new evidence of the existence of a rapid biochemical transformation at great depth in the ocean and therefore of the activity of the microflora, microfauna and meiofauna which are living in the superficial sediment.

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Contribution No. 49 de l'IFREMER     

Effects of food particle concentration on feeding current velocity in sex species of marine Bryozoa

Experiments were carried out using established methods to measure feeding current velocity in six species of marine Bryozoa collected in 1982 and 1983 around low-tide mark at Port St. Mary, Isle of Man (Flustrellidra hispida, Alcyonidium gelatinosum, A. hirsutum, Electra pilosa, Membranipora membranacea and Bowerbankia gracilis feeding on Tetraselmis suecica). It was found that there was a positive correlation between feeding current velocity and the concentration of food (phytoplankton) in the environment. It was also found that, at a fixed particle concentration, feeding current velocity was strongly correlated with lophophore height and (less strongly) with tentacle number. The competitive and evolutionary implications of these relationships are considered. It is tentatively suggested that interspecific competition for food may be of some significance in marine Bryozoa and that the removal of food supplies to competing colonies may play a role in colony overgrowth and competition for space.     

Ichthyotoxicity found in cultured media of Protogonyaulax spp.

Ichthyotoxicity was observed in the cultured media from Protogonyaulax catenella and P. tamarensis. No paralytic shellfish poison was detected in the cultured media. Test fish in the cultured media died showing signs of hypoxia. Histological observations of the gills of intoxicated fish indicated that the epithelial cells were swollen and exfoliated from the pillar cell. The cultured media had hemolytic activity against erythrocytes of various animals. The media also decreased the elasticity of eggs of rainbow trout Salmo gairdneri. From these results, it is concluded that the cultured media of both species of Protogonyaulax contain a cytotoxin which is lethal to fish.     

Replacement of reproductives in Nasutitermes princeps (Desneux) (Isoptera: Termitidae)

Summary The production of replacement reproductives in experimentally orphaned societies was investigated in Nasutitermes princeps (Desneux). From 1 to 180 replacement queens and multiple kings, all adultoids, were found in the 13 nests that were re-collected. Normal imagos, microimagos, or a mixture of the two forms were present, depending on colony composition at the time of orphaning. In colonies with alates, the corresponding forms were found as replacement reproductives. Where only young nymphs were present, microimagos differentiated. Neither the number of queens nor their level of physogastry was correlated with the time elapsed since orphaning, but the total egg-laying rates were. We suggest that competition among queens rather than time determines individual physogastric development. Observations show that the most likely cause of accidental queen death in nature is probably nest fall from the supporting tree. Even in this case, the queen may be able to migrate to a newly rebuilt nest. An experimental simulation of this situation showed that colony migration can occur. The data indicate that the replacement of the primary queen after her accidental death cannot by itself account for the high rate of polygyny (60%) encountered in N. princeps. Two other possible causes are the replacement of the ageing foundress as a normal event of colony life, and colony reproduction by budding off new nests with adultoid reproductives.King Léopold III Biological Station, Laing Island, Papua New Guinea, contribution no. 84Research Assistant of the National Fund for Scientific Research (Belgium)     

A comparison of macrofaunal and meiofaunal distribution and standing stock across a rocky shore,with an estimate of their productivities

In 1984 and 1985 algal, macrofaunal and meiofaunal standing stocks were estimated on a exposed rocky shore along the west coast of False Bay, South Africa, using comparable, area-based sampling techniques. The shore supported a rich growth of algae, particularly in summer, when a maximum standing crop of 403 g m^-2 was recorded in the low shore. In winter, the largest component of macrofaunal biomass comprised the filter-feeding barnacle Tetraclita serrata, which attained 75 g m^-2 in the middle balanoid; but as a result of late recruitment and high mortality of this species, the summer shore was dominated by herbivorous gastropods, particularly Patella cochlear, which attained a maximum biomass of 66 g m^-2 on the low shore. Meiofaunal numbers and biomass were closely correlated to the distribution of algal turfs and associated trapped sediments. Numerically, the most important components of the meiofauna were nematodes and copepods, while the biomass was more evenly shared among foraminifera, minute gastropods, copepods and insect larvae. Numbers and biomass peaked in the lower balanoid during winter (1.9×10⁶ individuals, or 8.5 g m^-2). Macrofauna:meiofauna numbers and biomass ratios are presented for each zone and the distribution patterns discussed in relation to the conditons in each. Numerically, meiofauna exceed macrofauna by an overall ratio of 1:391, with values ranging from 1:556 in the lower balanoid to 1:18 in the Littorina zone. Macrofaunal biomass exceeds that of meiofauna in all zones by an overall ratio of 10:1, but values range from 2.1:1 in the upper balanoid to 48:1 in the middle balanoid. By incorporating turnover ratios extrapolated from the literature, mean annual productivity ratios have been calculated. These indicate that macrofauna account for 75% of total secondary production and meiofauna for 25%. Failure to incorporate meiofauna in analyses of energy flow on rocky shore ecosystems would thus lead to considerable errors. The possible trophic role of meiofauna in such systems is discussed.     

A simple bioassay for feeding-stimulants for the young seahare Aplysia juliana

Water extracts of a green alga (Ulva sp.) are known to elicit phagostimulatory responses against a seahare Aplysia sp. In 1984 we happened, however, to find that a seahare shows its feeding preference for filter paper on which an ether extract of Ulva sp. had been absorbed. We succeeded in establishing a simple and reliable bioassay procedure for the feeding-stimulants for the seahare A. juliana, which is applicable to isolation of the active principles.Chemical Studies on Phagostimulants for Marine Gastropods, Part V. For Part IV, see Sakata et al. (1985)     

Biologie d'un copépode des mares temporaires du littoral méditerranéen français: Eurytemora velox

The feeding activity of Eurytemora velox, a brackish copepod from temporary lakes of the south of France, was studied in 1978–1979 using various foods (natural particles, monospecific algal cultures, and artificial food) under different conditions of temperature and salinity. Experiments with Amphidinium sp. or Tetraselmis maculata as food showed that the ingestion rate increased with food concentration according to an asymptotic or a linear relationship. Although of slightly smaller size, T. maculata was ingested at a higher rate than Amphidinium sp. Large maximum daily rations (up to 150% of body carbon with Amphidinium sp. and up to 250% with T. maculata) were attained. These values, which greatly exceed those generally obtained with marine copepods, could result from adaptation of the feeding processes of this copepod to its very rich trophic environment. A significant correlation was demonstrated between ingestion rate and fecal pellet production using T. maculata as food. Therefore, daily fecal production was used as an index of feeding activity in experiments carried out with natural food, T. maculata cultures and artifical food (Tetramin). Increased temperature generally resulted in an activation of grazing and filtration rates and of fecal production at low temperatures (10° to 15°C), but a strong decrease was observed over 22°C. Differences of 10 S over or under the natural salinity level led to a decrease in fecal production, suggesting unachieved acclimatization to salinity variation due to a too short acclimation period before the experiments. Fecal pellet production was higher during the day than during the night. It depended also on the quality of food used: high values were obtained with T. maculata, Phaeodactylum tricornutum, Rhodomonas sp. and Chlamydomonas sp., low values with Chlorella sp. and Amphidinium sp., and medium values with natural food material. The assimilation rate (A) was calculated by Conover's methods. A significant negative correlation was obtained between A and the ash content of the food. High assimilation rates were attained with chlorophycean algae, while natural particulate food produced variable assimilation rates, depending on the amount of inorganic material present.

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Biologie d'un copépode des mares temporaires du littoral méditerranéen français: Eurytemora velox

     

Autecological investigation on marine diatoms 3. Thalassiosira nordenskioeldii and Chaetoceros diadema

The temperature range for the best competitive position by growth of Thalassiosira nordenskioeldii Cleve has been determined by comparing generation times. It ranges from-1.5° to 6°C. At these temperatures, especially at lower light intensities, it was one of the fastest growing species, whereas above 6°C many other species grew faster. High light intensities at increasing temperatures became damaging. A flowering of the cold oligo-eurytherm diatom T. nordenskioeldii occurs not only in the upper layers, but can also occur at greater depth simultaneously, because decreasing daylengths at 6°C had the least influence on its growth. Continuous light at 6°C had a positive influence on its growth. The start of the T. nordenskioeldii spring flowering under the Arctic Sea Ice is discussed in connection with the occurrence of enclosed marine diatoms in Polar Sea Ice. The influence of the winter temperature on the spring flowering of the North Sea, the southern border for flowerings of T. nordenskioeldii, is discussed. For Chaetoceros diadema (Ehrenberg) Gran the best competitive position by growth is reached at-1.5° to about 6°C. It has the best opportunity of reaching high cell numbers at the lowest temperatures of the range. The occurrence of the cold oligo-eurytherm diatom Ch. diadema in plankton samples at temperatures above 10°C need not be incorret, for the species did grow in cultures at 12° and 16°C. The wrong interpretation of the experimentally determined optimum temperature of e.g. T. nordenskioeldii caused a discrepancy between experimental results and field data that does not exist. The question is discussed whether ecologically it is relevant to talk about a temperature optimum. On account of the results of T. nordenskioeldii the question of the adaptation of diatom cultures for the start of the real experiments is discussed.     

Food and feeding habits of the king crab Paralithodes camtschatica near Kodiak Island,Alaska

Stomach contents from 809 king crabs, Paralithodes camtschatica (Tilesius), from 6 areas near Kodiak Island, Alaska, and 9 sampling periods (1978–1979) were exammed quantitatively; 713 (88%) contained food. Mollusca (mainly the bivalves Nuculana spp., Nucula tenuis, and Macoma spp.) and Crustacea (mainly barnacles) were the dominant food groups in terms of percentage wet weight and frequency of occurrence; fishes were the next most important group of prey. No significant differences in feeding between sexes occurred; however, significant differences were apparent in the quantity of food consumed from different sampling periods, areas, depths, size groups, and crab molt-classes. Consumption was greater in spring and summer and in offshore locations at depths of 126 to 150 m. In addition, king crabs <140 mm carapace length (CL) consumed more food than crabs 140 mm CL. Adult, newshell (individuals that molted during the last molting period) females greater than 95 mm CL, and newshell males greater than 100 mm CL, each contained more food than did juvenile, newshell females <120 mm CL.Contribution No. 449, Institute of Marine Science, University of Alaska, Fairbanks, Alaska 99701, USA