Relation of RNA/DNA ratios to growth for the scallop Euvola (Pecten) ziczac in suspended culture

We examined the relation of RNA/DNA ratios to growth for three size groups of the tropical scallop Euvola ziczac maintained in suspended culture at 8, 21 and 34 m in depth in the Golfo de Cariaco, Venezuel. Various growth parameters indicated that production decreased with depth. This was more likely due to a decrease in seston quality with depth than to temperatures or seston abundance (which were similar at the various depths studied). The RNA/DNA ratio was correlated with the G-index of muscle growth for juveniles (r ²=0.55). A much weaker correlation was observed for the maturing scallops (r ²=0.18), probably because of the interaction between reproductive and somatic growth. In fully mature scallops, somatic growth was negligible and the RNA/DNA ratios appeared to be inversely related to the level of physiological stress of the scallops. Whereas RNA/DNA ratios are difficult to interpret for maturing E. ziczac, because an increased ratio can be due to either increased gonadal or somatic growth, they are useful in predicting growth in juveniles and physiological stress in fully mature scallops.     

Molecular data from the 16S rRNA gene for the phylogeny of Veneridae (Mollusca: Bivalvia)

Veneridae, a cosmopolitan and ubiquitous family in world-wide littoral environments, lists more than 500 species, many of which are often subject to intensive commercial exploitation due to their numerical dominance in benthic communities. Historically, the family has been divided into 12 subfamilies by M. Keen and, even though this taxonomical arrangement was adopted for convenience and does not necessarily reflect genetic relationships, as suggested by Keen herself, this classification is still accepted. To contribute to clarify the systematics and phylogeny of Veneridae, the portion of the nucleotide sequence corresponding to domains IV and V of the gene encoding the large subunit of mitochondrial ribosomal RNA was analysed in 14 species representative of 10 genera belonging to 6 different subfamilies. The results obtained using the maximum-parsimony and neighbour-joining methods indicate that the current placement of the genera into subfamilies does not always reflect a natural subdivision. In addition, the six species of Tapetinae studied, though confirmed to be a monophyletic clade, do not exhibit a correct attribution at the genus level.     

Nitrate metabolism in abyssal waters

Activities of nitrate assimilation and nitrate reduction were measured 50 cm above the ocean floor (5,845 m and 5,207 m) by an in situ ¹⁵N tracer technique at stations in the subtropical (28°29.8′N; 144°58′E) and subarctic (44°10.2′N; 154°03′E) western North Pacific Ocean. Nitrate assimilation ranged from 0.009 to 0.11 μg-at N/1/day, and nitrate reduction from 0 to 0.42 μg-at N/1/day in the presence of added peptone and yeast extract. Nitrate assimilation was higher than nitrite formation at the southern station, but the reverse was the case at the subarctic station. No correlation was observed between bacterial growth and nitrate metabolizing activities. Data are also presented on the effect of hydrostatic pressures upon nitrate metabolism by microbial populations in the surface waters.     

Effects of the polychlorinated biphenyl Aroclor® 1254 on the American oyster Crassostrea virginica

Young oysters (Crassostrea virginica) were continuously exposed to Aroclor^® 1254, a polychlorinated biphenyl (PCB), in flowing, unfiltered seawater. Growth rate (height and in-water weight) was significantly reduced (=0.05) in oysters exposed to 5 g/l (ppb) for 24 weeks. Growth rate was not affected in oysters exposed to 1 ppb for 30 weeks. Mortality was not significant in exposed and control groups. In oysters exposed to 5 ppb, greatest PCB residue (whole body) was 425 mg/kg (ppm), 85,000x the concentration in the water, and less than 0.3 ppm was retained after 28 weeks depuration in PCB-free water. In oysters exposed to 1 ppb, greatest residue was 101 ppm, 101,000x the concentration in the water, and less than 0.2 ppm was retained after 12 weeks depuration. Examination of oysters exposed to 5 ppb of this PCB for pathogenesis revealed atrophy of digestive diverticular epithelium and degeneration of vesicular connective tissues concomitant with leukocytic infiltration, but tissue recovery seemed excellent after 12 weeks depuration.Registered trademark, Monsanto Company, St. Louis, Missouri, USA. Mention of commercial products or trade names does not constitute endorsement by the Environmental Protection Agency.Contribution No. 146, Gulf Breeze Laboratory.     

Morpho-functional patterns of photosynthesis and UV sensitivity in the kelp <Emphasis Type="Italic">Lessonia nigrescens</Emphasis> (Laminariales,Phaeophyta)

The photosynthetic responses of the south Pacific kelp Lessonia nigrescens of the coast of Valdivia, Chile (40°S), were investigated by exposing its different thallus parts, fronds, stipes and holdfasts, to UV radiation in the laboratory. Biologically effective doses (BED_{photoinhibition300}) between 400 and 800 kJ m⁻² were required for a 40% inhibition in photosynthesis under UVA+UVB radiation. At BED_{photoinhibition300} close to 250 kJ m⁻² (in treatments without UVB), the inhibition of photosynthesis did not exceed 20%. These UV doses were in the range of current daily doses measured in Valdivia on cloudless summer days. In general, exposure to UVB for periods longer than 12 h reduced photosynthesis, measured as maximal quantum yield (F _v/F _m) and electron transport. The fronds were the most UV-sensitive section of this alga, coinciding with the highest pigments contents and carbon fixation. Evidence of a photodamage was also seen. After a 48 h exposure to PAR+UVA+UVB, a decrease of F _v/F _m in the fronds was close to 41%, while in the stipes and holdfasts it was 12 and 18%, respectively. Although the thalli from the different size classes showed marked differences in their morphology and morphometry, no obvious differences in the UV tolerance of the fronds were detected. The results indicated that the UV-related responses are integrated in the suite of morpho-functional adaptations of the alga. Although the fronds are spatially more exposed to solar radiation than basal structures (stipes and holdfast), due their high turnover rate they may compensate better detrimental effects of UV. In contrast, stipes and the holdfast are key support structures characterized by low replacement rates and designed to confer hydrodynamic resistance to drag forces.     

Biochemical composition of Nephrops norvegicus : changes associated with ovary maturation

Changes in the biochemical composition of the ovary of Nephrops norvegicus (L.) were examined throughout maturation at stations with fast and slow growing individuals in Scottish waters and in the Mediterranean. Ovary index (ovary wt:total body wt) increased significantly with maturation. Lipid, protein and water content of the ovary increased with maturation, while carbohydrate content decreased. Similar changes were also identified in the hepatopancreas. Significant spatial differences in ovary and hepatopancreas composition were identified, which may be related to whole-body growth rate. The ovary maturation scale commonly used for N. norvegicus was shown to reflect biochemically distinct stages in ovary development. Received: 7 February 1997 / Accepted: 25 February 1997     

The search for indigenous dune stabilizers: Germination requirements of selected South African species

The coastline of South Africa is characterized by extensive dune fields which are threatened by development, and thus the demand of stabilization of drift sand will increase. The non-invasive alien grass speciesAmmophila arenaria is at present the dominant sand stabilizer. Due to its foreign origin and invasiveness in North America its use was criticized and indigenous sand-binding species would be preferred. The germination requirements of the nativeArctotheca populifolia, Ipomoea pes-caprae. Myrica cordifolia andScaevola plumieri were investigated. The results showed that for all four species the total germination time and germination phase could be shortened and germination success (number of germinated seeds) improved. The different scarification and stratification treatments broke the dormancy ofI. pes-caprae, M. cordifolia andS. plumieri, whereas the seeds ofA. populifolia were not dormant. Seeds ofI. pes-caprae andM. cordifolia had induced an innate dormancy, respectively, whereas the type of dormancy in seeds ofS. plumieri dormancy processes remained unknown.     

Diel trophic interactions between vertically-migrating zooplankton and their fish predators in an eelgrass community

Diel changes in the composition of crustacean zooplankton and the diets of fish predators from an intertidal eelgrass flat were monitored concurrently. The zooplankton is characterized by two major components. The obligate zooplankters (holoplanktonic calanoid copepods and meroplanktonic decapod larvae) appear to exhibit vertical migration, being present in higher densities near the surface of the water column at night. The facultative zooplankton (amphipods and ostracods) are benthic during the day, but move up into the water column at night. Planktivorous midwaterdwelling fish consume calanoid copepods and decapod larvae during the day and cease feeding or switch their diet to amphipods at night. Benthic-dwelling fish consume some amphipods during both day and night. The factors important in prey selection by fish and the functional significance of vertical migration in both components of the zooplankton are discussed in the light of the changing patterns of fish predation.This paper is Publication No. 183 in the Ministry for Conservation of Victoria, Environmental Studies Series.     

Isolation of a new toxin from the sponge Latrunculia magnifica in the Gulf of Aquaba (Red Sea)

The sponge Latrunculia magnifica was found to be toxic for fish. A toxin has been isolated from this sponge by organic extraction-column chromatography and thin-layer chromatography. Several chemical properties of the toxin were determined by spectroscopic analysis. Toxicity tests were performed on the fish Gambusia affinis. In vitro experiments showed the toxin to be a cholinesterase inhibitor.     

The costs of intersexuality: a crustacean perspective

Increasing concerns over rising intersexuality in the animal kingdom and the ability of certain chemicals to disrupt the endocrine system have demanded a better understanding of the costs associated with such conditions. Whilst intersexuality appears relatively widespread throughout gonochoristic crustaceans, i.e. those crustacean species with two separate sexes, the fitness costs have rarely been reported. Through comparable investigation of normal and intersex specimens of the highly abundant marine/estuarine amphipod Echinogammarus marinus (Leach) these fitness costs were determined. Measurements taken to assess fitness costs included fecundity, fertility and embryonic development, maturation period, and any morphological deformities that might result in reduced pairing success. Results from this study suggest that intersex E. marinus suffer from reduced fecundity and fertility, and mature at a larger size than normal specimens. These fitness costs can also, to a certain extent, be related to the degree of intersexuality. It is suggested that the increased size and morphological abnormalities observed in intersexes may result in reduced pairing success. Investigations into intersex organisms, i.e. those organisms with known dysfunctional endocrine systems, and the costs associated with such conditions, should aid researchers in assessing effects at the population and community level.Communicated by J.P. Thorpe, Port Erin