Does displacement of spawning time occur in the sibling species Cerastoderma edule and C. lamarcki?

The spawning cycles of the sibling species Cerastoderma edule (L.) and C. lamarcki (Reeve) were studied in allopatric and sympatric Danish populations from 1978–1980. The results do not support earlier findings of reproductive character displacement in sympatric populations of the two species. New records of hybrid formation and intermediate forms are presented and discussed.     

Worker population structure and gyne production in the ant Myrmica

Summary Wild colonies of Myrmica rubra L. were sampled and cultured in the laboratory to assess their reproductive capability. Correlation analysis was then used to relate the reproductive performance to a number of worker population characteristics. This revealed an association between the magnitude of gyne production and the proportion of nurses in the population. The absence of big workers also increased gyne production.Artificially composed cultures were then made and used to confirm greater resistance of nurses and small workers to queen domination.It is suggested that rapidly growing colonies will have higher proportions of young nurse workers refractory to queens and able to deliver the food necessary for gyne production. Such colonies could optimise their reproduction in this way.     

Habitat selection of two congeneric bivalves,Cardium edule and C. glaucum in sympatric and allopatric populations

Habitat selection of two bivalve species, Cardium edule (L.) and C. glaucum (Bruguière) is described for sympatric and allopatric populations of both sibling species. It is demonstrated that C. edule grows faster than C. glaucum and is absent from localities with periodic low food-availability. The ability to burrow of C. glaucum is low compared with that of C. edule; the former species does not occur in very loose, well-sorted sand near the coast. Earlier studies which suggest that tidal range determine the species distribution could not be confirmed.     

Fluxes of dissolved and particulate calcium in selected tissues of Crassostrea virginica

Rates of calcium incorporation by selected tissues of Crassostrea virginica increased in a step-wise fashion from lowest values among organisms exposed to ambient total calcium concentrations of 45 mg l^-1, intermediate values among oysters exposed to 135, 225, and 315 mg l^-1, to highest rates for oysters exposed to 360 mg l^-1. Although excised visceral mass tissue had highest rates of calcium incorporation relative to mantle, muscle, and both organic and inorganic portions of the shell, mantle tissue appeared to have the most dynamic response to changes in ambient calcium concentrations. Rates of dissolved calcium incorporation from ambient water were approximately two to three orders of magnitude higher than comparable rates from ingested algal food. Behavioral response to concentrations of selected inoic, species in the ambient environment may have been responsible for observed differences in rates of calcium incorporation.     

Exploitation of the lobster fishery: Some empirical results

This paper analyzes the optimal and free market utilization of the lobster fishery and applies the results to two fishing areas in Canada. Biomass relationships and a production function are estimated and the empirical results are used to calculate hypothetical optimal fishing solutions. The welfare losses from overutilization of the fishing areas are examined.     

Nutritional effect of five species of marine algae on the growth,development, and survival of the brine shrimp Artemia salina

Five species of unicellular algae of the same age, cultured bacteria-free under standard growth conditions, were analyzed for chemical composition and fed to different size classes of Artemia salina. The green algae Chlamydomonas sphagnicolo, Dunaliella viridis, Platymonas elliptica and Chlorella conductrix had significantly higher percentages of protein and lipid than did the diatom Nitzschia closterium. Total ash value was highest in populations of N. closterium. Shrimp fed Chlamydomonas sphagnicolo cells assimilated highest percentages of organic matter, while those fed Chlorella conductrix had lowest assimilation rate. Respiration rates were inversely proportional to animal size (weight) and algal cell volume. Growth, survival, rate of sexual maturtion, and sex ratio were dependent on the growth and assimilation efficiencies obtained from each respective algal food. Shrimp fed Chlamydomonas sphagnicolo, D. viridis, or P. elliptica cells displayed highest growth and assimilation efficiencies.     

Distribution of visual pigments in the Teleostei — A comment

Two types of visual pigments have been identified in the retinal rods of vertebrates — rhodopsin (A₁) and porphyropsin (A₂). Wald (1960) suggested a specific pattern of distribution for these pigments in vertebrates on the basis of their habitat salinity. However, data published in recent years on visual pigments have raised doubts as to the validity of Wald's hypothesis, especially with reference to teleost fishes. Hence the available data, old as well as new, have been reanalysed and it is suggested that the distribution of visual pigments in teleost fishes is correlated with their phylogeny, rather than with their habitat salinity per se.     

Halocyprid ostracods in Atlantic neuston

Twenty-one species of halocyprid ostracods were identified from 7778 specimens caught in 144 neuston net hauls taken from the research vessel “Walther Herwig” in the Atlantic Ocean. Hauls taken during dusk were richer both in specimens and in species than later in the night. Few if any specimens occurred in daytime catches. Eighty-eight percent of the specimens were male Conchoecia spinirostris, which were observed to swarm at the surface at dusk in two positions. Many of the species occurred over a wide range of hydrographic conditions, and only in the region 40°S; 39°W did representatives of the cold-water fauna appear. The species could be categorised into 5 groups, depending on zoogeographical ranges and daytime depth distributions; the majority of the species ranged from 40°N–40°S, and had daytime maxima in the upper 100 m. It is concluded that ostracods only constitute important food items for carnivores feeding in the neuston when the latter are permanently in the neuston; the occurrence of vertically migrating carnivores does not coincide with the maximum occurrence of ostracods in the neuston.     

Shell repair in Nautilus macromphalus

The shell of Nautilus macromphalus, like that of N. pompilius, consists of an outer spherulitic-prismatic layer, a middle nacreous layer, and an inner semiprismatic layer. No periostracum was observed. When an area of shell 2 cmx2 cm over the living chamber was removed experimentally, it was replaced by shell of normal structure. Regeneration required 45 days. Observations of regenerated shell made with a scanning electron microscope showed that the spherulitic portion of the spherulitic-prismatic layer was formed from crystal grains that developed into spherulites. The nacreous layer was formed by the deposition of stacks of hexagonal crystals which, through lateral growth, made contact with crystals in adjoining stacks and formed continuous layers 1 crystal in thickness. The deposition of all the shell layers during regeneration was probably accomplished by a single mantle region rather than by different mantle regions as in normal shell growth.     

Oil pollution monitoring in the Lagoon of Venice using the mussel Mytilus galloprovincialis

Gas chromatographic analyses of mussels, Mytilus galloprovincialis, from different areas of the Lagoon of Venice show that these organisms contain a very complex mixture of hydrocarbons attributable to fuel oil contamination. The measured amounts normally range from 0.8 to 8.7 mg/100 g wet weight, but values as high as 22.0 mg/100 g have been recorded. This high value indicates a saturation limit for these organisms which is considerably higher than those values normally found in mussels from the lagoon. The aliphatic hydrocarbon levels in mussels are related to distance from pollution sources and to the degree of exchange between the sea and the area sampled. On the basis of this relationship between overall hydrocarbon pollution load and level of contamination of M. galloprovincialis, it appears that this bivalve might be effectively utilized as a self-integrating monitoring index of oil pollution in the wasters of the lagoon.