The Ectoparasitic Gastropod Boonea (= Odostomia) impressa: Population Ecology and the Influence of Parasitism on Oyster Growth Rates

Abstract. Boonea (= Odostomia) impressa is a common ectoparasite of oysters. In the laboratory, small oysters (Crassostrea virginica) parasitized by natural densities of B. impressa produced 75 % less new shell than unparasitized oysters. Shell deposition rates of previously parasitized oysters increased significantly after all B. impressa were removed. Thus, the decrease in growth rate, although significant, apparently was not permanent. B. impressa preferentially parasitized small, living oysters (≤2.5cm) in the field, even though a higher percentage of large, living oysters (>2.5cm) was available. The snails maintained an aggregated distribution on the oyster reef. The number of B. impressa per oyster clump was positively correlated with the number of living oysters per clump, however some clumps with few or no living oysters had many B. impressa. Thus, food availability only partially explained the pattern of distribution. B. impressa was very mobile. About 50 % of the population moved in one week. Reproduction occurred throughout the year with a peak period in May. Recruitment was greatest in July, however new recruits were observed throughout the year. The reduction in growth rate of parasitized oysters, the snaiľs propensity towards parasitizing small oysters and the snail's tendency to be contagiously distributed suggests that B. impressa potentially exerts a significant influence on the population structure and health of oyster populations.     

Study of the fauna inhabiting the holdfasts of Laminaria hyperborea (gunn.) fosl. along some environmental and geographical gradients

A survey of the holdfast fauna of Laminaria hyperborea was carried out at thirty-five sites around the UK, mostly along the North Sea and south coasts.Data from different age classes of holdfast from a polluted and unpolluted site indicate that volume of holdfast space is a most important measurement of sample size, a minimum size of sample being one litre and, preferably, three.Gradients of increased heavy metals were defined down the North Sea and west coasts and, by utilising measurements of kelp penetration, water clarity gradients were determined as increasing northwards on the west coast and both north and southwards on the North Sea coast from a point near Tyne and Wear county. Analysis of holdfast fauna showed numerous gradients of total numbers, species and diversity which correlate closely with the heavy metal and water clarity gradients, or with undetermined parameters analogous to latitude and longitude. Where there were increases of heavy metals or decreases of water clarity, various reciprocal relationships between suspension feeders and all other trophic groups were commonly observed. In the North Sea numbers of suspension feeders increased while numbers of all other trophic groups declined. On the west coast a heavy metal increase correlated with a decreasing species richness of all trophic categories except suspension feeders, while with total numbers only suspension feeders showed an increase. On the south coast transect neither gradient existed, and only here did all trophic categories covary, except at one very polluted site where the same reciprocal relationship was again indicated.In terms of species similarity the North Sea showed a greater pool of common species than occurred between sites of other regions and between North Sea sites with other regions, despite the widest range of heavy metal levels and wate clarity that existed there. Between-site similarity appeared to be much more dependent on geographical proximity than on the two measured environmental factors. It is suggested that effects of clarity-reduction can be measured by trophic analysis more successfully than by species presence or absence, and that changes of holdfast fauna along the North Sea coast are due largely to pollution.     

Concentrations of suspended matter and particulate cadmium,copper, lead and zinc in the Indian sector of the antarctic ocean

The concentrations of suspended matter and particulate Cd, Cu, Pb and Zn were determined for 36 samples collected at 6 stations in the Antarctic Ocean during December, 1970 and January, 1971 using membrane filters. The concentration of suspended matter was determined gravimetrically and trace metal levels were determined using anodic stripping voltammetry. For waters deeper than 100 m the concentration of suspended matter was < 100 μg l^?1. Concentrations up to 542 μg l^?1 were recorded between surface and 100 m. Individual concentrations of the metals were scattered with depth. Average concentrations of particulate metals were: Cd, 3.5 ng l^?1; Cu, 100 ng l^?1; Pb, 35 ng l^?1; and Zn, 230 ng ;l^?1 These measurements represent non-steady state conditions of early Antarctic summer as the ice pack disintegrates and biological activity increases.     

Genetic Diversity in Marine Molluscs: A Test of the Niche-Width Variation Hypothesis

Abstract. A test of the niche width variation hypothesis was conducted in the three Mediterranean littoral species of the family Trochidae: Monodonta turbinata, M. turbiformis and Gibbula richardi. Allozymic variation encoded by 26 gene loci was analyzed, and the levels of polymorphism (P), heterozygosity (H) and allele diversity per locus (A) were estimated and appear to support the niche-width variation hypothesis. The broad-niche species, M. turbiformis and G. richardi are more polymorphic and heterozygous than the relatively narrow-niche M. turbinata (P = 0.571; 0.731 and 0.417; H = 0.108; 0.116 and 0.078; A = 2.025; 2.489 and 1.965, respectively).     

Effect of major ion variations in the marine environment on the specific gravity-conductivity-chlorinity-salinity relationship

Partial equivalent conductances and partial equivalent volumes of the major constituents in seawater were used to evaluate the specific gravity-conductivity-chlorinity-salinity relationships in the marine environment. For example, in the open ocean, the relationships between Cl‰ and both S‰ and specific gravity are valid to within 0.014‰ and 0.014 σ_t, respectively. The relationships between conductivity and S‰ and specific gravity are valid to within 0.006‰ and 0.007 σ_t. In river diluted nearshore areas specific gravity anomalies inferred from Cl‰, can be as great as 0.06 σ_t and 0.04 σ_t when inferred from a conductivity ratio measurement.     

JONSWAP's parameters: Sorting out the inconsistencies

The original prognostic equations for the JONSWAP-spectrum contained inconsistencies. A subsequent paper (Hasselmann et al., 1976, J. phys. Oceanogr.6, 200–208) attempted to regularise the situation. This paper shows that there were still inconsistencies in the prognostic equations giving overestimations of the first moment of the spectrum and consequently the significant wave height. The prognostic equations are reworked systematically and results presented. It is shown that variable σ_a, σ_b and γ must be used to achieve consistent results     

Maternal transfer of bioactive polychlorinated aromatic hydrocarbons in spawning chinook salmon (Oncorhynchus tschawytscha)

The biological potency (relative to 2,3,7,8-tetrachlorodibenzo-p-dioxin. TCDD) of planar polychlorinated aromatic hydrocarbons (PCHs) in extracts of eggs and flesh from spawning female chinook salmon (Oncorhynchus tschawytscha) from Lake Michigan was determined by measuring the induction of 7-ethoxyresorufin O-deethylase activity in H-4-II-E rat hepatoma cells. TCDD-equivalents in flesh and egg samples ranged from 0 to 115·8 pg/g, and were approximately 5-fold greater in eggs than in flesh. These results suggest that the maternal transfer of PCHs may play a role in determining the reproductive success of Lake Michigan chinook salmon.     

Influence of Wind on Dynamics and Flushing of Shallow Estuaries

Observations of two small estuaries in Cape Cod, U.S.A. indicate large variations in salinity structure that are forced by variations in along-estuary wind stress. During onshore winds, the estuarine circulation is reduced, and the along-estuary salinity gradient increases as freshwater accumulates. During offshore winds, the surface outflow is enhanced, freshwater is flushed out of the estuary, and the along-estuary salinity gradient becomes weak. Constrictions block the wind-induced flushing, resulting in strong salinity fronts across the constrictions. The residence time of one of the estuaries varies by more than a factor of three in response to variations in wind-induced flushing. The other estuary has little variation of flushing associated with winds, due to a constriction at the mouth that inhibits the wind-induced exchange. The strong influence of winds on the flushing of these estuaries is due in part to their shallow depths, which accentuates the influence of wind stress relative to the effects of the horizontal density gradient. In addition, the residence times of the estuaries are comparable to the time scale of wind forcing, allowing large changes in water properties during wind events.     

Transient soil response in a porous seabed with variable permeability

The soil permeability of many natural marine sediments decreases with depth because of consolidation under overburden pressure. This is accompanied by a decrease in porosity and void ratio that also affect the permeability. Conventional theories for wave-induced soil response have assumed a homogeneous porous seabed. This paper presents a new approach for the wave-induced response in a soil matrix, with variable permeability as a function of burial depth. The soil matrix considered is unsaturated and anisotropic, and is subject to a three-dimensional wave system. The pore pressure and effective stresses induced by such a system are obtained from a set of equations incorporating a variable permeability. Verification is available through reduction to the simple case of uniform permeability. The results indicate that the effect of variable soil permeability on pore pressure and vertical effective stress may be significant, especially in a gravelled seabed and for unsaturated sandy soils.