Trace metal-binding proteins in marine molluscs and crustaceans

Some marine invertebrates, such as the American oyster, Crassostrea virginica, the blue crab, callinectes sapidus and the American lobster, Homarusamericanus, concentrate trace metals in their tissues. The occurrence of metallothionein, a low molecular weight, sulfur-containing metal-binding protein, has been correlated with elevated levels of trace metals in these organisms. It is our hypothesis that, whilst metallothioneins are involved in the sequestration of elevated levels of trace metals, they primarily function in regulating normal metal metabolism. In this paper we describe recent field and laboratory experiments designed to examine how oysters, blue crabs and lobsters manage accumulated cadmium, copper and zinc. The possible rôles of metallothionein, as well as the tissue distribution of metals, are emphasized. Metallothioneins were found in all animals we examined; concentrations of metallothioneins and the the amount of bound trace metals are related to time of exposure. We have also demonstrated that the laboratory developed metallothionein models for blue crabs and lobsters may be useful in predicting the partitioning of trace metals in animals living in environments polluted with trace metals.     

Detection of the water-soluble fraction of crude oil by the blue crab, Callinectes sapidus

The ability of the blue crab, Callinectes sapidus, to detect petroleum hydrocarbons was measured with behavioural techniques. When presented with a water-soluble fraction of Prudhoe Bay crude oil, blue crabs abruptly changed antennular orientation, began rhythmic beating of the maxillipedal flagellae, and increased antennular flicking rate. The threshold concentration at which 50% of the crabs detected the water-soluble fraction was 2 × 10^?6 mg/litre. The blue crab apparently can readily detect petroleum hydrocarbons at concentrations found in chronically polluted areas as well as oil spill situations.     

Semisubmersible response to transient ice forces

The paper presents an analytical and experimental study on the transient response of semisubmersibles to bergybit impact and the strength of bergybit ice to high strain-rate loadings. Two approaches have been proposed for the solution of the semisubmersible-bergybit interaction problem, one using the energy approach and the other using the conventional structural dynamics approach with initial velocity conditions. In addition the local behaviour of the impacted regions have been analysed for deformation and failure. Numerical results have been given for local behaviour of an impacted column and global behaviour of semisubmersible-bergybit system. Experimental study has been reported on the impact strength of iceberg ice at strain rates of 10⁻³, 10⁻² and 10⁻¹; the indentation impact strength of ice is found to be 3–4 times the unaixial compressive strength, at the same strain rate.     

Problems with biogenic silica measurement in marginal seas

Surface sediment samples from the Bohai, Yellow Sea, and the Pacific were used to assess biogenic silica (BSi) content and to study uncertainties in BSi measurements. The contents of BSi in the Bohai and Yellow Sea are all less than 1%. The dissolution of BSi in sediments from the Bohai and Yellow Sea is very important to maintain high levels of silicate in the water column. The non-biogenic silica from clay minerals has an obvious effect on BSi of sediment samples in the Bohai and Yellow Sea with low BSi and high clay minerals. The solid to solution ratio was found to have a great influence on BSi measurement, which can induce uncertainties up to 75%. The effect of loss by sorption and centrifugation is negligible. Interlaboratory comparison of techniques for BSi measurement by the wet alkaline extraction technique of Mortlock and Froelich [Deep-Sea Res. 36 (1989) 1415-1426] with clay correction was suggested to give no significant differences. However, differences in sediment compositions and reagent to sample ratio may limit the application of the wet alkaline extraction method.     

Magnetic anomalies in the canary basin and the Mesozoic evolution of the central North Atlantic

The data from a recent magnetic compilation by Verhoefet al. (1991) off west Africa were used in combination with data in the western Atlantic to review the Mesozoic plate kinematic evolution of the central North Atlantic. The magnetic profile data were analyzed to identify the M-series sea floor spreading anomalies on the African plate. Oceanic fracture zones were identified from magnetic anomalies and seismic and gravity measurements. The identified sea floor spreading anomalies on the African plate were combined with those on the North American plate to calculate reconstruction poles for this part of the central Atlantic. The total separation poles derived in this paper describe a smooth curve, suggesting that the motion of the pole through time was continuous. Although the new sea floor spreading history differs only slightly from the one presented by Klitgord and Schouten (1986), it predicts smoother flowlines. On the other hand, the sea floor spreading history as depicted by the flowlines for the eastern central Atlantic deviates substantially from that of Sundvik and Larson (1988). A revised spreading history is also presented for the Cretaceous Magnetic Quiet Zone, where large changes in spreading direction occurred, that can not be resolved when fitting magnetic isochrons only, but which are evident from fracture zone traces and directions of sea floor spreading topography.Deceased 11 November 1991     

Contemporary ocean and coastal management issues in Australia and New Zealand: an overview

The past decade has witnessed an unprecedented increase in the number of international treaties, conventions and agreements dealing with maritime issues and oceans governance. Most nations are attempting to cope with this expanding agenda at a time of fiscal constraint, competing environmental demands and the emergence of a new global strategic, political and economic order. However, similar issues do not always lead to similar outcomes. Australia and New Zealand share some common oceanic and coastal management problems, but variations in response arise from geographical differences, constitutional provisions, political style and administrative arrangements. This paper provides a brief overview of contemporary maritime issues and attempted solutions in both nations.     

Relationship between the seismicity and geologic structure of the Blanco Transform Fault Zone

Morphologic studies of an oceanic transform, the Blanco Transform Fault Zone (BTFZ), have shown it to consist of a series of extensional basins that offset the major strike-slip faults. The largest of the extensional basins, the Cascadia Depression, effectively divides the transform into a northwest segment, composed of several relatively short strike-slip faults, and a southeast segment dominated by fewer, longer faults. The regional seismicity distribution (m _b 4.0) and frequency-magnitude relationships (b-values) of the BTFZ show that the largest magnitude events are located on the southeast segment. Furthermore, estimates of the cumulative seismic moment release and seismic moment release rate along the southeast segment are significantly greater than that of the northwest segment. These observations suggest that slip along the southeast segment is accommodated by a greater number of large magnitude earthquakes. Comparison of the seismic moment rate, derived from empirical estimates, with the seismic moment rate determined from plate motion constraints suggests a difference in the seismic coupling strength between the segments. This difference in coupling may partially explain the disparity in earthquake size distribution. However, the results appear to confirm the relation between earthquake size and fault length, observed along continental strike-slip faults, for this oceanic transform.