No abstract

cordatum is presented which also allows incremental annual growth of an individual to be calculated.The parameter W, derived from the parameters k and LW of the von Bertalanffy growth model, was used to compare the growth rate of E. cordaturn at different sites. Analysis of approximately 2,000 specimens collected from different points along a north-south transect showed an increasing rate of growth from north to south. Maximum size of the organisms also increased in the same direction. No differences in longevity were observed. The causative factors are still speculative at this time. However, a number of physical parameters which form gradients along the transect, provide several interesting possibilities for future investigations. The most promising of these is bottom temperature. The highest rate of growth for this organism occurs in sediments containing the lowest amounts of organic matter and biomass. This poses interesting questions regarding its food and feeding habits.

The North Sea, one of the most productive of the earth's seas and oceans, is also surrounded by some of earth's most densely populated and heavily industrialized regions. A growing number of signals are being received which indicate that this valuable ecosystem is increasingly under stress. This has generated a corresponding increase in concern over the steps to be taken to protect the North Sea. While there are divergent views on what constitutes an 'ideal' North Sea, there is a general recognition that any decisions that are made should be based on a good understanding of this ecosystem. The intention of this paper is to give an overview of what is presently known, and to identify areas where more studies are needed. A brief summary of the hydrography and the biota of the North Sea is given. Biotic and abiotic structure justify partitioning the North Sea into three ecologically different regions: southern, central, and northern. For the most part, neither the top predators, e.g. marine birds and mammals, nor the macroatgae and sea grasses