The Partitioning Of Secondary Production Among Species In Benthic Communities

The way in which total secondary production is partitioned amongst species in various macrofauna communities (Amphiura, Venus, Abra, Modiolus) around the British Isles is discussed. When the proportion of total production is plotted for each species, ranked in order of productive importance, curves are produced which are characteristic of particular physical conditions. The shapes of the curves are independent of the actual species involved, but depend on the proportion of individuals in the community which adopt a particular feeding behaviour, and the scope for diversification within trophic groups. The form of these curves correlates closely with bottom currents and associated bed-stresses, since these affect both the nature of the food supply to bottom animals and the nature of the substrate. These observations have important implications for the structure and functioning of benthic communities. Comparison of production partitioning in the meiofauna of mud and sand substrates indicates a remarkable similarity within trophic groups although the partitioning of production between trophic groups is very different. The shapes of production-rank curves again appear to depend on the scope for diversification within trophic groups. In the meiofauna resources are partitioned more equitably than in the macrofauna. There is a marked discontinuity in the lognormal distribution of body sizes within integrated benthic communities at the meiofauna-macrofauna size boundary.

Effects Of Oil On Digestive Cells In Mussels - Quantitative Alterations In Cellular And Lysosomal Structure

Structural changes were observed in the digestive tubule epithelial cells of Mytilus edulis following long-term exposure to the water accommodated fraction (WAF) of North Sea crude oil (30 μg · l−1 total oil derived aromatic hydrocarbons). The changes observed involved a reduction in the height of the digestive cells beyond that demonstrated in a normal feeding cycle. In addition there was a loss of the normal synchrony of the digestive cells to a point where nearly all the tubules exhibited an appearance similar to that which is usually termed ‘reconstituting’. These alterations were quantified using an image analysis technique and the mean height of the digestive cells used as an index of digestive function or state. Long-term exposure also induced a radical alteration of the structure of secondary lysosomes within the digestive cells, resulting in the formation of large lysosomes, believed to be autolysosomes. Stereological analyses showed that these lysosomes are reduced in numbers and greatly increased in volume in comparison with controls. There is a concomitant increase in surface area of lysosomes per unit volume of digestive cell compared with control conditions. These alterations are indicative of fundamental changes in secondary lysosomal function involving an autophagic response to oil derived hydrocarbons. which would contribute to the reduction of digestive cell cytoplasm. These cellular alterations are discussed in terms of their use as indices of cell injury, in response to oil.

The Nematode-Copepod Ratio And Its Use In Pollution Ecology

The nematode/copepod ratio is critically examined with a view to adding some precision to its proposed use in pollution ecology. At two unpolluted intertidal sites, differing markedly in sediment grade, the metabolic requirements of copepods are shown to be equivalent to the requirements of that fraction of the nematode population which feeds in the same way. The partitioning of this total energy requirement among individuals depends on the distribution of individual metabolic body sizes and the relative rates of metabolism. The distribution of body sizes is constrained by the sediment granulometry, which affects nematodes and copepods differently. These considerations enable precise predictions of the nematode/copepod ratios expected in unpolluted situations, against which observed ratios can be compared.