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The class Bivalvia is of interest to ecologists studying pollution as it comprises sedentary filter-feeding invertebrates which accumulate pollutants from the environment. In particular mussels have been popular material for experimental studies. They are resistant to a wide variety of environmental conditions and they show a marked capacity to adapt to extremes of environmental change. Some aspects of the physiology of the mussel (Mytilus edulis) were studied in the first part of this thesis. The methods available to determine mussel pumping rate and filtration rate were modified and the resultant data compared with published information. These studies showed that the two bacteria Serratia marcescens and Bacillus subtilis var. niger were retained efficiently by Mytilus edulis during laboratory experiments. M. edulis from a mussel bed on a sewage polluted shore were sampled after separate release of the same two tracer bacteria and the temporal and spatial distribution from the point source were determined. The concentration by the mussels of S. marcescens and of B. subtilis var. niger was compared with their concentrations in the overlying water and with coliform distribution in the same area. Tracer bacteria were present in mussel tissue at higher levels than those existing in the water and detectable numbers were isolated from the shellfish for much longer periods. The higher numbers of tracer bacteria in mussel tissue were often associated with the higher coliform densities in the mussel tissue. These results were discussed in relation to some seasonal and climatic factors. Some aspects of the physiology of the tracer bacteria were studied, in particular the production of black pigment by B. subtilis var. niger L. Several media ingredients and cultural conditions were varied in an attempt to enhance this black pigmentation. In particular, the effects produced by yeast extract, trace elements, low nutrient levels and the absence of tyrosine were noteworthy. The new media which were devised caused all three strains of B. subtilis var. niger to yield maximum pigment density by all colonies within 48-72 hours. Pigment production was enhanced for spread plate, pour plate and membrane filtration technique.

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Studies on the growth dynamics and physiology of the paralytic shellfish toxin producing dinoflagellates <I>Alexandrium fundyense, A. minutum </I>and <I>Gymnodinium catenatum</I> were conduced under a number of different nutrient regimes, light, temperature and salinity levels. <I>G. catenatum</I> was very slow to respond to N-refeeding, with relatively low internal amino acid concentrations, a low glutamine:glutamate ratio, and a stable toxin content, showing little variation with N- and P-limitation or with decreased salinity. In contrast <I>Alexandrium</I> sp. respond to N-refeeding with an increased internal amino acid pool, an increased glutamine: glutamate ratio, especially with ammonium as a N-source, and an increased toxin content. P-limitation in <I>A. fundyense </I>leads to a significant increase in the toxin content but only when cells are also N-limited. Sub-optimal temperature and light levels lead to decreased growth rates: low temperature results in larger cells and an increased toxin content in <I>A. fundyense,</I> whilst the effect of low light on <I>A. minutum </I>cells varies with the N-source available. The N-uptake kinetics of <I>G. catenatum</I> revealed that the maximum uptake rates (V<SUB>mas</SUB>) and half-saturation constants (K<SUB>s</SUB>) for transport were higher for ammonium when compared with nitrate. In <I>A. funyense</I> values of K<SUB>s</SUB> were similar at 1 μM for both nitrate and ammonium whilst V<SUB>max</SUB> for the latter was up to 5-times greater. <I>A. fundyense</I> was shown to be able to utilize organic-N in the form of dissolved free amino acids. Maximum uptake rates of 0.85 pmol cell<SUP>-1</SUP> h<SUP>-1</SUP> occurred during exponential growth and differed from the uptake capabilities of other phytoplankton in that uptake was not enhanced by N- or C-stress. A preliminary model is presented and is capable of simulating the relationship between N-refeeding and P-limitation and cellular toxin content in <I>Alexandrium </I>sp.

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The edible cockle, <i>Cerastoderma edule, </i>is a marine bivalve of high commercial importance, in particular, in South Wales, UK. Similar to other commercial bivalves, <i>C. edule </i>can suffer mass mortality, resulting in multi-million pound losses to the fishing industry. Despite this major concern, little research has been devoted to the etiology of mass mortality. The present research characterises the immune defence reactions of <i>C. edule </i>and compares them with those of the marine mussel, <i>M. edulis </i>and the razor shell, <i>Ensis siliqua. </i>The effect of the polycyclic aromatic hydrocarbon, phenanthrene, on the immunocompetence of all three species was also investigated. In addition to providing valuable information on understanding disease and mass mortality, the research also helped establish whether <i>C. edule </i>is a suitable sentinel organism for environmental monitoring. Results showed that the immunocompetence of <i>C. edule </i>was of a lower level than <i>M. edulis,</i> but of higher level than <i>E. siliqua</i>, and this was also reflected in the differing susceptibility of the three bivalves to phenanthrene exposure. Further studies concentrated on the haemocytic encapsulation response of <i>C. edule</i>, the common immune defence reaction towards invading metazoan parasites. Studies on the dynamics of capsule formation revealed that non-specific electrostatic forces and humoral plasma factors play a synergistic role in haemocyte attachment and encapsulation. Finally, encapsulation-related proteins (ERPs), potentially involved in mediating encapsulation, were identified. One putative ERP, histone H3, was found to significantly affect haemocyte spreading, thus revealing novel roles for histone H3 in innate immunity, both in invertebrates and vertebrates.

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No description available.