Bucephaloides-Gracilescens - A Quantitative Study Of The Lysosomal Cellular Stress Response Induced By The Sporocysts And Developing Cercariae Within The White Furrow Shell Abra-Alba

Reproductive stress is apparent inAbra alba as a result of infection with the sporocysts ofBucephaloides gracilescens, culminating in castration in heavily infected specimens. The bivalve is also subject to mechanical stress from actively growing sporocyst tubules and nutritional stress due to the nutrient requirement of large numbers of germ balls within the sporocysts. Using the digestive cell lysosomal system ofAbra as a monitor, it was possible to demonstrate quantitatively a parasite-induced cellular stress response by applying a sensitive cytochemical test for lysosomal stability. Lysosomal stability was determined as the labilisation period for latent Nacetyl-β-hexosaminidase (NAH), measured by microdensitometry. In uninfectedAbra, digestive cell lysosomal NAH expressed structure-linked latency. Hence a significantly longer labilisation period was required compared with infectedAbra, where the parasitic burden with its associated stress effects resulted in a destabilisation of the lysosomal membrane. This reduced the latency of the enzyme, so that a much shorter labilisation period was required for the stressed tissue to express maximum lysosomal enzyme activity. It is suggested that the lysosomal system of the digestive cells inAbra can be used as a sensitive monitor of the stress induced by the sporocysts and developing cercariae ofBucephaloides.

Measurement Of The Responses Of Individuals To Environmental-Stress And Pollution - Studies With Bivalve Mollusks

Certain physiological differences between individuals in different populations of the mussel, Mytilus edulis, are described. In particular, the scope for growth differs in space and time and may be used to assess the animals' physiological condition. When the required measurements are made in the field, the rates of growth predicted from the physiological data agree well with observed rates of growth. An alternative approach utilizes mussels transplanted to various waters, with indices of condition then measured in the laboratory under standard conditions; an example of this approach is illustrated. Laboratory experiments are used to equate various levels of physiological condition with fecundity, in an attempt to equate physiological effects on the individual with likely population damage. A cytochemical index of stress is described, based on the latency of lysosomal enzymes; spatial variability in this index, and its relation with the scope for growth, are discussed. Finally, the results of some experiments on the effects of petroleum hydrocarbons on mussels are described and the presence of inducible activity of NADPH-dependent tetrazolium reductase in the blood cells is demonstrated. Certain considerations that apply in adopting similar measurements of biological effects of pollution in environmental monitoring programmes are discussed.

Physiological Indexes Of Stress In Mytilus-Edulis

Multiple regression equations and response surfaces are used to describe the combined effects of body size, food concentration, acclimation temperature and season on physiological integrations such as the scope for growth, growth efficiency and O:N ratio. Maintenance and optimum ration levels are estimated for Mytilus edulis adapted to different factor combinations. Response surfaces illustrate the validity and sensitivity of the physiological integrations in quantifying the 'physiological condition' and the degree of stress experienced, under conditions ranging from near-optimal, through sub-lethal to lethal.

The combined effects of seasonal community succession and adaptive algal physiology on lipid profiles of coastal phytoplankton in the western English channel

Lipids are key constituents of marine phytoplankton, and some fatty acids (key constituents of lipids) are essential dietary components for secondary producers. However, in natural marine ecosystems the interactions of factors affecting seasonal phytoplankton lipid composition are still poorly understood. The aim of this study was to assess the roles of seasonal succession in phytoplankton community composition and nutrient concentrations, on the lipid composition of the phytoplankton community. Fatty acid and polar lipid composition in seston was measured in surface waters at the time series station L4, an inshore station in the Western English Channel, from January to December 2013. Redundancy analyses (RDA) were used to identify factors (abiotic and biotic) that explained the seasonal variability in phytoplankton lipids. RDA demonstrated that nutrients (namely nitrogen) explained the majority of variation in phytoplankton lipid composition, as well as a smaller explanatory contribution from changes in phytoplankton community composition. The physiological adaptations of the phytoplankton community to nutrient deplete conditions during the summer season when the water column was stratified, was further supported by changes in the polar lipid to phytoplankton biomass ratios (also modelled with RDA) and increases in the lipid to chlorophyll a ratios, which are both indicative of nutrient stress. However, the association of key fatty acid markers with phytoplankton groups e.g. 22:6 n-3 and dinoflagellate biomass (predominant in summer), meant there were no clear seasonal differences in the overall degree of fatty acid saturation, as might have been expected from typical nutrient stress on phytoplankton. Based on the use of polyunsaturated fatty acids (PUFA) as markers of ‘food quality’ for grazers, our results suggest that in this environment high food quality is maintained throughout summer, due to seasonal succession towards flagellated phytoplankton species able to maintain PUFA synthesis under surface layer nutrient depletion.