The crystalline style of Choromytilus meridionalis Krauss contains a bacteriolytic enzyme capable of lysing the majorlty of free-living bacteria in the adjacent water column. Estimates of the carbon-to-nitrogen ratio (3.7:l) of free-living bacteria, and of the filtration capabilities of the mussels. indicate that bacteria could meet the nitrogen requirements of the mussels. The bacteriolytic agent in the style is subject to considerable adaptive changes in activity, correlated with water temperature.Water temperatures < 10°C are associated with ~nduction of the bacteriolytic agent. During upwelling, cold water depleted in particulate matter but containing significant numbers of bacteria occurs commonly amongst the kelp beds. It is suggested that low water temperature (or an associated environmental parameter) results in stimulation of bacteriolysis. This in turn permits efficient utilisation by the mussel of free-living bacteria which compensate for the depletion of phytoplankton available in the water column.

Bacteria in kelp-related ecosystems on the west coast of South Africa were isolated using random sampling techniques. The percentage of bacteria forming colonies on solid media was determined. The population composition in 4 adjacent habitats was determined by morphological and physiological criteria. These data were analysed by cluster analysis using the Bray-Curtis measure of similarity. Isolates from inshore waters were able to ferment a wide range of kelp-derived products, whereas offshore isolates had a more restricted spectrum of fermentable substrates. The similarity analysis indicates that bacteria isolated from the 4 adjacent hab~tats are essentially different. It is suggested that bacterial assemblages in adjacent habitats segregate into discrete populations in response to physical, chemical and biological factors.

Digestive enzymes of the anchovy Engraulis capensis in relation to diet' Department of Microbiology, University of Cape Town, Rondebosch 7700, South Africa Institute for Marine Environmental Research, Prospect Place, Plymouth PL1 3DH, United Kingdom ABSTRACT: The anchovy Engraulis capensis (Glch.) is capable of exploiting both diatoms and Crustacea as a food resource. Much of the crustacean exoskeletal rnatenal passes into the hindgut after initial dsruphon in the stomach. Both laminarinase and cl-amylase activity are relatively low in the oesophagus and stomach, but increase in the caeca and lumen of the intestine. There is no evidence of cellulolytic activity in the gut although numerous gut bacteria occur in the caeca and lumen of the intestine. Distribution of protease activity in the gut follows that of carbohydrases, most proteolytic activity being present in the lumen of the intestine, rather than in the oesophagus or stomach. In contrast, chitinase activity is found early in the digestive pathway and is capable of attacking the chitinous exoskeleton of Crustacea in the stomach, prior to hydrolysis of their contents by carbohydrases and proteases. Bacteria isolated from the intestinal caeca do not hydrolyse chitin, nor do they degrade long-chain polysaccharides or azocasein. Most of the isolates were capable of utilisation of simple sugars cornnlonly found in diatoms and released following hydrolysis of polysaccharides, and also of utilisation of N-acetylglucosamine formed as an endproduct of chitin hydrolysis. Anaerobic strains were, In addition, capable of urea utilisation. Our data thus suggest that digestive enzymes allow E capensjs to exploit a wide range of food items, including diatoms and Crustacea, without bacterial involvement. The gut rnicroflora may be primarily maintained by uptake of the endproducts of carbohydrate, protein and chitin degradation.