Relationships between invertebrate detritivores and gut bacteria in marine systems

Doctoral Thesis


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University of Cape Town

Aspects of the feeding strategies and digestive invertebrate-microbial interactions of two saltmarsh thalassinid detritivores, the mudprawn Upogebia africana (Ortmann) and the sandprawn Callianassa kraussi Stebbing were examined. Resources available in their respective habitats were investigated together with the feeding apparatus, diet and digestive enzymes necessary for hydrolysis of refractory compounds of detritus. U. africana inhabits the upper reaches of Langebaan lagoon (Geelbek),. while C. kraussi was sampled near the mouth (Oesterwal). Both species occur intertidally. Physical characteristics of sediment and water fluctuate more widely at Geelbek than at Oesterwal. Geelbek also has higher mud and clay content in the sediment, and greater particulate load in the water. The resources available in both sediment and water from Geelbek were of greater quality (assessed by proportion of living component, C:N ratio) and quantity. In terms of distribution ofthe resource, quality was highest in surface sediments, while quality was greatest at burrow linings. The mode of feeding, gut structure and diet of the two prawn species differ, although gut throughput rates are similar (ca. 6h). U. africana is a filter feeder which non-selectively ingests small particles which are further sorted in the modified filtertype gastric mill into larger particles which enter the midgut, and smaller particles which are channeled into the hepatopancreas. U. africana has a relatively large throughput gut (fore, mid, hind) allowing large meals to be taken. This may be related to its reliance on vascular plant detritus for both carbon and nitrogen requirements, as shown by stable isotope analyses. By contrast, C. kraussi feeds by a combination of deposit feeding and filter feeding.