Role of the sandprawn Callichirus kraussi as an ecosystem engineer in a South African temporarily open/closed estuary

The role of the sandprawn Callichirus kraussi as an ecosystem engineer was experimentally assessed using caging experiments over a four-month period in 2010 in the temporarily open/closed Kasouga Estuary on the south-eastern coast of South Africa. The sandprawn contributed to a significant increase in bioturbation, associated with a decline in microphytobenthic algal concentrations which coincided with a significant decrease in the abundance of the gastropod Nassarius kraussianus. The presence of the sandprawn did not contribute to a significant decline in sediment organic content, or to the abundance, biomass and species composition of the infauna, which comprised mainly amphipods, isopods and polychaetes. Nor did it contribute to a change in the macrofaunal community structure. The absence of any significant differences between the various treatments appears to reflect the low densities of sandprawns in the estuary during the study period.