Aspects of Sesarma catenata (Grapsidae, Crustacea) burrows and its implications in the event of an oil spill

Abstract

The shape and dimensions of Sesarma catenata crab burrows were determined by means of polyester resin casts. Relationships between burrow entrance size and volume as well as burrow entrance size and size of the occupant crab were established. The ‘average’ crab burrow penetrated into the mud by a distance of 11·34±3·02 cm from the surface at an angle of 55·5° resulting in a depth of 8·94±3·54 cm with a volume of 15·68±9·50 ml. The drainage rates of artificial crab burrows were determined and it was established that, depending on distance from the salting cliff, these burrows were between 48·5% and 22·9% full of water at the end of the tidal cycle. The natural crab burrows contained between 0% and 5% water at this stage. The crab burrows penetrated an average of 14·9% of the distance between the surface and the sea water level. In the event of an oil spill the crabs will come into direct contact with the oil when the water drains from the burrows during the ebbing tide or when they climb out of the burrow under conditions of increasing hypoxia. This carapace contamination by oil will result in adverse effects on the physiology and behaviour of these crabs.