Ecology and behaviour of burrowing prawns and their burrow symbionts

Abstract

Ecosystem engineers play important roles as determinants of community dynamics by modulating resource availability for other species. Marine soft-sediment ecosystems are dominated by burrowing engineers which indirectly create biogenic structures that often attract other species, often leading to the evolution of symbiotic relationships. Engineered structures provide non-trophic (e.g. refuge) and trophic functions (e.g. food) for burrow symbionts, however, the relative importance of these functions for symbionts is poorly understood. The behavioural interactions between burrowing engineers and their burrow symbionts are also poorly understood, mainly due to the difficulty in conducting behavioural observations in situ. This study aimed to enhance our understanding of the ecological processes and behavioural interactions underlying symbiotic relationships between a dominant South African ecosystem engineer (Callianassa kraussi) and its burrow symbiont (Betaeus jucundus) in soft sediment systems in Langebaan Lagoon. The study specifically quantified the relative importance of host abundance (a proxy for non-trophic functions) and food availability (trophic functions) provided by burrows of C. kraussi in influencing the abundance and distribution of B. jucundus. The second aim was to quantify behavioural changes of C. kraussi in the presence and absence of the symbiont B. jucundus and determine if the sex of C. kraussi influences its behavioural response to B. jucundus. Results indicate that at a patch scale, trophic functions (food availability) provided by burrows was more important than non-trophic functions in determining symbiont abundance and distribution. However, at an ecosystem scale, non-trophic functions could be a very important determinant of symbiont abundance and distribution. In terms of behavioural interactions, the presence of B. jucundus elicited three distinct behavioural responses from C. kraussi: intolerance, semitolerance and tolerance. In the absence of B. jucundus, there was no difference between male and female C. kraussi behaviour but this pattern changed in the presence of B. jucundus. Overall, the study has contributed to increasing our understanding of ecological processes that determine the abundance and distribution of burrow symbionts in marine soft-sediments as well as behavioural interactions between burrowers and their symbionts.