MEPS 347:1-14 (2007)  -  DOI: https://doi.org/10.3354/meps07054

ABSTRACT: The reworking of sediments by callianassid sandprawns has important effects on the adults of soft-bottom macrofaunal communities; however, its influence on juvenile stages has been neglected, even though this may dictate the composition of adult assemblages. We examined the effects of the southern African sandprawn Callianassa kraussi to test the hypotheses that (1) C. kraussi negatively affects juvenile recruitment and inhibits microbial biofilms on the sediment, and (2) depletion of microbial biofilms will in itself diminish juvenile recruitment. Comparisons between areas of high and low C. kraussi density in addition to field caging experiments demonstrated a significant retardation of biofilm development and recruitment of juvenile macrofauna by C. kraussi. Juvenile assemblages in sediments where C. kraussi was absent or rare differed significantly from those in which C. kraussi was abundant, with greater densities of suspension- and subsurface-feeding polychaetes and bivalves in cases where C. kraussi was rare or absent. Total abundance, taxonomic richness and diversity of juveniles were also significantly greater in cases where C. kraussi was rare. Experimental manipulation of sediment microbial films showed that biofilmed sediments had significantly different assemblages from unfilmed ones, with abundance, richness and diversity of recruits being significantly greater in biofilmed sediments. The effect of C. kraussi on juveniles of the macrofauna, apparently brought about via its effects on biofilms, emerges as one of the primary mechanisms structuring macrofaunal communities. The effects of sandprawns on juvenile stages must be considered if we are to understand the role of sandprawns in structuring soft-sediment assemblages.

KEY WORDS: Callianassa · Bioturbation · Juvenile · Recruitment · Microbial biofilm