Mangrove sesarmid crab feeding experiments in Peninsular Malaysia

Abstract

The feeding ecology of mangrove sesarmid crabs in Peninsular Malaysia was investigated by field and laboratory experiments using four mangrove leaf species ( Avicennia officinalis, Bruguiera gymnorrhiza, B. parviflora and Rhizophora apiculata) and leaves of different condition (fresh and senescent). Leaves tethered on strings at high ( Bruguiera zone) and low ( Rhizophora zone) intertidal positions, both upstream (Sungai Pasir) and downstream (Lower Merbok) showed significant amounts of leaf litter removal in 24 h (mean 79±3% initial dry mass). Significantly more B. gymnorrhiza was consumed in Bruguiera zones and significantly less senescent A. officinalis in the upstream Rhizophora zone. In Bruguiera zones, significant numbers of leaves were taken down burrows but there were no preferences for leaf species or condition of leaf taken down burrows at all sites. In 24 h, under laboratory conditions, the sesarmid crabs Sesarma (Perisesarma) eumolpe and S. (Perisesarma) onychophorum were offered with a mangrove species choice of either fresh or senescent leaves. There was no difference in mangrove species taken when the leaves were senescent for both crab species, but when the leaves were fresh, significantly more A. officinalis leaves were consumed by both sesarmid crab species. S. onychophorum ate significantly more B. parviflora than did S. eumolpe. The crab distribution in the field was related to the preferred tree species dominance, indicating that tree species may be important for crab species distribution, or vice versa. The mean rate of leaf consumption was not significantly different between the crab species; S. eumolpe was 29.9±5.9 and S. onychophorum was 35.3±7.2 mg dry mass per wet mass gram of crab in 24 h. Rhizophora spp. were the least preferred species in all feeding experiments, a finding which may have implications for ecosystem functioning in monoculture rehabilitation projects.