Reproduction strategies and population dynamics of two Diogenes hermit crabs (Superfamily: Paguroidea) in a tropical mangrove estuary

Two species of sympatric hermit crab, Diogenes moosai Rahayu & Forest, 1995 and D. lopochir Morgan, 1989, spatially defined in the Matang mangrove estuary, and facing high mortality due to tidal emersion, predation and competition are hypothesised to adopt different reproductive strategies for successful recruitment. The crabs were sampled by a small otter trawl at mid-estuary, river mouth, mudflat and shoal area along the estuary to adjacent coastal area. Diogenes moosai was widespread in the mudflat as well as in the subtidal shoal area where D. lopochir was dominant. Diogenes moosai showed year-round reproduction, whereas D. lopochir a discontinuous spawning pattern. Major reproduction in both species, however, occurred in January/February and July which resulted in two major recruitment pulses in a year. Diogenes moosai also suffered very high mortality resulting from cockle harvesting on the mudflat, twice that of D. lopochir. Our results show that the more widespread species at higher risk of exposure to extreme physical conditions (in the mudflat), predation and competition for shell resources, generally spreads its reproduction over the year, while the dominantly subtidal species at greater risk of predation only reproduces less regularly but at the most favourable period.