Adaptive traits in ecology, reproduction and early life history of Sesarma meridies, an endemic stream crab from Jamaica

Abstract

The endemic Jamaican freshwater crab Sesarma meridies lives in shady microhabitats on river banks, where temperature and pH are lower and ion concentrations higher than in mid-stream water. Ovigerous females were found to release up to 140 yolk-rich larvae (hatching period: 1 week; >90% at night). Larval development comprised two fully lecithotrophic zoeal stages and a feeding megalopa, which was also able to develop without food (facultative lecithotrophy). After metamorphosis in complete absence of food, juvenile crabs showed reduced body size, delayed moulting, and enhanced mortality. Endotrophic development was fuelled by internal lipid reserves; proteins were conserved as structural components of tissues and organs. Fed megalopae enhanced their protein content rather than re-stocking previously lost lipid reserves. Ecdysial biomass (CHN) losses were very low (zoeal stages: 1–2%; megalopa: 3–7%), showing an energy-saving production of thin exuviae. An extended hatching period may reduce intraspecific competition or cannibalism among juveniles; nocturnal hatching should reduce the predation on larvae. Large egg size, enhanced yolk reserves, an extended embryonic development (7 weeks at 24°C; implying a prolonged period of brood care), abbreviated and partially food-independent larval development, and reduced exuvial losses are considered as life-history adaptations to unpredictable planktonic food availability in the breeding habitat.