Effects of temporary starvation and feeding on the survival and developmental time to metamorphosis in megalopa larvae of two Neotropical mangrove crab species, genus Sesarma (Sesarmidae)

Abstract

Temporal variation in pelagic food supply may affect the larval development and recruitment success of many decapod crustaceans in marine coastal ecosystems. In the present study, we experimentally investigated the degree of nutritional vulnerability in megalopa larvae of two sesarmid crab species (Sesarma curacaoense and S. rectum) subjected to different conditions of nutritional stress. In the laboratory, Sesarma megalopae were initially starved for up to 9days followed by a constant feeding period in one experiment (i.e., point of no return), or they were fed at the beginning of their development for up to 9days followed by a continuous period of food deprivation in a second experiment (i.e., point of reserve saturation). Megalopae were also constantly reared in the absence and presence of food (Artemia sp. nauplii) in two control groups. The larval response to the different experimental conditions was evaluated through the percentage of survival (=% metamorphosed larvae), developmental time to metamorphosis, and Nutritional Vulnerability Index (= PRS50/PNR50). All megalopae died when reared under constant starvation whereas 100% of the larvae metamorphosed into the first juvenile crab stage after 13.1±4.4days (S. curacaoense) or 12.4±1.2days (S. rectum) when continuously fed. In the first experiment, the starvation periods did not affect the mean developmental time of the megalopae through metamorphosis (13.6±4.3days) of S. curacaoense and only those larvae initially starved for 7days presented the lowest percentage of metamorphosis to juvenile crab (73%). In S. rectum, by contrast, megalopae starved from 5 to 9days exhibited lower percentages of metamorphosis (≤86%) compared to larvae starved for 1 or 3days or those constantly fed. Furthermore, megalopae starved for 7 and 9days delayed by 1.6 and 3.5days their metamorphosis, respectively, compared to larvae constantly fed. In the second experiment, the Sesarma megalopae initially fed for only 1day presented lower percentages of metamorphosis (≤73%) than megalopae fed for 3 or more days or continually (≥93%). The mean developmental time to metamorphosis was shorter with 1day (8.1±0.7days in S. curacaoense) or 3days (11.3±1.6days in S. rectum) of temporary feeding. The estimated values of the PNR50 and PRS50 indices were respectively 7.34 and 0.93days for S. curacaoense and 9.01 and 1.78days for S. rectum. These values provided a Nutritional Vulnerability Index of 0.13 for S. curacaoense and 0.2 for S. rectum, indicating a reduced dependence on exogenous food by the megalopae of these two sesarmid crab species. This starvation tolerance associated with a short megalopal development should increase the likelihood of successful survival into the benthic life phase and avoid latent effects of the larval nutritional stress and/or delayed metamorphosis on early juvenile performance of both Sesarma species.