Edinburgh Napier University

  Competent larvae of most benthic marine invertebrates including brachyuran decapod crustaceans can delay their settlement and metamorphosis in the absence of suitable environmental cues. This however may carry significant costs for the post-larval performance and fitness of early benthic juveniles. In this paper, we examined in the laboratory whether delayed larval metamorphosis affects early juvenile performance of the mangrove crab Ucides cordatus, measured as survival and growth through the first five juvenile crab stages (JI–JV). We further investigated whether ‘carry-over’ effects of an extended larval period vary intraspecifically among juveniles from three different hatches (F1–F3). Ucides megalopae were cultivated in two treatments. In the first one, the control, megalopae were cultivated continuously in exposure to conspecific crab odours (adult-conditioned seawater = ACSW) until moulting to the first juvenile crab stage. In the second, the delay-treatment, settlement-competent megalopae were kept for 20 days in pure filtered seawater without metamorphosis-triggering odours. From day 21 onwards, megalopae were transferred to ACSW to induce larval moult. The results showed that delayed metamorphosis affects early juvenile survival and growth of U. cordatus. In the delay-treatment, survival rates of juveniles (JI–JV) from F1–F3 were 11–31% lower and intermoult development periods 1.5–4.2 days longer than in the control. Delayed juveniles (F1–F3) exhibited 9.2–14.1% smaller body sizes (carapace width) and 1.4–3.9% lower growth rates mostly in the first two moulting events compared to specimens derived from non-delayed megalopae. Most of the detrimental effects were observed in almost all five crab stages studied, indicating that the costs of delayed metamorphosis may persist throughout early juvenile development. Juvenile morphology, however, was not affected. Our study also showed that carry-over effects of delayed larval moult vary intraspecifically among offspring produced by different females. This plasticity in phenotypic effects could relate to differences in the nutritional state, health or age of the females, to stressful environments during embryogenesis or to genetic differences. The observed carry-over effects of delayed settlement on early juvenile performance may affect the overall recruitment success and population dynamics of U. cordatus. In the field, such a situation would appear when new mangrove areas void of conspecific crabs are colonized or when degraded sites are re-populated by larvae originating from elsewhere populations.