Effects of substrata and conspecific odour on the metamorphosis of mangrove crab megalopae, Ucides cordatus (Ocypodidae)

Abstract

Environmental cues associated with the adult habitat induce metamorphosis in many marine invertebrate larvae and thus settlement in a place appropriate for completing their life-cycle. Ucides cordatus is a semi-terrestrial crab that exemplifies organisms living in mangrove estuaries as adults, but whose larvae develop offshore and return to the estuarine environment prior to metamorphosis. We investigated the influence of substrata (burrow mud, channel-bank mud, dead wood, sand, nylon mesh) and conspecific adult cues (crab conditioned seawater) on metamorphosis and the duration of the megalopal phase. Our results suggest that U. cordatus megalopae settle in areas populated by conspecific crabs and/or muddy habitats. High moulting rates were observed in the treatments with mud and/or adult odour (67-91 %), whereas in the other substrata treatments and in the seawater control less than 20% and 5% of the megalopae metamorphosed, respectively. Megalopae are also capable of delaying metamorphosis. Over channel bank mud they moulted 8 days later at an average, compared to the treatment with crab conditioned seawater. Such a delay could result in a reduced juvenile fitness. In seawater control almost all megalopae died prior to metamorphosis, without moulting spontaneously as observed in other species. This reflects the crucial importance of habitat cues for the settlement and recruitment of this ecologically and economically important species. We outline the necessity of future research concerning post-metamorphic carry-over effects, the possible role of biofilms in absorbing and/or producing settlement cues, as well as the question whether the megalopae react specifically to the odour of U. cordatus, or also to other species. The latter is of particular interest against the background of the spreading lethargic crab disease that results in massive mortalities of U. cordatus, but not of co-occurring-species.

First field record of mangrove crab Ucides cordatus (Crustacea: Decapoda: Ucididae) recruits co-inhabiting burrows of conspecific crabs

“…Recent laboratory experiments showed that chemical cues emitted by conspecific crabs, regardless of gender, enhance the survivorship and induce the settlement of U. cordatus megalopae (DIELE & SIMITH 2007, SIMITH & DIELE 2008. As U. cordatus odour concentrations are likely to be higher inside conspecific burrows than outside, settlement may indeed occur more frequently (or exclusively?)…”

Mangrove expansion into temperate marshes alters habitat quality for recruiting Callinectes spp.

“…Conspecific cues enhance settlement and metamorphosis (Forward et al 2001, Diele & Simith 2007, while predator cues generally reduce metamorphosis or accentuate habitat choices (Moksnes et al 1997, Welch et al 1997. If the juvenile cue treatment was perceived as conspecifics, we would have expected settler distributions to remain even among habitat types.…”

Distribution patterns of the crab Ucides cordatus (Brachyura, Ucididae) at different spatial scales in subtropical mangroves of Paranaguá Bay (southern Brazil)

“…These may be related to the patchy distribution of microhabitats, small-scale changes in environmental conditions, behavior and competition. For example, habitat choice and recruitment of U. cordatus megalopae are strongly induced by environmental cues associated with the presence of conspeciWc crabs and muddy sediments (Diele and Simith 2007), which is likely to be more important in regulating patterns of distribution at small scales. Other small-scale processes, such as intraspeciWc competition, may explain the diVerences in the spatial patterns of non-commercial and commercial size crabs, since large crabs apparently exclude smaller ones from preferred habitats (Piou et al 2009).…”