Recruitment limitation and competent settlement of sesarmid crab larvae within East African mangrove forests

Abstract

The functioning of many ecosystems is highly dependent on their faunal communities, dominated by brachyuran crabs. Key to the maintenance of crab populations are the factors that influence their recruitment into the system, particularly the settlement of their megalopae. While spawning is normally highly synchronised, settlement is often not, implying temporal disruption between spawning and settlement. We examined the roles of several key factors (vegetation type, day/night cycle, and lunar phase) on settlement, testing for generality by working in mangroves at 2 sites in Kenya and South Africa. At each site, larval settlement was quantified using artificial collectors placed in 2 vegetation zones for 12 h periods throughout the part of the neap-spring tidal cycle when tide was sufficient to cover the collectors. This continued for 6 mo in Kenya and 11 mo in South Africa, giving the first long-term settlement dataset for east African mangroves. Moon phase proved to have a major role in megalopal settlement, which demonstrated a high degree of spatial specificity. Settlement was correlated across species with tidal amplitude on both short (monthly) and long time scales and focussed on the vegetation zones occupied by conspecific adults. As the distribution of mangrove species is tightly related to local hydrology, this implies a feedback situation with the conservation of mangroves requiring the maintenance of patterns of water flow within the system to support both the vegetation and the associated fauna.

Response of Fish and Invertebrate Larvae to Backreef Sounds at Varying Distances: Implications for Habitat Restoration

“…The PERMANOVA indicated that larval assemblages differed between moon phases and mean settlement was greater during full moon overall, though this was likely driven by a few individual taxa, particularly the clam Lima. Marine organisms such as corals (Harrison et al, 1984;Brady et al, 2016) and fish (Farmer et al, 2017) use the lunar cycle to time the release of larvae, many of which settle around specific moon phases [fishes-bluehead wrasse (Victor, 1986); damselfish and surgeonfish (Sponaugle and Cowen, 1996), decapods-crabs (Cannicci et al, 2019), lobster (Acosta et al, 1997)].…”

Diversity, phylogeny and DNA barcoding of brachyuran crabs in artificially created mangrove environments

“…During flooding and competent larvae settling, brachyuran crab larvae are transported into mangrove ecosystems (Epifanio, 1995). Most brachyuran crab larvae were highly competent in locating conspecific adults colonizing the forest area (Cannicci et al, 2019). Parasesarma capensis is more abundant in the Rhizophora mucronata characterized areas (Fratini et al, 2019).…”

“…Parasesarma capensis is more abundant in the Rhizophora mucronata characterized areas (Fratini et al, 2019). During settlement and colonization, different species of brachyuran crab larvae prefers different mangrove species (Cannicci et al, 2019).…”

Settlement patterns of two sesarmid megalopae in the Sai River Estuary, Ishikawa Prefecture, Japan

“…In addition, the larval recruitment processes of benthic invertebrates remain unclear (Hasek & Rabalais 2001, Pineda et al 2010. Since the larvae of sympatric Decapoda species, such as C. haematocheir and C. dehaani are difficult to identify morphologically and are treated as congeneric species, interspecific differences in their larval recruitment processes are not well understood (Baba & Miyata 1971, Epifanio et al 1988, Oh et al 2007, Anger 2006, Cannicci et al 2019. Recent studies have shown the effectiveness of genetic analyses for identifying morphologically similar crustacean species (Radulovici et al 2009, Raupach et al 2015.…”

“…Megalopa samples collected from the river were identified based on DNA sequencing. Sesarmid crab megalopae have been reported to return to areas near their adult habitats (Paula et al 2003, Cannicci et al 2019. Therefore, we also investigated the distribution of the adults of each species within the land area adjacent to the river during their active period, based on the hypothesis that megalopa larvae will return to an environment dominated by adults of the same species.…”