A long-term symbiotic relationship: Recruitment and fidelity of the crab trapezia on its coral host pocillopora

Abstract

The symbiotic relationship between the crab Trapezia spp. and pocilloporid corals has been characterized as obligate. Although this relationship is considered common and has been widely registered within the distribution areas of these corals, the initiation of this symbiotic relation and its potential persistence throughout the life cycle of the crustacean is still poorly described. To un-derstand the Trapezia–Pocillopora symbiosis, determining the time and conditions when Trapezia re-cruits a coral colony and the factors influencing this process are key. Thus, in the present study, healthy, small and unrecruited coral fragments were attached to the substrates (using cable ties) of nearby adult Pocillopora colonies. All fragments were monitored for two years to measure their growth and size at the first evidence of Trapezia crab recruitment, as well as the abundance and permanence of the crabs on the coral fragments. Results showed a relation between the space available (coral volume) and crab recruitment as an increase in substrate complexity is required to pro-vide protection for the crabs and hence maintain the symbiosis, while abiotic conditions such as sea temperature and the distance of the fragments from the adult coral colonies seemingly did not affect the recruitment process. In addition, crabs are able to move between colonies, thus discarding the theory that once recruited, crabs are obligate residents on this specific colony.