Recruitment of Homalaspis plana in intertidal habitats of central Chile and implications for the current use of Management and Marine Protected Areas

Information about the life history of the stone crab Homalaspis plana was n ecessary to investigate the possible reasons for the failure of Marine Prot ected Area (MPA) and Management and Exploitation Area (MEA) in increasing s tone crab abundance, in contrast with other exploited benthic species. In t his study, we analyzed some aspects of the early Life history of the stone crab, focusing especially on (1) recruitment patterns among habitats and be tween years in intertidal zones, (2) habitat preferences, including some in tra- and interspecific interactions that may affect habitat use, and (3) in traspecific interactions that may affect survival. We also evaluated the pe rcent cover of suitable habitats for juvenile stone crabs in a MPA and a ME A. Sheltered habitats showed higher densities of juvenile H, plana than exp osed areas, and sand with boulders showed the highest crab densities, follo wed by shell hash with boulders. Differences in mean densities were detecte d for all benthic stages among sheltered substrates, except for megalopae. Bare substrates (without boulders) showed the lowest density. Throughout th e settlement period, abundance of smaller instars (<J2) was 3 times higher in 1995 than in 1996, while densities of >J4 were twice as high in 1996 tha n in 1995. Neither intra- nor interspecific space competition seems to expl ain the distribution of juvenile stone crabs in the field. However, canniba lism among juveniles may have an important effect on survival. Cannibalism among juveniles is density-dependent, and may have greater effects as the a bundance of larger conspecifics increases since mutual interference does no t affect proportional prey mortality per predator. We suggest that losses a re high in low quality habitats (probably through emigration, predation or habitat disturbance due to wave impact), and cannibalism is an important so urce of mortality in high quality habitats (where crab density is high). Al though substrate type and post-settlement processes can help explain the di stribution of juvenile stone crabs, wave action seems to be the major deter minant of juvenile distribution. Neither sheltered habitats nor the most su itable substrate are common in the MPA and MEA studied. These factors are n ot currently being considered in the assignation of MEAs or planning of MPA s, although they could explain the lack of effect of both protection strate gies in increasing the abundance of the stone crabs in Chile in comparison to other exploited benthic species.