title: The influence of simulated exploitation on Patella vulgata populations: protandric sex change is size-dependent.
abstract: Grazing mollusks are used as a food resource worldwide, and limpets are harvested commercially for both local consumption and export in several countries. This study describes a field experiment to assess the effects of simulated human exploitation of limpets Patella vulgata on their population ecology in terms of protandry (age-related sex change from male to female), growth, recruitment, migration, and density regulation. Limpet populations at two locations in southwest England were artificially exploited by systematic removal of the largest individuals for 18 months in plots assigned to three treatments at each site: no (control), low, and high exploitation. The shell size at sex change (L 50: the size at which there is a 50:50 sex ratio) decreased in response to the exploitation treatments, as did the mean shell size of sexual stages. Size-dependent sex change was indicated by L 50 occurring at smaller sizes in treatments than controls, suggesting an earlier switch to females. Mean shell size of P. vulgata neuters changed little under different levels of exploitation, while males and females both decreased markedly in size with exploitation. No differences were detected in the relative abundances of sexual stages, indicating some compensation for the removal of the bigger individuals via recruitment and sex change as no migratory patterns were detected between treatments. At the end of the experiment, 0-15 mm recruits were more abundant at one of the locations but no differences were detected between treatments. We conclude that sex change in P. vulgata can be induced at smaller sizes by reductions in density of the largest individuals reducing interage class competition. Knowledge of sex-change adaptation in exploited limpet populations should underpin strategies to counteract population decline and improve rocky shore conservation and resource management.
authors: Centre for Biological Sciences University of Southampton Life Sciences Building 85, Highfield Southampton SO17 1BJ UK; Centro Interdisciplinar de Investigação Marinha e Ambiental, CIIMAR-Porto Laboratório de Biodiversidade Costeira Rua dos Bragas, 2894050-123 Porto Portugal; The Marine Biological Association of the United Kingdom The Laboratory, Citadel Hill Plymouth, Devon PL1 2PB UK.
authors: Carla D G
authors: CD
authors: Borges
authors: Centre for Biological Sciences University of Southampton Life Sciences Building 85, Highfield Southampton SO17 1BJ UK; The Marine Biological Association of the United Kingdom The Laboratory, Citadel Hill Plymouth, Devon PL1 2PB UK; Ocean and Earth Science National Oceanography Centre University of Southampton Waterfront Campus European Way Southampton SO14 3ZH UK.
authors: Stephen J
authors: SJ
authors: Hawkins
authors: Centre for Biological Sciences University of Southampton Life Sciences Building 85, Highfield Southampton SO17 1BJ UK; Earth Institute and School of Biology and Environmental Science University College Dublin Belfield Dublin 4 Ireland.
authors: Tasman P
authors: TP
authors: Crowe
authors: Centre for Biological Sciences University of Southampton Life Sciences Building 85, Highfield Southampton SO17 1BJ UK.
authors: C Patrick
authors: CP
authors: Doncaster
keywords: Human exploitation; limpets; protandry; sex change; size at sex change; size‐selective harvesting