MEPS 327:193-206 (2006)  -  doi:10.3354/meps327193

Mesoscale variation in reproduction, recruitment and population structure of intertidal mussels with low larval input: a bay/open coast comparison

C. D. McQuaid*, T. E. Phillips

Department of Zoology & Entomology, Rhodes University, Grahamstown 6140, South Africa

ABSTRACT: Several studies suggest invertebrate recruitment is affected by coastal configuration, implying effects on population structure. Mesoscale (1 to 100 km) variability in spawning and recruitment of intertidal mussels was examined at 12 sites on the South African south coast. There were 3 shore types: Algoa Bay shores (sandstone) and open coast shores (sandstone or dune rock). Timing of spawning and recruitment did not differ among shore types, but intensity did. All shores had continuous spawning and trickle recruitment, with peak periods. Spawning at each shore peaked 3 to 4 times per year with poor synchrony among sites, even sites only 3 to 4 km apart. Spawning correlated negatively with air and sea temperature, being most likely in winter/spring. Individual gamete output was greater in Algoa Bay. Recruitment was poorly pulsed and much lower than in most boreal studies; 1 to 2 juvenile cohorts appeared on each shore each year, with no synchrony among shores. Each cohort recruited over 2 to 3 mo. Subsequent mortality and growth were density independent, which suggested that pre-settlement factors are important in population regulation. New cohort densities correlated with spawning intensity, and were significantly greater in Algoa Bay. Spawning intensity, new cohort density, growth and mortality accounted for 76% of the variation in recruitment into adult populations (multiple regression). Differences in spawning and recruitment were associated with differences in population size structure and adult longevity. Mesoscale differences in recruitment and a spawning output/new cohort density correlation can be accounted for by limited dispersal of larvae on scales of tens of kilometres, with open coast and Algoa Bay populations acting as semi-discrete elements of a metapopulation.

KEY WORDS: Mussels · Recruitment · Intertidal communities · Population dynamics · Larval dispersal · Perna perna · Metapopulation · Spawning

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