Variation in owl limpetLottia giganteapopulation structures, growth rates, and gonadal production on southern California rocky shores

Abstract

The size structures of Lottia gigantea populations were studied at 8 southern California sites, 4 of which were longstanding Marine Protected Areas (MPAs). Greater mean sizes and higher frequencies of larger individuals occurred at sites with lowest human visitation. Mean L. gigantea shell lengths (SLs) were negatively correlated with the number of visitors and collectors per 10 m of shoreline. Limpets never achieved SLs greater than 79.0 mm at any of our 8 sites, a size well below the maximum for this species. Mean SLs were comparable to sizes at other sites where L. gigantea is intensely collected. The presence of collectors, small mean SLs, and the absence of large limpets suggest that L. gigantea populations are affected by humans at our sites. Lower densities and higher frequencies of larger limpets were found in a subpopulation living on open-rock surfaces compared with a subpopulation occupying smaller, patch habitats within mussel beds. Larger limpets were mostly female and gonadal mass increased exponentially with SL in both subpopulations. Limpets < 40 mm SL exhibited highly variable growth rates; however, limpets in patch habitats grew slower and produced less gonadal mass than limpets inhabiting open rocks, despite the availability of more microalgal food. Ages of the largest limpets in the open-rock subpopulation were estimated to be >8 yr. Given the age of larger limpets and the potential for collectors to remove larger individuals and shift populations towards smaller size structures, effective MPAs may take decades to reverse the effects of human impacts on L. gigantea populations in southern California.

Reproductive output and consistency of source populations in the sea star Pisaster ochraceus

“…The potential for a site to act as a reproductive source may depend on a variety of factors including population density, age and size structure, total population size, per capita reproductive output, and local hydrodynamics (Denny et al 1992, Levitan et al 1992, Quinn et al 1993, Kido & Murray 2003, Wing et al 2003, Leslie et al 2005. Overall, our results suggest that Pisaster at NSJ had consistently higher per capita reproduction than those at SH, despite considerable variation among years in oceanographic conditions and reproductive output.…”

“…Similarly, the reproductive output of barnacles is often higher in areas of high primary productivity (Bertness et al 1991, Leslie et al 2005. However, only a handful of studies have tested whether the reproductive output of marine consumers at higher trophic levels is sensitive to resource quality, and these studies have focused mostly on herbivores such as limpets and sea urchins (Rogers-Bennett et al 1995, Kido & Murray 2003, Wing et al 2003; but see also McIntyre & Hutchings 2003).…”

Biophysics, environmental stochasticity, and the evolution of thermal safety margins in intertidal limpets

“…The population then suffers increased mortality during the next extreme year, and, after particularly extreme events, the population goes functionally extinct. Longer life span [for L.gigantea, >>8.5years (Denny and Blanchette, 2000;Kido and Murray, 2003)] allows for some genetic 'memory' of extreme thermal events, and the higher lethal limits thereby maintained are sufficient to ensure the persistence of a population in the face of subsequent extreme events.…”

Thermal stress on intertidal limpets: long-term hindcasts and lethal limits

“…In particular, it competes with the mussel M. californianus, and on the California coast, where settlement rates of mussels are low, L. gigantea and M. californianus appear to be co-dominant. Furthermore, L. gigantea is an important food source for both shore birds and human subsistance harvesters (Lindberg et al, 1987;Pombo and Escofet, 1996;Lindberg et al, 1998;Kido and Murray, 2003). It is therefore of ecological interest to understand when and where L. gigantea may be killed by thermal stress, and what environmental factors control these lethal events.…”