Lottia gigantea size and density differences in rocky intertidal communities near Monterey Bay, California

Shae Mitchell, California State University, Monterey Bay

Thesis (M.S.) Division of Science and Environmental Policy


Owl limpets (Lottia gigantea) are ecologically important grazers that live on exposed rocky intertidal shores of the west coast of North America. In recent years Lottia gigantea have been impacted by human access via visitation and harvesting. Owl limpet size and density have been correlated with human access in Southern California, where higher access leads to reduced size and density. Human visitation may have different effects on owl limpets in central California, where space may not be a limiting factor in owl limpet populations. The goal of this study was to investigate the relationship between humans and their potential impact on owl limpet populations at four sites between Point Lobos, California and southern Monterey Bay, California. Site-level differences of accessibility were used to infer how owl limpet density and size distribution have been affected by human access. A mixed effects model was used to analyze owl limpet size data while a negative binomial general linear model was used to analyze owl limpet density data. Contrary to previously published findings, this study found owl limpets were larger and less dense in high access sites and smaller and more dense at low access sites. There was also more open rock and lower species diversity at high access sites. Owl limpets are important ecosystem engineers modifying rocky intertidal habitat, which is an important and rare habitat within Monterey Bay National Marine Sanctuary (MBNMS). Therefore, understanding owl limpet dynamics and human access in MBNMS may assist management and conservation of rocky intertidal habitats.