Date

Spring 2021

Document Type

Master's Thesis (Open Access)

Degree Name

Master of Science (M.S.)

Department

Moss Landing Marine Laboratories

Abstract

Habitat use can affect ecological and biological processes, such as resource use, survival, and reproduction. For many species, habitat use can vary with season as their energetic needs change, for example increasing foraging area in the energetically costly reproductive season. In this study, I sought to understand the seasonal and temporal scales of spiny lobster (Panulirus interruptus) habitat use in a southern California ecosystem by integrating habitat surveys using GIS (Global information system), lobster demographic surveys, and diet analysis using stable isotopes. I focused on the California spiny lobster (Panulirus interruptus) because the species uses a variety of habitats at different seasonal and spatial scale and is economically and ecologically important. My two study sites on Santa Catalina Island, California, Bird Rock and Big Fisherman Cove, were characterized by rocky substrate and high algal cover, but exhibited differences in the cover of mussels. Results indicated that Bird Rock had a higher density of lobsters than Big Fisherman Cove and intertidal habitat recorded higher density of individuals than subtidal habitat at both sites during nocturnal high tides. At Bird Rock, the proportion of females was 25% higher, and their reproductive condition was 43% greater than that at Big Fisherman Cove. I detected a distinct seasonal change in the diet of spiny lobsters, such that a higher diversity of prey resources was consumed in the summer, when nighttime high tides permit movement and foraging from the subtidal to the intertidal, compared to the winter, when high tides rarely overlap with nocturnal foraging behavior and winter storms can make it inaccessible. Stable isotope results indicated that lobsters at Bird Rock foraged on the mussel beds that are present at the site, while no mussel consumption was detected at Big Fisherman Cove. Seasonal foraging in the intertidal habitat acts as a diet subsidy for the spiny lobsters during the reproductive season, a time of high energetic cost. Observed differences in the reproductive condition of the lobster population are likely due to the presence of the mussel bed at Bird Rock. Understanding fine scale spatial and seasonal habitat needs of target species can help create better protected areas, not only for the spiny lobster, but other critically important species.

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