Available at: https://digitalcommons.calpoly.edu/theses/1889
Date of Award
MS in Biological Sciences
Recruitment, the addition of new individuals to a population, must be understood to make predictions about population growth of marine invertebrates. Red abalone (Haliotis rufescens) represent a former important commercial fishery in California, and until recently, supported a major recreational fishery. However, there have been statewide declines since the 1960s due to overfishing, disease, and climatic factors. Thus, understanding population dynamics to inform management and population restoration is critical. Recruitment dynamics of red abalone are poorly understood, with no prior knowledge of seasonal trends. To address this knowledge gap, I assessed monthly (July 2016-June 2017) and annual (2012-2016) settlement rates of red abalone in the Monterey Bay, which has low density abalone populations due to sea otter predation. I evaluated associations between abalone recruitment and oceanographic factors (temperature, wave forces, and upwelling index) and food availability (kelp density) to understand potential predictors of recruitment. Abalone recruitment occurred year round, with generally higher recruitment in late summer to early fall (July-October) and peaks in August and October. This is the first demonstration of year-round abalone recruitment in the field. On a monthly basis, there were no statistically significant relationships between recruitment and oceanographic factors or food availability. Annual abalone recruitment was consistent in all years, with the exception of 2015 when recruitment majorly decreased during the second year of the North Pacific marine heatwave (i.e., warm blob and El Niño Southern Oscillation (ENSO) events). The failure of recruitment during only the second year of warm temperature suggests that prolonged extreme temperatures lead to reproductive failure. The consistent annual recruitment in the Monterey Bay contrasts with sporadic recruitment observed in Sonoma and Mendocino Counties in northern California. This finding was unexpected because red abalone in northern California were twice as dense as those in Monterey Bay at the time of the study. Possible hypotheses behind the observed consistent recruitment in Monterey Bay despite low densities include that: sheltered embayments retain larvae and promote recruitment, predation by sea otters aggregates abalone in crevices and promotes fertilization success, and the perennially present Macrocystis pyrifera kelp forests better support abalone growth and fecundity than northern California forests dominated by annual Nereocystis leutkeana.