Masters Thesis

Growth inhibition of red abalone (haliotis rufescens) infested with an endolithic sponge (cliona sp.)

Understanding the effects of biotic and abiotic pressures on commercially important marine species is crucial to their successful management. The red abalone (Haliotis rufescensis) is a commercially important mollusc, whose shell surface is frequently populated with bright yellow colonies of Cliona sp., an endolithic sponge known to excavate substrates on which it grows. To determine whether a relationship exists between the growth of red abalone and infestation by Cliona sp., divers with the California Department of Fish and Game surveyed abalone in multiple areas within Mendocino and Sonoma counties. Individual abalone (n = 786) were scored for shell length and relative shell coverage by Cliona sp. Animals were tagged, released and resurveyed one year later (12±2 mo). Statistical analyses of this previously unpublished data demonstrated a significant, inverse correlation between the growth of red abalone and extent of shell coverage by Cliona sp. Red abalone acquiring even minimal infestation by Cliona sp. showed significantly inhibited shell growth, with the growth of smaller abalone affected to a greater degree than larger animals. Further surveys by this author in 2010 and 2011 were conducted to determine whether differences exist between the frequency and extent of Cliona sp. infestation of red abalone located in Humboldt County (n =89) versus Mendocino County (n = 106). The frequency of infestation in these counties was not significantly different, but the extent of Cliona sp. infestation was found to be significantly greater in Mendocino County than in Humboldt County. The results strongly suggest that red abalone growth is inhibited by Cliona sp. infestation and that regions of the northern California abalone fishery are differentially impacted by this infestation.

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