Spatial patterns in recruitment and growth of the mussel Mytilus californianus (Conrad) in southern and northern California, USA, two regions with differing oceanographic conditions

Abstract

Mussels, Mytilus californianus, and other benthic invertebrate populations on the wave-exposed intertidal coast of the eastern North Pacific are impacted by a suite of biotic and abiotic factors on both local and larger geographic scales. Previous surveys of mussel abundances along the California coast have revealed that mussels, in general, are very abundant in northern California while low in southern California. Nevertheless, mussel abundances in southern California are highly variability with a small number of sites that are characterized as having moderately high to high abundances. To elucidate driving factors of mussel abundances in these regions, we investigated recruitment and growth rates of mussels in 1) northern and southern California, two regions separated by ca. 900 km and exposed to vastly different oceanographic processes and 2) within southern California at sites with moderately high mussel abundances and at sites with low abundances. We found that recruitment and, to a degree, growth may be important factors driving variable abundances of mussels within southern California but could not explain patterns along the entire California coast. Recruitment and growth rates were low in northern California even though mussels were highly abundant. Conversely, recruitment and growth in southern California were significantly higher than northern California and, within the region, were higher in sites characterized by moderately high abundances. Among regions, differences in recruitment and growth are likely driven by large scale oceanographic patterns such as upwelling affecting larval transport and temperature affecting growth. Within southern California, local oceanographic processes likely enhanced or inhibited recruitment or growth leading to differences in measures between closely located sites.