Influence of Abiotic Factors on the Persistence of Kelp Habitats Along the North Coast of Santa Monica Bay

Abstract

The distribution and abundance of kelp forests flanking Santa Monica <br /><br />Bay are spatially and temporally variable and have shown an overall decline in <br /><br />biomass over the past few decades, especially along the northern arm of the bay <br /><br />in Malibu. Our objective was to quantify the within patch abundance of giant <br /><br />kelp Macrocystis pyrifera (L.) C. Ag. fringing northern Santa Monica Bay and <br /><br />to measure a suite of physical factors that may influence its local distribution and <br /><br />abundance. For comparison, these factors were also measured for the southern <br /><br />arm of the Bay along the Palos Verdes Peninsula, an area characterized by larger, <br /><br />more persistent kelp forests. Of the measured factors, the amount and stability of <br /><br />suitable substrate and the sediment type appear to have the largest influence on <br /><br />kelp density. The amount of hard substrate available for kelp recruitment and <br /><br />growth is higher along the Palos Verdes peninsula as compared to the Malibu <br /><br />coastline, but both regions' rocky reefs demonstrate temporal shifts in areal extent. <br /><br />Furthermore, sediment size also varies along the two coasts with Malibu sediment <br /><br />consisting of a lower percentage of larger particles which typically are resus- <br /><br />pended less than smaller, more mobile particles. These abiotic factors may strong- <br /><br />ly regulate the size of Macrocystis pyrifera populations in the Santa Monica Bay <br /><br />and may help explain the observed difference in kelp abundance between the <br /><br />Bay's two coastlines.