Effects of El Ni�o events on natural kelp beds and artificial reefs in southern California

Abstract

Since 1978, bottom characteristics and giant kelp ( Macrocystis pyrifera ) population dynamics of three historically productive natural kelp beds located south of San Clemente, California, have been monitored on a semi-annual basis using diver observations, sidescan sonar, and downlooking sonar. Aerial photographs of the kelp-bed surface canopies have been recorded annually since 1968. Since 1981, studies have been intermittently performed on the Pendleton Artificial Reef. Ecological studies were also conducted pre- and post-1997–1998 El Niño and qualitatively from 1994 to 1999 at the Mission Beach Artificial Reef. El Niño events have been associated with catastrophic ecological conditions in the southern California nearshore zone that may have significant influence on both reef structure and reef community. The variation of kelp populations in the three natural kelp beds is reviewed relative to recent El Niño events, local wave climate, local sea surface temperatures, and regional precipitation. The local temperature and precipitation data show that El Niño periods have had varying and non-consistent effects with respect to kelp growth. Yet, periods of low kelp density appear to be related to extended periods of above normal sea surface temperatures and increased precipitation generally associated with El Niño events. Examination of artificial reef data from the standpoint of substrate and kelp persistence through the latest 1997–1998 El Niño event revealed effects that are consistent with natural kelp bed information. The population dynamics of natural kelp beds through various El Niño periods indicate that the range of kelp density fluctuations over time on an artificial reef designed for kelp can be expected to be quite high. Copyright 2002 International Council for the Exploration of the Sea. Published by Elsevier Science Ltd. All rights reserved .