DISTRIBUTION OF TAR AND RELATIONSHIP TO CHANGES IN INTERTIDAL ORGANISMS ON SANDY BEACHES IN SOUTHERN CALIFORNIA

Abstract

ABSTRACT Surveys on sandy beaches for 10 years following the Santa Barbara oil spill (1969–1978) revealed that large amounts (2 g per square foot) of tar are frequently found at sites adjacent to natural oil seep areas. Tar is intermittently found on most other open coast southern California beaches. This is in contrast to few records of tar on over 40 surveys at sites in the area just north of Point Conception. The sources of tar is both difficult and costly to determine. However, available information suggests that with the exception of major oil spills, most tar on the beaches in the Southern California Bight originates from natural oil seeps. On the open coast beaches, the residence time of this tar appears to be short (generally days and perhaps weeks) but after exceptional storms such as those in the winters of 1969 and 1978, tar could be buried for longer periods. In most instances deeply buried tar would be removed by the approximately annual cut and fill cycle. At the sheltered site at Cat Harbor on Santa Catalina Island, tar appears to remain at the site and become gradually buried in the sediments. Wave action is apparently not sufficient to remove the tar and the site is gradually silting up. At all sites, natural environmental variables such as sediment grain size, had a greater impact on the distribution and abundance of species than tar. Within this framework, changes in populations at Cat Harbor following contamination by wet sticky tar in early spring 1976, appear to be a response to this tar. Conservative estimates currently suggest a two-year recovery period. This may be revised after further research.