The Effects of Natural Oil Seepage on Intertidal Communities in Santa Barbara, CA. Paul Owens Abstract Of the 1.9 billion gallons of oil entering the world’s oceans each year, 1.9% of this occurs naturally in the Santa Barbara channel off the coast of Santa Barbara, California. The beaches, Coal Oil Point and Campus Point are closest to major seep sites and appear most heavily impacted. Intertidal organisms such as limpets show 100% mortality rates when subjected to high levels of oil, periwinkles show ~35% mortality, and mussels display 0% mortality. Three rocks were surveyed at each of 7 beaches to determine if natural levels of oil in the Santa Barbara area affect intertidal communities. Coal Oil Point and Campus Point served as the heavily oiled sites and beaches north and south of those as low oiled sites. A 30X30 cm quadrat was placed across a randomly marked strip on the rock at the low tide line. Species within the quadrat were counted. Data were analyzed using ANOVA single factor. There was no statistical difference in populations of mussels or periwinkles between oiled and low/non-oiled sites. However, there was a significant difference in populations of limpets between the sites. It was expected that there would be no differences in mussels due to their ability to withstand high amounts of oil. Differences in periwinkle populations were also expected to be statistically insignificant because of their moderate tolerance to high levels of oil. Also, levels of oil reaching Coal Oil Point and Campus Point are not high enough to warrant disastrous effects such as after an oil spill. Limpets were expected to show a difference because of their low tolerance of oil. Factors such as seasonal, spatial, and temporal variations may also have been a factor but sampling methods were designed to eliminate these variances.Introduction One billion gallons of oil enter the worlds oceans each year, 36% is from runoff, 12% is accidentally released from tankers, 22% is intentionally released from oil tankers as normal operating functions, and 8% is from natural seeps (Suchanek 1993). Hydrocarbon seeps occur naturally in the Santa Barbara channel offshore of Coal Oil Point, California. Oil related activities including heavy tanker traffic also occur in this region with some spillage reported although actual amounts are unknown. Oil seepage is estimated to be 3150 gallons per day or 11931.8 liters per day. Of the total amount of oil naturally seeping into the world’s oceans annually, 1.9% occurs in the Santa Barbara basin. Because of the low density of oil and the stratification of coastal waters the seeps consisting of hydrocarbon gas bubbles with oil rims, oil, and tar will form complex plumes often concentrating at the surface (Jordan 1999). The highest concentration is found within a few kilometers of the shoreline. Jordan (1999) shows that as hydrocarbons seep into density stratified coastal waters the plumes may extend for 12 kilometers. Surface currents, controlled by local winds, tidal forcing, surface waves, eddies, and large-scale pressure gradients, can push contaminated off shore water directly into the shore (Barrick et. al 1985, Quigley 1996). Contaminants can concentrate in pools, end up on the beach, and cover intertidal rock zones where many organisms live. Dissolved oil content in shore water changes daily with moving water and seep rates. Oil concentrating in the water after an oil spill has been shown to have adverse affects on intertidal communities (Newey 1995). The most immediate effect of high levels of oil on intertidal organisms would be narcosis, and the inability of organisms to adhere to there substrate (Newey 1995). Mussels, particularly M. edulis and have been studied extensively under the conditions of high oil concentrations. Roberts (1976) showed that mussels exposed sub-lethal concentrations of oil were able to survive and elute 80-90% after being exposed to clean saltwater. Thomas et.al. (1999) found concentrations as high as 8 micrograms/gram of oil in the living tissues of mussels after an oil spill with little effects on their health. Other organisms such as limpets, periwinkles, topshells, and barnacles do show increased mortality and population declines under increased oil content (Carthy 1968, Nagelkerken and Debrot 1995, Simpson et.al. 1995, Newey and Seed 1995, Simpson et.al. 1995). Simpson (1999) showed significant differences in species richness, especially a sharp decline in the limpet after an oil spill. Nagelkerken, (1995) showed a 20.6% decrease in mollusk densities at an oiled site compared to an un-oiled one and a species richness increase of 63.8%compared with an oiled site. Nagelkerken, (1995) showed that at unpolluted sites mollusk densities averaged 1000 snails, limpets, and chitons per square meter at an unpolluted site and at an oiled site there were 20.7 species per square meter. The biological effects of oil on littoral communities are dependent on concentrations, with high concentrations showing higher differences (Steichen, 1996). Cold, nutrient rich water upwelling from the California current make California’s coastal waters nutrient, and species rich (Alden 1998). However, studies show that where hydrocarbons are present in the water at high concentrations species relying on coastal waters may decline (Newey 1995). Grazers and filter feeders such as mussels, limpets, barnacles, and topshells are an important source of food for many other species. Because of the limited number of space on intertidal rocks competition is particularly important. Oil will alter natural competitive relationships by removing sensitive species. The major effect of oil is to create a uniform species environment around the toxic area (Newey 1995). Also, without key grazing species opportunistic algae may then appear in thick mats. In Santa Barbara, the most heavily impacted areas are the beaches between El Capitan beach and Goleta point (Venoco 2000). This study aims to determine the difference between species composition, richness, and density between heavy and low oiled sites. The species I will be looking at will include mussels, limpets, and periwinkles because of their known sensitivity as indicated by previous studies (Carthy 1968). Description of Study Subjects The species’ of interest is the common California mussel (Mytilus californianus) of which an average size is 152.4 mm. The