Hydrocarbon effects on fouling assemblages: the importance of taxonomic differences, seasonal, and tidal variation

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Effects of hydrocarbon-contaminated substrata on recruitment of three species of fouling organisms were studied along the Louisiana gulf coast. Clay tiles (232 cm2) were exposed to crude oil, 10% water soluble fraction of crude oil, or 25 g/kg artificial seawater, and placed out at two locations, in two seasons, and at two tidal levels in an estuary near Port Fourchon, Louisiana. Bryozoan (Membranipora savartii) recruitment was significantly reduced in all experiments on crude oil-exposed tiles. However, oysters (Crassostrea virginica) and barnacles (Balanus eburneus) exhibited recruitment facilitation, and oysters grew to larger size, on crude oil-exposed tiles in 1-4 of the five experiments. When oyster larvae were exposed to the same treatments in the laboratory, settlement was, however, significantly depressed on crude oil-exposed tiles as compared with controls, although oyster size was larger on crude-oil exposed tiles. Recruitment on tiles exposed to the water soluble fraction of crude oil was similar to control tiles in nearly all experiments for all taxa. We suggest naturally occurring biofilms (which hydrocarbons facilitate) may promote or inhibit recruitment, depending on the taxon, because hydrocarbons facilitated recruitment only in field experiments, not in lab experiments without biofilms. However, stronger currents in the field experiments may have more rapidly diluted hydrocarbons, and hydrocarbon effects were not large in comparison with natural seasonal and tidal variation in recruitment.

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Marine environmental research

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