Modelling contaminant effects on deposit feeding nematodes near Gulf of Mexico production platforms

A time dynamic model was used to simulate contaminant effects on the energetics of the nematode community near hydrocarbon production platforms in the Gulf of Mexico. The model is calibrated by the measurements of biomass of deposit feeding nematodes at 75 stations around three platforms. The sampling design for each platform included: five distances, five radii and two replicates over four cruises. Inputs to the model include: temperature, total organic carbon, macrobenthos abundance, and zinc concentrations in sediments. Zinc is used as a proxy for total trace metal contaminants, because in high concentrations, it is known to cause biological effects, and could be consumed by deposit feeders as they process sediment. Production efficiency (production · assimilation−1 · 100%) of nematodes was calculated using the model. On average, deposit feeding nematodes in the Gulf of Mexico have a production efficiency level of around 30%. The effect of contaminants is to decrease production efficiency to less than 15% at the stations within 50–100 m near the platforms. It appears also that the communities at the three platforms have different energetic characteristics. The predation pressure, temperature effects, food availability, and contaminant effects are all different among the three communities. Therefore, using production efficiency as a bioindicator of sublethal effects is suitable within a community (i.e. within a platform), but not among different communities (or platforms).