The impact of the ixtoc-1 oil spill on zooplankton

Zooplankton data on seven cruises in the southern part of the Gulf of Mexico between 1979 and 1982 show a decrease in biomass levels of almost four orders of magnitude, lower than previously observed (De la Cruz. 1972), when mean biomass reached 389 mg m^-3. Seasonal biomass changes observed before and after the spill show the same pattern, with maximum in summer and minimum in spring; together with specific diversity, the highest heterogeneity of the community was present in the spring and the lowest diversity in the fall. Areas of high plankton productivity are the coastal zones of Campeche City. Términos Lagoon and off the estuaries of Grijalva and Usumacinta rivers. Changes in the organization and structure of the zooplankton community occurred after the spill, reaching a lower level of stability. Most samples appear to be contaminated by hydrocarbons, but the role of the Ixtoc- l oil spill as a factor in this is hard to determine. Decay of oil in zooplankton occurs exponentially: persistent levels of aliphatic hydrocarbons suggest a persistent pollution source, with damaging effects on plankton lower than those produced by the lxtoc-l.