The impact of the Ixtoc-1 oil spill on zooplankton

Zooplankton data on seven cruises in the southern part of theGulf of Mexico between 1979 and 1982 show a decrease in biomasslevels of almost four orders of magnitude, lower than previouslyobserved (De la Cruz. 1972), when mean biomass reached 389 mgm^–3. Seasonal biomass changes observed before and afterthe spill show the same pattern, with maximum in summer andminimum in spring; together with specific diversity, the highestheterogeneity of the community was present in the spring andthe lowest diversity in the fall. Areas of high plankton productivityare the coastal zones of Campeche City. Trminos Lagoon andoff the estuaries of Grijalva and Usumacinta rivers. Changesin the organization and structure of the zooplankton communityoccurred after the spill, reaching a lower level of stability.Most samples appear to be contaminated by hydrocarbons, butthe role of the Ixtoc- l oil spill as a factor in this is hardto determine. Decay of oil in zooplankton occurs exponentially:persistent levels of aliphatic hydrocarbons suggest a persistentpollution source, with damaging effects on plankton lower thanthose produced by the lxtoc-l.