LOSS OF GENETIC DIVERSITY IN HARPACTICOIDA NEAR OFFSHORE PLATFORMS

Offshore oil and gas production platforms can be a source of chronic s tress that could lead to sublethal impacts on resident benthic organis ms. In June 1993 and January 1994, genetic diversity of Harpacticoida (Copepoda) living proximal to operating, offshore platforms in the Gul f of Mexico was estimated to test if platforms are associated with str ong selective pressures. Because harpacticoids have short generation t imes and direct benthic development, they are suitable organisms for e xamining population responses. Genetic diversity was estimated by comp aring restriction fragment length polymorphisms generated from mitocho ndrial DNA amplified by the polymerase chain reaction on individuals o f five species (Cletodes sp., Enhydrosoma pericoense, Normanella sp., Robertsonia sp., and Tachidiella sp.). Populations living at Near regi ons (stations < 50 m from a platform) had significantly less haplotype diversity than populations of the same species living at Far regions (stations > 3 km from a platform). The levels of haplotype diversity e xhibited by the Far populations were similar at three different platfo rms located hundreds of kilometers apart. The differences in haplotype diversity between Near and Far regions were the result of a higher pr oportion of dominant haplotypes, and a loss of less common haplotypes. Haplotypic diversity was inversely correlated with a multivariate mea surement of levels of sediment contaminants. The pattern of haplotype diversity on the Gulf of Mexico continental shelf seems to consist of a uniform level of haplotype diversity, punctuated by islands of lower diversity around oil and gas platforms. The selective pressures that lead to a loss of genetic diversity may be the result of contaminants, other differences in the physico-chemical environment, or disturbance in general.