Lack of development of pollutant-resistance or genetic differentiation in darter gobies (Gobionellus boleosoma) inhabiting a produced-water discharge site

Physiological acclimation, genetic adaptation and genetic differentiation were examined in darter gobies (Gobionellus boleosoma) inhabiting a coastal marsh with a long history of PAH contamination. No acclimation was detected; a 2-week pre-exposure at the polluted site resulted in a decreased rather than an increased resistance in a subsequent laboratory exposure to polluted sediment. Similarly, fish collected from sites with elevated sediment PAH levels did not exhibit an increased resistance in bioassays with polluted sediment, confirming the lack of acclimation and indicating a lack of adaptation to the pollutants. No differences were detected in frequencies of allozyme genotypes when comparing gobies from the polluted area to those from a nearby control site, and overall levels of heterozygosity were similar in the two populations. While lack of UV-induced toxicity in the laboratory exposures could have played a role, at least four other factors may explain the apparent lack of adaptive responses and genetic differences. First, bioavailability of the contaminants to the darter goby could have been low, though other evidence contradicts this. Second, the contaminated marsh contains a large number of different chemicals and acclimation, adaptation and genetic differentiation are expected to be less likely when more contaminants are involved. Third, the hydrocarbon distribution at the contaminated marsh is very patchy, such that fish may avoid exposure to the highly-contaminated sediment. Fourth, gene flow may be sufficiently high in this mobile species to prevent local adaptation.