Effects of Gas-Producing Platforms on Continental Shelf Megafauna in the Northwest Gulf of Mexico: Reproductive Status and Health

Abstract

One component of the Gulf of Mexico Offshore Operations Monitoring Experiment (GOOMEX) was to assess the reproductive effort and health (defined as the prevalence and intensity of parasites or pathologies) of mobile macroepifauna collected near-to and far-from gas-producing platforms. The stage of reproductive development as determined by visual inspection or histological analysis was rarely significantly different between near-field and far-field sites. Tissues were examined histologically to determine the prevalence and intensity of parasitism and disease. If a difference in parasitism or pathology existed, individuals collected far-from the platforms typically had higher prevalences while individuals living near-to the platforms usually had higher intensities. Parasitism and disease had little effect on stage of reproductive development except at MU-A85 where individuals with increased disease and parasitism also had decreased reproductive development. Variations in infection intensity were not due to differences in age structure of populations. Larger, older individuals were not consistently more heavily parasitized. Trend in reproductive stage and population health did not follow trends in environmental contamination; the fewest significant differences were observed at the most contaminated platforms. Patterns of differences in parasitism, disease and reproductive effort between the near and far-field stations were platform specific, indicating that the physical and chemical characteristics unique to each platform probably control reproductive effort and levels of disease and parasitism in populations living there. The influence of structure, a variable common to all platforms, did not exert an overriding influence. Mobile taxa such as shrimp exhibited near-field/far-field differences as frequently as the less mobile species such as starfish. Thus, mobile epifauna maintain discrete populations over long-enough time periods to develop different population histories. Shallow-water sites were more likely to exhibit platform-specific near-field/far-field differences in population structure suggesting that trends in water depth and the intensity of seasonality may explain the apparent uniqueness of each platform's effect on population structure and health.