Role of hydrocarbon pollutants, salinity, tidal height, bioenergetics and competition in colonization of oyster reefs by commensal assemblages

Abstract

Effects of hydrocarbons, salinity, tidal height, bioenergetics and competition on the oyster reef fauna were studied. Dried oyster shell was exposed to crude oil in the laboratory and plastic trays filled with control and oil-exposed shell were then deployed at two locations, in two seasons and at two tidal levels, with immersion periods of two and five weeks. Salinity exhibited a significant effect with sub tidal site having higher diversity. Hydrocarbon effects were less prominent. To determine effects of cleaners, Corexit 9580 was applied both alone and in combination with oil on cultch. At high concentrations, the cleaner ameliorated hydrocarbon effects. Hydrocarbon effects seemed to be less prominent than salinity and aerial exposure. In the next chapter, effects of salinity on the survival and bioenergetics of mud crabs Panopeus simpsoni and Eurypanopeus depressus were examined. Crabs were exposed to a range of salinities to determine the effects of salinity on tolerance. P. simpsoni exhibited a 28d LC50 of 6.97 PSU while E. depressus had a 28d LC50 of 0.19 PSU. Crabs were exposed to four salinities for bioenergetic measurements. Energy expenditure was highest at the lowest salinity and decreased as salinity increased. Scope for growth declined below 17.5 PSU. E. depressus was capable of surviving lower salinities than P. simpsoni. However, the physiological responses do not significantly differ between the two species. In the next chapter laboratory experiments were conducted to see if these two crab species differ in resource holding potential. Crabs were placed in aquaria at two salinities and refugia were checked daily for shelter occupancy. To determine if resource holding potential for refugia influenced predation risk, a second laboratory experiment was performed with a blue crab predator in each tank. The numbers of mud crabs of each species surviving were recorded. E. depressus was dominant over P. simpsoni in occupying the shelters at both salinity levels. E. depressus exhibited a higher survival in the presence of the predator. E. depressus’s ability to tolerate lower salinities, and its dominance in resource holding potential, may lessen predation risk and allow colonization of more estuarine sites.