Impacts of diesel fuel exposure on the microphytobenthic community of an intertidal sand flat

Abstract

This study employed simulated spills of weathered diesel fuel and measured the initial effects on the intertidal sand flat microphytobenthic (MPB) communities. The goals were to examine the impacts of short-term (hours) and longer-term (days) exposure to petroleum on the native sand flat MPB in coastal North Carolina and to assess recovery of the community following the exposure. We assessed changes in biomass (chlorophyll a), primary productivity ( 14C bicarbonate incorporation), photophysiology ( P vs. I curves) and species composition (microscopy) and compared diesel exposed samples to unamended controls. We found that short-term impacts of diesel fuel pollution were confined to primary productivity and photophysiology of sand flat MPB. Short-term effects were only detected at relatively high concentrations that are not common outside of a major spill event. In the longer term, diesel fuel was again found to have effects on primary productivity, but at higher concentrations than would be likely to occur in industrialized coastal areas. However, negative impacts on photophysiology were detected at diesel fuel concentrations slightly above typical ambient conditions in coastal waters in industrialized areas. Biomass as measured by chlorophyll a was not affected by any concentration in the longer-term exposure to diesel fuel. Cell counts in the longer-term experiments found cyanobacteria had larger negative impacts from diesel fuel exposure than did diatoms. The recovery portion of this study showed the sand flat MPB communities were fairly resilient following both additions of diesel fuel. However, photophysiology and cell counts did not return to conditions equivalent to the control. Data from this study indicate that the effects of petroleum pollution on the MPB community of tidal sand flats should be considered alongside effects on other coastal microalgae in ecological and damage assessments.