The response of southern hemisphere saltmarsh plants and gastropods to experimental contamination by petroleum hydrocarbons

Abstract

Field experiments examined the response of two common perennial saltmarsh plants and their gastropod epifauna to the effects of weathered petroleum hydrocarbons. Application of the petroleum hydrocarbons to the saltmarsh mimicked an accidental spill, but confined the contamination to small areas. Populations of the perennial chenopod, Sarcocornia quinqueflora, and the perennial grass, Sporobolus virginicus, showed little inertia and senesced rapidly after the application of weathered Bass Strait crude oil and diesel (11· m −2). No resprouting from underground stems or recruitment of seedling was detected up to 17 months after the application of hydrocarbons to Sarcocornia. Dead stems of the perennial grass Sporobolus persisted in areas treated with oil and diesel for up to 12 months, but showed no signs of resprouting from basal shoots or rhizomes originating from culms within the treated areas. Slow recovery from rhizomes originating outside the plots was evident after a few months but tiller growth appeared to be inhibited by residual hydrocarbons. No recruitment of seedlings was observed in the denuded plots and no other macrophytes were observed to colonise these areas until the end of the study (17 months). The response of saltmarsh gastropods to petroleum hydrocarbons shows greater inertia and stability than the vascular plants. Initial mortality was high, but migrations from the edges of the treated areas restored densities to control and pre-treatments levels within a few months. The reduction in cover of plants apparently had little effect on the abundance of gastropods although residual effects of the hydrocarbons may have inhibited predators of gastropods from the openings created by the death of saltmarsh plants. We predict that the widespread contamination of saltmarshes in south-eastern Australia by spills of crude oil or diesel would result in the loss of vegetation cover and reductions in the abundance of gastropod epifauna.