ABSTRACT: Sulphide concentrations in estuarine sediments are likely to increase with increased organic matter fluxes (eutrophication) and increased temperatures (global warming). The short-term effects of sulphide on the growth, nutrition and morphology of the seagrass Halophila ovalis (R.Br.) Hook. f. were investigated in situ. Sediments within a H. ovalis meadow were enriched with Na₂S equivalent to 0, 1.1 and 4.2 g m^–2. Sulphide diffusion tubes were estimated to increase sulphide concentrations by 1 to 4 mmol l^–1, concentrations typical of elevated sulphide measured in natural systems. Biomass, internode distance and growth rate (mg apex^–1 day^–1) were determined, and plant material was analysed for soluble carbohydrate, carbon, nitrogen and phosphorus. Sulphide exposure caused significant reduction in growth (63%), average leaf weight (30%) and internode distance (15%). Above-ground tissue phosphorus concentration and internode distance were significant predictors of growth (R² = 0.63, p < 0.01). These results demonstrate the plasticity of H. ovalis in response to a short-term sulphide pulse, and may have implications for recovery from transient sulphide stress.