Intra-annual changes in seagrass standing crop, Green Island, Northern Queensland

Abstract

A visual estimation technique was used to estimate the standing crop of a mixed-species seagrass meadow at Green Island, northern Queensland. This technique measured monthly changes in the standing crop of seagrass within 10 fixed quadrats along three fixed transects from May 1987 to April 1988. The mean standing crop fluctuated by a factor of two from 60 g dry weight (DW) m^-2 (August 1987) to 133 g DW m^-2 (December 1987). The climatic factors that correlated with mean monthly standing crop were investigated. Owing to the high degree of association between these factors, principal-components analysis was used to create new orthogonal variables to be included in an 'all- subsets regression'. The best regression model explained only 12% of the variation in seagrass standing crop. This model and the magnitude and direction of the loadings of the vectors associated with the first principal component suggested that seagrass standing crop was positively correlated with any day length and temperature and negatively correlated with number of strong-wind days. These variables were indirect measures of light availability and temperature, suggesting that fluctuations in seagrass standing stock at Green Island were influenced by changes in temperature and light availability.