PRODUCTIVITY OF RUPPIA - SEASONAL-CHANGES AND DEPENDENCE ON LIGHT IN AN AUSTRALIAN ESTUARY

Ruppia shows seasonal changes in biomass with peak standing crops which differ between sites and years, but which are usually at a maximum in late spring and early summer. Ruppia produces annually some 75-500 g dry wt. m-2 in the estuary, and the total annual net production for the whole estuary is of the order of 700-1900 tonnes dry wt. Mesh enclosures were used to investigate effects of shading on standing crop. Increased light attenuation significantly reduces the contribution of this species to primary production. With increased duration of shading, higher light intensities are required to sustain high standing crops. Ruppia may be precluded if its ambient light intensity is reduced by 80% or more for up to 100 days; a reduction by 20% for 250 days results in a significant decrease in biomass. © 1979.