EFFECTS OF PROLONGED SHADING STRESS ON GROWTH AND SURVIVAL OF SEAGRASS POSIDONIA-AUSTRALIS IN JERVIS-BAY, NEW-SOUTH-WALES, AUSTRALIA

Experimental shading reduced the light reaching a shallow Posidonia au stralis meadow in Jervis Bay, New South Wales, Australia, to less than 10% of incident light. Shaded seagrass had significantly lower leaf g rowth rate, shoot density, shoot weight and epiphyte weight than seagr ass in control plots. The structure of the epiphyte community also cha nged under shade as the fleshy macroalgae disappeared during the first month of shading and the leaves were dominated by encrusting inverteb rates. The magnitude of the decrease in shoot number and leaf growth v aried among 3 experiments at different times of year. Shading in early summer had a more severe effect on the seagrass than shading at the e nd of summer. There was no significant recovery of P. australis in the shaded plots during 17 mo following removal of the shades.