RAPID INVASION OF A SPONGE-DOMINATED DEEP-REEF BY CAULERPA-SCALPELLIFORMIS (CHLOROPHYTA) IN BOTANY BAY, NEW-SOUTH-WALES

We document the rapid spread of the green alga Caulerpa scalpelliformi s (R. Brown ex Turner) C. Agardh following its establishment in Botany Bay. In February 1996 we estimated that this alga occupied at least 0 .35 hectares of the substratum within the Bay. Coincident with the inc rease in algal cover on the deep-reef habitat has been a substantial d ecline in the cover of sessile invertebrates, predominantly sponges, c olonial ascidians and bryozoans. Within 12 months of the appearance of the alga at Inscription Point, random photoquadrats (n = 15) revealed that it had reached an average cover of 56 +/- 11% with an estimated average fresh biomass of 5.2 +/- 1.1 kg m(-2) (+/- sem). Over the same period the average cover of sessile invertebrates declined from 45 to 23%; a significant change by mixed-model nested ANOVA. No such declin e was observed in reference sites at Henry Head at the northern entran ce to the Bay. Within 12 months, the alga had spread to an additional location some 300 m to the east of the originally monitored location, underscoring its ability to rapidly expand across continuous reef. Mor eover, the appearance of small isolated plants at the northern entranc e to the Bay, indicates that it is also capable of establishing on non -continuous reef.