THE CRASH IN SUSPENSION-FEEDING BIVALVE POPULATIONS (KATELYSIA SPP) IN PRINCESS-ROYAL HARBOR - AN UNEXPECTED CONSEQUENCE OF EUTROPHICATION

Abundances of two species of suspension-feeding bivalves (Katelysia sc alarina L. and K. rhytiphora L.) on the unvegetated sandflat of the so utheastern shore of Princess Royal Harbour declined from around 160 . M-2 in 1983-1985 to nearly zero in 1992. Based on replicated estimates of annual mortality from 1983-1985, 414 out of 2013 individually mark ed Katelysia were expected to remain alive after 7 years inside field enclosures. Not one marked Katelysia did survive and of the 166 marked empty shells recovered, 65-90% showed growth equivalent to just over a year of life beyond their last measurement in April 1985. Not only h ad adult abundances crashed, but recruitment of young Katelysia was ne gligible at levels two orders of magnitude less than observed in 1983- 1985. These dramatic declines in abundances of a previously dominant c omponent of the fauna of Princess Royal Harbour co-occurred with eutro phication, seagrass die-off and macroalgal blooms, suggesting that the environmental problems of this harbour have cascaded through the ecos ystem to alter its ability to sustain natural secondary production and ecosystem function.