Date of Award

2000

Degree Type

Thesis

Degree Name

Bachelor of Science Honours

Faculty

Faculty of Communications, Health and Science

First Advisor

Dr Jackie Alder

Second Advisor

Dr Jane Fromont

Abstract

This thesis examines environmentally and economically viable ways to manage a sponge that is bioeroding the pearl oyster, Pinctada maxima, in pearl oyster farms throughout north-western Australia. The sponge is causing a massive loss in revenue to the pearling industry as a result of damage to the half-shell, the pearl and, often, death of the oyster. The information arising from this study is important for pearl producers and the Australian pearling industry, to ensure that the best quality P. maxima can be grown in a way that will not have adverse effects on the pristine environment in which these sensitive organisms live. It is of uttermost importance to the pearl oyster farms that solutions to the problem are environmentally appropriate. Control of the sponge, of the family Clionidae and the genus Cliona in addition to other related genera, was based on knowledge of its reproductive cycle, so that a deterrent to egg release can be applied at a time when the sponge is at a vulnerable stage in its life cycle. The reproductive cycle of the sponge was examined using light microscopy, after the sponge samples had been processed using histological methods. The reproductive cycle of the sponge was examined over a 12-month period at five different pearl oyster farms in north-western Australia. Reproductive activity was correlated with environmental parameters, including water temperature and salinity. The results of these studies were integrated and management recommendations based on these results were made, The study on reproduction of the sponge found no indication of reproductive activity for three of the farms (Morgan Pearl farm and both Paspaley Pearl farms at Vansittart Bay and Port Bremer) participating in the study. The samples from Maxima Pearl presented some reproductive activity, while Arrow Pearl had relatively high reproductive activity. Additionally, reproduction occurred at two different times of the year. This study concluded that management of the bioeroding sponge can be improved with knowledge of its reproductive cycle. Other longer-term studies are, however, essential for improved management recommendations. The current management technique recommended, the application of a paint that will smother and kill the sponge infestation, is thought to be environmentally benign and has the potential for pearl producers to reduce the revenue lost as a result of the sponge. This technique should be continued with modifications on the timing of the application to coincide with reproductive activity of the sponge, thereby reducing sponge settlement and consequently reducing farm costs. For the recommended management strategies to be effectively utilised, further research is needed into the origins and reproductive cycle of this bioeroding sponge.

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