Cliona sponges burrow into shell causing damage and occasionally death, rendering the half-shell, and occasionally the pearl, unsaleable. Estimates of cost to the industry from Cliona sp. run into the millions of dollars per year (Moase et al. 1999) and preliminary studies have identified the species responsible and some aspects of their reproductive cycle relevant to pest management and control (Rawlinson 2000, Fromont et al.submitted). However, there is need to understand, and then control, the recruitment/ infection rate of Cliona, and the project shall provide this knowledge. The specific knowledge sought is an understanding of the process of recruitment or transmission of sponges onto pearl oysters, and an assessment of the source of bioeroding sponges in the environment. Key areas of investigation are the distribution and abundance of Cliona sp relative to size and age of oysters, and in the fishing ground habitats, and key biological questions are: is the incidence of Cliona increasing in wild stocks over time, and what effect is the biomass of bioeroding sponges in large, unfished pearl shell having on the fished proportion of the population? Effective management of these sponges in the pearling industry requires that the recruitment issue be resolved, so remedial action can be focused correctly. Management outcomes from the project may include changes to wild-shell fishing practices, shell treatment and shell discard processes, all of which will ameliorate the economic impact of Cliona sp on the industry and maintain the health of the wild stocks.

In October 2006 unexplained high mortalities of P. maxima oysters were reported. Many farms are affected and the cause is not known. The disease is termed Oyster Oedema Disease (OOD) and it is likely that an infectious agent is involved. The disease spread rapidly and there are no known control measures, no knowledge of a causative agent, no understanding of how widespread the disease was, and no way to test for it. Molecular and electron microscope research into the mortalities resulted in the discovery of two undescribed Chlamydiales-like organisms (CLO’s) associated with affected shell, and their involvement in OOD is unknown but it is considered unlikely that they are by themselves the major pathogen. However, it is possible that these organisms are contributing to the onset of OOD and further work is required to eliminate or confirm these organisms as a factor in OOD. A report detailing the OOD mortality event (AusVet Report on OOD, 2007) concludes that it is likely that more than one factor contributes to the onset of OOD. Therefore one or both of these CLO’s may play an important role in OOD. Preliminary research in WA suggests a link between OOD-affected animals and the presence of at least one of these CLO’s. The discovery of CLO’s in oysters is a new finding.

Mortalities continue to be reported and OOD still represents a high risk to surviving and young oysters. This proposal seeks to continue the work started at the Department of Fisheries WA in 2007 with the discovery of two CLO’s in P. maxima oysters. There is a need to further characterise these two organisms in relation to each other and to similar organisms worldwide, determine if they play a role in the onset of the fatal OOD, and represent a risk to surviving pearl oysters.