2022-05-16 GC Agenda - Item 7 - Attachment 1 - Report from Marine Approval Specialists

sydneyi has a lifecycle which involves at least two hosts, which means QX cannot be passed directly
from one oyster to another (is not directly transmissible).

The parasite enters into the soft tissue of SRO through its gills and palps (near the oyster's mouth). If
it progresses to cause disease, the parasite divides and proliferates. It then migrates to the digestive
gland which surrounds the oyster’s stomach and intestine. There it undergoes further development
and multiplication to produce spores (sporulation), the end-stage of infection in oysters. Sporulation
damages the digestive gland of the oyster, resulting in starvation and eventual death of the oyster.

Time from infection until death can vary between several weeks to several months. Affected oysters
can be in poor condition and appear translucent or “watery”. The digestive gland can also appear to
be a light tan colour instead of the usual dark brown.

Prior to death of the oyster, the spores are released into the environment where they are taken up
by alternate host(s) required in the life cycle of QX. The identity of the alternate host(s) has not been
confirmed, but there is evidence suggesting that a polychaete worm (Nephtys australiensis) could
play a role in the development of the parasite (Adlard and Nolan, 2015).

Winter mortality is a protozoan born disease affecting the production of the SRO industry greatly.
This disease causes high oyster mortality during periods of low water temperature and high salinity.
It has the potential to severely impact the SRO industry through both stock losses and restrictions on
market access.

A species of Mikrocytos (subsequently renamed as a species of Bonamia) was historically thought to
be the cause of the disease, but a definitive link between its presence and disease outbreaks has
never been found.

Over the past few decades, breeding lines of SROs have been selected for resistance to Winter
mortality and QX disease.



4.5.2 Adequacy of controls
TNC proposes a monitoring and adaptive management framework informed by close consultation
with relevant industry experts. The management framework is considered sound. We note that the
framework relies on the careful implementation of the Noosa Oyster Ecosystem Restoration Project
- Project Restoration Plan and development of an appropriate Restoration Monitoring, Evaluation
and Reporting System. The latter has not been provided as part of the application material.

The primary mitigation measure if there are outbreaks of these diseases is the introduction of
hatchery-produced QX-resistant S. glomerata and this is acknowledged by TNC as a fundamental
response. As the causes of outbreaks of these diseases remain poorly understood, monitoring and
development of mitigation strategies in consultation with the network of experts proposed by TNC
are considered appropriate controls.