3. Noosa Project Restoration Plan V12

5.5 Composite substrate

A small portion (<20 percent) of the restoration substrates will be a mixture of rock and cured oyster
shell as per the specifications. This composite is being used to further explore whether oyster
recruitment is enhanced by mixing oyster shell with the rock or not. Restoration scientists generally
expect that oyster shell provides chemical cues that may attract oyster larvae to settle on a particular
restoration site, but this has not yet been fully tested.

The composite mix will comprise up to 10 percent shell. In lower flow locations, such as in Noosa Sound,
the proportion of shell may be increased to 20 percent, subject to confirmation of the stability of the
structure by engineers. A higher proportion of shell may be considered subject to constructability and
monitoring outcomes, as per the specifications.

When used as a composite, the cured oyster shell will be evenly mixed through the rock to achieve
good interlocking. The shell will not be placed in alternating layers with rock. Mixing will occur in small
volumes on the barge immediately prior to placement to avoid shell damage due to rehandling. An
example of a rock oyster restoration substrate displaying a mix of rock and shell is given in Figure 5.5.




Figure 5.5: An example of rock oyster restoration substrate (augite) augmented with oyster cultch
(unseeded) in Port Stephens, NSW. Source: Craig Bohm, TNC.




                                                                                                        47