2015-10-13 Planning & Organisation Agenda Attachment 1 to Item 7 Oyster Recruitment Assessment Report

4 Discussion and Recommendations

4.1 Spatial Variation in Recruitment in Noosa Estuary
Surface orientation can be an important determinant of intertidal and subtidal sessile
assemblages, with common differences in the type and diversity of species found between
vertical and horizontal surfaces (Glasby & Connell 2001; Walker et al. 2007). In this case,
differences in recruitment between horizontal and vertical surfaces were most pronounced in
intertidal habitats. The most likely cause of the lack of recruitment, particularly on the upper
horizontal surface, which were smothered by fine sediment (Figure 13).




    Figure 13. Sediment smothering upper horizontal surface of settlement tiles after 2 months

Spatial differences in recruitment of oysters between intertidal and subtidal areas could be
due to a range of factors including: variation in the length of time oysters are exposure to
predators (intertidal sites can be exposed to lower predatory stress); increased
sedimentation in shallow intertidal habitats; and differences in the success of settlement and
in larval supply through stratification of larvae in the water column similar to that found in
barnacles (Grosberg 1982; Cummings 1994; Walker et al., 2007). Differences are also likely
to be due to competition with other sessile organisms such as the bryozoan S. unicornis,
which was particularly common and covered a large area on tiles deployed subtidally. While
they add to the overall biodiversity of sub-tidal reef habitats during early formation, fast
growing pioneer species such as bryozoans and sponges can recruit quickly to new space


Restoration of Noosa Estuary: An Assessment of Oyster Recruitment                                15