2015-11-10 - P&O Agenda - Item 7, Attach 2 - Assessment of Oyster Recruitment

Executive Summary

With the support of the Noosa Shire Council and The Thomas Foundation, The Nature
Conservancy undertook an assessment of oyster recruitment in the Noosa Estuary. This
assessment is a critical piece of information to inform the viability and design or future oyster
reef restoration projects in the estuary.

This report presents the findings of the assessment, which involved deploying over 160
settlement tiles (10 cm x 10 cm squares made from fibrous cement sheet) for periods of up to
5 months between December 2014 and June 2015. Settlement tiles were deployed at seven
intertidal (0.1 m above low water mark) and five subtidal sites (typically 1 m below the
surface) around the Noosa River Estuary. Key findings from the analysis of these settlement
tiles are:


      Oysters recruited in moderate numbers at nearly all sites, with the highest observed
       recruitment occurring in Weyba Creek, the main channel around Tewantin, and in the
       narrow channel between Goat Island and Noosa North Shore. The growth rates
       oysters recruiting onto the settlement tiles was reasonably fast.
      There were at least two major oyster recruitment events in intertidal habitats
       (December–January and March–April), with the greatest number of oysters recruiting
       in approximately March-April 2015. Two to five times fewer oysters recruited to tiles
       deployed at subtidal depths than intertidal.
      Sediment was a major issue and prevented oyster recruitment of the upper surface
       and most vertical surfaces such that settlement was restricted to the underside of the
       tiles.
      Two species of oysters dominated the recruitment, Planostrea pestigris and Pinctada
       maculate. Surprisingly, no Sydney rock oysters (Saccostrea glomerata) were
       observed settling despite the widespread presence of adults in the estuary. Possible
       explanations for the lack of S.glomerata recruitment include, the presence of high
       sediment loads associated with runoff and re-suspension of fine sediments early in
       this past summer, or that settlement occurred at a different time of the year. The lack
       of S. glomerata does not preclude settlement and recruitment of this species on
       restored reefs, however it is an important consideration because the species of
       oysters that did recruit successfully during this assessment are not known to be reef
       building species. The oyster species that did recruit to the tiles do still provide
       structural habitat and an important food source for commercially and recreationally
       important fisheries species.
      An encouraging sign was the recruitment of numerous other species of marine life on
       the settlement tiles, including barnacles, mussels, bryozoans, ascidians, sponges,
       and polychaete worms. These types of sessile species provide an important