Can oysters provide a refuge for coastal biodiversity in a changing world?

Intertidal organisms are highly susceptible to climate warming as many already live close to their thermal limits. Ecosystem engineers, such as oysters, that provide shading and trap moisture during aerial exposure may provide... [ view full abstract ]

Intertidal organisms are highly susceptible to climate warming as many already live close to their thermal limits. Ecosystem engineers, such as oysters, that provide shading and trap moisture during aerial exposure may provide a refuge to intertidal invertebrates in a changing climate. However, this will depend on the ability of the oysters themselves to persist under warmer conditions. This study assessed: 1) the ability of the Sydney Rock Oyster, Saccostrea glomerata, to persist and form three-dimensional habitat under warmer conditions; and 2) whether there are particular oyster genotypes that display greater thermal tolerance, and could benefit restoration projects targeting climate change adaptation. Juvenile S. glomerata that had either been selectively bred for rapid growth and disease resistance or that were wild-type were exposed to a temperature gradient by attaching them to white, grey and black pavers that reached high temperatures of 36oC, 47oC and 60oC during summer low-tides, respectively. Each type of oyster displayed greater mortality and reduced growth rates on the black than the grey or white plates. Selectively bred oysters showed higher mortality than wild-type oysters on white and black pavers, while no significant difference between the two groups on grey pavers. By 12 months there was complete mortality of selectively bred oysters on black pavers. Although selectively bred oysters grew significantly faster than wild type oysters on the white pavers this advantage was lost at higher temperatures, with no significant difference in growth rates of the two oyster types on the grey or black pavers. The greater survivorship of wild-type oysters resulted in their greater habitat provision than selectively bred oysters on white and black pavers. Overall temperatures were cooler on all plates with than without oysters, but cooler microclimates were recorded among wild-type than selectively bred oysters on grey and black pavers, presumably due to increased habitat cover. Invertebrate recruitment was greater on all oyster tiles than bare control pavers, while no significant differences were recorded between oyster genotypes. Potentially, selection for fast growth and disease resistance has come at the cost of tolerance of oysters to extreme temperatures.