Characterising tropical oyster reefs: invertebrate-environment associations and a newly documented reef building species

Oyster reefs were once widespread across the global tropics but have often been excluded from global assessments of historical distributions, declines and conservation needs. Consequently, little is known about tropical oyster reefs, including ecological function, which species are reef-building, structural characterisations of remnant reefs, associated biodiversity, and whether conservation actions are needed to ensure their recovery. We compared the characteristics of newly documented tropical oyster reefs across three Australian locations to gain a foundational understanding of their ecology. At each location, structural reef traits were assessed, and associated invertebrate communities were quantified taxonomically and functionally. Location had a strong effect on invertebrate communities, with reefs in Gladstone hosting a greater abundance, and larger, invertebrates, followed by Mapoon, and then Proserpine. Most invertebrates were positively associated with the lower intertidal zone and shelly sediment - we hypothesise that heat stress, interstitial reef spaces, and the proportion of habitat edges could be explanations for these observed patterns, however, further research is needed to confirm this. Reef-building oysters identified using molecular markers at all locations were predominantly Saccostrea lineage B, a species broadly distributed across tropical Australia and the Indo-Pacific. These characterisations provide novel insights into the ecology of tropical oyster reefs and baseline information to inform appropriate conservation strategies.