Effects of spatial attributes of oyster reefs on epifaunal assemblages vary at regional scales

Local spatial attributes of habitat patches (e.g., area, rugosity) are well-known to affect biodiversity, but such effects may interact with regional environmental processes resulting in variations in those relationships at large spatial scales. Hence, it is unclear whether associations between spatial attributes and biodiversity can be generalized to inform biodiversity conservation and restoration. This study investigated: (i) the relationships between epifauna assemblages and spatial attributes of Sydney rock oyster (Saccostrea glomerata) reefs, including within-patches (e.g. rugosity, distance to patch edge and elevation), whole-patch (size and shape) and amongst-patch attributes (i.e., landscape connectivity) in three estuaries spanning ∼250 km coastline of eastern Australia; and (ii) the variation in epifauna assemblages among the three estuaries to understand the variation in those relationships at regional scales. At each estuary, we collected random oyster cores from different oyster patches and counted and identified all epifauna >1 mm. Multivariate assemblage composition of epifauna showed large variations among estuaries, with little associations to spatial attributes. At local scales, attributes such as elevation, patch area and patch isolation were strong predictors of richness and total abundance in some estuaries. However, none of these relationships were consistent in strength and/or direction across estuaries. Thus, results suggest that the influence of local spatial attributes of oyster reefs on epifaunal assemblages is small and likely related to variations in species pools and environmental setting among estuaries. A greater understanding of the drivers of assemblages, especially at larger spatial scales, may lead to improved outcomes of management and restoration strategies for biodiversity associated with foundation species.