Ecological effects of foreshore stabilisation on temperate estuarine fish assemblages

Foreshore stabilisation is rapidly increasing to protect growing coastal populations from climate-change-driven erosion and sea level rise. While hard stabilisation structures such as rock revetments and groynes are known to alter hydrodynamic and sedimentary processes in estuarine systems, their ecological effects on fish communities remain poorly understood. This study examined whether rock revetments and groynes alter fish community ecology within sand-, reef-, and seagrass-associated habitats by quantifying fish abundance and measuring foreshore structural complexity (rugosity). Rock revetments supported greater fish taxa richness, total MaxN abundance, and fish diversity (Shannon–Wiener) in reef-associated habitats. In contrast, rock groynes supported higher fish taxa richness, total MaxN abundance, and diversity in sand and seagrass habitats. Differences in foreshore rugosity indicated that increased terrain complexity at stabilised sites was a key driver of these patterns. Despite these increases in diversity and abundance, stabilisation altered fish community composition in sand and seagrass habitats, revealing species-specific responses to different stabilisation types. Commercially and recreationally important species such as Yellowfin Bream ( Acanthopagrus australis ) and Luderick ( Girella tricuspidata ) were more abundant in stabilised sand and seagrass habitats, whereas other valuable species such as Sand Whiting ( Sillago ciliata ) were less abundant. These findings indicate that hard stabilisation structures can shift fish assemblages depending on the surrounding habitat. Overall, this study provides strong evidence that rock revetments and groynes can be ecologically engineered to enhance fish diversity in shallow estuarine environments, though habitat-specific designs and planning are required to support native fish communities and maintain ecosystem values.