Structural attributes of dominant seagrass species modulate invertebrate assemblages within the Shark Bay world Heritage Area

This is the authors' abstract. We don't add key points for this paper.

The structural complexity of seagrass meadows plays a central role in shaping the diversity and composition of associated invertebrate assemblages. In the Shark Bay World Heritage Area of Western Australia, the dominant species Amphibolis antarctica and Posidonia australis differ markedly in their above- and below-ground morphology, yet the invertebrate assemblages they support remain poorly characterised. This study provides the first contemporary assessment of these habitat–invertebrate relationships, a timely contribution given the region’s increasing exposure to frequent and extreme climatic events. We identified 13,124 invertebrates from 7 phyla, 16 classes and 55 orders/families and highlight marked differences between epifaunal assemblage structure inhabiting the canopies (above-ground component) of the two seagrasses. The canopies of A. antarctica supported nearly tenfold the density of invertebrates compared to P. australis , particularly peracarid crustaceans such as amphipods and isopods, tubiculous polychaetes including sabellids and serpulids, and small gastropod grazers such as rissoids and collumbellids. Moreover, A. antarctica stored more than triple the amount of plant biomass in leaves and stems. In contrast, P. australis possessed substantially greater below-ground biomass, and this extensive root–rhizome matrix supported infaunal assemblages comparable to those of A. antarctica . These findings demonstrate that the two seagrass species do not function as homogenous habitats: A. antarctica plays a disproportionate role in supporting dense and diverse above-ground invertebrate assemblages, whereas P. australis provides an ecological safeguard below-ground, reflecting functional overlap in habitat provision. These findings underscore the importance of protecting the mosaics of mono-specific seagrass meadows in Shark Bay to sustain ecosystem productivity and resilience.