Seagrasses are productive and valuable habitats providing many important ecosystem functions and services. Seagrass ecosystems have been declining globally over the last century and are at risk of further loss from anthropogenic impacts and extreme climate and weather events. A key function of seagrasses are the habitats they form that support a diverse array of fauna including ecological and economically important fish species at different life stages. When this habitat is lost it generally leads to a reduction in biodiversity.
In Cairns Harbour, tropical north Queensland, seagrass meadows and associated fish assemblages have been monitored periodically for the last four decades. A series of floods and cyclones in the late 2000’s led to the almost entire collapse of intertidal meadows within the harbour followed by a slow decade-long recovery. This allowed for the study of changes in fish assemblages using a beam trawl dataset spanning pre-disturbance, disturbance, and recovery periods of seagrass.
Loss of seagrass from storms and floods were associated with significant reductions in fish abundance (~84%) and taxonomic richness (~73%), likely due to the loss of structurally complex habitat. Following disturbance, both abundance and richness recovered to levels comparable to pre-disturbance conditions, indicating numerical recovery of fish assemblages. However, assemblage composition, both structurally (taxonomic) and functional (trophic) differed significantly between pre- and post-disturbance sampling events, reflecting a long-term shift in fish species following seagrass loss and recovery. This highlights the importance of incorporating multiple variables for biodiversity when assessing ecosystem recovery in tropical seagrass habitats.