Functionally Rich Fish Assemblages Support Greater Rates of Multiple Ecological Functions in Seagrass Meadows

Animals move between ecosystems, facilitating important ecosystem functions. The context, connectivity, and complexity of habitats alter faunal assemblages and associated ecological functions that regulate ecosystem structure, functioning, and resilience. Fish assemblages in seagrass meadows are functionally diverse and contribute essential ecological functions which are necessary for energy transfer within food webs, such as carnivory and herbivory. However, not all species support these functions equally, and it is their functional traits that modify how different species deliver ecological functions. This aim of this study was to investigate how the functional diversity of fish relates to multiple ecological functions within seagrass meadows of Moreton Bay, Queensland, Australia. This study surveyed fish community structure, using baited and unbaited remote underwater video stations, the rates of carnivory and herbivory using in-field assays, and the composition of seagrass meadows at 50 replicates across 10 seagrass meadows in Moreton Bay, Queensland, Australia. Carnivory and herbivory increased with increasing levels of functional diversity. Seagrass cover correlated positively with functional diversity, while seagrass species diversity correlated negatively. Additionally, seagrass meadows with fewer mangroves nearby and further from reefs supported greater levels of functional diversity and, when closer to the ocean, they supported greater overall ecosystem functioning. Carnivory was greatest in seagrass meadows nearer coral reefs, while herbivory was greatest when seagrass was sparser. These findings demonstrate the importance of a functionally diverse food web and spatial context for sustaining resilient seagrass meadows and when conserving seagrass meadows in the future, understanding the functional composition of fish and seagrass will be critical. Management should prioritise the conservation and restoration of seagrass beds that are well connected with the open ocean and consider using functional diversity metrics to monitor these ecosystems given the efficacy of these metrics in reflecting broader condition and functioning.