A trait-based approach to understanding and predicting ecosystem services of seaweed in marine forests

Ecosystem services provided by seaweeds are increasingly recognised, yet we lack frameworks to explain and predict how these services vary across species, space, and time. Here, using large brown canopy-forming macroalgae as a focal group, we propose a novel framework and set of hypotheses linking functional traits to ecosystem services. We first argue that seaweed trait variation can be understood through their ecological strategies, with key axes of variation expected to include the 'pace of life' (slow - fast), 'space use' (expand - extend), and 'resistance investment' (low - high). Different coordinated sets of traits are predicted to relate to these axes, with, for example, traits associated with resource acquisition (e.g., specific thallus area) increasing with the pace of life. In turn, species' positions in the strategy space and attendant traits should determine their impact on ecosystem services, with different services maximised in distinct parts of trait space. Existing evidence on species replacements in seaweed forests suggests that global change and other disturbances commonly shift assemblages in several dimensions of trait space, towards faster and less three-dimensionally complex forms, indicating that species' responses to environmental change and associated consequences for ecosystem services may be explained by strategies and associated traits. Finally, we provide a vision for testing our framework, through standardised trait-screening protocols and data compilation efforts.