Handbook for the standardised measurement of seaweed functional traits

Millie Parks¹, Alizée Mauffrey¹, Laura Cappelatti², Matthew Bracken³, Robin Fales⁴, Hannah Hall³, John Griffin¹

¹Swansea University, UK - ²Origin by Ocean, Finland - ³University of California Irvine, USA - ⁴Soka University, USA

Functional traits are individual-level characteristics that influence an organism’s fitness and contributions to ecological processes. As a cornerstone of ecological research, traits enable generalizations about the links between form and function across species, assemblages, and regions. Importantly, they help predict species’ vulnerability to environmental change and the consequences for ecosystem functioning. In seaweeds, trait-based approaches have historically been constrained to single or few species, rigid morpho-functional groups (e.g., Steneck and Dethier), or qualitative expert assessments. However, direct measurement of multiple traits at the individual level, as established in terrestrial plant ecology, holds great promise. It can capture intra- and interspecific variability, allow the flexible application of context-relevant traits, and advance functional ecology across scales. While trait screening efforts for seaweeds are emerging, standardized protocols are urgently needed to ensure comparability and maximize their utility. Here, inspired by the standardization efforts in terrestrial systems, we present a comprehensive “handbook” of seaweed trait measurements—a standardized protocol encompassing sample collection, trait quantification, and data curation. We provide the rationale for each trait’s measurement based on its links to individual fitness and ecological processes. Drawing on our database of >350 species from NE Atlantic and Pacific coasts, we quantify intraspecific variability to guide sampling strategies. Additionally, we assess inter-trait relationships to identify traits that best capture distinct axes of functional variability. Collectively, we envision these protocols as a global benchmark for seaweed trait research, enabling universal comparability of trait data. This approach will support the creation of a global seaweed trait database, facilitating the analysis of environmental change impacts across spatial and temporal scales.