Selecting functional traits that capture trade-offs for intertidal macroalgae provides a roadmap for future studies.

Abstract

Increased impacts from anthropogenic stressors are motivating the search for novel tools and approaches to understand ecosystem shifts and community change. Although trait-based approaches have provided powerful tools for many taxa, the functional ecology of marine macroalgae remains rooted in functional group models from the 1980s. Thus, we sought a core set of macroalgal traits to capture the diversity of ecological strategies that maintain ecological functions in a changing ocean. We first measured and analyzed a large number of functional traits to capture ecological strategies, and then used quantitative methods and examined the literature to select six core traits that captured the same strategies. We chose rocky intertidal sites, as they compress large shifts in environmental drivers into a small spatial scale, and chose seven morphologically diverse species collected across habitats and seasons. Permutational multivariate analyses of variance that included either 16 or six traits both determined significant differences across traits among species, with nearly equal explanatory power. In both data sets (16 vs. six traits), we discovered a resource acquisition trade-off along an axis of variation that maximizes either thallus height to facilitate resource acquisition by preemptive capture or relative surface area to increase uptake efficiency when lower resource supplies are available. Being taller, however, requires strength to resist disturbance (drag), whereas individuals with more surface area are shorter and weaker. Thus, we posit only six core traits are needed to capture ecological strategies for intertidal macroalgae in this rocky intertidal system, streamlining future research. Our results provide a roadmap for selecting traits that can rapidly advance exploration of trait-based ecology in other macroalgal-dominated ecosystems, providing a strong foundation to continue developing trait-based ecology for macroalgae across systems.