Developing quantitative relationships between functional traits and performance of tropical seaweed.

The development of trait-based ecology has deepened our understanding of community response to environmental challenges. Here we provide a conceptual underpinning for seaweed trait-based ecology by establishing relationships between traits and performance. We conducted a field experiment to determine if intra- and interspecific trait variation predicts variation in growth rate of three morphologically distinct species of tropical seaweed. We measured two traits for all species and three traits for the most 'plant-like' (exhibiting differentiated structures that resemble leaves, branches, and stems) species. These traits were either commonly used in previous seaweed studies or are analogs to traits commonly used for vascular plants. We hypothesized there would be positive relationships between growth and the nutrient acquisition trait and a negative relationship between growth and the herbivory and disturbance resistance trait. Across all species, we found significant relationships for both traits, with the resource acquisition trait (thallus surface area to thallus volume ratio) related positively and the resistance trait (thallus dry weight to thallus wet weight ratio) related negatively to growth. When the most 'plant-like' species was analyzed individually, we found all three resource allocation traits (blade wet weight to thallus wet weight ratio, blade volume to thallus volume ratio, and blade surface area to thallus surface area ratio) related positively to growth. To the best of our knowledge, we are the first to empirically link traits of tropical seaweed individuals directly to their performance, thereby identifying functional traits that can be used as proxies for the ecosystem function of productivity.