Temperature and light explain spatial variation in growth and productivity of the kelp Ecklonia radiata

Abstract

Understanding the relative importance of environmental variables on growth and productivity of macroalgae is key to understanding how they might be influenced by environmental change. This study evaluates spatial and temporal patterns in growth and productivity of the kelp Ecklonia radiata in Marmion Lagoon (Western Australia) and tested how well these patterns could be explained by temperature, light, water movement and nutrient concentrations. Growth rates (thallus extension and productivity, measured as biomass accumulation and massstandardised biomass accumulation) varied between seasons, with the highest rates observed during spring, followed by summer. Temperature and light best explained spatial patterns in growth and productivity of E. radiata. Bottom water velocity and nutrient concentrations typically explained less of the variation, but in some cases they were well-correlated with patterns in productivity. Temperature was the best explanatory variable in summer, when higher water temperatures were associated with lower growth and productivity. Light explained patterns in growth and productivity during winter and spring, when light intensities were lower at some sites, especially at deeper offshore sites, than in summer. The repeated associations between temperature or light and patterns in thallus extension and biomass accumulation suggest that these 2 variables are the most important influences on growth and productivity of E. radiata in Marmion Lagoon. This inference is supported by the knowledge that these 2 variables strongly influence rates of photosynthesis. Our findings suggest that a sustained increase in temperature or reduction in light will reduce growth and productivity of E. radiata.