Forests of the sea: Predictive habitat modelling to assess the abundance of canopy forming kelp forests on temperate reefs

Large brown seaweeds (kelps) form forests in temperate and boreal marine systems that serve as foundations to the structure and dynamics of communities. Mapping the distributions of these species is important to understanding... [ view full abstract ]

Large brown seaweeds (kelps) form forests in temperate and boreal marine systems that serve as foundations to the structure and dynamics of communities. Mapping the distributions of these species is important to understanding the ecology of coastal environments, predicting consequences of climate change and the potential for carbon production. We demonstrate how advancements in seafloor mapping technology, models of wave energy and modeling approaches can be used to map the distribution and relative abundance of seaweed forests of Ecklonia radiata and provide complete coverage over 100s of kilometers at comparable resolutions to those typically used in terrestrial studies. Using generalized linear mixed models (GLMMs), we associated observations of E. radiata abundance from video transects with environmental variables. These relationships were then used to predict the distribution of E. radiata across our 756.1 km2 study area off the coast of Victoria, Australia. A reserved dataset was used to test the accuracy of these predictions. We found that the abundance distribution of E. radiata is strongly associated with depth, presence of rocky reef, complexity of the reef topography, and wave exposure. In addition, the GLMM methodology allowed us to adequately account for spatial autocorrelation in our sampling methods. The predictive distribution map created from the best GLMM accurately predicted the abundance of E. radiata with an accuracy of 69% (Figure 1). Our results indicate that the abundance distribution of E. radiata is strongly associated with multiple environmental variables and these associations can be used to accurately predict its distribution across broad scales. Structure-forming macroalgae are foundational species in many coastal zones around the world but their broad scale distributions are often unknown. Using methods like those presented in this study, we can accurately map the distribution of these species, which will give insight into ecological communities, biodiversity distribution, carbon uptake, and potential sequestration.