Drivers of kelp forest productivity from warm to cool range edgesMacroecology

Karen Filbee-Dexter^1,2, Albert Pessarrodona^1,3, Morten F. Pedersen⁴, Thomas Wernberg^1,2

¹University of Western Australia, Australia - ²Institute of Marine Research, Norway - ³Conservation International - ⁴Roskilde University, Denmark

Human activities are increasingly transforming temperate reefs, with important consequences on their function and the flow of ecological benefits to society. Yet, shifts in ecological functions can be challenging to predict, and are not only explained by changes in species abundance, but also the rates at which species deliver functions, which can depend on environmental conditions along a species range. A key function of kelp forests is primary productivity, which underpins their contributions to coastal food webs, carbon cycling, oxygen production and nutrient filtration. Kelp forest productivity can vary with temperature and species, yet it is unclear how this function will change into the future. In this talk I will explore patterns of net primary productivity for kelp forests in Norway measured from across the distribution of Laminaria hyperborea and Saccharina latissima. I will present species-specific productivity rates, collected by divers from 44 sites ranging from the opening Arctic (78°N) to the warming Skagerrak (58°N). Temperature appears to be a significant driver of kelp productivity, with peak productivity occurring at midpoints along the range. When combined with areal maps of these two species, these relationships suggest future productivity may be reduced for kelp forests at warm ranges and may increase in cool ranges. We also find these kelp forests make up a significant component of coastal and Arctic primary production and should be better included in ocean carbon cycles.