Untangling the roles of physical and demographic controls on kelp forest dynamics

Kelp forests are dominant, structure-forming ecosystems on subtidal rocky reefs along temperate coasts. The giant kelp (Macrocystis pyrifera) is a globally distributed, canopy-forming species that underpins a biodiverse and economically important ecosystem through its high rates of primary production and complex three-dimensional structure. To sustain this productivity, giant kelp requires adequate supplies of both nutrients and light. However, elevated temperature events, such as El Nino or marine heatwaves, can exceed the species' thermal limits and lead to declines. Beyond these physical drivers, demographic processes operating at the scales of individual plants and fronds shape the structure and persistence of kelp forests. These intrinsic population dynamics often defy expectations based solely on environmental conditions. In this seminar, I will discuss my lab's research combining field and laboratory studies to investigate the drivers of giant kelp physiological condition and productivity, and how we have used novel remote-sensing observations to reveal the scales at which seasonal upwelling of nutrients and frond senescence regulate canopy dynamics. I will conclude by highlighting how these insights help us disentangle the roles of physical forcing and demographic processes in shaping the spatial dynamics of giant kelp forests from local to global scales.

Speaker: Tom Bell, marine ecologist