Foundation species and biodiversity support and stabilize kelp forest ecosystems

Undersea forests of the giant kelp Macrocystis pyrifera are highly productive biodiversity hotspots found in temperate coastal oceans worldwide. Long-term data from the Santa Barbara Channel suggests that biodiversity of kelp forests increases temporal stability and resilience of these productive ecosystems. Giant kelp, the world’s largest alga, plays an outsized role in the kelp forest ecosystem through its massive physical structure rather than as a food source. We show that temporal stability of giant kelp increases the temporal stability of understory algae and sessile invertebrates. Long-term observations and experiments suggest that these effects result from strong interactions between kelp and sessile communities. In particular, shading of the seafloor by the kelp forest canopy depresses the diversity and abundance of algae while positively affecting sessile invertebrates. These results show that foundation species such as giant kelp may not only play a key role in defining community structure, but may disproportionately contribute to the dynamic properties of ecosystems. Future long-term experiments by the Santa Barbara Coastal LTER will investigate the mechanisms behind these interactions, particularly competition for space between sessile species in kelp forests, and how they are shaped by recruitment dynamics and predation.