It’s a claim repeated often enough that it’s easy to take for granted: kelp forests protect the coast by soaking up wave energy before it reaches shore. A 2023 study put that assumption to a direct test, and the answer turned out to be “yes, but less than you’d think.”
Researchers from UC Davis’s Bodega Marine Laboratory, Stanford’s Hopkins Marine Station, San Diego State University and The Bay Foundation measured wave energy across a restored giant kelp bed at Marguerite Reef, on the Palos Verdes Peninsula, comparing conditions before kelp grew back, during regrowth, and once the canopy was fully established at around eight stipes per square meter. They tracked this across a full year of wave conditions, from calm days to swells over four meters.
The seafloor itself, it turns out, already does most of the work, cutting incoming wave energy by about 12% on its own. A mature kelp canopy added roughly 7 percentage points on top of that, for a combined damping effect of around 19%, concentrated mostly on smaller, longer-period waves rather than the biggest storm swells. The authors were candid that this is a meaningfully smaller effect than kelp’s reputation as a coastal defense suggests, and they’ve called for the assumption to be re-tested across kelp forests of different densities and wave climates before it’s built into coastal protection planning.
Further reading: Elsmore, K. et al., “Wave damping by giant kelp, Macrocystis pyrifera,” Annals of Botany (2023).