Predictable patterns within the kelp forest can indirectly create temporary spatial refugia for ocean acidification

Seaweeds are gaining recognition as a significant CO2 sink with a role in active mitigation and

climate change adaptation, and specifically so in the application of an innovative coastal CO2 removal belt, effectively utilizing seaweed habitats to mitigate the adverse effects of ocean acidification (OA). However, assessing OA modification strength requires an understanding of the multiple parameters’ potential buffering effects, especially in highly dynamic systems. Exactly how kelp might generate more favorable conditions for marine calcifiers, has not been taken into account in previous studies to date. We studied the effects of sugar kelp (Saccharina latissima) on an experimental farm at the north end of Hood Canal, Washington—a low retentive coastal system. This study can serve as a natural analogue for many coastal bay habitats where prevailing physical forcing drives chemical changes. In this field mesocosm study, pelagic and benthic calcifiers were exposed with or without the kelp’s putatively protective proximity at locations in the middle, on the edge, and outside the kelp array. Model outputs were used to identify dominating factors in spatial and temporal kelp dynamics, while wavelet spectrum analyses helped in understanding predictability patterns. We linked these results to biological assessments, including biomineralization, growth and subcellular energetics responses of the examined species. We found our studied kelp array system did not modify carbonate chemistry parameters, but changed pH autocorrelation patterns towards higher predictability that was more favorable for marine calcifiers. Kelp also improved habitat provisioning through kelp-derived particulate organic resource utilization. Because of this, the co-culture of bivalves and seaweed can protect the calcifiers from negative effects of projected near-future OA. However, our study shows that a complex combination of physical, chemical and biological processes determines the efficiency of the kelp farms for creating more favorable habitats with respect to OA. Future macrophyte studies should focus significantly on the importance of predictability patterns, which can additionally improve the conditions for marine calcifiers as well as ecosystem services, with important implications for the aquaculture industry.