Kelp forests versus urchin barrens: a comparison of ecosystem functions and services provided by two alternative stable marine habitats.

Kelp forests and urchin barrens are two stable states in rocky reef ecosystems, each providing unique ecosystem functions like habitat for marine species and primary production. While studies frequently show that kelp forests support higher levels of some ecosystem functions than urchin barren habitats, no research has yet compared average differences. To address this gap, we first conducted a meta-analysis of studies that directly compared the ecosystem functions, services and general attributes provided by each habitat. We also compiled individual studies on ecosystem properties from both habitats and qualitatively assessed the benefits provided. The meta-analysis included 388 observations from 55 studies across 14 countries. We found that kelp forests consistently delivered higher levels of ecosystem properties such as biodiversity, species richness, abalone abundance and sea urchin roe quality. Urchin barrens supported higher urchin density and crustose coralline algae cover. The qualitative review further supported these findings, showing that kelp forests ranked higher in 11 out of 15 ecosystem properties. These findings can help guide decisions on managing rocky reef habitats and demonstrate the benefits of preserving or expanding kelp forests.