Soundscapes indicate kelp forest condition

Soundscapes are promising indicators of marine habitat condition, yet this approach remains untested in many ecosystems, and soundscape-ecological relationships remain unclear. In this study, we analyzed soundscapes in kelp forest habitats off the coast of California, USA, in Channel Islands National Park. We investigated if (1) soundscape features correlated with ecological variables and (2) these features differed inside and outside of marine protected areas (MPAs). We recorded 1 min every 15 min at 5 sites from 12 May to 23 June 2018. Three sites were in MPAs with high kelp cover and low urchin density, while 2 were in adjacent, unprotected habitats with low kelp cover and high urchin density. To analyze the data, we calculated soundscape features using detection algorithms and acoustic indices, which we then correlated with annual ecological data from 2016 to 2018. We found that drivers of regime shifts in kelp forests, i.e. sea urchin density, kelp cover, and fish diversity, were significantly related to soundscape features. Sea urchin density was positively correlated and kelp cover negatively correlated with the rate of shrimp snaps. Fish species richness and abundance were positively correlated with the intensity and diel dynamics in the low-frequency bands that contained most fish vocalizations. This study demonstrates that marine soundscapes indicate the condition of kelp forests, which are vulnerable to destruction from urchin overgrazing. If marine soundscapes can reliably indicate the status of ecological drivers, then this approach could be a valuable complement to diver surveys in fully assessing marine ecosystem health.