Cascading impacts of earthquakes and extreme heatwaves have destroyed populations of an iconic marine foundation species

Aim Ecologists traditionally study how contemporary local processes, such as biological interactions and physical stressors, affect the distribution and abundance of organisms. By comparison, biogeographers study the distribution of the same organisms, but focus on historic, larger-scale processes that can cause mass mortalities, such as earthquakes. Here we document cascading effects of rare biogeographical (seismic) and more common ecological (temperature-related) processes on the distribution and abundances of coastal foundation species. Location Intertidal wave-exposed rocky reefs around Kaikoura, New Zealand, dominated by large, long-lived, and iconic southern bull kelps (Durvillaea antarctica and Durvillaea willana). Methods In November 2016, a 7.8 Mw earthquake uplifted the coastline around Kaikoura by up to 2 m, and a year later the region experienced the hottest summer on record. Extensive sampling of intertidal communities over 15 km coastline were done shortly after the earthquake and heatwaves and 4 years after the earthquake. Results Durvillaea lost 75% of its canopy to uplift and the heatwaves reduced canopies that had survived the uplift by an additional 35%. The survey done 4 years after the earthquake showed that Durvillaea had not recovered and that the intertidal zone in many places now was dominated by small turfs and foliose seaweed. Main conclusions Cascading impacts from seismic uplift and heatwaves have destroyed populations of Durvillaea around Kaikoura. Surviving smaller and sparser Durvillaea patches will likely compromise capacity for self-replacement and lower resilience to future stressors. These results are discussed in a global biogeographical-ecological context of seismic activity and extreme heatwaves and highlight that these events, which are not particularly rare in a geological context, may have common long-lasting ecological legacies.

Automated summary

The study documents the cascading effects of seismic uplift and heatwaves on coastal foundation species in Kaikoura, New Zealand, with significant losses to the dominant bull kelps. The impacts are likely to compromise the self-replacement capacity and resilience of these species, highlighting the long-lasting ecological legacies of seismic activity and extreme heatwaves.