Marine heat wave and multiple stressors tip bull kelp forest to sea urchin barrens

L Rogers-Bennett,C A Catton

doi:10.1038/s41598-019-51114-y

Abstract

Extreme climatic events have recently impacted marine ecosystems around the world, including foundation species such as corals and kelps. Here, we describe the rapid climate-driven catastrophic shift in 2014 from a previously robust kelp forest to unproductive large scale urchin barrens in northern California. Bull kelp canopy was reduced by >90% along more than 350 km of coastline. Twenty years of kelp ecosystem surveys reveal the timing and magnitude of events, including mass mortalities of sea stars (2013-), intense ocean warming (2014–2017), and sea urchin barrens (2015-). Multiple stressors led to the unprecedented and long-lasting decline of the kelp forest. Kelp deforestation triggered mass (80%) abalone mortality (2017) resulting in the closure in 2018 of the recreational abalone fishery worth an estimated $44 M and the collapse of the north coast commercial red sea urchin fishery (2015-) worth $3 M. Key questions remain such as the relative roles of ocean warming and sea star disease in the massive purple sea urchin population increase. Science and policy will need to partner to better understand drivers, build climate-resilient fisheries and kelp forest recovery strategies in order to restore essential kelp forest ecosystem services.

Highlights

Extreme climatic events have recently impacted marine ecosystems around the world, including foundation species such as corals and kelps
Similar impacts seem to be developing in kelp forests from Baja California to Alaska, so that the dynamics described from this northern California case study will be critical for tracking and understanding the biological responses to these multiple climate-related stressors and resulting degradation of fisheries and other ecosystem services[37]
We document the catastrophic declines in northern California kelp forests during the Marine Heat Wave (MHW), and the subsequent rapid shift of historically persistent kelp ecosystems to wide-spread urchin barrens

Summary

Introduction

Extreme climatic events have recently impacted marine ecosystems around the world, including foundation species such as corals and kelps. Temperate kelp forests in northern California (Fig. 1) were vulnerable to the MHW and other concurrent ecological stressors This region, which was historically very productive, supported robust fisheries including the recreational red abalone, Haliotis rufescens, fishery (valued at $44 M yr−1 36) as well as the commercial red sea urchin, Mesocentrotus franciscanus, fishery (valued at $3 M yr−1). The long-term kelp forest monitoring program was critical for tracking and understanding the biological responses to these multiple climate-related stressors and resulting degradation of fisheries and other ecosystem services[37]. Similar impacts seem to be developing in kelp forests from Baja California to Alaska (personal communications), so that the dynamics described from this northern California case study will be critical for tracking and understanding the biological responses to these multiple climate-related stressors and resulting degradation of fisheries and other ecosystem services[37]. We discuss the vulnerability of ecosystem services affecting economic outcomes for the region (e.g. fisheries collapse, loss of tourism), and explore opportunities to enhance resilience[38] against climate changes which are predicted to increase in the future

Methods

Results

Conclusion