Abstract
The desire to use sentinel species as early warning indicators of impending climate change effects on entire ecosystems is attractive, but we need to verify that such approaches have sound biological foundations. A recent large-scale warming event in the North Pacific Ocean of unprecedented magnitude and duration allowed us to evaluate the sentinel status of giant kelp, a coastal foundation species that thrives in cold, nutrient-rich waters and is considered sensitive to warming. Here, we show that giant kelp and the majority of species that associate with it did not presage ecosystem effects of extreme warming off southern California despite giant kelp's expected vulnerability. Our results challenge the general perception that kelp-dominated systems are highly vulnerable to extreme warming events and expose the more general risk of relying on supposed sentinel species that are assumed to be very sensitive to climate change.
Highlights
The desire to use sentinel species as early warning indicators of impending climate change effects on entire ecosystems is attractive, but we need to verify that such approaches have sound biological foundations
Coastal marine ecosystems supported by foundation species in temperate seas are reported to be sensitive to ocean warming and low-nutrient availability associated with climate change[8], and are expected to have been greatly affected by the extraordinary warming that recently occurred off the Pacific coast of North America[9]
Giant kelp populations are naturally quite variable, so changes in kelp forests can be misinterpreted unless viewed in the context of long-term data[29]
Summary
The desire to use sentinel species as early warning indicators of impending climate change effects on entire ecosystems is attractive, but we need to verify that such approaches have sound biological foundations. A recent large-scale warming event in the North Pacific Ocean of unprecedented magnitude and duration allowed us to evaluate the sentinel status of giant kelp, a coastal foundation species that thrives in cold, nutrient-rich waters and is considered sensitive to warming. The ecological effects of global warming are expected to be large[1,2], but are proving difficult and costly to measure This has led to a growing interest in using sentinel species as early warning indicators of impending climate change effects on entire ecosystems[3,4]. The warm water ‘blob’ moved eastward, and by October 2014 spread to fill the coastal domain from the Gulf of Alaska to the tip of Baja California, Mexico[12,13] This phenomenon was followed by severe El Nino conditions, which prolonged the warming through 2015. The resilience of giant kelp to the unprecedented warming highlights the limitations in our understanding of the ecology of kelp-dominated ecosystems, and questions their general use as early indicators of climate change
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