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Biology

The Kelp in the Coal Mine: can kelps act as an indicator for climate change?

 

 

Article: Reed, Daniel, et al. “Extreme warming challenges sentinel status of kelp forests as indicators of climate change.” Nature Communications 7 (2016).

Background:

Fig. 1: Massive kelps are good at creating habitat for others but have proven sensitive to changes in climate. Could they be canaries in the coal mine for detecting climate change? (Photo: Riverview Science)

Fig. 1: Massive kelps are good at creating habitat for others but have proven sensitive to changes in climate. Could they be canaries in the coal mine for detecting climate change? (Photo: Riverview Science)

Studying the effects of climate change can be difficult. It’s hard to recreate ecological systems, the network of species interactions, and the variance of environmental conditions within a lab setting. Likewise, modeling the effects of climate change comes with varying degrees of precision. As such, scientists are often looking for the canary in the coal mine, or a sentinel species that can act as an early warning indicator of climate change. There have been numerous studies that show kelp species are sensitive to changes in ocean temperature and in nutrient levels. Their sensitivity, coupled with their rapid growth, seem to make kelps ideal sentinel species (Fig. 1). In addition, kelps play a critical role in providing habitat and food for a wide range of marine creatures, so their sensitivity to climate would be important in determining the impact on entire ecosystems.

Fig. 2: The Blob, was a mass of warm water sitting off the Pacific coast of North America. The dark red on this map show areas where water temperatures were 2 or more degrees (C) higher than normal (Photo: NOAA).

Fig. 2: The Blob, was a mass of warm water sitting off the Pacific coast of North America. The dark red on this map show areas where water temperatures were 2 or more degrees (C) higher than normal (Photo: NOAA).

Just a few years ago, the waters off the Pacific coast of North America began to warm. Temperatures were as much as 3 degrees Celsius warmer than had been observed since the 1980s. Higher atmospheric pressure meant that oceans held onto their heat a little longer and decreased winds prevented cooler deeper water from upwelling. All of this resulted in a large mass of warm water, affectionately called “The Blob” by scientists,  that sat off the coast starting in 2014 (Fig. 2). Followed by El Nino, waters off the California coast remained warm through 2015. In addition, the lack of upwelling along the coast reduced the amount of nutrients available for kelp. This long spell of warmer-than-usual ocean water and low nutrient conditions provided an opportunity for scientists to investigate how marine communities, specifically kelp communities were affected. If there was evidence of an impact of warmer, nutrient poor water on kelp then we may very well use it as a sentinel species.

The Study:

The coast of southern California has kelp forest that have been studied for a long time. Relatively permanent plots within forests of giant kelp, Macrocystis pyrifera (Fig. 3), have been monitored for a number of years. By comparing the biomass and cover of Macrocystis between previous years and “Blob years,” scientists could determine whether this prolonged period of warm, low nutrient water was causing problems for kelp forest ecosystems.

Fig. 3: Macrocystis pyrifera, a giant kelp, is found along the west coast of the US.

Fig. 3: Macrocystis pyrifera, a giant kelp, is found along the west coast of the US.

Fig. 4: Coverage of giant kelp declined compared to previous years, but this decline is likely due to a longer term trend rather than a few warmer years.

Fig. 4: Coverage of giant kelp declined compared to previous years, but this decline is likely due to a longer term trend rather than a few warmer years. Here, the x-axis represents years 2001-2015, the last two dots (red) reference the Blob years.

 

 

 

 

 

 

 

 

Researchers did find a decline in the cover of giant kelp in southern California during the blob years. However, compared with trends over a 15-year period, the scientists showed that the kelp decline observed in the warmer years was actually just part of a larger trend in kelp decline — the decrease in coverage was not necessarily linked to the change in ocean condition (Fig. 4). In addition, surveys of other kelp forest associated creatures showed similar declines (Fig. 5). Similarly, the canopy biomass of kelp during blob years was variable, and didn’t stray far from previous estimates of biomass (Fig. 6).

Fig. 5: Kelp forest inhabitants were also monitored. Declines in sessile (non-moving) invertebrates (d) also follow a long term trend. The drop in sea stars (f) was not directly linked to temperature but rather a spread of wasting disease. Sea urchins (e), important kelp consumers, showed no trend over the long term data, but declines under Blob years a linked to the increase in disease spread due to warmer waters.

Fig. 5: Kelp forest inhabitants were also monitored. Declines in sessile (non-moving) invertebrates (d) also follow a long term trend. The drop in sea stars (f) was not directly linked to temperature but rather a spread of wasting disease. Sea urchins (e), important kelp consumers, showed no trend over the long term data, but declines under Blob years a linked to the increase in disease spread due to warmer waters.

Fig. 6: At three sites off the southern California coast, anomalies in kelp biomass are variable (a), with no clear impact of warmer years (red dots). At the same sites, temperature anomalies were found in Blob years (b).

Fig. 6: At three sites off the southern California coast, anomalies in kelp biomass are variable (a), with no clear impact of warmer years (red dots). At the same sites, temperature anomalies were found in Blob years (b).

 

The Significance:

The Blob provided a unique opportunity to study longer term impacts of climate change on important marine species and communities in a natural setting. Kelp species were thought to be sensitive and vulnerable to warmer waters and low nutrient concentrations, but results of this study show that despite a decline, the kelp cover and biomass fit a larger trend that is independent of prolonged warming. This shows that giant kelps are potentially more resistant to global climate change than previously thought. As such, it wouldn’t make sense to classify kelps as sentinel species. The lack of a clear response to the Blob highlights an inability to act as an early warning or an indicator. This does not mean, however, that climate change will not negatively impact these species and ecosystems, rather, it shows that we should be careful when trying to predict the impacts of change and the dangers in establishing sentinel species.

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