Plankton might evolve to survive climate change

Here’s two things we know: One, the oceans are getting warmer. Two, the oceans are becoming more acidic. Here’s one thing we don’t know: what those two things mean for phytoplankton. The tiny microscopic plants form the base of the marine food web, and are responsible for about half of the planet’s primary production – the transformation of simple molecules, like carbon dioxide and water, into complex ones. The good news is that many species of phytoplankton reproduce fast, so they can evolve rapidly.

To see how one important phytoplankton species, Emiliania huxleyi, might respond to our changing climate, a group of researchers led by Lothar Schlüter of Germany’s GEOMAR Helmholtz-Centre for Ocean Research exposed them to seawater at three different concentrations of dissolved carbon dioxide and two different temperatures. They reported their results this week in the journal Nature Climate Change.

The researchers picked that species because of the critical role it plays in the global carbon cycle. According to Schlüter, “[it] is considered to be the single most important calcifying algae in the world’s ocean, with blooms that can be seen from outer space.”

E. huxleyi reproduces asexually. Over the course of a year, the researchers’ samples descended through 460 generations. It may not seem like a lot, but that’s quite a bit of evolutionary time. (Assuming that a human generation is approximately equivalent to 25 years, that would be analogous to 11,500 years. For perspective, our species had just begun to develop agriculture 11,500 years ago.)

First, the researchers divided their algae into three groups, which were kept for three years in 15 degrees Celsius (59 degrees Fahrenheit) seawater with three different levels of dissolved carbon dioxide. The lowest was set to mimic current ambient CO2 levels. A medium sample was “intended to simulate an end-of-the-century worse-case scenario,” while the highest concentration corresponded to the predictions regarding the highest future level of ocean acidification.

Then, each of those three groups was divided in half again. One sample each was kept as a control at 15 degrees Celsius. To see whether the algae could evolve to cope with increasing temperatures, the others were subjected to increases of 1 degree Celsius until they reached a final temperature of 26.3 degrees Celsius, or 79.34 degrees Fahrenheit.

They discovered – contrary to their expectations – that E. huxleyi successfully adapted to both the increased acidification and temperature. It was reasonable to expect the algae to adapt to either one in isolation, but there were also “no apparent antagonistic effects” when selecting for both adaptations simultaneously. In fact, population growth fully recovered even under what Schlüter called “the most stressful future ocean scenario.”

However, adaptation to high temperature occurred six times faster than adaptation to the elevated CO2 concentration, and the researchers do not yet have a good explanation for that. It’s possible, they say, that genetic mutations related to temperature-related adaptations may have a larger beneficial effect than similar mutations for acidification-related adaptations.

The finding suggests that phytoplankton may be more “evolutionarily flexible than previously thought.” Even though the experiment was limited to a single set of genetically identical individuals from a single species, the researchers suspect that their findings apply more broadly, at least among E. huxleyi. In other words, there is no reason to suspect that other genotypes from within the same species would not similarly adapt to changing ocean conditions.

When predicting the effects of an ocean that’s getting hotter and more acidic, researchers will have to consider the dynamic processes of evolution. It’s an important reminder that during and after the Anthropocene, life on Earth will continue…even if our own species can’t adapt quite as fast. – Jason G. Goldman | 17 September 2014

Source: Schlüter L., Magdalena A. Gutowska, Joachim P. Gröger, Ulf Riebesell & Thorsten B. H. Reusch (2014). Adaptation of a globally important coccolithophore to ocean warming and acidification, Nature Climate Change, DOI: http://dx.doi.org/10.1038/nclimate2379

Header image: A scanning electron micrograph of three Emiliania huxleyi cells, via Dr. Kai T Lohbeck (GEOMAR), used with permission.

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