Marine communities are vulnerable to rising ocean temperatures as well as local climate events like heat waves
Brown University
The paper, published in the Annual Review
of Ecology, Evolution, and Systematics, highlights the interplay between the
trend of climate warming and the fluctuations in local temperature. These two
properties cause atypically warm events such as marine heatwaves to occur with
increasing frequency and magnitude.
However, the interaction between the steadily warming
climate and the spikes in local temperatures tends to be underappreciated,
according to study co-author Jon Witman, a professor of biology at Brown
University.
“Climate change studies often focus on the trend of global warming,” Witman said. “But organisms in the ocean are also experiencing temperature fluctuations, and that’s less studied and therefore less understood. What we’re trying to do is to add more reality into ocean climate change studies by considering both the smooth, upward trend of climate warming as well as the variability on top of that trend.”
The paper proposes a new approach for understanding and
modeling the effects of marine climate change, with suggestions for future
research.
Witman offered coral as an example that illustrates the
need for a new approach. While an organism like coral is already trying to
adapt to the trend of rising temperatures, he noted, it then endures a heat
wave, which causes a large and sudden spike in temperature.
Temperature spikes tend to lead to coral bleaching, which
is when metabolically stressed corals expel the beneficial microscopic algae
living within them and turn white. If the temperature stays high and algae are
unable to return to their host coral, the bleached coral will die.
Witman pointed to heat waves in the Mediterranean that
have led to an increase in coral bleaching and death of corals and sea fans.
Extreme events such as heat waves may alter or damage
marine ecosystems in ways that leave them more vulnerable to both progressive
climate change as well as the next temperature fluctuation, Witman added. A
more realistic model may help scientists better identify areas where coral is
more likely to die off in an extreme event leaving coral-dependent organisms at
risk over time, he said.
In other cases, temperature variability can lead to an
opposite response in the affected organism: an ability to acclimatize or adapt
to temperature extremes, depending on their frequency and intensity.
These responses to variable events like heat waves
compound and are compounded by the effects caused by rapidly and steadily
increasing ocean temperatures, Witman said.
Witman collaborated with Andrew Pershing of the nonprofit
Climate Central, who studied biology as an undergraduate at Brown, and John
Bruno, a professor of biology in the University of North Carolina at Chapel
Hill, who earned a Ph.D. in ecology and evolutionary biology from Brown.
In their paper, Bruno, Pershing and Witman considered how
organisms and communities adapt or adjust to both smooth trends and variable
changes, and then reviewed processes that influence the rate at which marine
communities adjust to changes in their physical environment — as well as those
processes that might hamper adaption or acclimatization. The researchers
stressed that all of these factors illustrate why it’s key to consider both
types of change when studying marine climates.
“If we just study how organisms respond to the smooth
trend, we miss all the variability, which is driving ecological change,” Witman
said. “It’s not just a matter of worsening physiological stress over time;
there are also variable events that have their own ripple effects.”
In the paper, the researchers created a global model that
shows the variability in temperature relative to trend, highlighting regions
where extreme temperatures are likely to have particularly deleterious effects.
In the areas of the Gulf of Maine, the Caribbean Sea and the Mediterranean Sea,
they write, there are high probabilities of exceptional warming events and
“ecological surprises.” Research shows that key foundation species in these
regions, such kelp and corals, have already experienced substantial
climate-related changes.
“These areas, especially, warrant investigation to
improve our understanding of what's going to happen in the future — as well as
our conception of what we’re calling, ‘the new ocean,’” Witman said.
This work was supported by the National Science
Foundation, Biological Oceanography Program (OCE-2035354, OCE-1851866,
OCE-2128592).
