12 July 2018
Blooming under heat
Published online 27 September 2017
The results of simulations of an ocean warming scenario are at odds with the Metabolic Theory of Ecology.
To gauge the long-term impact of ocean warming on marine organisms, scientists from Spain and Saudi Arabia performed thermal experiments on four marine bacterial groups, monitoring changes in their growth rate.
Over one year, the researchers incubated them for short periods in varying temperatures. Besides, growth, they measured changes in carrying capacity — the maximum population size a species can reach in a given environment.
“According to our results, ocean warming may promote the growth and ultimately the increase in abundance of marine bacteria, likely leading to higher bacterial biomass in the future ocean,” says Nestor Arandia-Gorostidi, corresponding author of this study, and researcher of marine biology at the Spanish Institute of Oceanography in Madrid.
The study yielded several revelations: illuminating how changes in ocean temperature usually affect these bacterial groups and helped the scientists predict which groups are more likely to prevail in warmer conditions.
“This paper puts forth interesting hypotheses about how marine bacteria respond to temperature,” says Shady Amin, assistant professor of chemistry at New York University Abu Dhabi, who is not involved in this study.
While the study reports an interesting direct correlation between increasing temperature and increasing biomass and carrying capacity, the predictions of the Metabolic Theory of Ecology (MTE), widely-held by marine scientists, do not really support these findings.
MTE states that, under the same environmental conditions, a decrease in carrying capacity is expected, given that growth rates are increasing.
So were the scientists able to reconcile their findings with the predications of MTE?
"While the MTE is still a valid framework at synthesizing metabolism, temperature and cell size, new models are necessary to account for this as well as other major discrepancies found in a theory aimed to be universal and complete,” says Xosé Anxelu G. Morán, co-author of the study.
From his side Amin says that follow-up studies are certainly needed to ascertain whether the observations reported here represent true deviations from the theory or are simply ‘bottle effects’ that would not be replicated if the experiment was conducted differently.
“For example, the authors filtered out all large cells (larger than 0.8 µm) to perform their incubations. This treatment removes grazers as well as most phytoplankton, which undoubtedly will affect the results of incubations.” explains Amin.
Although this study contributes to the understanding of the future of marine biota, and hence the abundance of resources following ocean warming, further research is still needed to gain a better idea about the correlation between temperature change and the abundance and metabolism of marine organisms.
- Arandia-Gorostidi, N. et al. Testing the Metabolic Theory of Ecology with marine bacteria: Different temperature sensitivity of major phylogenetic groups during the spring phytoplankton bloom. Environmental Microbiology. http://dx.doi.org/10.1111/1462-2920.13898 (2017).