As sea levels rise due to climate change, encroaching sea water will likely make freshwater environments saltier. In a new study, MIT researchers have shown how that increase in salinity might affect microbial ecosystems found in environments such as rivers and estuaries. These microbial communities play important roles in the carbon cycle, and they also help to decompose organic matter such as algae. The MIT team found that when salt levels rise, these populations lose diversity as faster-growing strains tend to take over the community, but they maintain their overall growth rate. “At higher salinity, you lose diversity, which is ultimately not good for an ecosystem. But what we were surprised at is that in the meantime, even though diversity decreases, the growth of the community and the production of biomass is not impacted that much,” says Jana Huisman, an MIT pos…

Over two weeks, the researchers measured the communities’ growth rates and found that overall, each community maintained the same growth rate at each of the three concentrations. However, in the communities exposed to higher salt environments, the overall composition became less diverse. Further studies showed that these communities tended to be dominated by faster-growing species. “We saw that those communities that had been propagated at higher salinity had reached a markedly different composition than the ones that lower salinity,” Huisman says. To explore whether their lab results might correspond to what happens in natural ecosystems, the researchers analyzed publicly available genomic data from microbes found in different aquatic ecosystems, including the Che…