As sea levels rise due to climate change, encroaching seawater will likely make freshwater environments saltier. MIT researchers have shown how this increase in salinity might affect microbial ecosystems found in rivers and estuaries. These microbial communities play crucial roles in the carbon cycle and help decompose organic matter.
The MIT team found that when salt levels rise, these populations lose diversity as faster-growing strains dominate, yet they maintain their overall growth rate. "At higher salinity, you lose diversity, which is not good for an ecosystem. However, we were surprised that despite the decrease in diversity, the community growth and biomass production were not significantly impacted," says Jana Huisman, an MIT postdoc and lead author of the study.
Microbes living in aquatic environments are typically adapted to thrive in fresh or salt water. The researchers took samples from three aquatic environments with varying salinity: the Charles River (4 g/L), Boston Harbor (30 g/L), and a beach in Nahant, Massachusetts (35 g/L). They then grew each population in three salinity environments — 16, 31, or 46 g/L.
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 higher salt environments, the overall composition became less diverse, dominated by faster-growing species.
To explore whether their lab results correspond to natural ecosystems, the researchers analyzed publicly available genomic data from microbes in different aquatic ecosystems, finding that environments with higher salinity also tended to be dominated by faster-growing species. The loss of diversity may reduce microbial populations' ability to withstand other environmental stresses.
"Whether you want faster-growing species to take over or not might also relate to the identity of those species. That is something I’m interested in looking at in the future," Huisman says. The research was funded by a Human Frontier Science Program Fellowship and a Schmidt Science Polymath Award.
Blogger's Review: This study reveals the profound impact of salinity changes on microbial ecosystems, emphasizing the importance of diversity. As climate change intensifies, understanding the dynamics of microbial communities will provide critical insights for ecological protection and restoration strategies. Future research should focus more on the ecological functions of these fast-growing species, particularly their adaptability and potential risks under environmental changes.