After a year at a different temperature, bacteria in seabed samples still differed from the resident communities in two Swedish bays. Warming brought larger changes than cooling in the peer-reviewed experiment, while deeper layers retained traces of earlier conditions. The findings describe delayed biological adjustment after prolonged heating, without establishing that the changes are permanent.
Bacterial communities in Baltic seabed samples retained traces of prolonged warming after a year in cooler water. In a single peer-reviewed experiment, sediments exchanged between two Swedish bays moved partly towards the communities native to their new surroundings. The adjustment remained incomplete, and deeper layers particularly retained the bacterial signatures of their former bay.[1]
For around 50 years, the Oskarshamn nuclear plant has discharged warm cooling water into one bay; the control site lies about 1.5 kilometres farther north. The experiment ran from August 2021 until September 2022. Average temperature reached 16.1 degrees Celsius in the heated bay, against 10.7 degrees Celsius at the control site. The study concerned temperature effects.[1]
Researchers collected 48 sediment cores, reserving 16 for initial measurements. Other cores were returned to their original bay or moved to the other one. A missing cage left 30 cores available after a year. Bacterial DNA sequences were compared at different depths alongside measurements of methane, sulfate and porewater chemistry.[1]
Moving cooler sediments into heated water was accompanied by stronger changes than the reverse transfer. Diversity stayed high in cooled samples. DNA measurements can include cells that are no longer viable, and sealed core bottoms interrupted exchanges with deeper sediments. These features limit extrapolation to an undisturbed seabed. The one-year observations cannot establish whether recovery eventually becomes complete.[1]
