Melting Ice Is 'Freshening' Antarctic Waters, Threatening Coastal Marine Life

A new study by researchers at the University of Plymouth and the British Antarctic Survey warns that "freshening," a drop in the salt content of seawater caused by melting glaciers, increased rainfall and extreme weather, could threaten marine invertebrates living in shallow coastal waters around Antarctica. Many of the region's smallest animals have evolved so that their body fluids closely match the chemical makeup of seawater, making them highly sensitive to changes in salinity.

The research, published in the journal Marine Environmental Research, focused on the giant Antarctic amphipod Paraceradocus miersi, a relative of the sandhoppers found on temperate beaches. Using amphipods collected from Ryder Bay on the Antarctic Peninsula, the researchers exposed them to a simulated freshening event and measured how their body fluids and organs responded.

The amphipods could still regulate some key chemicals, including calcium, when exposed to reduced salt levels, but their overall control of the ions that make up seawater was impaired. As a result, the animals lost salts, gained water, and suffered damage to their gills. The researchers said this effect likely contributed to deaths among shallow-dwelling amphipods during a real freshening event recorded at Rothera Research Station on the Antarctic Peninsula in 2017.

Lead author John Spicer, a professor of marine zoology at the University of Plymouth who has studied the effects of climate change on marine organisms for nearly 40 years, said the health of many invertebrate species could be severely affected even by a small amount of freshening. Co-author Simon Morley, an ecophysiologist at the British Antarctic Survey, said melting ice is adding large quantities of freshwater to the Southern Ocean, and that lowering its salinity could reshape communities living on the seafloor.