Under the pump

A decline in a group of microscopic Southern Ocean algae could cascade up the food chain to penguins and whales.

- BY VERONIKA MEDUNA

Climate change often manifests as dramatic, extreme events - collapsing glaciers, flooded valleys, burnt forests. But invisible changes are under way, too, with equally profound consequences for life as we know it.

A study based on water samples from the Southern Ocean over several decades shows the composition of phytoplankton - the microscopic single-celled algae that sustain the ocean food web - is shifting. Researchers warn we may be witnessing a fundamental reorganisation of life that could, over time, cascade through the marine food system and affect the ocean's capacity to take up carbon.

Phytoplankton, known as the "grass of the ocean", are complex, with thousands of species and ever-changing connections between them. As the Southern Ocean changes - with rising surface temperatures, less mixing between water layers and vanishing sea ice - phytoplankton communities adjust. But even subtle changes in the food web's foundation can reverberate through the entire system, from microscopic grazers to fish, seabed corals and top predators, including seals, whales and penguins.