As global temperatures edge past the critical 1.5°C threshold, researchers warn that marine plankton, the foundation of the ocean's ecosystem, may struggle to cope with the pace of modern climate change, unlike their resilience during past extreme weather shifts like the Ice Age.
In a study published in Nature, scientists examined the adaptability of plankton to rising ocean temperatures. These tiny organisms, including algae (phytoplankton) and animals (zooplankton), float in the upper layers of the ocean, playing a vital role in producing oxygen, fixing carbon, and supporting marine food chains.
Modern climate change is altering ocean conditions, including temperature and stratification, leading to significant changes in plankton distribution.
Models suggest a migration of plankton towards the poles in search of cooler waters and a decline in zooplankton populations in tropical regions. However, short-term satellite data limit our ability to assess long-term trends.
To better understand plankton's capacity to adapt, researchers studied fossil records of Foraminifera, a type of plankton with hard shells, comparing their response to the last Ice Age 21,000 years ago with current trends. These records, collected globally since the 1960s, offer insights into how plankton adapted to natural climate fluctuations.
The study found that during natural warming periods, subtropical and tropical plankton species thrived in warmer waters, while colder-water species successfully migrated to favorable habitats. This adaptability was possible even without evolutionary changes, aided by the slower pace of geological climate changes.
However, today's human-induced climate change is occurring at an unprecedented rate, creating conditions that are far more challenging for plankton. Rising temperatures, combined with ocean stratification that limits nutrient availability, are disrupting their growth and reproduction.
Plankton are critical to the ocean's ecosystem, contributing around 50% of the Earth's oxygen and forming the base of the marine food web. Phytoplankton also act as natural carbon sinks, storing 45 times more carbon than the atmosphere.
Declines in plankton populations could cascade through the food chain, affecting fish, marine mammals, and ultimately, human communities reliant on seafood as a primary protein source. Species such as whales, which feed on plankton, may face food shortages, while fish stocks could diminish, posing risks to marine biodiversity and global food security.
To protect plankton and, by extension, ocean health, urgent action is needed to reduce greenhouse gas emissions, limit global warming, and slow the pace of climate change.