What to Know About How Climate Change Threatens Global Fish Stocks

A groundbreaking study recently published in Nature Communications reveals that climate change is compromising the ocean's capacity to support fish populations. Even minor reductions in plankton levels, as revealed by the research led by Dr. Angus Atkinson from the Plymouth Marine Laboratory and Dr. Axel Rossberg from Queen Mary University of London, could precipitate significant declines in fish stocks.

The study emphasizes the immediate necessity to incorporate climate change considerations into fisheries management and advocates for a comprehensive approach, recommending the integration of data on plankton size structure with advanced computer simulation models.

This research unveils an “amplifying mechanism” within the ocean's intricate food web. The study highlights that a relatively modest decline of 16-26% in phytoplankton levels, projected in regions such as the North Atlantic due to global warming, translates into a substantial 38-55% reduction in the carrying capacity for fish.

Global-scale computer models predict a decline in phytoplankton levels in response to warming waters, particularly in low and mid latitudes, where surface layers become isolated from nutrient supplies below. The North Atlantic has already witnessed a decline in plankton over the last five decades. However, the impact on the larger food web and commercially exploited fish stocks remains uncertain, with various models offering conflicting projections.

This study takes a fresh and independent approach, relying on field data rather than computer simulations. By examining the size structure of plankton, the researchers created a global database on marine and freshwater plankton size structure, providing a direct measure of how efficiently the food web transmits energy from small phytoplankton to larger fish.

The surprising finding is that temperature, often considered a primary factor in food web disruptions, plays a secondary role. Instead, the crucial driver is the overall amount of phytoplankton, dictating the efficiency of energy transfer through the food web.

"Our global analysis sheds light on a hidden vulnerability," Dr. Atkinson said. "We were surprised to find temperature didn't directly affect food web efficiency. Instead, we see ecosystems adapting to warming by changing plankton size. This suggests the main threat comes from reduced nutrient supply, leading to smaller plankton, longer food chains, and inefficient foraging."

Dr Rossberg puts the findings into context, highlighting that the lack of nutrients from deeper waters becomes a “major bottleneck” at vast scales relevant to climate change.