Ferreira, A., Mendes, C. R., Costa, R. R., Brotas, V., Tavano, V. M., Guerreiro, C. V., … & Brito, A. C. (2024). Climate change is associated with higher phytoplankton biomass and longer blooms in the West Antarctic Peninsula. Nature Communications, 15(1), 6536.
The Southern Ocean, which surrounds Antarctica, is experiencing some of the largest and fastest effects of climate change. The temperatures of the atmosphere and ocean have been increasing for the best several decades, reducing the extent of glaciers and ice sheets and decreasing the thickness of sea ice. These changes impact marine organisms at all levels of the food web.
Phytoplankton are the foundation of marine food webs, filling the same role as plants on land. These marine algae perform photosynthesis, transforming energy from the Sun into biomass; animals such as zooplankton and fish eat phytoplankton, and eventually that energy reaches the highest levels of the food web, like whales and seals. Any changes to phytoplankton will also affect every other part of the ecosystem, but how exactly are these phytoplankton communities changing? In a recent study, scientists used new modelling techniques and satellite data to get a better picture of phytoplankton communities over the bast 25 years in part of the Southern Ocean.
Studying the oceans from space
Phytoplankton are very small, so it might be surprising that one of the best ways to study them is from very, very far away. Scientists study phytoplankton using satellites. We can measure phytoplankton abundance by looking at ocean color, as algae literally change the color of the ocean. They make a pigment called chlorophyll, the same as in land plants, to photosynthesize; the more chlorophyll there is in the water, the greener it is, and this can be measured over large scales from space. The Southern Ocean is actually a tough place for satellites because of extreme cloud cover and sea ice. Researchers, including those in this current study, are still working on mathematical and physical models to improve satellite color data in this part of the world.
A long growing season
Unlike land plants, which can stick around year after year, phytoplankton are ephemeral—individual algae only live for hours or days, and the community changes very quickly. Phytoplankton experience huge
blooms—short-term explosions in growth, usually in early spring and fall, that create a huge but temporary food source for other organisms. Therefore, the timing of phytoplankton blooms is a major factor for marine ecosystems.
In this study, the researchers observed longer phytoplankton blooms in the region, causing increased biomass especially in the early fall. This is mainly due to declines in sea ice, creating more and longer-lasting opportunities for phytoplankton growth. Sea ice blocks light, so algae get more energy from the sun on ice-free days.
What does this mean moving forward? Well, sea ice is going to keep melting and bloom durations in the spring and fall will probably get longer. However, even if there is no ice, the blooms can’t last forever because there is very little sunlight in the Antarctic winter.
Wait, is this such a bad thing?
If you’re used to thinking about climate change as strictly destructive, you might be surprised to learn that some organisms are doing better under climate change. And more productivity from phytoplankton means more food for penguins and whales, doesn’t it?
Unfortunately, it’s complicated.
It’s definitely true that under climate change, there are going to be “winners” and “losers”. Some organisms, in some parts of the world, will adapt to changing conditions and may benefit or increase in biomass, while others will go extinct. Some parts of the ocean, like the polar oceans, may become more productive. However, we can’t predict how drastic changes like this will affect other parts of the ecosystem. Some phytoplankton may do well, but animals like penguins that rely on sea ice will still struggle even if there is more food in some areas. Also, this study only shows one specific region in the Southern Ocean. Other phytoplankton communities in different areas may have very different dynamics, and gains in productivity in some areas will probably be accompanied by reduced productivity in others. Again, this makes predicting the impacts of climate change over the whole polar ocean very difficult, which is exactly why we need studies like this to understand how our oceans are changing.
I am a PhD student at MIT and the Woods Hole Oceanographic Institution, where I study the evolution and physiology of marine invertebrates. I usually work with zooplankton and sea anemones, and I am especially interested in circadian rhythms of these animals. Outside work, I love to play trumpet, listen to music, and watch hockey.
