Plankton, the microscopic organisms essential to marine ecosystems, produce half of the Earth’s oxygen and absorb up to 40% of global carbon emissions. However, climate change is threatening plankton populations through warming oceans and shifting photic zones, posing risks to biodiversity and human interests, reports 24brussels.
Plankton are organisms that drift with ocean currents and are classified into phytoplankton (plant-like) and zooplankton (animal-like). Phytoplankton, the smaller of the two, are vital to the marine food web and require sunlight for photosynthesis. During this process, they not only produce energy but also generate oxygen, contributing significantly to the global oxygen supply.
According to the U.S. National Ocean Service, phytoplankton are responsible for approximately half of the Earth’s atmospheric oxygen, with the smallest phytoplankton, Prochlorococcus, contributing up to 20% of the total oxygen in the biosphere. They serve as the foundational food source for zooplankton which are in turn eaten by larger marine animals, establishing a complex food web that supports diverse marine life.
Phytoplankton play a crucial role in regulating atmospheric carbon levels via the biological pump, a process that transports carbon from the surface to the deep ocean. The carbon fixation process, akin to how terrestrial plants absorb carbon, is critical for this function. Though much of the carbon recycles back into surface waters, a portion sinks to the deep ocean, where it can be stored for centuries.
Zooplankton, which inhabit oceans, lakes, and ponds, are key secondary consumers in the marine food web that feed on phytoplankton. A 2023 study highlighted the significant role zooplankton play in carbon sequestration as their waste products contribute to sinking carbon that can then be stored in ocean depths.
The Southern Ocean demonstrates the impact of these organisms, as it sequesters around 40% of anthropogenic CO2 absorbed by oceans. Seasonal migrations of zooplankton enhance the downward transport of carbon and nutrients, consequently supporting marine life.
“Our work shows that zooplankton are unsung heroes of carbon sequestration,” said Guang Yang, lead author of the study and a marine ecologist. “Their seasonal migrations create a massive, previously unquantified carbon flux.”
Climate Crisis
The climate crisis is exacerbating threats to plankton populations, with 2024 marking the warmest year on record. The average sea surface temperature rose to a significant high, according to data from Copernicus.
This rise can stimulate harmful algal blooms, which further threaten aquatic ecosystems by depleting oxygen in sunlit waters. Recent algal blooms, such as a toxic event in Australia from Karenia Mikimotoi, resulted in the deaths of over 450 marine species.
Research from the University of Bristol indicates that the rapid increase in ocean temperatures adversely affects plankton, jeopardizing species that depend on them. “Plankton are the lifeblood of the oceans,” Rui Ying, lead researcher, stated. “If their existence is endangered, it will disrupt the entire marine ecosystem with wide-reaching consequences.”
This disruption extends to human food supplies as species reliant on plankton face survival challenges. Further studies suggest that under rising temperatures, plankton may transition from carbon sinks to sources of carbon emissions.
Through studies by the University of Plymouth, it has been revealed that the photic zone’s depth has decreased by over 50 meters from 2003 to 2022, leading to darker ocean conditions that threaten marine biodiversity. “Changes in plankton communities can have widespread darkening effects, reducing resources for marine life,” noted Thomas Davies, an associate professor at the University of Plymouth.
As the climate crisis unfolds, the fate of plankton remains inextricably linked to the health of our oceans and, by extension, human survival.