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How do oil spills harm phytoplankton and zooplankton in marine ecosystems?

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Diagram showing ocean zonation by depth and region, with labeled layers: littoral, sublittoral, bathyal, abyssal, and hadal along the seafloor, and epipelagic, mesopelagic, bathypelagic, and abyssalpelagic in open water. The littoral zone is at the high-tide mark. Vertical scale marks photic and aphotic zones from surface to 10,000 meters. — Marine ecosystem Zonation of the ocean. Note that in the littoral zone the water is at the high-tide mark.

Oil spills cause significant harm to marine ecosystems by altering the physical and chemical properties of the water, which directly impacts foundational organisms like phytoplankton and zooplankton.

When oil spreads across the ocean surface, it creates a barrier that prevents sufficient sunlight from penetrating the water column. Because phytoplankton rely on photosynthesis to survive and grow, this reduction in light availability can severely inhibit their productivity. Furthermore, oil spills reduce the levels of dissolved oxygen in the water, creating conditions that are detrimental to the survival of both phytoplankton and zooplankton.1

Beyond these physical changes, oil introduces toxic compounds into the marine environment. Research indicates that oil and chemical dispersants used during cleanup efforts can be fatal to various microorganisms that serve as essential components of the marine food web. By damaging these primary producers and primary consumers, oil spills disrupt the base of the ecosystem, leading to cascading negative effects on larger marine life that depend on these organisms for sustenance.2