What are the effects of a marine parasite that kills all phytoplankton?

The extinction of phytoplankton due to a marine parasite would have catastrophic effects on ocean ecosystems and global climate. Phytoplankton are crucial for producing oxygen and serving as the base of the marine food web; their disappearance would lead to a collapse of marine biodiversity and disrupt food chains. Additionally, the loss of phytoplankton would significantly reduce carbon dioxide absorption, exacerbating climate change by increasing atmospheric CO2 levels. Overall, this scenario would threaten not only marine life but also human populations reliant on ocean resources.