SEATTLE (AP) — For years, scientists believed that Prochlorococcus — the tiniest and most plentiful phytoplankton in the ocean — would flourish as global temperatures climbed. But recent findings show these microscopic organisms, which play a crucial role in ocean ecosystems and climate regulation, could drastically decline in warmer seas. A new report in the journal Nature Microbiology warns that Prochlorococcus populations could drop by up to 50% in tropical waters within the next 75 years