You mean like this research which finds that this particular Sargassum event is creating dead zones in the ocean? https://www.fau.edu/newsdesk/articles/nitrogen-seaweed-study.php
"Using a unique historical baseline from the 1980s and comparing it to samples collected since 2010, researchers from Florida Atlantic University’s Harbor Branch Oceanographic Institute and collaborators have discovered dramatic changes in the chemistry and composition of Sargassum, transforming this vibrant living organism into a toxic “dead zone.”
Their findings, published in Nature Communications, suggest that increased nitrogen availability from natural and anthropogenic sources, including sewage, is supporting blooms of Sargassum and turning a critical nursery habitat into harmful algal blooms with catastrophic impacts on coastal ecosystems, economies, and human health. Globally, harmful algal blooms are related to increased nutrient pollution."