Red Algae and Diatoms

Most varieties of marine algae are edible to humans, offering a potent mix of iodine, potassium, calcium and agar. Diatoms, seen here attached to rock comb algae, create roughly half of the planet’s oxygen; warming oceans are stressing diatoms and in some situations, reducing their numbers. The journal Nature has reported a (controversial) 40% global decline in marine phytoplankton in the last one hundred years. How this will trend could influence food webs and nutrient cycling remains to be seen, although another eastern Atlantic ocean study predicts a northeasterly plankton shift (which would reduce fish populations along the mid-Atlantic coast.)

https://www.nature.com/articles/nature09268
https://psmag.com/environment/global-warming-is-putting-phytoplankton-in-danger
https://www.pnas.org/content/113/11/2964.abstract