This is a pretty big deal. Decreasing bottom-of-the food chain biomass like diatoms and dinoflagellates in the context of climate change is a pretty big problem. These guys are everywhere, in fresh- and saltwater bodies, all over the planet. Disruption of them has implications vis a vis carbon sequestration (they die, their shells sink, and get buried at the bottom), but most importantly, every other species of animal in the ocean is dependent on them. It's food chain 101 stuff. Fish like, say, sardines, that filter feed on these guys may not have their populations do so well if there are big decreases, or, as the article suggests, increases and decreases in areas where this historically doesn't happen, and thus other species that feed on them cannot adapt.

Also, things won't get better unless some really big changes are made (i.e, actually combating climate change). Or, as the article so succinctly puts it:

> Assuming the underlying mechanisms do not change, the next few decades could bring further decreases in diatom and dinoflagellate biomass, with a shift towards diatoms in much of the North Atlantic and a shift towards dinoflagellates in the Arctic. These changes have likely had notable consequences for carbon export and the amount of biomass transferred up the food web.

If you’re interested in more context for this, the book The Blue Machine by physical oceanographer Helen Czerski. There’s a great discussion of this and other ocean issues.