Do you have a citation for this ?
https://www.scientificamerican.com/article/phytoplankton-pop...
https://edition.cnn.com/2002/TECH/space/08/14/satellite.plan...
https://news.mit.edu/2015/ocean-acidification-phytoplankton-...
https://www.pmel.noaa.gov/co2/story/What+is+Ocean+Acidificat...
https://www.sciencebuzz.com/the-effects-of-ph-on-the-abundan...
Why would the onus be on a commentator to provide citations for a fact one could readily <branded search engine verb> for in less time than our roundtrip efforts combined?
(me not being the commentator either, to boot!) it almost sounds like you can't believe peanut butter is sticky...
I mean, I suppose "calfiferous plankton" is kinda a giveaway that ocean acidification would affect it...
Because a simple search results in it not being "old news", but actually having conflicting results: https://en.wikipedia.org/wiki/Phytoplankton#Environmental_co...
"Conflicting" only if you want to ignore a significant part of the text behind the very link you give:
"A more recent multi-model study estimated that primary production would decline by 2-20% by 2100 A.D.[12] Despite substantial variation in both the magnitude and spatial pattern of change, the majority of published studies predict that phytoplankton biomass and/or primary production will decline over the next century.[11][40][41][42][43][44][45][46][47]"
(Note the majority and how many of them are cited (all the numbers in brackets) and could be checked. It's surely not "one says yes, one says no".)
> increased ocean acidity
It's generally phrased that a decrease in alkaline is due to acidification (an increase in acid) and vice versa. The average ph is not specifically relevant.
Phytoplankton is the basis for the entire marine food chain.