It has been a long known fact that higher CO2 concentrations improve the growth of plants. Most greenhouses in NL get CO2 supplied from the harbor of Rotterdam. Anyway salt water infiltration will also kill a lot of plant life and floodings will cause the soils to cause more salt. And salt isn't exactly a thing most plant species endure very well.
Anywho as other said CO2 also causes oceans to accidify which causes corals to bleach and nearly a third off al fish species need coral to survive. Also the exo skeletons of shell fish and krill are desolving because of this acidification. So if anything climate change will rather cause the 6th mass extinction than a new bloom of life.
So the only sector really happy with this are farmers and companies that cultivate wood for furniture.
This is possibly false, since it has been implied the acids used to simulate the more acid water of warmer oceans doesn't lead to accurate results, and certain animals might calcify more, not less, in the presence of more CO2.
Such data is consistent with the absence of mass extinction of corals back on the Cretaceous or the P-E, when temperatures were more than 10º C warmer than the present and sea temperatures might have casually risen above 35º C on tropical waters.
Of course, that doesn't mean it won't face another issues such as bleaching etc. but, really, plastic polution, overfishing and commercial navigation are much, much larger issues on all likehood to marine ecosystems, and issues which doesn't get the same level of attention on top of that.