The Makazi Bahraini wiki is originally written in Dutch, references can be consulted and most references used in the articles are in English. Google translate may help you out if you want to know more.When you speak of nitrogen availability as opposed to nitrate when discussing algae growth, what form of nitrogen are you speaking of?
I thought CO2 was present in seawater at equilibrium with atmospheric CO2 and not limited. Are you maybe speaking of organic carbon rather than CO2? I can't read the link, it only comes up in what I think is Dutch.
The nitrogen source used is determent for the possible growth rate. Most organisms prefer ammonia-nitrogen and inhibit the use of nitrate-nitrogen if ammonia is sensed. A lot of photo-autotrophs are able to use both at the same time but will favor ammonia, then nitrite. The nitrate level does not influence growth rates, 1ppm or 5ppm, they will grow at about the same rate if using nitrate-nitrogen. but will grow as long as all essential building materials are available. Using nitrate-nitrogen as a nitrogen source reduces growth rates.
CO2 dissolved in seawater will become bicarbonate. Rubisco uses CO2. Corals need CO3 and calcium for calcification , the transcalcification process releases CO2. ref: https://www.baharini.eu/baharini/doku.php?id=nl:makazi:chemie:calcificatie Halimeda uses Photosynthesis-induced calcification, needing calcium and CO2. ref: https://www.baharini.eu/baharini/doku.php?id=nl:makazi:chemie:calcificatie#fotosynthese_geïnduceerde_calcificatie A lot of algae calcify, some need CO2 for both, calcification and photosynthesis. A lot of autotrophs are able to use carbonate as a carbon source but must transform it into CO2 internally.