Seawater carbonate chemistry and ocean alkalinity enhancement on Oikopleura dioica abundances and their house production capacity

Here, we assessed the response of a key gelatinous zooplankton species to ocean alkalinity enhancement in a 53-day mesocosm experiment in a temperate Norwegian fjord. Oikopleura dioica is a globally distributed zooplankton member, known for its high secondary production capacity and key role in vertical carbon flux. O. dioica continuously produces mucous feeding structures ('houses'), which efficiently retain submicron particles. Once discarded, these houses can sink rapidly and contribute to vertical carbon exports. To test the impacts of OAE on O. dioica abundances and their house production capacity, we exposed natural plankton communities to non-CO2-equilibrated OAE scenarios spanning a ΔTA range from 0–600 μmol/kg, using silicate-based (olivine) and calcium-based (slaked lime) minerals. Population dynamics of O. dioica were monitored alongside the plankton community, and targeted bottle incubations were used to quantify house production and feeding rates.