[BPT04-P04] Combined impacts of ocean acidification and desalination: culture experiments on the coastal species Ammonia sp. and Elphidium crispum
Keywords:Coastal ocean acidification, Desalination, Culture experiment, Benthic foraminifera, Calcification process
The purpose of this study was to evaluate the combined effect of two typical environmental stressors on the coast - salinity and pH – on calcifying organisms. We performed culture experiments on living benthic foraminifera to study the combined effects of lowered pH and salinity on the calcification abilities and survival of the coastal, calcitic species Ammonia sp. and Elphidium crispum.
We found that these two species could tolerate low pH and low salinity, which reflects the environmental variations in their natural habitats. However, in open ocean conditions (salinity ~35) and lower pH treatment, the species displayed resistance to test dissolution for a longer time than in brackish conditions (salinity ~5 to 20). Moreover, the response of foraminifera to the different treatments was species-specific, and Ammonia sp. appeared more resistant than E. crispum when placed in the same conditions of pH and salinity. We also observed living dissolved specimens of juveniles Ammonia sp. under the combined effect of low pH and very low salinity, and we showed that desalination is one cause for the decalcification. However, they were not able to recalcify when returned to higher salinities, probably due to a sensitive balance in environmental parameters. Finally, we highlight the ability of foraminifera to survive under Ωcalc < 1, and that high salinity and [Ca2+] as building blocks are crucial for the foraminiferal calcification process.
We conclude that coastal benthic foraminifera will not immediately be affected by ocean acidification, but rather by a combination of decreasing salinity and lowered pH.