Phytoplankton community shift in response to experimental Cu addition at the elevated CO2 levels (Arabian Sea, winter monsoon)

Abstract

Understanding phytoplankton community shifts under multiple stressors is becoming increasingly important.Among other combinations of stressors, the impact of trace metal toxicity on marine phytoplankton under the ocean acidification scenario is an important aspect to address.Such multiple stressor studies are rare from the Arabian Sea, one of the highest productive oceanic provinces within the North Indian Ocean.We studied the interactive impacts of copper (Cu) and CO2 enrichment on two natural phytoplankton communities from the eastern and central Arabian Sea.Low dissolved silicate (DSi < 2 �M) favoured smaller diatoms (e.g.Nitzschia sp.) and non-diatom (Phaeocystis).CO2 enrichment caused both positive (Nitzschia sp.and Phaeocystis sp.) and negative (Cylindrotheca closterium, Navicula sp., Pseudo-nitzschia sp., Alexandrium sp., and Gymnodinium sp.) growth impacts.The addition of Cu under the ambient CO2 level (A-CO2) hindered cell division in most of the species, whereas Chla contents were nearly unaffected.Interestingly, CO2 enrichment seemed to alleviate Cu toxicity in some species (Nitzschia sp., Cylindrotheca closterium, Guinardia flaccida, and Phaeocystis) and increased their growth rates.This could be related to the cellular Cu demand and energy budget at elevated CO2 levels.Dinoflagellates were more sensitive to Cu supply compared to diatoms and prymnesiophytes and could be related to the unavailability of prey.Such community shifts in response to the projected ocean acidification, oligotrophy, and Cu pollution may impact trophic transfer and carbon cycling in this region.