Responses of Caulerpa with and without CO2 concentrating mechanisms to elevated ocean acidification (text & video)

OA Week 2021, PI-TOA (Pacific Islands & Territories) Hub Session

Ms. Aleluia Taise, School of Biological Science, Victoria University of Wellington, New Zealand


Caulerpa is a widely distributed genus of chlorophytes. They are important for their dietary, social, and coastal ecosystem values. Caulerpa is one of the rare few genera that have species both with and without CO2 concentrating mechanisms (CCMs) that allow active uptake of HCO3-. Two of the most common Caulerpa species in New Zealand, C. brownii and C. geminata, could have vastly different responses to ocean acidification (OA). This is because of their divergent dissolved inorganic carbon (DIC) uptake. C. geminata possesses a CCM while C. brownii does not have a CCM. We investigated growth, photo-physiology and DIC utilization responses by C. brownii and C. geminata at four mean seawater pH treatments (8.03, 7.93, 7.83 and 7.63). In all cases, mean and variability in growth rates of C. brownii increased under OA scenarios, while growth rates for C. geminata declined under OA. This concurs with predictions that non-CCM species will be gaining benefits from additional CO2, while species with a CCM may gain less benefits from additional CO2, while at the same time demonstrating that DIC use alone does not predict responses to OA. We show divergent responses of two Caulerpa species that could have implications for their future abundance in Australasia.

Ocean Acidification Week 2021 was sponsored by the following organizations:

(1) GOA-ON, the Global Ocean Acidification Observing Network,

(2) NOAA, the United States National Oceanic & Atmospheric Administration,

(3) IAEA OA-ICC, the International Atomic Energy Agency – Ocean Acidification International Coordination Centre, and

(4) IOC-UNESCO – the Intergovernmental Oceanographic Commission of the United Nations Educational, Scientific and Cultural Organization

For more information, please visit

GOA-ON, YouTube, 24 September 2021. Text and video.

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