Abstract
Continued anthropogenic carbon emissions are expected to result in an increase in atmospheric
CO2 concentration to 700 ppm by the end of this century. This will cause a corresponding drop
in the global average surface water pH of the oceans by ~0.4 units to ~7.8 and an increase in the CO2 concentration
of seawater. Ocean acidification may potentially both stimulate and reduce primary production
by marine phytoplankton. Data are scarce on the response of marine phytoplankton growth rates
to lowered pH/increased CO2. Using the acid addition method to lower the seawater pH and manipulate
the carbonate system, we determined in detail the lower pH limit for growth rates of 2 model species
of common marine phytoplankton. We also tested whether growth and production rates of 6 other
common species of phytoplankton were affected by ocean acidification (lowered to pH 7.0). The lower
pH limits for growth of the dinoflagellate Heterocapsa triquetra and the cryptophyte Teleaulax amphioxeia
were pH ~6.0 and 6.3, respectively. The growth rates of these 2 species were significantly reduced
in the range of pH 6.4 to 6.5. Cell volume, growth, and production rates of the 6 other phytoplankton species
were statistically similar in the pH range of ~7.0 to 8.5. Our results and literature reports on growth
at lowered pH indicate that marine phytoplankton in general are resistant to climate change in terms of
ocean acidification, and do not increase or decrease their growth rates according to ecological relevant
ranges of pH and free CO2. We speculate about whether common natural pH fluctuations in time and
space from 7.0 to 9.0 make phytoplankton capable of tolerating near-future ocean acidification. However,
due to the less fluctuating pH environment of oceanic regions compared to coastal regions, truly
oceanic species may be more sensitive to lowered pH than coastal species.
CO2 concentration to 700 ppm by the end of this century. This will cause a corresponding drop
in the global average surface water pH of the oceans by ~0.4 units to ~7.8 and an increase in the CO2 concentration
of seawater. Ocean acidification may potentially both stimulate and reduce primary production
by marine phytoplankton. Data are scarce on the response of marine phytoplankton growth rates
to lowered pH/increased CO2. Using the acid addition method to lower the seawater pH and manipulate
the carbonate system, we determined in detail the lower pH limit for growth rates of 2 model species
of common marine phytoplankton. We also tested whether growth and production rates of 6 other
common species of phytoplankton were affected by ocean acidification (lowered to pH 7.0). The lower
pH limits for growth of the dinoflagellate Heterocapsa triquetra and the cryptophyte Teleaulax amphioxeia
were pH ~6.0 and 6.3, respectively. The growth rates of these 2 species were significantly reduced
in the range of pH 6.4 to 6.5. Cell volume, growth, and production rates of the 6 other phytoplankton species
were statistically similar in the pH range of ~7.0 to 8.5. Our results and literature reports on growth
at lowered pH indicate that marine phytoplankton in general are resistant to climate change in terms of
ocean acidification, and do not increase or decrease their growth rates according to ecological relevant
ranges of pH and free CO2. We speculate about whether common natural pH fluctuations in time and
space from 7.0 to 9.0 make phytoplankton capable of tolerating near-future ocean acidification. However,
due to the less fluctuating pH environment of oceanic regions compared to coastal regions, truly
oceanic species may be more sensitive to lowered pH than coastal species.
| Original language | English |
|---|---|
| Journal | Marine Ecology - Progress Series |
| Volume | 416 |
| Pages (from-to) | 79-91 |
| Number of pages | 13 |
| ISSN | 0171-8630 |
| DOIs | |
| Publication status | Published - 2010 |
