AUTHOR=Robinson Alex , Bouman Heather A. , Tilstone Gavin H. , Sathyendranath Shubha 

TITLE=Size Class Dependent Relationships between Temperature and Phytoplankton Photosynthesis-Irradiance Parameters in the Atlantic Ocean

JOURNAL=Frontiers in Marine Science

VOLUME=4

YEAR=2018

URL=https://www.frontiersin.org/journals/marine-science/articles/10.3389/fmars.2017.00435

DOI=10.3389/fmars.2017.00435

ISSN=2296-7745

ABSTRACT=<p>Over the past decade, a number of methods have been developed to estimate size-class primary production from either in situ phytoplankton pigment data or remotely-sensed data. In this context, the first objective of this study was to compare two methods of estimating size class specific (micro-, nano-, and pico-phytoplankton) photosynthesis-irradiance (<italic>PE</italic>) parameters from pigment data. The second objective was to analyse the relationship between environmental variables (temperature, nitrate and PAR) and <italic>PE</italic> parameters in the different size-classes. A large dataset was used of simultaneous measurements of the <italic>PE</italic> parameters (<italic>n</italic> = 1,260) and phytoplankton pigment markers (<italic>n</italic> = 2,326), from 3 different institutes. There were no significant differences in mean <italic>PE</italic> parameters of the different size classes between the chemotaxonomic method of Uitz et al. (<xref ref-type="bibr" rid="B124">2008</xref>) and the pigment markers and carbon-to-Chl <italic>a</italic> ratios method of Sathyendranath et al. (<xref ref-type="bibr" rid="B109">2009</xref>). For both methods, mean maximum photosynthetic rates (<inline-formula><mml:math id="M100" xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msubsup><mml:mrow><mml:mi>P</mml:mi></mml:mrow><mml:mrow><mml:mi>m</mml:mi></mml:mrow><mml:mrow><mml:mi>B</mml:mi></mml:mrow></mml:msubsup></mml:math></inline-formula>) for micro-phytoplankton were significantly lower than those for pico-phytoplankton and nano-phytoplankton. The mean light limited slope (α<sup><italic>B</italic></sup>) for nano-phytoplankton were significantly higher than for the other size taxa. For micro-phytoplankton dominated samples identified using the Sathyendranath et al. (<xref ref-type="bibr" rid="B109">2009</xref>) method, both <inline-formula><mml:math id="M2000" xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msubsup><mml:mrow><mml:mi>P</mml:mi></mml:mrow><mml:mrow><mml:mi>m</mml:mi></mml:mrow><mml:mrow><mml:mi>B</mml:mi></mml:mrow></mml:msubsup></mml:math></inline-formula> and α<sup><italic>B</italic></sup> exhibited a significant, positive linear relationship with temperature, whereas for pico-phytoplankton the correlation with temperature was negative. Nano-phytoplankton dominated samples showed a positive correlation between <inline-formula><mml:math id="M333" xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msubsup><mml:mrow><mml:mi>P</mml:mi></mml:mrow><mml:mrow><mml:mi>m</mml:mi></mml:mrow><mml:mrow><mml:mi>B</mml:mi></mml:mrow></mml:msubsup></mml:math></inline-formula> and temperature, whereas for α<sup><italic>B</italic></sup> and the light saturation parameter (<italic>E</italic><sub><italic>k</italic></sub>) the correlations were not significant. For the Uitz et al. (<xref ref-type="bibr" rid="B124">2008</xref>) method, only micro-phytoplankton <inline-formula><mml:math id="M466" xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msubsup><mml:mrow><mml:mi>P</mml:mi></mml:mrow><mml:mrow><mml:mi>m</mml:mi></mml:mrow><mml:mrow><mml:mi>B</mml:mi></mml:mrow></mml:msubsup></mml:math></inline-formula>, pico-phytoplankton α<sup><italic>B</italic></sup>, nano- and pico-phytoplankton <italic>E</italic><sub><italic>k</italic></sub> exhibited significant relationships with temperature. The temperature ranges occupied by the size classes derived using these methods differed. The Uitz et al. (<xref ref-type="bibr" rid="B124">2008</xref>) method exhibited a wider temperature range compared to those derived from the Sathyendranath et al. (<xref ref-type="bibr" rid="B109">2009</xref>) method. The differences arise from the classification of mixed populations. Based on these patterns, we therefore recommend using the Sathyendranath et al. (<xref ref-type="bibr" rid="B109">2009</xref>) method to derive micro-phytoplankton <italic>PE</italic> parameters at sea water temperatures up to 8°C during monospecific blooms and the Uitz et al. (<xref ref-type="bibr" rid="B124">2008</xref>) method to derive <italic>PE</italic> parameters of mixed populations over the temperature range from 8 to 18°C. Both methods exhibited similar relationships between pico-phytoplankton <italic>PE</italic> parameters and temperatures &gt;18°C.</p>