title: Abiotic influences on bicarbonate use in the giant kelp, Macrocystis pyrifera, in the Monterey Bay.
abstract: In the Monterey Bay region of central California, the giant kelp Macrocystis pyrifera experiences broad fluctuations in wave forces, temperature, light availability, nutrient availability, and seawater carbonate chemistry, all of which may impact their productivity. In particular, current velocities and light intensity may strongly regulate the supply and demand of inorganic carbon (Ci) as substrates for photosynthesis. Macrocystis pyrifera can acquire and utilize both CO2and bicarbonate (HCO3-) as Ci substrates for photosynthesis and growth. Given the variability in carbon delivery (due to current velocities and varying [DIC]) and demand (in the form of saturating irradiance), we hypothesized that the proportion of CO2and bicarbonate utilized is not constant for M. pyrifera, but a variable function of their fluctuating environment. We further hypothesized that populations acclimated to different wave exposure and irradiance habitats would display different patterns of bicarbonate uptake. To test these hypotheses, we carried out oxygen evolution trials in the laboratory to measure the proportion of bicarbonate utilized by M. pyrifera via external CA under an orthogonal cross of velocity, irradiance, and acclimation treatments. Our Monterey Bay populations of M. pyrifera exhibited proportionally higher external bicarbonate utilization in high irradiance and high flow velocity conditions than in sub-saturating irradiance or low flow velocity conditions. However, there was no significant difference in proportional bicarbonate use between deep blades and canopy blades, nor between individuals from wave-exposed versus wave-protected sites. This study contributes a new field-oriented perspective on the abiotic controls of carbon utilization physiology in macroalgae.
authors.affiliation: Department of Ecology and Evolutionary Biology, University of California, Santa Cruz, Santa Cruz, California, 95060, USA.
authors.forename: Sarah Tepler
authors.initials: ST
authors.lastname: Drobnitch
authors.affiliation: School of Natural Sciences, California State University, Monterey Bay, Seaside, California, 93955, USA.
authors.forename: Kerry
authors.initials: K
authors.lastname: Nickols
authors.affiliation: Department of Biology, San Diego State University, San Diego, California, 92101, USA.
authors.forename: Matthew
authors.initials: M
authors.lastname: Edwards
mesh_terms: D001639:Bicarbonates / Q000378:metabolism*; D002140:California; D002245:Carbon Dioxide / Q000378:metabolism*; D004777:Environment; D044423:Kelp / Q000378:metabolism*; D044662:Macrocystis / Q000378:metabolism*; D010140:Pacific Ocean
chemical_list: D001639:Bicarbonates; D002245:Carbon Dioxide
keywords: 
  Macrocystis pyrifera
  ; acclimation; acetazolamide; bicarbonate; microenvironment