title: Resource supply overrides temperature as a controlling factor of marine phytoplankton growth.
abstract: The universal temperature dependence of metabolic rates has been used to predict how ocean biology will respond to ocean warming. Determining the temperature sensitivity of phytoplankton metabolism and growth is of special importance because this group of organisms is responsible for nearly half of global primary production, sustains most marine food webs, and contributes to regulate the exchange of CO2 between the ocean and the atmosphere. Phytoplankton growth rates increase with temperature under optimal growth conditions in the laboratory, but it is unclear whether the same degree of temperature dependence exists in nature, where resources are often limiting. Here we use concurrent measurements of phytoplankton biomass and carbon fixation rates in polar, temperate and tropical regions to determine the role of temperature and resource supply in controlling the large-scale variability of in situ metabolic rates. We identify a biogeographic pattern in phytoplankton metabolic rates, which increase from the oligotrophic subtropical gyres to temperate regions and then coastal waters. Variability in phytoplankton growth is driven by changes in resource supply and appears to be independent of seawater temperature. The lack of temperature sensitivity of realized phytoplankton growth is consistent with the limited applicability of Arrhenius enzymatic kinetics when substrate concentrations are low. Our results suggest that, due to widespread resource limitation in the ocean, the direct effect of sea surface warming upon phytoplankton growth and productivity may be smaller than anticipated.
authors.affiliation: Departamento de Ecología y Biología Animal, Universidad de Vigo, Vigo, Spain.
authors.forename: Emilio
authors.initials: E
authors.lastname: Marañón
authors.affiliation: Instituto de Ciencias del Mar, Consejo Superior de Investigaciones Científicas, Passeig Maritim de la Barceloneta 37-49, Barcelona, Spain.
authors.forename: Pedro
authors.initials: P
authors.lastname: Cermeño
authors.affiliation: Department of Chemical and Biological Engineering, The University of Sheffield, Sheffield, United Kingdom.
authors.forename: María
authors.initials: M
authors.lastname: Huete-Ortega
authors.affiliation: Instituto de Ciencias del Mar, Consejo Superior de Investigaciones Científicas, Passeig Maritim de la Barceloneta 37-49, Barcelona, Spain.
authors.forename: Daffne C
authors.initials: DC
authors.lastname: López-Sandoval
authors.affiliation: Departamento de Ecología y Biología Animal, Universidad de Vigo, Vigo, Spain.
authors.forename: Beatriz
authors.initials: B
authors.lastname: Mouriño-Carballido
authors.affiliation: Departamento de Ecología y Biología Animal, Universidad de Vigo, Vigo, Spain.
authors.forename: Tamara
authors.initials: T
authors.lastname: Rodríguez-Ramos
mesh_terms: D018533:Biomass; D002734:Chlorophyll / Q000378:metabolism; D000077194:Chlorophyll A; D010839:Phytoplankton / Q000254:growth & development*; D012623:Seawater / Q000382:microbiology*; D013030:Spain; D013696:Temperature
chemical_list: D002734:Chlorophyll; D000077194:Chlorophyll A