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Physiological potential of the chlorophyte Caulerpa prolifera for proliferation across the Mediterranean-Atlantic basin in a warmer ocean

I. Olivé*, E. Varela-Álvarez, J. Silva, E. A. Serrão, R. Santos

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ABSTRACT: Ocean warming is altering the metabolic balances of organisms, favouring the expansion of thermo-tolerant individuals. The fast-growing macroalga Caulerpa prolifera is rapidly expanding in Ria Formosa lagoon (Portugal), a connection area between Mediterranean and Atlantic basins. This study aims at assessing the metabolic capacity of C. prolifera to cope with ocean warming, to elucidate its expansion potential. The photosynthetic and respiratory plasticity of 4 populations of C. prolifera spread along the Mediterranean-Atlantic basin, was assessed under the temperature range of 20 to 30 ºC. In addition, molecular markers were used to investigate the genetic identity of the strain found in Ria Formosa, which confirmed its Mediterranean origin. All populations assessed showed large physiological thermo-tolerance and metabolic plasticity to warming. The photosynthetic efficiency of C. prolifera improved by 50% with temperature and maximum photosynthetic production doubled along the temperature range tested. Respiration did not vary with temperature whereas the metabolic quotient raised by more than 70% from 20 to 25-30 ºC. Minor differences in the photosynthetic descriptors were detected among populations attributing light and dark-adapted physiology to Mediterranean and Atlantic populations, respectively. Our results show that all populations of C prolifera tested have the physiological potential to cope with temperature increases up to 30ºC, which indicates that ocean warming may contribute to the expansion of C. prolifera at the Mediterranean-Atlantic basin.