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 the Ria Formosa lagoon (Portugal), a connection area between Mediterranean and Atlantic basins. We investigated 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 basins was assessed under a temperature range of 20 to 30°C. In addition, molecular markers were used to investigate the genetic identity of the strain found in Ria Formosa, which confirmed its Mediterranean origin. All examined populations showed large physiological thermo-tolerance and metabolic plasticity to warming. The photosynthetic efficiency of C. prolifera improved by 50% with temperature, and the maximum photosynthetic production doubled along the temperature range tested. Respiration did not vary with temperature, whereas the metabolic quotient increased by more than 70%when temperature increased from 20 to 25-30°C. Minor differences in the photosynthetic descriptors were detected among populations, reflecting light- and dark-adapted physiology of Mediterranean and Atlantic populations, respectively. Our results show that all tested populations of C. prolifera have the physiological potential to cope with temperature increases up to 30°C, which indicates that ocean warming may contribute to the expansion of C. prolifera in the Mediterranean-Atlantic basins.
Highlights
Marine systems are being exposed to pressures linked to global climate change
MATERIALS AND METHODS Algal collection and acclimation Four different populations of Caulerpa prolifera spreading along the Mediterranean-Atlantic basin, including the population recently rediscovered in Ria Formosa (Culatra), were selected to study their thermal physiological plasticity
Physiology of Caulerpa prolifera The maximum photochemical performance, maximum quantum yield (Fv/Fm), of C. prolifera ranged between 0.71 and 0.78 and did not vary among populations (Table 1), indicating a good physiological status of all C. prolifera specimens selected for P−E curves (Malta et al 2005)
Summary
Marine systems are being exposed to pressures linked to global climate change. Among these, global warming is a major threat affecting marine life and ecosystem functioning (Pörtner et al 2014). Warming is globally affecting the functioning of all marine systems, but coastal areas are sensitive habitats where the effects of temperature and heat waves are more extreme than in the open ocean (Helmuth et al 2006). Ocean warming is predicted to affect the physiology and metabolic balance of organisms (Koch et al 2013) by altering the energetic costs of metabolic processes and forcing energetic trade-offs (Yvon- Durocher et al 2010) This may have subsequent impacts on the functioning of the whole ecosystem to which they belong (Pörtner et al 2014). Physiological plasticity and genetic identity of populations are key factors to be considered when studying the acclimation and adaptation capacities of Caulerpa spp. to global warming and its colonization potential. We investigated the capacity of C. prolifera to cope with global warming by evaluating the physiological tolerance of different populations of C. prolifera spread along the
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