Response of kelps from different latitudes to consecutive heat shock

Abstract : Although extensive work has focused on kelp responses to constant temperature, little is known about their response to the consecutive temperature shocks they are often exposed to in the shallow subtidal and intertidal pools. Here we characterized the responses of the two southernmost forest-forming kelp species in the Northeast Atlantic, Laminaria ochroleuca De La Pylaie and Saccorhiza polyschides (Lightf.) Batt. to multiple cycles of thermal stress. Individuals from the upper vertical limit of the geographical distribution edges where the two species co-occur forming forests, France and Portugal, were exposed to 4 consecutive cycles of thermal shock simulating a spring tide. A 24 h cycle consisted of culture at 15 °C, plus 1 h heat shock at one of five levels (20, 22.5, 25, 27.5 or 30 °C). The maximum quantum yield (Fv/Fm) of chlorophyll fluorescence of photosystem 2 (PS2) was used to detect impaired reaction center function, as a proxy for individual fitness costs, during recovery from heat shock. Both species showed resilience to temperatures from 20 to 25 °C. While exposure to 27.5 °C caused no inhibition to Fv/Fm of S. polyschides, a threshold was met above this temperature and exposure to 30 °C caused the death of all individuals. In contrast, L. ochroleuca from France was damaged but able to survive 30 °C shocks and individuals from Portugal showed complete resilience to this treatment. In both species, blade elongation decreased with increasing temperature, with necrosis surpassing growth at higher temperatures. Resilience to high temperature exposure may confer an advantage to L. ochroleuca to colonize intertidal pools on the Portuguese coast, in agreement with the observation that both species recruit in tide pools but only L. ochroleuca reach adulthood. Our results indicate that as summer temperatures increase with climate change, the disappearance of S. polyschides from intertidal pools and a decrease in the density of L. ochroleuca can be expected.
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Submitted on : Tuesday, April 28, 2015 - 3:25:16 PM
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Tânia R. Pereira, Aschwin Engelen, Gareth Pearson, Myriam Valero, Ester Serrão. Response of kelps from different latitudes to consecutive heat shock. Journal of Experimental Marine Biology and Ecology, Elsevier, 2015, 463, pp.57-62. ⟨10.1016/j.jembe.2014.10.022⟩. ⟨hal-01146583⟩



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