Physiological responses of Ulva fasciata Delile (Ulvales, Chlorophyta): comparison of two populations from thermally distinct sites from Brazilian coast

Abstract

Ulvales, Chlorophyta): comparison of two populations from thermally distinct sites from Brazilian coast. Respostas fisiológicas de Ulva fasciata Delile (Ulvales, Chlorophyta): comparação de duas populações de locais termicamente distintos do litoral brasileiro. São Paulo 2016 2 Nuno Tavares Martins Physiological responses of Ulva fasciata Delile (Ulvales, Chlorophyta): comparison of two populations from thermally distinct sites from Brazilian coast. Respostas fisiológicas de Ulva fasciata Delile (Ulvales, Chlorophyta): comparação de duas populações de locais termicamente ABSTRACTIn a global warming scenario, an increase temperature is expected in addition to the occurrence and intensity of extreme climate events. One example of extreme events is the marine heat waves, which are a major threat to marine macroalgae. Ulva fasciata is a cosmopolitan species that occur in the whole Brazilian coast. This study was performed in two regions of Rio de Janeiro State (RJ) coast. Both regions are tropical, however, Arraial do Cabo/RJ is naturally colder than Niterói/RJ due upwelling phenomenon. This study aimed to: (i) confirm that U. fasciata individuals from these two Brazilian coast regions are of the same species; and (ii), physiologically analyze individuals of U. fasciata in the field and under in-laboratory controlled temperature experiment. We hypothesized that U. fasciata populations grown at thermally different locations would present distinct ecophysiological responses. In the field, it was accessed maximum quantum yield (Fv/Fm) and pigment content, and in laboratory, it was also evaluated growth rate. The in-laboratory controlled experiment comprised three phases: (i) a temperature gradient; (ii) a 5-day heat wave (+ 5 °C);and (iii) a 5-day recovery (-5 °C). The molecular data allow us to state that the two populations belong to the same species. No differences of the fluorescence-derived factors were observed between individuals from both populations in the field, suggesting acclimation. However, differences were detected along all three experimental phases. The analysis of pigment content field data evidenced that individuals from the population of Niterói (warmer site) had higher concentrations of chlorophyll a than individuals from Arraial do Cabo (colder site). However, individuals of population from Niterói when cultured at 21 °C showed the lowest values of pigment. The differences observed suggest ecotypes. In conclusion, as the planet becomes warmer and extreme weather events become more frequent, the likelihood that heat wave to occur is higher. Therefore, U. fasciata from Arraial do Cabo showed better physiological responses to the effects of heat wave, what could confer them higher competitiveness ability to overcome thermal stress.