Ecotypic differentiation in populations of Brazilian coast: recognizing adaptation to temperature in Gracilariopsis tenuifrons (Gracilariales, Rhodophyta)

The Brazilian coast presents diverse abiotic characteristics, such as temperature, and we know that surface seawater temperatures are rising as a result of climate change. Therefore, to better interpret the effects of such changes, we chose to investigate Gracilariopsis tenuifrons, a species of red algae widely occurring on the Brazilian coast. We specifically evaluated the effect of different temperatures (18–35 °C) on growth rates (GRs), photosynthetic parameters, and pigment contents of female gametophytes from five different populations distributed along 7450 km of coastline, including Maranhão State (MA, 2.4°S), Rio Grande do Norte State (RN, 5.4°S), Bahia State (BA, 14.48°S), and São Paulo State (SP1, 23.5°S and SP2, 24.2°S). All samples tolerated temperatures between 18 and 33 °C, but none of them could tolerate temperatures of 35 °C, irrespective of the populations. However, the highest GRs varied among populations (MA, 23–30 °C; RN, 28–33 °C; BA, 23–28 °C; SP1, 25–28 °C; SP2, 28 °C). MA and BA populations showed the highest maximal measurement (µmax) of the thermal performance curve when compared to SP1 and SP2 populations. The RN population showed the worst µmax values, 5.6% day−1; however, it was more resilient to stressful temperatures (33 °C) than the others. The BA population presented some physiological characteristics similar to populations from the northeastern and southeastern regions. Our data showed that Gp. tenuifrons presents latitudinal ecotypes associated with temperature. Northeastern populations could be more vulnerable in a drastic scenario of climate change (up to 4 °C); otherwise, this species could occupy regions further to the south of its current distribution.