Efeitos de ondas de calor marinhas em macroalgas do gênero Gracilaria

Abstract

Marine macroalgae play crucial roles in coastal ecosystems, acting as primary producers, shelter, and food for various marine species. As primary producers, they actively participate in nutrient cycling and oxygen production. Species of the genus Gracilaria, besides being ecologically relevant, have considerable economic importance, being widely used for agar production and the extraction of other bioactive compounds. Thus, this study investigated the effects of simulated marine heatwaves (MHWs) on the growth, photosynthetic performance, and pigment content of Gracilaria caudata and Gracilaria birdiae from northeastern Brazil, collected during the dry and rainy seasons. Gracilaria caudata exhibited higher relative growth rates (RGR), ranging from 5.07% to 6.69% per day before MHWs over rainy season, while G. birdiae showed RGRs between 0.5% and 2.2% per day. During MHWs, G. caudata withstood temperatures of up to 32 °C in the dry season, whereas G. birdiae did not tolerate the simulated MHWs for this climatic season. Overall, photosynthetic performance, measured by effective quantum yield (ΔF/Fm′), decreased in both species during MHWs, except for G. caudata in the rainy season. Regarding pigment content, G. caudata from the dry season showed a reduction in chlorophyll a and phycoerythrin pigments under MHWs, whereas specimens from the rainy period were not affected in their pigment content by MHWs. The results indicate that G. caudata, often found in upper intertidal zones, has higher thermal tolerance and recovery capacity after thermal stress, which suggests its greater potential for aquaculture under climate change scenarios.