Short-term effects of temperature on morphology and physiology of turf-forming Hypnea species (Rhodophyta) from southeastern Brazil

Abstract

The current study is related to the United Nations Sustainable Development Goal 13, “Climate action”. As a consequence of environmental variations caused by global climate change, turf-forming algae supposedly tend to replace dominant foundation species, resulting in loss of marine biodiversity. Hypnea brasiliensis, H. cervicornis and H. spinella are three turf-forming species widely distributed along the Brazilian coast with a problematic taxonomic history. Specimens from the warm temperate region are morphologically similar, and their correct identification is only possible based on molecular markers. In the present study, specimens- were cultivated in the laboratory, and temperature gradient experiments (20, 24, 28 and 32°C) were carried out for 21 days. At 28°C, the growth rate, branching ratio, and photosynthetic pigment content were higher in all species, however in vivo chlorophyll fluorescence parameters were at the lowest. Moreover, no species survived at the warmest temperature 32°C. The effects of temperature on the three Hypnea species revealed that useful morphological characters for species identification were only observed in specimens cultured at 28°C, and the morphology of the three species was basically identical in low temperature treatments of 20 and 24°C. The annual average temperature of the sea surface in the Brazilian warm temperate region is 24°C, which may explain the current difficulty of distinguishing the three Hypnea species from this region using only morphology. Furthermore, our findings show that these turf-forming Hypnea species are negatively impacted by rising temperatures, emphasizing the importance of species-specific research to better understand the effects of global climate change. Consequently, predictions of the replacement of dominant foundation species by turf-forming seaweed in an elevated sea surface temperature scenario are less certain. The negative impact of temperature increases raises awareness of the importance of public policies to mitigate the future degradation of marine ecosystems.

Keywords

• Hypnea brasiliensis
• Hypnea cervicornis
• Hypnea spinella
• climate change