Influences of ocean warming on sperm viability and oxidative status of the Brazilian reef-building coral Mussismilia braziliensis (Verrill, 1868)

Abstract

Climate changes from anthropogenic activities have resulted in increased temperature in the Earth's atmosphere and, consequently, in the ocean. Coral reefs are highly sensitive to environmental variations, and considering they are home to at least 25 % of all marine life, impacts on shallow-water reefs can lead to irreversible damages to human society. Despite one of the biggest threats to corals has been the severe bleaching events, little is known about how the increasing ocean temperature impacts reproduction of Tropical South Atlantic corals under marginal turbid conditions. Thus, this study aimed to evaluate the impacts of increasing temperature on sperm viability of the endemic reef-building species Mussismilia braziliensis. Spermatozoa were exposed to different temperatures: 28 °C, Recife de Fora local temperature; 29.7 °C, considering the milder scenario RCP2.6; and 32.8 °C considering the most critical scenario RCP8.5 of IPCC climate projections. Sperm viability and oxidative parameters status were assessed up to 7 h after spawning. We observed that at higher temperatures sperm motility drops rapidly, compromising spermatozoa viability right after spawning. Furthermore, as the temperature increased and time passed, there was a drop in spermatozoa exhibiting normal morphology and an increase in flagella damages. Lipid peroxidation, protein carbonyl and reduced glutathione levels did not change among temperatures. This is the first time that spermatozoa of Mussismilia braziliensis is evaluated in an ocean warming scenario. Information gained from this study may help to better understand how broadcast spawners deal with sexual reproduction in a wide spectrum of ocean temperatures.