Abnormal average increase in sea surface temperature may promote the first documented mortality event of a marine sponge in the Southeastern Brazil

Abstract

Abstract Frequent heat waves and mass mortality events on marine biota are positively correlated to ocean warming. Although literature has indicated some species of marine sponges, and some oceanic regions, like the Brazilian Exclusive Economic Zone, may be less affected or seem to be more resilient under future scenarios of climate changes, few studies have focused on the species responses on the climate change issue along Brazilian coast. This paradigm was undone throughout 2019 after an exceptional average increase of 2 °C in the sea surface temperature (SST) and on precipitation values since 2015 at Ilha Grande Bay (IGB, SE Brazil). The combination of SST and precipitation average increase possibly favored an environmental context for the unprecedented strong population decline and mass mortality rate of the marine sponge species Desmapsamma anchorata in the austral spring. The species used to be one of the most frequent benthic species at IGB however it was only recorded in 41.7% sites (n = 12). From 162 individuals recorded at Abraãozinho along 180 m rocky shore, 83 individuals (51.2%) were healthy, 74 (45.7%) were intensively covered by cyanobacteria and locally bleached, and five (3.1%) were completely bleached or died. Desmapsamma anchorata population deterioration in a biogeographic transition zone (Rio de Janeiro state) may reflect a shift in the marine community of IGB, opening space for opportunistic species establishment and coverage increase, since IGB has a high species turnover. The three-dimensionality, the shelter for several species, the high competitive ability and the potential to indicate polluted or not polluted areas make D. anchorata a key species for IGB monitoring in a climate change scenario.