Massive populations of the non-indigenous bivalve species Electroma vexillum (Reeve, 1857) and its effects on native phytal benthic communities of tropical coastal reefs

The Vulsellidae is a family of marine bivalves distributed worldwide, with several species recognized as invasive. The present study reports, for the first time, a massive population of the vulsellid Electroma vexillum in macroalgae of coastal sandstone reefs on the tropical Brazilian coast (Boa Viagem beach) and describes its effects on epifaunal communities. To test the hypothesis that the abundance of bivalves was species-specific, samples of ten species of macroalgae were collected. To identify the effects of bivalves’ aggregations on macrobenthic phytal communities, samples of three macroalgae species with and without bivalves were used. These three species were chosen because they have been monitored since 2019, and only of them had samples without bivalves, collected in June 2021. The abundance of E. vexillum varied depending on the macroalgal species, with the highest values in Bryopsis sp. The presence of bivalves significantly altered the structure of the epifaunal community, leading to higher richness (including some exclusive taxa) and greater abundance. E. vexillum was also found in macroalgae in Pina, Paiva, Enseada dos Corais, and Toquinho, but with very low abundance. The difference in the abundance of E. vexillum among algae species may be a response of the bivalves to changes in the complexity and anatomy of macroalgae. The occurrence of bivalves increases the three-dimensional complexity of the substrate, favoring the epifauna by enhancing the availability of space for colonization, protection, and food. The record of E. vexillum on other beaches serves as a warning about the risk of the species spreading and its associated impacts on native communities.