Influence of Tubastraea spp. coverage (Scleractinia: Dendrophylliidae) on mollusc assemblage structure of artificial substrata in Brazil

Abstract

The conservation of marine biodiversity faces significant challenges, especially with the introduction of exotic species such as Tubastraea corals, which can significantly impact ecosystems. This study was conducted in Todos-os-Santos Bay, Brazil, between 2019 and 2023 and investigated how different Tubastraea coverage levels influence the diversity and composition of molluscan micro- and macrofauna. Ten subtidal sampling stations with artificial substrates were surveyed, and Tubastraea coverage was classified into four categories: “Absent,” “Low,” “Medium,” and “High,” using quadrats for evaluation. We collected all organisms that could easily be removed from substrates within quadrats, and the delimited area was scraped. After quantifying and identifying the organisms in the laboratory, we used ecological descriptors involving univariate and multivariate analyses to verify the influence of coral cover on mollusc assemblages. We collected 9,085 specimens belonging to 81 taxa and 46 families of Bivalvia, Gastropoda, and Polyplacophora, with greater diversity and abundance of bivalves and gastropods such as Chama, Isognomon, and Caecum. Although the generalized linear mixed model showed no significant variations in ecological descriptors across categories, PERMANOVA analysis revealed differences in mollusc assemblage structures based on composition and abundance. Despite the expected negative impact of sun coral on benthic invertebrate diversity, no significant changes were observed in mollusc species richness, abundance, or diversity. While community structure was altered, the presence of Tubastraea spp. did not appear to have affected the malacofauna, which possibly benefited from the heterogeneity of the substrate provided by the corals. However, space competition among sessile species could intensify long-term threats to bivalves. We also highlight the need to define clear metrics to assess the impact of sun coral on local biodiversity and to adopt diversified methodological approaches that account for marine invertebrate groups with different lifestyles and sizes.