Invasive coral Tubastraea spp. population growth in artificial habitats and its consequences to the diversity of benthic organisms

Abstract

Marinas create physical and biotic conditions distinct from those in natural habitats which can facilitate the establishment of non-indigenous species (NIS) in coastal ecosystems. Using a series of images spanning nine years, we detected the introduction and followed the expansion of the NIS Tubastraea coccinea and T. tagusensis populations at a recreational marina in a region of Southeastern Brazil where sun-corals are rarely found on natural substrates. Because sun corals are known to reduce diversity in natural invaded environments, we evaluated how different densities of sun-corals affected the benthic community. Overall, the NIS populations have grown exponentially from 2010 to 2019 inside the marina, occupying up to 60% of the available space. However, the population growth in the breakwater stopped in 2016. Local variation in the population growth across the marina might be associated with the high phytoplankton biomass and larval retention inside the marina, which are results of the lower hydrodynamics. The expansion of sun-coral coverage did not significantly affect the richness of benthic communities but was associated with a reduction of the native bryozoan Amathia brasiliensis, the overall abundance of mobile crustaceans, and an increase in the area covered by the exotic bryozoan S. errata. The fast substitution of a native ecosystem engineer for a NIS suggests signs of invasion meltdown associated with the expansion of Tubastraea spp.