Invasive species are leading to ecosystem changes and socioeconomic deterioration around the globe. In 2018, unknown soft corals were noticed forming a massive ‘blue carpet’ on a shallow reef environment at Todos os Santos Bay, South-west Atlantic. In this study we identified the species, quantified their distribution and abundance as a first step for baseline invasion monitoring, and discussed origin, vector and impacts on native competitors. Coral samples were identified based on morphology and a multilocus DNA barcode, and benthic structure was characterized using digital photoquadrats. Our results revealed two new harmful non-native octocorals in this tropical rocky reef, the ‘blue polyps’ genus Sarcothelia (Xeniidae), native to Hawaii but likely an undescribed cryptic species, and Briareum hamrum (Briareidae), native to the Indian Ocean. Sarcothelia sp. was the dominant taxon in the rocky reef (mean cover 23.66% ± 21.46), exhibiting high coverage as well in the sandy and patch reef habitats (15.83% ± 15.81), however, only three colonies of B. hamrum were found, all outside the sampling area. These octocorals were in physical contact with native benthic organisms, mainly with the most abundant group, but apparently avoid turf algae in sandy and patch reef habitats. We suggest that irresponsible marine aquarium releases likely introduced these species to Brazilian reefs. After identifying the aquarium trade as the main vector of octocoral introductions, we reinforce the importance of inspecting marine species importation and the urgent need to implement a government plan to mitigate invasive species' impacts on the natural reefs of Brazil.

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The morphology of sessile invertebrates, such as scleractinian corals, can be controlled by environmental and genetic mechanisms and, consequently, it is highly variable. Morphological variation has puzzled taxonomists by posing challenges to species classification within cryptic species complexes. The 'Atlantic Siderastrea Complex' is a suitable example. Because of overlapping diagnostic traits, the morphological interspecific limits of this group remain controversial and often resulted in doubtful synonyms. In addition, the recent identification of the Caribbean S. radians in the Southwestern Atlantic has revealed that intraspecific variation has been equivocally assessed. Traditionally, hierarchical categories of variation have been the criteria used to investigate the patterns of modular organisms as corals. However, despite its taxonomic and ecological implications, the category 'intracolonial' has been largely neglected. To evaluate the influences of intracolonial morphological variation in the identification of Atlantic siderastreids, colonies from Bahia State, northeastern Brazil, were collected and measured. Six characters were selected in S. radians and S. stellata, and the variation in these characters was analyzed with Discriminant Canonical Analysis. The columellar depth and diameter varied consistently within S. stellata and S. radians, but the septal number was the most important for differentiating the two species. The results of the study also represent the first report of S. radians on the northern coast of Bahia.

Siderastrea is a small genus of scleractinian corals, composed by zooxanthellate massive colonial forms. Besides contributing to the consolidation of the reef structure, represent a group with significant resistance to environmental stress. Until the 70's, its taxonomy was a complicated task, limited by the difficulty in identifying morphotypes. More recently, interspecific boundaries were redefined for 'Atlantic Siderastrea Complex'. However, despite new perspectives, including the occurrence of S. radians and S. siderea for Brazil, morphological patterns are still poorly studied and inconspicuous for several coastal areas. In order to characterize levels of intraspecific and interspecific morphological variation in S. stellata and S. radians, morphometric analysis were carried out in colonies from Bahia State coast. Samples were taken in Todos-os-Santos Bay and North Coast. We applied the Canonical Discriminate Analysis upon six corallite characters to evaluate the different levels of variation. The tests revealed that diameter of corallites, columella depth and number of septa varied among populations. Number of septa was the most important character for the species differentiation. Siderastrea stellata, with three different morphological patterns, was more variable than S. radians.