ABSTRACT. Comparative analysis of the invasive coral Tubastraea spp. (Cnidaria, Anthozoa) on natural and artificial substrates at Ilha Grande, Rio de Janeiro, Brazil. Exotic sun corals or cup corals (Tubastraea coccinea Lesson, 1829 and T. tagusensis Wells, 1982) have invaded sessile biological communities on rocky shores at Ilha Grande Bay, Rio de Janeiro, Brazil. Artificial structures (piers, docks or decks) were selected at four sites in Ilha Grande and compared with natural substrates on the adjacent rocky shore by quantifying the density of each species of Tubastraea, as well as the percentage coverage of the benthic biota. The overall average density of Tubastraea tagusensis was 80.3 individuals.m -2 , about double that of T. coccinea. Both invasive species modified the structure of the invaded communities as relative abundance and richness of the species changed due to their presence. Tubastraea coccinea was more abundant on artificial substrates than on natural ones but no difference was detected in the abundance of Tubastraea tagusensis between substrates. The abundance of both species also varied with depth and site and a positive relation between artificial substratum age and abundance of the corals was observed. Apparently T. tagusensis is competitively superior to T. coccinea with a greater ability to occupy/invade native communities on natural substrates. Both species showed high competitive potential and can use artificial substrates to start to establish in new areas. KEYWORDS.Biological invasion, competition, community, density, Scleratinia. Wells, 1982) invadiram as comunidades biológicas sésseis dos costões rochosos da Baía da Ilha Grande, Rio de Janeiro, Brasil. Estruturas artificiais (piers, decks ou cais) foram selecionadas em quatro locais na Ilha Grande, e comparadas com substratos naturais adjacentes através de quantificação da densidade de cada espécie de Tubastraea, além da porcentagem de cobertura da biota bêntica. A densidade média geral de Tubastraea tagusensis foi de 80,3 indivíduos.m -2 , aproximadamente o dobro encontrado para T. coccinea. Tendo em vista que sua presença alterou as abundâncias relativas e a riqueza de espécies, ambas as espécies invasoras modificaram a estrutura das comunidades invadidas. Tubastraea coccinea foi mais abundante em substratos artificiais do que naturais, porém, não foi detectada diferença na abundância de Tubastraea tagusensis entre substratos. A abundância de ambas as espécies variou com a profundidade e o local, e houve uma relação positiva entre a idade do substrato artificial e a abundância dos corais. Aparentemente T. tagusensis é competitivamente superior à T. coccinea, com uma inserção maior nas comunidades nativas em substratos naturais. Ambas as espécies tem grande potencial competitivo e podem utilizar substratos artificiais para iniciar seu estabelecimento em novos locais. RESUMO. Os corais exóticos coral-sol (Tubastraea coccinea Lesson, 1829 e T. tagusensis

Monitoring surveys provide data needed to assess ecosystem conditions in places where bioinvasion occurs. The collection of data by volunteer researchers (citizen science) is an alternative for scientists and research agencies that lack information but do not have sufficient financial resources. The objective of the study was to evaluate the potential of volunteer divers with different diving experiences and the use (or not) of an invasive marine species identification guide at eight diving sites distributed between the north of Ilha Grande and the municipality of Angra dos Reis in the Central Channel of Ilha Grande Bay, Rio de Janeiro state. During the three months of study, 207 questionnaires were evaluated. The results showed that the group of volunteer divers with more experience identified a greater number of invasive exotic species compared to the group of divers with less experience. No statistical difference was found in the number of species identified between the groups of volunteer divers with and without a species identification chart. As a recommendation for the use of citizen science, it is necessary to use divers with greater diving experience. Developing stricter protocols for the identification of invasive exotic marine species is essential for the collection of quality data. The improvement of monitoring programs based on citizen science can provide useful information for research on biodiversity in marine environments, significantly reducing financial costs and time in the field, in addition to contributing to the ecological knowledge, awareness and environmental education of participants.