Hydroids (Cnidaria, Hydrozoa) from the Northern and North-eastern coast of Brazil: addressing knowledge gaps in neglected regions

Hydroids are benthic cnidarians that have adapted to diverse marine environments through a wide variety of reproductive strategies and high phenotypic plasticity. This study aims at enhancing our understanding of the benthic hydroid diversity in underexplored areas of Brazil by analyzing hundreds of previously unexamined specimens. The study encompasses material collected from stations spanning the continental shelf and slope, ranging from the intertidal zone to a depth of 3,800 m across nine states in the North and Northeast regions of Brazil. This study represents the most extensive survey of benthic hydrozoans ever conducted in Brazil in terms of the sampled area, number of specimens collected, and bathymetric range. A total of 59 hydroid species, belonging to 32 genera and 14 families, were identified. In the states with the highest number of stations, we observed a greater number of specimens collected and, consequently, a greater richness, highlighting the importance of faunal surveys in neglected areas. The number of records and species richness declined with increasing depth, with 0–50 m exhibiting the highest number of records and species richness. Biogenic substrates, particularly sponges, hosted numerous epizoic hydroids. The significance of conducting new faunal surveys in underexplored areas of the Brazilian coastline is emphasized to address the knowledge gap regarding benthic hydrozoans in a vast area of the western South Atlantic.