Amphipoda (Crustacea, Peracarida) associated with the octocoral Carijoa riisei (Cnidaria, Anthozoa) in estuarine and reef environments of northeastern Brazil

Carijoa riisei is a branching colonial octocoral widely distributed in reef and estuarine environments along the coast of Pernambuco, northeastern Brazil. Owing to the structural complexity of its colonies, it provides both habitat and substrate for a diverse assemblage of associated organisms. This study investigated the structure of the amphipod community associated with C. riisei in two contrasting environments on the southern coast of Pernambuco: Porto de Galinhas Beach and the Rio Formoso Estuary. Four sampling campaigns were carried out, two at each site, encompassing both the dry and rainy seasons. During each campaign, 12 octocoral colonies were collected, resulting in a total of 48 samples. A total of 26,683 amphipods representing 21 species were recorded. The most abundant species were Ericthonius brasiliensis (57.28%), Laticorophium baconi (10.93%), Podocerus brasiliensis (7.65%), Monocorophium acherusicum (7.54%), and Dulichiella ankeri (5.89%), which together accounted for 89.22% of all individuals collected. Amphipod abundance in the Rio Formoso Estuary was approximately six times greater than that recorded at Porto de Galinhas. Moreover, L. baconi and M. acherusicum were exclusively found in the estuarine environment. Comparisons of ecological descriptors revealed significant differences between the two sites, with the estuary exhibiting higher amphipod abundance and diversity. These findings suggest that estuarine conditions, including greater nutrient availability, higher sediment input, and the influence of water flow and reduced light penetration, promote the establishment of more diverse amphipod assemblages associated with C. riisei.