Long-term assessment of the presence of the non-native estuarine copepod Pseudodiaptomus trihamatus Wright, 1937 (Calanoida) and spatial investigation after 30 years of invasion in Northeastern Brazil

We aimed to investigate the presence of the copepod Pseudodiaptomus trihamatus in an estuary in Northeastern Brazil, from a long-term perspective (1987–2023), and its distribution in other nearby estuaries, after 30 years of invasion, especially considering its impacts on native congeneric species. We tested the following hypotheses: (i) The abundance of P. trihamatus increases over time and the abundance of native species decreases; (ii) The β diversity decreases over time; (iii) Copepod composition and β diversity differs over time. The study was carried out in six estuarines systems in Pernambuco, in the Northeastern Brazil. The investigation of long-term variation (1987–2023) was based on the Capibaribe River Estuarine System (CRES), while for the spatial variation (2020–2021), six estuarine systems were considered. We observed that P. trihamatus has occurred in CRES since 1991, 10 years before the first record of the species in Pernambuco. The abundance of P. trihamatus did not increase over time. Furthermore, β diversity increased over time, showing that the presence of P. trihamatus did not cause biotic homogenization through loss of biodiversity. In the spatial variation (2020–2021), we found P. trihamatus in four of the estuaries and was it the third most representative species of the family. The occurrence of P. trihamatus did not significantly affect the Pseudodiaptomidae family and the copepod assemblage, for either long-term or spatial variation. The undetected or negligible impact of P. trihamatus need to be monitored, to prevent a sleeper population from becoming highly abundant and, perhaps, disruptive in this region of Brazil.