Impact of Drought-Induced Hydrological Changes on Copepod Communities in an Amazonian Estuary

The influence of the drought event on the structure and distribution of the copepod community was investigated in the Caeté Estuary, northeast of Pará, Brazil, through field surveys performed in three sectors of the estuary from June/2013 to June/2014. The occurrence of a dry event in June/2013 was marked by low rainfall and consequently by lower river runoff, increased seasonal average salinity (19.71 ± 5.64), dissolved nutrient concentrations, and high phytoplankton biomass (chlorophyll-a). These conditions allowed a substantial increase in copepod density, particularly toward the mouth of the estuary, which was dominated by estuarine and coastal species such as Pseudodiaptomus richardi, Oithona hebes, Acartia lilljeborgii, Acartia tonsa, and Paracalanus quasimodo, which presented higher densities in Jun/2013 than those obtained during the normal precipitation period (June/2014). Marine species allowed a slight increase in diversity and richness, possibly caused by the increased recruitment rate from adjacent coastal waters. Results highlight that salinity, driven by precipitation, regulates copepod distribution and composition, with droughts affecting estuarine trophic dynamics in the Caeté Estuary. Future studies focused on conservation efforts must consider connectivity between resident and transitory species while addressing trophic interactions like predation and food availability. Adaptive management strategies that integrate these factors can help sustain estuarine ecosystems against climate anomalies and anthropogenic pressures in tropical estuarine systems with similar characteristics in the Amazon region and worldwide.