The present study describes the population dynamics and life history parameters of the enigmatic tanaid Chondrochelia dubia collected in Paiva Beach, tropical coast of Brazil. The region was impacted by a large, unexpected oil spill from August to October 2019. Samples were taken monthly between July 2019 and July 2020 in beds of the red seaweed Jania capillacea. The abundance of individuals was negatively correlated with monthly rainfall, with higher abundances in drier months. There was an unexpected significant drop in abundance in September, possibly caused by contact with the crude oil, but the population recovered fully within two months. The parameters of the von Bertallanfy growth equation, calculated for the first time for the species, were L_inf =5.26 mm; k=3.36 year^-1; t₀=0.0. Compared with other studies, the specimens are very small (2.04 ± 0.95 mm in length), females reach sexual maturity very early (L₅₀=2.3 mm), and natural mortality is high (Z=M=5.77 year^-1), indicating an opportunistic life strategy. This study reinforces the bioindication potential of C. dubia and the use of bootstrapped length-based methods to estimate key population parameters in small marine invertebrates.