Despite high proportion of shell fisheries for livelihood and food security, documentation of brachyuran crabs from Devi estuary, east coast of India, recognized as ‘arribada’ of Olive Ridley turtles, remains sparse. To deal with this gap, 3-year investigation (2014–2017) on the estuary and adjacent mangrove-fringed mudflats across 17 GPS fixed sites was undertaken; the main objective being species’ reconnaissance, abundance, and diversity in relation to environmental conditions. Overall, 40 species of brachyurans (27 genera and 17 families) were recorded from mangrove mudflats and estuary, of which Portunids outnumbered others. Nine species namely, Elamena xavieri, Carcinoplax longimana, C. longipes, Typhlocarcinus villosus, Arcania heptacantha, Paranursia abbreviata, Leucosia anatum, Venitus latreillei, and Arcotheres purpureus are new records for this region. Multivariate analysis through Bray–Curtis similarity using SIMPROF in PRIMER, recognized four brachyuran assemblages (ANOSIM, Global R 0.936; p<0.001) characterizing mangrove mudflats (Neodorippe callida-Scylla serrata assemblage; salinity 21.88 PSU; silty loam sediments, organic matter 2%); seaward areas (Charybdis hellerii assemblage, salinity, 27.41 PSU; loamy sand, organic matter 0.85%); mid-estuary (Portunus sanguinolentus-P. pelagicus assemblage; salinity, 23.29 PSU, sandy, 0.64% organic matter) and riverine-end (Doclea rissonii assemblage; low salinity, 19.69 PSU; sandy, 0.58% organic matter). Tubuca rosea-Austruca triangularis assemblage remained as an outlier (intertidal silty sand, organic matter 1.28%). Species accounting for dissimilarity (97.51%; SIMPER) between sites were identified. Rarefaction of samples recognized minimum brachyuran crab diversity at the riverine end and transitional areas in comparison to the seaward zone followed by mid-estuary and mangrove mudflats. Accessibility of food resources such as detritus and leaf litter through tidal surging from immediate mangrove environs appeared to support diverse species of crabs. Canonical correspondence analysis (CCA) delineated sediment texture and organic matter as significant factors influencing brachyuran crab community patterns. The study benefited towards building species repositories at the baseline for future monitoring assessments and eco-conservation strategies.