Invasion dynamics and management of the Atlantic blue crab (Callinectes sapidus) in a European salt marsh: Evidence from the Bay of Cádiz, Spain

Abstract

Biological invasions are reshaping coastal ecosystems, yet invader performance in aquaculture-influenced salt marsh habitats remains poorly resolved. We conducted an 18-month survey (January 2023–July 2024) at two contrasting salt marsh sites in the Bay of C´adiz, Spain, to compare the invasive Atlantic blue crab (Callinectes sapidus) with the native European green crab (Carcinus maenas). Monthly fyke-net sampling was paired with concurrent prey assessments and water-column measurements. We captured 168 C. sapidus and 1086 C. maenas individuals. Mean abundance (individuals net 1 24 h 1 ) was higher for C. sapidus at the Fish site (1.83 ± 0.36) and for C. maenas at the Oyster site (16.28 ± 1.91). Biomass (ash free dry mass, g) was higher for C. sapidus at the Fish site (11.63 ± 2.08 vs 4.58 ± 1.15 at the Oyster site) and for C. maenas at the Oyster site (10.53 ± 1.22 vs 1.12 ± 0.43 at the Fish site). Body sizes mirrored these patterns (C. sapidus at Fish site: +14.5 mm carapace width, +5.9 mm carapace length relative to Oyster site; C. maenas at the Oyster site: +2.7 mm carapace width, +2.3 mm carapace length versus the Fish site; p < 0.05). Seasonal peaks differed (C. sapidus: late spring–early summer; C. maenas: winter–spring), with a winter non detection of C. sapidus. Linear mixed-effects models showed that C. sapidus abundance increased under warmer, macroinfauna-rich conditions, whereas C. maenas was more abundant in cooler, more turbid waters with higher availability of fish and hyperbenthic prey. These patterns suggest thermal-prey pathways in aquaculture-modified salt marshes and provide cues for targeted monitoring, removal, and future management.