Trophic interaction of invertebrate zooplankton on either side of the Charlie Gibbs Fracture Zone/Subpolar Front of the Mid-Atlantic Ridge

Trophic relationships and vertical distribution patterns of dominant mesozooplankton (2–20 mm) and macrozooplankton (> 20 mm) invertebrates (Euphausiacea, Copepoda, Decapoda, Amphipoda, Thecosomata and Lophogastrida) were investigated within the epi- and meso-pelagic zone (0–200 and 200–800 m depth), north (54° N) and south (49° N) of the Subpolar Front (SPF) on the Mid-Atlantic Ridge (MAR). Dietary relationships were explored using stable isotope ratios of nitrogen and carbon, and fatty acid trophic markers (FATM). Individuals from the southern stations (~ 49° N) had higher concentrations of the dinoflagellate FATM (22:6(n-3)), and individuals from northern stations had higher concentration in Calanus sp. and storage FATMs (20:1(n-9) and 22:1(n-9)). Energy pathways on either side of the SPF showed retention of δ13C differences (as measured in POM) in bathypelagic species. Observations of FATM levels and abundance patterns are consistent with present theories pertaining to primary production patterns at the base of the food chain, which states that the peak of the production is higher in the northern sector than in the south.

► We describe vertical patterns of epi and meso-zooplankton in two sectors over the Mid-Atlantic Ridge. ► We compare abundances between two sectors of different primary production regimes. ► Trophic relationships in the two sectors are elucidated, using stable isotope and fatty acid analysis. ► Spatial differences in faunal abundance, fatty acids and stable isotopes are consistent with primary production patterns.