Limited connectivity of zooplankton communities across the Labrador Front: role of physical oceanography, insights from individual motility

Near the western margin of the highly productive Labrador Sea, the Labrador Current creates a large and steep oceanographic front between the Arctic‐origin shelf waters and the Atlantic offshore waters (i.e. the Labrador Front), presumably segregating or accumulating plankton communities. Because mesozooplankton have critical role in funneling energy in marine food webs, understanding the physical processes shaping their distribution and diversity is essential for ecosystem‐based management and conservation of the marine resources in the region. In this study, we combine data from depth‐stratified nets, active hydroacoustics, and environmental DNA to investigate the impact of the Labrador Front on the distribution of zooplankton communities. We demonstrate that the Labrador Front segregates mesozooplankton in terms of density and diversity (i.e . abundant Arctic communities over the shelf and at the front surface; diverse and Atlantic‐influenced communities at depth). The limited inshore‐offshore connectivity is attested by the presence of four distinct mesozooplankton communities from coastal fjords to deep waters. However, a weak ecological dissimilarity between the two zooplankton clusters across the frontal zone suggested some, limited, vertical connectivity. In addition to several physical mechanisms that can lead to the passive reorganization of zooplankton communities, we take a trait‐based approach to explore how active vertical motility of zooplankton could contribute to smooth their distribution across the front. We also discuss the permeability of the front in the context of climate change. This study provides knowledge on pelagic structure to delineating the ecological boundaries needed to establish a representative network of marine conservation areas in the Labrador Sea.