Small-Scale Currents Focus Marine Food Webs in Palmer Deep Canyon

Prey patchiness in the ocean strongly influences predator foraging strategies, yet the role of small-scale ocean currents in shaping food web interactions remains unclear. At Palmer Deep Canyon, Antarctica, we examined how variations in surface current structures influence the spatial distribution of phytoplankton and Antarctic krill. Previous studies have demonstrated that oceanic features responsible for accumulating free-floating particles referred to as attractive Lagrangian Coherent Structures (LCS) tend to coincide with phytoplankton patches, krill aggregations, and areas of penguin foraging. Nonetheless, the physical mechanisms responsible for generating these attractive LCS remain unresolved. Using in-situ optical sensors, we mapped phytoplankton patches, while high-resolution acoustic data captured krill swarms. These data spanned two levels of the food web, allowing us to examine their spatial relationships with ocean surface transport features. High-Frequency radars measured hourly surface currents, which we analyzed to identify attractive dynamic zones where particles converge. Our results revealed that the patterns in LCS, phytoplankton patches, and krill swarms form two distinct spatial modes during the different phases of the tidal cycle. This study provides compelling evidence that tidally driven LCS concentrates prey, spatially focusing food webs on the dynamic Antarctic ecosystem. By highlighting the role of small-scale ocean currents, our findings underscore the importance of physical transport processes in maintaining the productivity of the marine food web and the underlying mechanisms that drive these patterns.