An in situ stereo‐imaging system for characterizing behavior, distributions, and aggregations of meso‐ and macro‐zooplankton in diverse aquatic environments

Zooplankton play a critical role in aquatic ecosystems, serving as a key link in food webs and contributing to nutrient cycling and the biological pump. Despite their importance, challenges remain in capturing high‐resolution in situ data, especially for understanding zooplankton behavior and aggregation across multiple size classes. This study introduces a custom‐built stereo‐imaging system capable of precise spatial 3D estimation, enabling characterization of individual and group behavioral observations of meso‐ and macrozooplankton and other organisms (e.g., micronekton) in the ~ 0.5 mm to 9 cm size range in their natural habitats. The stereo‐imaging system employs two high‐resolution monochrome cameras, offering real‐time visualization and adaptive sampling. Laboratory validation experiments demonstrated consistent and reliable performance across various configurations for spatial 3D measurement within the imaging volume, with overall coefficients of variation < 2%. Field deployments successfully highlighted the in situ observational capabilities of the system, with data processing allowing for computation of both individual and aggregation metrics, including but not limited to organism swimming speeds and acceleration, swarm/school densities, orientation, polarization order, and nearest neighbor distances. The comprehensive observations enabled by the stereo‐imaging system can potentially offer valuable insights into complex behavioral patterns, social interactions, and predator–prey dynamics, highlighting how future applications in targeted studies could enhance our understanding of meso‐ and macrozooplankton ecology.