Method-dependent differences in zooplankton abundance and size metrics: microscopy versus ZooScan; abundance, body-length, and ESD measurements from the northeastern East China Sea (2022–2023)

This dataset consists of two components: (1) taxon-specific size class proportion data, and (2) SizeIndex values that quantify the differences between direct length measurements and ZooScan-derived equivalent spherical diameter (ESD). These data were generated to assess zooplankton size structure and evaluate measurement biases between traditional microscopy and image-based approaches.