Taxon-specific mesozooplankton biovolume and normalized biovolume size spectra from Multinet samples under the influence of the Amazon River Plume during RV Meteor cruise M174

Zooplankton samples were collected during the RV Meteor cruise M174 (April–May 2021) using a Multi Plankton Sampler (Multinet Midi, 200 µm mesh size). Sampling included oblique tows at discrete depth intervals (0–25, 25–50, 50–100, and 100–200 m), integrated oblique tows (0–200 m), and horizontal tows at selected stations. The cruise surveyed coastal and oceanic waters both under and beyond the influence of the Amazon River Plume, encompassing five habitats: Riverine (RIV), Young Plume Core (YPC), Old Plume Core (OPC), Western Plume Margin (WPM), and Oceanic Waters (OSW). Stations that could not be assigned to a habitat are indicated as NI (Not Identified). Zooplankton samples were separated into two size fractions (>1 mm and <1 mm), digitized using a ZooScan imaging system (2400 dpi resolution), and processed with ZooProcess software. Images were subjected to automated classification followed by manual taxonomic validation using the EcoTaxa web application. Morphometric measurements obtained from scanned images were used to estimate individual biovolume, which was subsequently integrated for each taxonomic group and standardized by the sampled water volume. When multiple tows sampled the same depth interval, biovolume values were combined using midpoint integration to obtain weighted mean estimates representative of the corresponding depth interval. Data were subjected to quality control, and Normalized Biovolume Size spectra (NBSS) were computed following the protocols of the Pelagic Size Structure Database (PSSdb; https://pssdb.net/) using a lower size threshold of 500 µm. This dataset provides taxon-specific mesozooplankton biovolume (mm³/m³) together with sample-specific NBSS slope and intercept (µm³/L/µm³) for stations sampled across a gradient of Amazon River Plume influence, encompassing different depth strata during cruise M174.