Dataset: Zooplankton biomass measured from net tows conducted during ongoing monthly cruises, from April 1994 to December 2025, at the Bermuda Atlantic Time-series Study (BATS) site in the Sargasso Sea

Sampling was conducted on ongoing monthly cruises, starting in April 1994, at the Bermuda Atlantic Time-series Study (BATS) site (31° 40' N 64° 10'W) in the Sargasso Sea. Mesozooplankton were collected with a rectangular frame (0.8 x 1.2 meters) net with 202 micrometer (µm) mesh. Two replicate double oblique tows through the euphotic zone at a ship speed of 1 nautical mile per hour (nm/h) were made during the day (between about 0900 and 1500 h) and night (between about 2000 and 0200 h) on each BATS cruise. The targeted maximum net depth was between 150 and 200 meters (m) and absolute depth was recorded with a temperature-depth recorder. The volume of water filtered by the net (m³) was measured with a General Oceanics flowmeter.

Samples from the tows were split immediately on board. One half-split was fractionated by wet sieving through nested sieves with mesh sizes of 5.0, 2.0, 1.0, 0.5, and 0.2 millimeters (mm), with individual fractions transferred to preweighed disks of 0.2 mm nitex netting and frozen for subsequent wet and dry weight (in milligrams) analyses.