Dataset: Ichthyoplankton density and plankton displacement volume data collected using MOCNESS plankton nets on the NSF RAPID Plankton Cruises in the Northwestern Gulf of Mexico in 2017-2018

The MOCNESS Plankton Net was deployed over the aft to horizontally sample three discrete depth strata in the water column: (1) Under Chla maximum layer above bottom, (2) within the Chla maximum layer, (3) Above Chla maximum layer underneath the surface. Ship speed was 1.5-2.0 knots and was adjusted according to online flowmeter readings.

One net per sampled stratum was analyzed for ichthyoplankton (net # 1, 5, 7). Nets were rinsed and processed on board and samples were preserved in 200 proof Ethanol (ETOH) according to NOAA SEAMAP Operations Manual upon retrieval of nets. After 24 hours, ETOH was exchanged with fresh ETOH. Plankton samples were stored in 1000ml plastic jars until processing in the Geist Early Life History Research Laboratory at Texas A&M University Corpus Christi during 2017 and 2020. Total Zooplankton Displacement Volume was determined using a calibrated 1000ml measuring cylinder by subtracting the volume of ethanol without sample from the volume of ethanol with sample. The plankton sample was separated from ethanol using a concentrator sieve with a mesh size < than the net mesh size. Then the plankton sample was resuspended in Ethanol. Larval fish were picked under dissecting microscopes using feather steel tweezers. Every sample was looked through twice for quality check purposes.