Mesozooplankton Size-Fractionated Dry Weight, cruise PTS02, Spring 2016

Mesozooplankton samples were taken during the spring of 2016 between March 30 and April 9 aboard R/V Point Sur using a mininess (BIONESS) tow system. Samples were taken from three nets, corresponding to three depth intervals (e.g. bottom, midwater, surface). Nets had 202 micrometer mesh size, but in some cases samples were taken from nets with 0.333 micrometer mesh. Samples were transferred into a bucket immediately after retrieval and carbonated water was added to the sample to stop or avoid further 'net feeding' or regurgitation from individual zooplankton. Typically, each net sample was split in two aliquots using a Folsom Splitter aboard the ship. The 1/2 aliquot separated from the original sample was then split further in two subsamples: one was used to measure mesozooplankton dry weight and the other was processed for gut fluorescence (data reported in GRIIDC UDI: R4.x260.000:0035). When samples were too thick, the initial sample was split into smaller aliquots (clearly indicated in the dataset). The corresponding aliquot was then size fractionated into five classes using sieves with meshes measuring: 0.212, 0.5, 1, 2, and 4.75 mm. Filtered seawater was used during sample split and size fractionation. Next, each size fraction was filtered onto pre-weighted nitex circles (2.5 mm diameter) with a 0.202 mesh size. Nitex circles were individually put in labeled plastic petri dishes and stored stacked inside sealed plastic bags to avoid moisture from getting in touch with the nitex before using them. After fractionation, each sample was poured onto a nitex circle using a filtering system aboard the ship, rinsed with DI water, transferred to its pre-labeled petri dish and frozen immediately after filtering. At the lab, the samples were dried up in an oven at 60 degrees Celsius over a period of 48 hours and weighted immediately after taking each sample out of the oven. The difference between the weight of the filter minus the weight after drying the sample constituted the mesozooplankton dry weight. These data will be used in combination with other mesozooplankton net data to study zooplankton processes in the river-dominated northern Gulf of Mexico.