Abstract:

Mesozooplankton samples were taken during the summer of 2016 between July 24-30 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. 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. 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.

Suggested Citation:

Briseño-Avena, Christian, Alison L. Deary, Robert K. Cowen, Frank J. Hernandez, and Jeffrey W. Krause. 2017. Mesozooplankton Size-Fractionated Dry Weight, cruise PTS03, July 2016. Distributed by: GRIIDC, Harte Research Institute, Texas A&M University–Corpus Christi. doi:10.7266/N7QJ7FN0

Purpose:

The dataset was developed to provide mesozooplankton size-fractionated information that will be used, among other, to normalize mesozooplankton grazing rates measured through the gut fluorescence.

Data Parameters and Units:

CRUISE_ID = research cruise unique identifier. YEAR = Year sample was collected. Month = Month sample was collected. Day = Day sample was collected. Time_UTC_HH = hour sample was collected, in UTC. Time_UTC_MM = minutes when sample was collected, in UTC. Latitude = Latitude (decimal). Longitude = Longitude (decimal). Negative sign indicate latitude west. Sampling_Type = Name assigned to the transect or location in which the station took place, usually indicating the type of study. Tow_ID = Unique Net Tow identifier. MN indicates it was mininess net. Net_ID = mininess number from which the sample was taken. Petri_Dish_Number = label on the petri dish for each pre-weighted nitex circle. Mesh_Size_um = mesh size of the net used during tow. Gear_Type = The gear used for the plankton tow. Size_Fraction_mm = size of the sieve mesh, the values correspond to, in millimeters. Pre_Bake_Weight_g = weight of the nitex circle alone prior to utilization (i.e. blank weight), in grams. Post_Bake_Weight_g = weight of the nitex circle and mesozooplankton sample combined, in grams. Balance_Offset_g = two different balances were used in some cases. To test the difference in readings from both balances, ten pre-weighted (empty) circles were measured again in the second balance. We found a difference of 0.001 g difference in the reported weights between balances, in grams. Post_Bake_Offset_g = The same empty nitex circles were measured before and after baking, in grams. We found there was a weight loss by the nitex circle alone of 0.002 g. Adjusted_Dry_Weight_g = This is the weight of the mesozooplankton sample (post-bake minus pre-bake weights, taking offsets into consideration). Net_Split = Initial Sample split from net sample. Final_Aliquot = fraction of the original sample used for this experiment. Begin_Depth_m = depth in meters where the net was opened and started sampling. End_Depth_m = depth in meters where the net was closed and stopped sampling. Depth_Range_m = depth interval sampled by the net between opening and closing interval. Swept_Volume_m3 = water volume (meters cubed) filtered (i.e. sampled) by the net. Dry_Weight_mg_m3 = volumetric mesozooplankton dry weight (milligrams of mesozooplankton dry mass per meter cube). Areal_Dry_Weight_mg_m2 = aerial mesozooplankton dry weight (milligrams of mesozooplankton dry mass per meter square). Carbon_Mass_ugC_L = volumetric Mesozooplankton Dry Weight converted into volumetric Mesozooplankton Carbon Mass (micrograms of Carbon per liter).

Methods:

An attempt was made to "ground truth" CONCORDE mesozooplankton dry weight measurements by comparing them to existing data from the Northern Gulf of Mexico. Since no dry weight measurements were found in publicly available datasets, dry weight data was converted to Carbon Mass (micrograms of Carbon per L) by following Moriarty and O-Brien (2013), and using the equations from Wiebe et al. (1975), and Wiebe (1988). Carbon Mass was then directly compared to other measurements (model estimates) available for the region, which includes data from all seasons. For the direct comparison, data from all size classes coming from each sample were pooled together since no size-fractionated Carbon Mass was found. Moriarty, R. & O'Brien, T.D. (2013). Distribution of mesozooplankton biomass in the global ocean. Earth Syst. Sci. Data, 5: 45-55. doi: 10.5194/essd-5-45-2013 Weibe, P.H., Boyd, S.H., & Cox, J.L. (1975). Relationships between zooplankton displacement volume, wet weight, dry weight, and carbon. Fish. Bull. 73(4): 777-786. Wiebe, P.H. (1988). Functional regression equations for zooplankton displacement volume, wet weight, dry weight, and carbon : a correction. Fish. Bull. 86: 833-835.

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