Abstract:

Marsh and subtidal sediment for microscopic analysis were collected in the vicinities of Terrebonne Bay, Grand Isle, and Port Sulphur, Louisiana in spring, summer, and fall of 2015, 2016, and 2017. Cell concentrations are presented, along with weights of sediments extracted for the counts.

Suggested Citation:

Price, Andrea, Rabalais, Nancy N.. 2020. Marsh and subtidal sediment microphytobenthos from three regions of coastal Louisiana: Cell concentration microscopy data from 2015-05-12 to 2017-10-13. Distributed by: GRIIDC, Harte Research Institute, Texas A&M University–Corpus Christi. doi:10.7266/CB8XFQWH

Purpose:

To determine the impact of the Deepwater Horizon oil spill on benthic microplankton in Louisiana marshes.

Data Parameters and Units:

Date: Date samples were collected in the field (MM/DD/YYYY); Station: User-defined identifier assigned to each sampling location; LAT: Latitude of sampling location in decimal degrees; LONG: Longitude of sampling location in decimal degrees; Marsh/Subtidal: Denotes whether sample was collected from the marsh or subtidal sediments; Sample Weight (g): Weight of the sample in grams; Concentrations of nine categories of phytoplankton enumberated from sediment samples (Pennates >90 µm, Pennates <90 µm, Stacked/ Sliding Pennates, Melosira, Skeletonema, Odontella, Coscinodiscus, Anabaena-type, Merismopedia). Units are microgram per gram dry sediment.

Methods:

Marsh surface sediment samples were collected using 60 mL plastic syringes with the ends cut off. Syringes were pushed approximately 2-3 cm into the marsh and the sediment plugs extruded by placing the syringe plunger back in and creating a vacuum pressure. The top 0.5 to 1 cm from each syringe was placed into a 125 ml plastic sample bottle containing 1 ml of 50% glutaraldehyde. Filtered, ambient salinity water was added to the plastic sample bottles to make a diluted glutaraldehyde solution of 0.5 % then placed on ice and taken to the lab where they were refrigerated. If root biomass prevented good penetration of the corers, then they were used to imprint an outline, from which the sediment was scraped to 1-cm depth. Subtidal samples were collected in approximately 1 m water depth using a 7.62 cm diameter PVC coring device. Cores were approximately 5 cm long, and the overlying water was carefully siphoned off before the top 1 cm was extruded. The subtidal samples were processed the same as the marsh surface sediments. MPB in marsh and subtidal surface samples were extracted following the method of Baustian et al. (2011), modified to extract only larger autotrophs (8-63 µm). One to three milliliters of suspended material were analyzed. Microscopic counts were made using an Olympus epifluorescence microscope (EFM) with blue and green excitation light and transmitted light. Filters were first examined at 200x until 100 cells or 100 fields were reached. The magnification was then changed to 100x and half of the same filter was scanned again for organisms not seen at the 200x count (this step allows for identification of large rare species). Diatoms were classified into seven categories (pennates <90 µm, pennates >90 µm, sliding/stacked pennates, Melosira, Skeletonema, Odontella, Coscinodiscus). Cyanobacteria were enumerated either as chain-forming Anabena-type or colonial Merismopedia. After cell extraction, sediment pellets were dried and weighed.

Provenance and Historical References:

Baustian, M., Rabalais, N., Morrison, W., & Turner, R. (2011). Seasonal microphytobenthos on the hypoxic ­northern Gulf of Mexico continental shelf. Marine Ecology Progress Series, 436, 51–66. doi:10.3354/meps09262

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