Abstract:

The long-term effects of heavy oil exposure on southern ribbed mussel (Geukensia granosissima) facilitation of salt marsh ecosystem function and stability were assessed with a field manipulation experiment conducted at heavily oiled sites (n=5) and reference sites with no visible oiling (n=5) in northern Barataria Bay, Louisiana. In March 2017, replicate 0.25m2 plots of two treatments were established at each site along the marsh edge in areas dominated by Spartina alterniflora: (1) two plots with all G. granosissima removed, and (2) plots with G. granosissima added at a density of 100 individuals/m2. One replicate plot of each treatment was sampled at each site in November of 2017 and 2018.

Suggested Citation:

Sean Graham. 2020. Southern ribbed mussel (Geukensia granosissima) transplant experiment data, northern Barataria Bay, 2017-11-27 to 2018-11-13. Distributed by: GRIIDC, Harte Research Institute, Texas A&M University–Corpus Christi. doi:10.7266/n7-9tvv-bb44

Purpose:

To assess the long-term effects of heavy oil exposure on southern ribbed mussel (Geukensia granosissima) facilitation of salt marsh ecosystem function and stability.

Data Parameters and Units:

The dataset contains one Excel file and data are organized under different worksheets that includes: Oiling Category [Reference (RF; n=5), Heavy Oil (HV; n=5)]; Site ID [Identifier used to specify and distinguish different sites]; Latitude [decimal degrees]; Longitude [decimal degrees]; Mussel Treatment [whether transplanted or not]; Live Aboveground Biomass [g/m2]; Dead Aboveground Biomass [g/m2]; Sampling Date [Date of sample collection, MM/DD/YYYY]; Spartina alterniflora Green Tissue Carbon [%]; Spartina alterniflora Green Tissue Nitrogen [%]; Live Root Biomass [g/m2]; Live Rhizome Biomass [g/m2]; Dead Belowground Biomass [g/m2], Soil Bulk Density [g/cm3]; Soil NH4-N [mg/kg]; Soil Phosphorus [mg/kg]; Soil Depth [cm]; Average soil redox potential [Eh; in mV]; Soil Depth Increment [cm]; Avg Shear Strength [kPa], Juvenile Transplanted Mussel Growth Rate [mm/yr]; Adult Transplanted Mussel Growth Rate [mm/yr], Total Transplanted Mussel Growth Rate [mm/yr]; Juvenile Transplanted Mussel Survivorship [%]; Adult Transplanted Mussel Survivorship [%]; Total Transplanted Mussel Survivorship [%]; Juvenile Mussel Recruitment to Transplant Plots [#/m2]; Adult Mussel Recruitment to Transplant Plots [#/m2], and Total Mussel Recruitment to Transplant Plots [#/m2]. Please note that the following variables were measured at all plots: aboveground plant biomass (g/m2), aboveground plant tissue carbon and nitrogen content (%), belowground plant biomass (g/m2), soil redox potential (Eh [mV]), soil bulk density (g/cm3), soil nutrient concentrations (mg/kg), and soil shear strength (kPa); and the following additional variables were measured at mussel transplant plots only: transplanted mussel growth rates (mm/yr for shell length), transplanted mussel survivorship (%), and mussel recruitment to transplant plots (#/m2).

Methods:

Long-term effects of Deepwater Horizon oil exposure on Geukensia granosissima (southern ribbed mussel) facilitation of salt marsh function were assessed in a field manipulation experiment conducted at randomly selected heavily oiled sites and sites that received no visible oiling as a reference (n=5). On March 19, 2017, replicate 0.25 m2 plots of two treatments were randomly established at each site approximately 1 m from the marsh edge in areas dominated by Spartina alterniflora. Each site consisted of two control plots with all G. granosissima removed (No Mussel treatment), and two mussel-transplant plots with all G. granosissima removed then added back at a density of 100 individuals/m2 (Transplant treatment). Transplanted mussels were collected from marshes unaffected by oiling near the reference sites. Upon collection, the maximum length of all mussel shells were individually measured to the nearest 0.01 mm with calipers. Both juvenile (30-60 mm shell length) and adult (>60 mm shell length) mussels were transplanted. Mussels were transplanted into randomly assigned plots in a 5 cm x 5 cm grid pattern with alternating adult (n=13) and juvenile (n=12) mussels. Transplanted mussels were inserted umbo down, leaving approximately 50% of the shell exposed. Mussel recruitment into Transplant plots was allowed to take place. Mussels that recruited to No Mussel plots were cut out of the soil with a knife and placed outside of the plot, and any voids were closed by hand or filled with soil. Disturbances to the soil and vegetation resulting from mussel removal were replicated in mussel transplant plots. Sampling of the manipulative experiment occurred at the end of the growing season on November 17, 2017 (year 1) and November 13, 2018 (year 2). During each year, one randomly selected replicate plot from each treatment was sampled at each site. Aboveground plant biomass (g/m2) was determined in each plot by clipping all vegetation at the ground surface. Harvested biomass was separated into live and dead components, dried at 60 °C, and weighed. Tissue samples from 10 green, S. alterniflora leaves were ground using a Wiley mill and analyzed for total carbon (%) and nitrogen (%) using a Costech 4010 CHNS/O Elemental Combustion System. Belowground biomass (g/m2) was assessed in each plot by collecting one standing crop core (7.62 cm diameter x 30 cm deep). All cores were sieved over a 2-mm mesh screen, and the remaining biomass categorized as live roots, live rhizomes, and dead (roots + rhizomes) belowground biomass, then dried to a constant mass at 60 °C and weighed. Two 15 cm soil cores were collected from each plot using a 5-cm semi-cylinder peat corer to assess soil physicochemistry. One soil core was analyzed for soil bulk density (g/cm). The other core was analyzed at field moisture for exchangeable ammonium-N (NH4-N) and phosphorus (P) (mg/kg). Ammonium-N was determined using the automated phenate method following 2 M KCl extraction and 0.45 µm filtration. P was determined by inductively coupled plasma (ICP) spectrometry following extraction with Mehlich 3 test solution. Soil redox potential (mV) was measured in each plot by inserting three bright platinum electrodes and a calomel reference electrode into the soil of each plot to soil depths of 2 and 10 cm. The three readings at each depth were averaged by plot and corrected for the potential of the reference electrode. Soil shear strength (kPa) was determined at 0-5 cm, 5-10 cm, and 10-15 cm depth increments using a 5 cm long x 3.3 cm wide shear vane (Geotechnics Limited, Auckland, NZ). The average growth rate of transplanted mussels (mm/yr) were determined for each plot by comparing shell length measurements collected prior to transplantation in March 2017 to those of the mussels harvested in November 2017 and 2018. Transplanted mussel survivorship was calculated as the percentage of transplanted mussels that survived until sampling. Recruitment of mussels into transplant plots was determined by harvesting all mussel recruits within each plot to a depth of 10 cm. Harvested recruits were measured for maximum shell length to the nearest 0.01 mm with calipers and categorized into adult (>60 mm) and juvenile (≤60 mm) size-classes. The total number of recruits in each size class was converted to abundance on a m2 basis (#/m2).

Individual Files: