Abstract:

Hardened shorelines and the shallow (<2 m) soft sediment estuary bottom along the southern Corpus Christi Bay, Texas shoreline were assessed for the presence of the Eastern Oyster (Crassostrea virginica) populations from 2023-05-24 to 2023-06-01. Oyster densities, heights, and infection with dermo disease were quantified where oysters occurred. Oyster populations were sampled at 105 sampling stations. Sediment grain size characteristics were quantified at 20 sampling stations.

Suggested Citation:

Palmer, T.A., N.J. Breaux, and J. Beseres Pollack. 2024. Assessment of oyster populations along the southern Corpus Christi Bay, Texas shoreline 2023-05-24 to 2023-06-01. Distributed by: GRIIDC, Harte Research Institute, Texas A&M University–Corpus Christi. doi:10.7266/ydagmj3s

Purpose:

The purpose of collecting these data was to verify where oysters are occurring and sediment grain size characteristics along the southern Corpus Christi Bay shoreline in an attempt to verify whether the shoreline would be suitable for artificial oyster reef restoration.

Data Parameters and Units:

Sample ID, Sta (station name), Date (ddMMyyyy), Time (hh:mm), Sample Depth (m), Temperature (degrees C), Specific Conductance (mS/cm), Dissolved Oxygen saturation (%), Dissolved Oxygen concentration (mg/l), Salinity (ppt/PSU), pH, Turbidity (NTU), Total depth (m), Secchi disc-derived water clarity (m), rock cover (%), mud cover (%), sand cover (%), shell hash cover (%), whole shell cover(%), number of live oysters (n), number of dead oysters (n), oyster height (mm), proportion silt (%), proportion sand (%), proportion clay (%), oyster bill condition (sharp, regressed), oyster tissue condition index (1-9), oyster dermo infection intensity (0-5)

Methods:

Methods Sampling Design Sampling of oyster populations and dermo disease in oysters occurred along the southwest Corpus Christi Bay shoreline from the Corpus Christi Marina to the Corpus Christi Naval Air Station from 24-25 May 2023 (Figure 1). A total of 88 sampling stations were spaced evenly (approx. 190 m, 620 ft apart) along an estimated 1-m deep contour line (based on a Digital Elevation Model), roughly parallel with the shoreline. Stations were moved to shallower locations if the actual depth at the time of sampling was greater than 1.5 m. Sampling occurred on hard substrates, either along the shoreline or on hard structures (pipes and pillars) throughout the study area. In total, 17 hard substrate stations were sampled. Oyster densities were determined at all stations. Grain size characteristics were estimated visually and tactilely at all stations where soft sediments dominated the sea floor. Quantitative grain size samples were taken at a subset of 19 stations. Measurements of water quality (salinity, temperature, dissolved oxygen, pH) were taken at 17 stations within the study area. Measurements of dermo disease were taken when live oysters large enough to be analyzed (>30 mm) occurred at sampling stations. Data Collection Water Quality Discrete measurements of water depth, temperature, conductivity, dissolved oxygen, salinity, pH, and turbidity were taken at the surface (0.1 m from surface) and bottom of the water column (0.1 m from bottom) at seventeen locations along the study area, using a YSI ProDSS multiparameter instrument (YSI 2016). A total water depth measurement was taken at each sampling location using a weighted measuring tape. Sediment Grain Size Quantitative sediment grain size samples were taken using a 6.3-cm diameter core tube to a sediment depth of 10 cm. The sediment was then refrigerated until processing in the laboratory. To analyze sediment characteristics, samples were first homogenized. Organic materials were digested from a subsample of the homogenized sediment using ≤ 30% hydrogen peroxide with daily refreshment until digestion was complete (≤ 21 days). Samples were centrifuged (3500 x g [RCF]) to remove the hydrogen peroxide supernatant. Processed samples were run through a Beckman Coulter LS 13 320 Laser Particle Sizing Analyzer (Beckman Coulter Life Sciences, Indianapolis, IN) to derive the relative quantities of sand (63-2000 µm), silt (4-63 µm), and clay (< 4 µm). Sediment in this report is reported as proportion of mud, which is the sum of clay and silt, and proportion of sand within a sample. Oyster Populations The 88 soft-sediment stations and 18 hard substrate stations were sampled for live oyster density and if oysters were present, live oyster size. At each soft sediment station, snorkelers placed a 0.25 m2 quadrat on the sea floor, estimated the proportion of sand, mud and rock on the sediment surface, and then collected all surficial bottom material within. Samples were placed into bags and brought to the boat where they were quantified for oyster density. At each hard substrate station, which was usually ± 0.1 m of the water level, live and dead oysters were enumerated and measured in place within a 0.25 m quadrat. Dermo Disease Up to 12 oysters were collected from each location that oysters occurred. These included both market-sized (>75 mm) and submarket-sized (75 mm ≥ x >25 mm) oysters. The collected oysters were brought back to the laboratory on ice, and assessed for the protozoan oyster parasite, Perkinsus marinus, the causative agent of Dermo disease. Dermo is known to cause severe mortalities in Gulf of Mexico oyster populations. Dermo causes reduction in oyster growth followed by mortality of susceptible infected oysters, and thus is of interest when considering the health and viability of oyster populations. In the laboratory, the collected oysters were assessed for P. marinus infection using Ray’s Fluid Thioglycollate Method (Ray 1966). Briefly, a 5 x 5 mm section of mantle tissue was removed and incubated in Ray’s Fluid Thioglycollate Media (RFTM) for one week. Tissue cultures were then stained with 75% Lugol’s solution and examined microscopically for P. marinus hypnospores. Infection intensity was scored using a 6-point scale (uninfected (0) - heavily infected (5)) adapted from Mackin (1962) by Craig et al. (1989). Prevalence of infection (the proportion of oysters infected with P. marinus) was calculated by dividing the number of infected oysters by the number of oysters sampled. Weighted prevalence, a measure of the relative severity of P. marinus infection in a population, was calculated by multiplying mean infection intensity by prevalence. Weighted prevalence values ≥2.0 denote many severe infections and the potential for high oyster mortality (Mackin 1962, Burreson et al. 1994). Because P. marinus accumulates in oyster tissue over time and large oysters tend to have higher infection levels and parasite-related mortality than small individuals, data were separated into submarket (25-75 mm, 1-3” shell height) and market (≥76 mm, ≥3”) size classes.

Provenance and Historical References:

Burreson, EM, RS Alvarez, W Martinez, and LA Macedo. 1994. Perkinsus marinus (Apicomplexa) as a potential source of oyster Crassostrea virginica mortality in coastal lagoons of Tabasco, Mexico. Dis Aquat Org 20(1): 77-82. https://doi.org/10.3354/dao020077 Craig, A, EN Powell, RR Fay, and JM Brooks. 1989. Distribution of Perkinsus marinus in Gulf Coast oyster populations. Estuaries 12:82-91. https://doi.org/10.2307/1351499 Mackin JG. 1962. Oyster diseases caused by Dermocystidium marinum and other microorganisms in Louisiana. Publ Inst Mar Sci Univ Tex 7:132-229. Ray SM. 1966. A review of the culture method for detecting Dermocystidium marinum, with suggested modifications and precautions. Proc Natl Shellfish Assoc 54:55–69. YSI Inc. 2016. ProDSS User Manual. Document #626973-01REF, Rev D, September 2016. Yellow Springs, Ohio, USA

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