March 1, 2020
Glebe Bay Oyster Sanctuary Reef Population Survey
On 26 June 2019, Shayna, Evan, and Brad SCUBA dove the Glebe Bay Oyster Sanctuary Reef in the South River. The purpose of this dive was to collect five random samples of oysters among the Reef to complete an oyster population survey. From 11:20-16:00, just before high tide and at high tide, they collected five samples from five prechosen random coordinates.
The collection team used a .25 x .25 m quadrat to sample the oysters. After collecting the five random samples, the collection team transported the oysters to the Oak Grove Marina where Federation staff measured the length and width of almost all spat and the length, width, depth, and hinge of mature oysters with a caliper. Shayna then organized the data to display an oyster spat budget (live-dead), percent live spat, and approximate spat length for each sample.
Check out Shayna’s interview where she explains the project in more depth and the video Shayna created of the underwater footage from the collection dive of the Reef.
Interview with the Project Diver and Surveyor
Underwater Footage of the Glebe Bay Sanctuary Reef
If you are interested in completing your own oyster sanctuary reef population survey, learn more about Scuba and Population Survey Protocol. Or continue scrolling to check out the population data from the Glebe Bay Sanctuary Reef!
Google Earth view of the locations of the five random samples taken from the Glebe Bay Oyster Sanctuary Reef and approximate location of the healthy and mature oysters that reside on the Reef.
The number of live spat counted in each sample. Samples 4 and 5 had the lowest percentage of live spat but had the largest numbers of live spat compared to the other samples. Compare the number of live spat to percentage of live spat.
Representation of the percent of live spat in each sample. The higher the percent, the healthier that sample of oysters. Sample two had the highest percentage of live spat while sample five had the lowest percentage of live spat. Sample 1 did not have a lot of substrate and the bottom sand covered a large amount of the oyster substrate.
The oyster spat budget from each sample (live spat-dead spat=oyster budget). The higher the oyster budget, the healthier the Reef. These numbers show there are more dead spat than live spat on 2/5 of the samples. Sample 2 has the highest oyster budget, which made it the healthiest sample taken, and sample 5 had the lowest oyster budget, which made it the least healthiest sample taken.
Representation of the length of spat measured in each sample. Limitations in accuracy prevented staff from measuring all spat. Sample 2 tended to have a smaller spat length than any other sample while spat from sample 4 were longer than spat from the other samples.
N=number of spat counted
Sample 1 N=33 ; Sample 2 N=33 ; Sample 3 N=43 ; Sample 4 N=30 ; Sample 5 N=45
The area where the random coordinates were taken had very little substrate and a number of the oysters were buried in the sediment where they were receiving very little oxygen. Runoff after rain or wind events could be carrying the polluted sediment into the bay area where the oysters are growing. This sediment could be piling onto the oysters and reducing their amount of exposure to the oxygen rich waters. The Federation hypothesized that the small amount of substrate and low oxygen caused low spat budgets and low percentages of live spat. Sample two had the highest budget and had a lot of valuable substrate for the oysters to utilize at the location and very few oysters were in the sediment. These factors probably contributed to the high survivability and live spat.
There were substantially more mature oysters and a high amount of spat on shell for spat to thrive closer to the creek side of the bay. It looked as though the oysters have had more time to grow and establish themselves in that area. The Federation is still unsure why the oysters there were more established than the oysters closer to the center of the bay. However, staff will continue this project for several years ahead. Shayna created a population and SCUBA dive protocol (located at the link below) for the Federation and any other interested parties to use in order to complpete a population survey of the Reef annually. As the project continues, the Federation will have even more of an understanding of their largest Sanctuary Reef in the South River