Shellstring Anchor Survey of Eastern Oysters

within the Elizabeth River

IntroductionThe Craney Island Eastern Expansion (CIEE) mitigation plan for oyster restoration consists, in part, of constructing a network of oyster reefs throughout the Elizabeth River in partial compensation for ecological services lost due to the construction of the CIEE and associated Virginia Port Authority (VPA) port facility. In order to document fully the long-term stability, and regional impact, of the mitigation reefs, the impact of the reefs on local oyster recruitment must be determined. The most cost-effective and accurate way to determine the impact using present monitoring methods is to conduct a shellstring survey for several years post-construction within the Elizabeth River. In 2012, 2013, and 2014, a shellstring survey was conducted from June to September at seven sites in this river system. A component of each of shellstring apparatus – there were 28 – was a large and small anchor. The large anchor was either a concrete cinder block, pre-fabricated miniature concrete reef with an oyster shell veneer, or a large, dense metal weight; the small anchor was a brick. After observations made during the 2012 survey, it was determined that the anchors should be collected at the end of each season to quantify oyster density at 4 months post-deployment. Comparisons between shellstring settlement patterns at selected sites and their respective anchors for the 2013 and 2014 seasons were made to determine if there is a direct correlation between weekly oyster spat settlement on the shellstring shells and the oyster recruitment recorded on the large and small anchors at respective sites.

Blake Ivey* and Russell P BurkeChristopher Newport University

AcknowledgmentsDr. Russell Burke for orchestrating the project and serving as mentor, Mr. Darryl Nixon for safe transportation, expertise and leadership in the field. Special thanks to the Norfolk

District of the United States Army Corps of Engineers for this research opportunity. This research was completed under Prime Contract No. W91236-12-C-0024.

DiscussionThe results from the data and comparisons to the cumulative counts from the shellstring survey indicate that there is ahigh correlation between settlement patterns on the shellstrings and the anchors. As demonstrated in Figure 5, there wasoyster recruitment on both the shellstring and anchors in the years of 2013 and 2014. The presence of barnacles and theirequivalent access to both the shellstrings and anchors indicate that availability of substrate is a limiting factor within theElizabeth River system, and competition for settlement space is high. Across all three years, temperature has been theapparent dominant physical factor determining settlement of larvae; both temperature and salinity are indeed rather site-specific, though, so location remains an important consideration in siting reefs. And, given that once larvae cementthemselves to a substrate, the rest of their lives are spent in that specific location; therefore, careful selection of a high-quality habitat is crucial to enhance the probability of steady growth and high survival. Gilligan Creek demonstrated thegreatest recruitment of spat and was highest in 2013. This site had the highest mean temperature and lowest salinity outof the seven sites, and was one of the furthest sites in comparison to the others. Surrounded by small intertidal creeks,high tidal amplitudes likely direct larvae to this area of river confluence, resulting in high settlement patterns. There wasmore recruitment on the brick anchors in 2014, with Gilligan creek being the most developed. The oyster recruitment onthe brick anchor was highly significantly correlated with the shellstring spatfall and strengthens the findings presented inthe shellstring survey. The recruitment of barnacles was similar to the oysters and also strengthens the findings of theshellstring survey. The comparison between reef anchor recruitment and the recruitment observed from the shellstringsurvey is not significant. These findings suggest that the bricks oyster recruitment data were more significant than the reefanchor recruitment data. This study will be continued over the next two survey seasons.

Figure 1. Apparatus used to deploy

shellstrings. The design allowed for the strings

to hang vertically 0.5 m above bottom sediment

providing substrate for oyster veligers.

Figure 2. Researcher Blake Ivey counts the

total number of oysters and barnacles on each

anchor and brick.

Materials and MethodsThe shellstring anchor survey was conducted through the tallying of both large and small anchors attached to the shellstringapparatus (figure 1). The counts were conducted for the large anchor various shapes, including cylindrical, cinder block and cow-patty. Cylindrical was a plain cylinder with shells ingrained into the cement. The cow-patty anchor was a flatter cylinder and also was created from shells in concrete. The cinder blocks, as shown in figure 3, were the average blocks used in everyday building materials. The cinder blocks consisted of only concrete. The small anchors consisted of red masonry bricks. Tallies were made for each oyster development observed, as well as each barnacle growth on the anchors. Blake Ivey was the sole researcher responsible for the counting of oysters and barnacles. This was conducted to avoid observer bias.

ResultsThroughout the counting process, there was a level of variation between the multiple sites. This trend was also seen in theshellstring survey, which monitored both oyster and barnacle development within the Elizabeth River. The sites that theanchors were retrieved from included Gilligan's Creek, Lambert’s Point, Norfolk International Terminal, and TidewaterMarina. There is a high correlation between the reef anchor barnacle recruitment and shellstring cumulative barnaclespatfall (P < 0.0001, R2 = 0.9700). The brick barnacle recruitment with the shellstring cumulative barnacle spatfall was lessthan the barnacle data but still highly significant (P = 0.0009, R2 = 0.7462). When observing the oyster recruitment on thebrick anchor compared to the shellstring cumulative oyster spatfall, there is a high level of significance (P < 0.0001, R2 =0.5996). There was no clear trend between the brick anchor oyster recruitment and the brick anchor barnacle recruitment.Similarly, there was no correlation between the reef anchor oyster recruitment and the shellstring cumulative oysterspatfall. Gilligan's creek was a unique site because it was the only site in both 2013 and 2014 that had more oysterrecruitment on the brick than the reef anchor.

Figure 3. A cinder block from the 2012

year survey that has a high level of oyster

development.

Figure 4. An example of oyster recruitment

on one brick anchor from the 2014 year.

Figure 5. Comparison between the oyster spatfall on the shellstrings,

reef anchors, and bricks based on site and year. Figure 6. Chart revealing no correlation between reef

anchor oyster recruitment and shellstring cumulative

spatfall

Figure 7. Chart showing a significant positive correlation

between brick anchor barnacle recruitment and shellstring

barnacle spatfall.

Figure 8. Chart showing a significant positive

correlation between brick anchor oyster recruitment and

shellstring oyster spatfall.