Teaming up with nature to protect shorelines usually conjures up the use of various types of native plants to stabilize the banks. However, members of the animal kingdom can also provide some assistance. For instance, a recent study suggested that including oysters as part of a barrier system can help mitigate the effects of sea level rise.1
The study was conducted in a cove off the Chesapeake Bay, USA that has had increased erosion due to sea level rise. The planned experiment involved the placement of breakwaters made of concrete and oyster shells that were seeded with oyster larvae for colonization. However, the larvae did not colonize the breakwaters in the cove, so a modeling approach was used to predict the effects of oysters growing on the breakwaters. Under controlled conditions, the oyster larvae did colonize the breakwaters and grew well so this was shown to be possible under the right conditions.
Measurements of wave attenuation indicated that the breakwaters were effective, reducing wave height by 45% to 95% depending on the tide, and sediment accumulation was evident for the breakwaters farther from the cove inlet. The model was compared to these field results and shown to be in good agreement. The authors showed that over the coming 50 to 100 years the breakwaters would become ineffective due to sea level rise unless they were populated with oysters that grew with the higher water. They recognized a number of limitations to the model approach, such as the oysters changing the geometry of the barrier as well as the height but suggest that their results provide a solid foundation for further research. Since many areas of the Chesapeake Bay are protected by similar breakwaters, finding ways to make them resilient to sea level rise is important.
Sea Otters Stabilize Banks
Sea otter populations have been recovering on the West Coast of the United States, and a recent study suggests that this has had a positive effect on tidal creek bank stability in the Monterey Bay area of California, USA.2 Lateral erosion of the streambanks increased after a sea otter population crash in the late 1990s but declined after the population rebounded and reestablished in the tidal creek studies by the authors. This decrease in erosion occurred in spite of sea level rise and other factors that should have maintained high erosion rates. The authors suspected that the otters were reducing the population of burrowing crabs, which physically weakened the banks through burrowing and by eating the roots of the bank vegetation. To make this case, they created otter exclusions on the banks and measured the vegetation and bank stability inside and outside the exclusion cages. Over three years, the areas where otters were excluded had more crabs, less vegetation and lower soil bulk density. Furthermore, they found a strong relationship between higher sea otter populations in 13 tidal creeks and lower erosion rates. The authors suggest more broadly that the reintroduction of top-level predators can have positive effects on the ecosystem in which they operate and also suggested for other predators in other ecosystems. However, in this case, this relationship was established experimentally along with correlation analyses which is relatively unique among such studies.
References
- Vona I, Nardin W. 2023. Oysters’ integration on submerged breakwaters offers new adaptive shoreline protection in low-energy environments in the face of sea level rise. Journal of Geophysical Research: Earth Surface,128, e2023JF007249. https://doi.org/10.1029/.
- Hughes BB, Beheshti KM, Tinker MT et al. 2024. Top-predator recovery abates geomorphic decline of a coastal ecosystem. Nature 626, 111–118. https://doi-org.prox.lib.ncsu.edu/10.1038/s41586-023-06959-9.
About the Expert
- Rich McLaughlin, Ph.D., received a B.S. in natural resource management at Virginia Tech and studied soils and soil chemistry at Purdue University for his master’s degree and doctoral degree. He has retired after 30 years as a professor and extension specialist in the Crop and Soil Sciences Department at North Carolina State University, specializing in erosion, sediment and turbidity control. He remains involved with the department as professor emeritus.
