Oysters can save the planet! And its oceans!
Oysters are bivalve mollusks that are called filter-feeders: they feed on particles in the ocean, such as algae and other food particles from the water. They are natural mechanisms that help to maintain water quality, control pollution, and capture carbon. These unique organisms can be used to fight the pollution and climate change rampant along the Indian coast. These species are in danger – but scientists have found ways to rebuild oyster reefs in a low-cost and effective way. The oyster reef may not be as aesthetically pleasing as the coral reefs but they have just as much to offer to help the environment.
(Also Read: Corals: a story of death and rebirth)
What are oysters, and what do they do?
Most oysters live in estuaries or other places of variable salinity, including the mangrove forests of the tropics and subtropics. They occupy the intertidal or the shallow subtidal, attached to hard substrates, where they typically form clusters of individuals which may become assembled into oyster reefs or bars. Oysters are filter feeders that feed upon suspended particles in the water column, pumping such a high rate of water flow that they are considered an important biofilter that helps maintain system functioning.
Experimental manipulation of oyster populations has proven that oysters can impact water quality by reducing phytoplankton biomass, microbial biomass, nutrient loading, and suspended solids in the water column. Oysters seize carbon from the water column as they form calcium carbonate shells. As a carbon sink, oyster reefs potentially reduce concentrations of greenhouse gases. A healthy oyster can filter up to five liters of water per hour, thus, cleansing it of algae and pollutants.
Are oyster reefs disappearing?
Oyster reefs are part of nature’s natural defenses that break down waves, absorb rainfall and minimize erosion. They protect the shoreline which results in calm waters where seagrasses can grow. Together the marsh, the seagrass, and the reef provide an ideal habitat for other sea animals.
Even though individual oysters are still present in many places, records show that many reefs that were once common are now rare. It is estimated that globally 85% of oyster reefs are lost. Reasons for decline in oyster populations include:
Erosion from development
Wetland loss, and excessive nutrient pollution
Outdated harvesting methods
Overfishing
Water quality affected by runoff and erosion from industry
Farming activities that lower the water salinity and the oxygen levels, and release waste, toxins, and excess nutrients in the water
All these activities result in the weakening of the oysters and increase the spread of diseases. As oysters decline in health and numbers, their remarkable ability to filter water is diminished, resulting in poorer water quality.
How can we rebuild them?
Artificial oyster reefs are already commonly used to reduce water pollution through the oysters’ natural filtering abilities. Restoration projects have used recycled, fossilized, or dredged native oyster shells, as shells were recognized as the optimal hard substrate for oyster settlement and growth. To create an artificial oyster reef, scientists reuse oyster shells collected from restaurants and other places which are then put into bags or put in oyster reef structures and then deployed out in the water to provide a starting point for the next generation of oyster to grow on.
This type of reef is green infrastructure and an alternative to sea walls. There are a number of advantages of doing this, one of them being that they can be put further out the shore so you don’t have to give up the natural shoreline in order to be protected from the waves. Instead of breaking down over time, an oyster reef can actually rebuild itself. There are several factors that obstruct the construction and restoration of artificial oyster reefs, some of which include sedimentation, substrate limitation, degraded water quality, predation, and diseases that affect the oyster population.
However, the increased demand for oyster shells in many systems and the decreasing overall amount of shells have limited the availability and affordability of natural oyster shells for restoration projects. Due to this many restoration projects have turned to various alternative materials to create hard reef structures where oyster larvae can naturally settle or be planted. There is a diversity of alternative substrates available for oyster restoration efforts.
Oyster reefs perform essential ecosystem services. Ongoing threats to oysters mean that, unless deliberate efforts are made to protect and restore them, we are in danger of losing the benefits oyster reefs provide. When oyster reefs are only used as a place to harvest commercial oyster meat, they can become degraded. But when they are restored and managed as a sustainable resource, oyster reefs and that habitat they provide can contribute billions of dollars in value to the economy.
(Also Read: Feeding the Future)
References
Jonathan H. Grabowski and Charles H. Peterson. (2007). Ecosystem Engineers - Plants to Protists. RESTORING OYSTER REEFS TO RECOVER ECOSYSTEM SERVICES, 281–298. https://sci-hub.st/10.1016/s1875-306x(07)80017-7
Walles, B., Troost, K., van den Ende, D., Nieuwhof, S., Smaal, A. C., & Ysebaert, T. (2016). From artificial structures to self-sustaining oyster reefs. Journal of Sea Research 1–8. https://sci-hub.st/10.1016/j.seares.2015.11.007
Oyster Reef Habitat. (n.d.). Https://Www.Fisheries.Noaa.Gov/National/Habitat-Conservation/Oyster-Reef-Habitat. https://www.fisheries.noaa.gov/national/habitat-conservation/oyster-reef-habitat
Goelz, T., Vogt, B., & Hartley, T. (2020). Alternative Substrates Used for Oyster Reef Restoration: A Review. Journal of Shellfish Research, 39(1), 1. https://doi.org/10.2983/035.039.0101