Mangroves are salt-tolerant shrubs that thrive in the harshest conditions. Still, new UniSA research shows that they are also avid coastal protectors, capable of surviving in heavily metal-contaminated environments.
The researchers discovered that grey mangroves (Avicennia marina) can withstand high levels of lead, zinc, arsenic, cadmium, and copper in contaminated sediment without suffering adverse health effects.
guardians of the environment for our coastline
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The health of the grey mangroves close to the Port Pirie smelter was the subject of the study.
Mangroves were found to be unaffected by metallic contaminants when leaf chlorophyl content was used as a proxy for plant health, despite lead and zinc levels being 60 and 151-fold higher than regulatory guidance values.
The findings emphasize the critical role of mangroves in stabilizing polluted areas and the importance of protecting these "coastal guardians" around the world.
The study also coincides with a federal government initiative worth $3 million to restore mangrove forests in Adelaide's north.
According to Dr. Farzana Kastury of UniSA's Future Industries Institute, mangroves' ability to withstand high metal concentrations makes them invaluable in managing polluted environments.
Dr. Farzana believes that mangroves are the ideal eco-defenders because they not only protect our coastlines from erosion and sustain biodiversity, but they also have an incredible ability to trap toxic contaminants in their sediments.
"While gray mangroves are known for their tolerance of potentially toxic elements, little is known about their health in the Upper Spencer Gulf."
The ability of gray mangroves to adapt and survive exposure to very high levels of lead and zinc without adverse health effects in their chlorophyll content demonstrates how valuable they are to coastal ecosystems, according to research.
Other ongoing research at Port Pirie by UniSA's Associate Professor Craig Styan suggests that mangrove sediments may contain 4-7 times more metals than adjacent unvegetated mudflats.
According to Assoc. Prof. Styan, a higher concentration of metals found in sediments means a higher risk of contamination for the animals and plants that live on or in them.
The levels of bioavailable metals measured in the surface sediments of mangrove stands are the same as those measured in adjacent mudflats, indicating that, despite mangroves storing significantly more metals, the risk of contamination for the many animals that use mangrove habitats does not appear to have increased, according to Prof. Styan.
Mangroves (along with tidal marshes and seagrasses) are part of the blue carbon ecosystem; when they are protected or restored, they sequester and store carbon; however, when they are degraded or destroyed, they release stored carbon into the atmosphere as greenhouse gases.
Understanding the role of mangrove forests in safely stabilizing metallic contaminants in highly polluted areas, according to Dr. Kastury, is critical not only for South Australian communities but also for communities worldwide.
By preventing erosion and absorbing storm surge impacts during extreme weather events such as hurricanes, mangroves provide natural infrastructure and protection to nearby populated areas.
They are also vital to the ecosystem. Their dense roots aid in soil bind and construction. Their above-ground roots reduce coastal erosion by slowing water flows and encouraging sediment deposits.
The complex root systems of mangroves filter nitrates, phosphates, and other pollutants from the water, improving the quality of water flowing from rivers and streams into the estuarine and ocean environments.
Mangrove forests absorb massive amounts of CO2 and other greenhouse gases from the atmosphere, trapping and storing them in their carbon-rich flooded soils for millennia.
As we face climate change, this is an important ecosystem service.
Because it is stored underwater in coastal ecosystems such as mangrove forests, seagrass beds, and salt marshes, this buried carbon is referred to as "blue carbon."
A diverse range of wildlife, including birds, fish, invertebrates, mammals, and plants, can be found in mangrove forests.
Estuarine habitats with coastal mangrove shorelines and tree roots are frequently important spawning and nursery grounds for juvenile marine species such as shrimp, crabs, and a variety of sport and commercial fish species such as redfish, snook, and tarpons.
Mangrove branches serve as bird rookeries and nesting sites for coastal wading birds such as egrets, herons, cormorants, and roseate spoonbills.
Red mangrove roots are ideal for oysters in some areas because they can attach to the portion of the roots that hang into the water.
Endangered species like the smalltooth sawfish, manatees, hawksbill sea turtles, Key deer, and Florida panthers all rely on this habitat at some point in their lives.
