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One afternoon in February 2024, a tiny crab in a shell crawls down the side of a small concrete structure under the waters of Chilika lake, near Satapada town in Odisha. It is surrounded by seaweed, prawns and other aquatic life forms that have attached themselves to the 100 rectangular, cemented structures, or artificial reefs, in the lake.
“While we do not have the exact numbers, we have observed juvenile crabs, prawns and fish attach themselves to the artificial reefs,” Dinabandhu Sahoo, marine scientist and professor at Delhi University’s botany department, tells Down To Earth.
The scientist, along with Sanjukta Sahoo, head of the civil engineering department of Kalinga Institute of Industrial Technology, Bhubaneswar, spearheaded the initiative to place the cemented structures in Chilika lake, which is protected under the Ramsar Convention on Wetlands, since March 2023. This is the first such initiative not just for the lake, but also for the Odisha coastline.
Artificial reefs are structures that may be submerged underwater along the coastal areas to provide conducive habitats for reef-dwelling organisms.
The structures cannot mimic the biological functions of natural coral reefs, like nitrogen-fixing and regulation of the carbon cycle in the water. But they fulfil some structural functions, such as providing shelter and space for reproduction of many fish, prawn and crab species.
They can also break the strong seawaves to create more conducive conditions for the growth of seaweed, seagrasses and marine plants that provide food to other organisms.
“While artificial reefs cannot replace natural coral reefs, they can aid in restoration of such ecosystems. With proper survey and study of target areas, such experiments can help not just maintain biodiversity but also mitigate greenhouse gas emissions by facilitating the growth of carbon-absorbing marine plants, and boost livelihoods of communities living near the area,” says Dinabandhu Sahoo.
Chilika lake is not a known natural coral reef area, but there are some corals towards the mouth of the lake. The scientists chose the part of the lake near Satapada as it is home to several fishing families. “Chilika lake is the biggest brackish water ecosystem in Asia, and fisheries activities are the major source of livelihood for communities living here,” says Dinabandhu Sahoo.
“But we have observed a decline in the catch of fisheries at the lake, as well as a loss of biodiversity. So we decided to try and introduce artificial reefs in the lake. We thought that demonstrating artificial reefs to the fishers living in Satapada, which is also a tourist spot, would help create awareness about their significance in enhancing fish productivity and maintaining biodiversity,” he adds.
After choosing the location, the team experimented with different materials to build the reef structures. “We made four different types of concrete reefs, checked their material and engineering properties, and tested their resistance to salt,” says Sanjukta Sahoo. “The structure that we finalised is a combination of cement, coarse and fine aggregates, and crushed and fine sea shells. All these materials were procured from local markets, with the seashells collected from the Puri beach,” she says.
The scientists took the help of fishers and other local people in Satapada in constructing and submerging the 100 structures, lined up to create an artificial reef wall 200 m long spread over an area of 0.5 sq km. They submerged the first 40 structures in September 2023 and the remaining 60 in February 2024.
They have also been monitoring the site closely to observe whether the presence of the artificial reefs has led to any ecological changes. “We visit the lake periodically and observe the structures during low tides, when water levels recede. What we are tracking is succession of biological communities, which is basically how quickly organisms start attaching to the reefs and ecological niches are created,” says Dinabandhu Sahoo.
“That various species have taken well to these reefs and made it their home is good news for Chilika lake, which has been under threat from over-fishing and the impacts of erratic weather, such as the storm surges from tropical cyclones,” he adds.
Storm surges are sudden increases in levels of coastal waters caused by strong cyclonic winds and rising sea tides. In May 2019, when cyclone Fani hit Odisha, storm surges opened up four new mouths in Chilika lake. This increased the amount of seawater entering the lake and disturbed its salinity gradient, impacting several sea and brackish water species. This led to a decline in fish catch from the lake.
“Our fisheries collections have gone down in recent years and we are not allowed to cultivate fish and prawns in the lake. We can only collect them. I think, as the experts have explained, this initiative will increase our collection of fish and prawns. We are also helping them in whatever way we can,” says Pravat Kumar Nayak, a fisher from Satapada involved in the initiative. The scientists are planning to deploy more artificial reefs in other parts of the lake. They want to experiment with materials for building the reefs such as fly ash and iron slag, which can also be implanted within existing natural coral reefs.
While Odisha may have just seen its first artificial reef initiative, similar experiments have been conducted across the country since the 1990s. The earliest experiment was conducted by the Indian Council of Agricultural Research-Central Marine Fisheries Institute (ICAR-CMFRI) in Lakshadweep and Tuticorin. In Tamil Nadu, ICAR-CMFRI and the state government have deployed artificial reef modules in at least 207 sites.
“The tidal characteristics in Tamil Nadu are the most conducive for artificial reefs. The modules, each with 220-250 artificial reef units, are also designed keeping in mind tidal characteristics like rate of sedimentation in the coastal area and average height of tides, and are tested for saltwater durability,” says Joe K Kizhakudan, principal scientist at ICAR-CMFRI. “Many of the artificial reef areas in Tamil Nadu like Nagapattinam and Vilupuram have become popular fishing and diving sites in recent years,” he adds.
Artificial reefs have also been deployed in Andhra Pradesh and Gujarat.
In January 2024, the Kerala government announced a plan to deploy 6,300 artificial reefs in all the villages near Thiruvananthapuram. The project, worth R13.2 crore, is led by the Kerala State Coastal Area Development Corporation, with technical support from ICAR-CMFRI. It is being implemented under the Union government’s Pradhan Mantri Matsya Sampada Yojana as part of a larger initiative proposed by the department of fisheries to introduce artificial reefs in 3,477 villages along the coast.
Further, while announcing the Union Budget for 2024-25, Union finance minister Nirmala Sitharaman laid out Blue Economy 2.0, a new scheme “for restoration and adaptation measures, coastal aqua-culture, and mariculture with an integrated and multi-sectoral approach.” This scheme may include measures such as the cultivation of indigenous seaweeds, deployment of artificial reefs and stabilisation of beach sand dunes for both adaptation and mitigation.
“Globally, construction and deployment of artificial reefs is a multi-billion dollar industry; countries like the US, France, Japan, China, Korea and Australia have deployed millions of structures along their coasts,” says Sanjukta Sahoo. She estimates that approximately 500,000 structures have been deployed in 3,400 artificial reef and beach restoration projects in more than 70 countries.
Not all of these artificial reefs are specially designed. In several places, pre-existing objects and debris from shipwrecks work well. In the US, for example, the Redbird Reef in the state of Delaware produces 400 times more food than the surrounding waters. The reef is made up of 2 million tonnes of rock; 100,000 tonnes of concrete; 86 tanks and armoured personnel carriers; 1,329 retired subway cars and 27 retired vessels, as per the Delaware government website.
In Japan, artificial reefs have been used for nearly two centuries. Between 1844 to 1847, groups of fisherfolk collected stones covered with sprouts of the edible seaweed Laminaria, known as kombu in the country.
These stones were then deployed to other areas to enhance seaweed productivity, as per a February 2000 paper published in the journal Current Science. The country launched a national reef programme in 1976. More such efforts can protect the coasts against erosion, restore biodiversity and also generate some livelihood opportunities.
This was first published in the 16-31 July, 2024 Print edition of Down To Earth