Man-made reefs help save corals

Last Updated 23 July 2022, 16:36 IST

Vijay Chouhan, 51, ventures into the sea 10 days a month to catch fish. He is a fisherman from Bhimrana, a village in Devbhumi Dwarka district in Gujarat. The coast of the Arabian Sea is a mere 1.5 km from the village. "During my grandfather and father’s time, fish in the ocean was abundant. I’m not so lucky," he rues.

Fringing patchy natural coral reefs run from Okha in the north to Shivrajpur in the south, covering 12 sqkm in discontinuous fragments. Bhimrana lies somewhat in the middle. The village is also 11 km south of the Tata township in Mithapur. The natural reef adjoining the Bhimrana-Mithapur stretch is around 5 sqkm.

The livelihood of 350 families depends on the Mithapur reef. 200 of them are fishermen families, most being economically marginalised artisanal fishers with a negligible carbon footprint. However, they are directly experiencing the brunt of pollution — a massive drop in fish caught due to the degrading health of the reef.

Natural reefs are rocky patches in the seabed made of the fused exoskeletons of several living corals and tiny invertebrate marine organisms. Corals allow algae to settle and multiply on them. In return, the algae provide the corals with essential nutrients necessary for their growth and multiplication and give them their distinctive colours. When this relationship is broken and the algae are expelled when the corals become stressed, it is called coral bleaching. In the absence of the algae, the corals have no source of nutrient supply and would eventually die.

Natural coral reefs and the associated ecosystem they provide are considered endangered across the world. Human activities have contributed to an alarming level of carbon-di-oxide rise in the atmosphere. The ocean absorbs most of this which results in a fall in its pH and a rise in its temperature. The phenomenon is known as the acidification of the ocean. It is a major stressor that causes coral bleaching.

The stresses on the reef

In 2008 when B M Praveen Kumar, a marine biologist working for Wildlife Trust of India (WTI), first surveyed the Mithapur reef, the live coral cover was only 12% in the sampled reef area of 3.5-4 sqkm. “Above 50% coral cover on a reef is considered good, 25-50% is considered average, and anything below 25% is considered bad,” he said.

The Mithapur reef has been impacted by the mass coral bleaching that happened in 1998, 2010 and 2016 due to the combined impact of ocean acidification and El Niño, a strong warm ocean current that generates in the Pacific. There have also been quite a few local threats — coast-based urbanisation, sewage dumping, shipping activities and sand mining.

“According to our 2008-09 survey, in Mithapur reef, the average catch in an hour was only 0.5 kgs of fish,” said Praveen. This survey formed the basis of the Mithapur Coral Reef Recovery Project — an attempt to recover natural reef life by constructing artificial reefs.

How man-made reefs help

Artificial reefs are structures that are dropped into the seabed by humans to facilitate marine life. Floating larvae of already existing corals are expected to attach themselves to it and form colonies. These coral colonies will then attract diverse marine flora and fauna.

The project, funded by Tata Chemicals CSR and implemented by WTI, started in 2008. Since then, 1,415 artificial reefs have been created by piling locally quarried boulders of limestone and basalt in a conical manner in depths ranging from 5-11 metres. They cover an area of 3,594.1 sqm.

In 2016-17, fishermen helped in retrieving partially damaged corals. Around 1,040 retrieved coral boulders were then put on a custom-made iron table underwater. Initially, the corals are manually tied with a copper wire, but over time corals grow above the copper wire and fuse into the skeletal structures by forming basal plates that acted as nurseries for coral gardens.

“Once I notice the coral boulders are trying to get attached to the substrate by forming basal plates, I relocate them on top of the artificial reefs," said Praveen. According to his observation, after four years, the mortality rate of these rescued corals was only 3.5% which means 96.5% of rescued corals have survived.

In 2021-22, they started using the mineral accretion method and installed a biorock to accelerate coral colonisation. In this method, biorock is an iron cage sunk underwater, connected to two solar panels stationed in a floating buoy. The electricity of 4-6 volts is passed through the cage during daylight hours.

The cage acts as a cathode. Under such conditions calcium carbonate combines with dissolved magnesium, chloride and hydroxyl ions that are already present in seawater to slowly deposit around the cathode, coating it with a thick layer of magnesium oxychloride cement. On this layer, over time, coral colonies form. This is the fastest way of building artificial reefs.

Quality of marine life

To understand how well the reef is doing Praveen periodically conducts surveys of the regional fish catch. After the implementation of the project, the average fish catch increased to 3.6 kgs per hour. Live coral cover on the natural reef has also increased to 16%.

According to a 2016-17 survey conducted by WTI in the reef waters, 28 species of hard corals, four species of soft corals, 64 species of fin-fish, 28 species of seaweed, five species of sea-horses, starry puffer fish, less-common green spoon-worm and many more were recorded, marking an improvement in biodiversity of the area.

Praveen emphasised that while judging biodiversity it is important to look at the ecological niche of the organisms and the purpose they are serving.

Farukhkha Bloch, a sociologist working as the project head of Mithapur Coral Reef Recovery, says the integration of the local communities dependent on reef fishing was instrumental in the success of the project.

“You can gain the acceptance of the communities only when you are involving them at each stage of your interventions,” he said. WTI and the local community have come together and eradicated threats like sewage dumping, sand mining, and coastal urbanisation through dialogue. By conducting awareness drives, monthly meetings and by listening to the local communities' complaints and requests, WTI has managed to maintain a ‘no-take zone for fishing’ in the water that covers 50,000 sqm where fishing is banned.

Vijay, the fisherman, said that though the no-take zone is a temporary inconvenience, it is not a major problem. "We are abiding by the rules as we expect this will increase the fish stock in future." No-take zones for fishing create breeding and nursing grounds for fish, which help the fish to multiply, grow and eventually spill over to adjacent reef regions.

Praveen said that marine conservation projects take time to deliver the desired results. “This is a test of patience for everyone involved, hope we pass the test.”

El Nino remains a threat

The mass coral bleaching incident that happened in 1998, 2010 and 2016 was due to ocean acidification El Nino, a warm ocean current that is generated in the Pacific Ocean which proved to be destructive. Currently, although the pH of the ocean is worrisome, it is still alright for corals to grow and thrive.

However, if El Nino occurrence becomes more frequent in future, the corals may not get enough time to recover. The combo of El Nino and acidification has destroyed the coral reef ecosystem.

An artificial reef is an attempt to recreate this ecosystem so that the corals that are alive get an ecosystem where they can multiply. Hypothetically speaking, if El Nino starts happening every year, this will not work.

In the Mithapur region, the localised threats to the reef, namely sewage dump, sand mining, urbanisation and shipping-related destruction, were taken care of and eradicated through dialogue. Science can show us a way to save the reef/coasts/environment but it is only when locals are also integrated into the process it would be successful.

(Published 15 July 2022, 12:56 IST)

Follow us on