When 1000 kilometres of mangrove tidal wetland vegetation, along the shoreline of Australia’s remote Gulf of Carpentaria, died en masse in a short span of time between late 2015 and early 2016, it caught the global scientific community by surprise. While the actual causes were unknown, it was noticeable that it coincided with an extreme weather event—drought.
“You don’t expect mass mortality in a wetland species due to drought,” said principal scientist, Kerala Forest Research Institute (KFRI), Sreejith Ashtamoorthy. Intrigued by this phenomenon, he set out to understand climate resilience of mangrove species in Kerala. One property stood out in six true mangrove species in the study area of Kollam district in Kerala — foliar water uptake, a mechanism that allows plants to acquire water from the atmosphere through their leaves.
Climate change
Sreejith, along with scientists from the Ghent University, Belgium who were involved in the study, said that considering the probability of frequent droughts in the future due to climate change, the salinity of the water could alter which could affect the mangroves’ ability to take up water. This, in turn, could adversely impact their productivity. The scientists hypothesise that the foliar water uptake feature may help mangrove species tide over extreme climate variations.
The study revealed that the foliar water uptake capacity differed between species and that the salt-excreting species showed a higher capacity for it than the non-excreting ones. A salt-excreting species, Avicennia marina showed a distinct leaf anatomical trait, trichomes—not observed in the other species—which the researchers presumed could be involved in the water absorption process.
Aside from Australia, the Maldives too has witnessed extensive mangrove die-back in the recent past. The Maldives government approached Cochin University for Science and Technology (CUSAT) in Kerala last year to probe the cause and find a solution to it. While the report has not been published yet, one of the researchers, Sreelekshmi Susheela alluded to the probability of the recently concluded La Niña event in the Indian Ocean having an effect on the mangrove ecosystem in the Maldives.
Sreejith and colleagues are currently studying foliar water uptake in the remaining species and its pathway. They are also looking at the temperature tolerance of the species. Kerala has 16 true mangrove species and 54 mangrove associates.
The health of mangroves depends on three aspects, explained Selvam Vaithilingam, an expert in science-based, community-centred coastal resources management including mangrove restoration and conservation, “freshwater flow, tidal amplitude and the slope of the land”. Mangrove ecosystem varies in varying geographies due to these factors. “You cannot replicate Sundarbans-like mangrove patches in Tamil Nadu,” he said. Given mangroves are a climate-sturdy species, he considers die-back events as isolated ones. If the salinity of the water changes, they may not be as productive and their growth may be affected since they need to spend more energy on damage control, he explained. “Mass mortality is not likely to happen here,” he said.
Anthropogenic activities
As far as the health and distribution of the mangroves in Kerala are concerned, climate change is just one of the many pressing concerns, experts concur. Various anthropogenic interventions, primarily land conversions, have destroyed more than 90 percent of mangroves in Kerala in the last three decades, reducing their range from 700 sq. km. in the 1980s to just 17.82 sq. km. spread over 10 districts, according to a 2020 study by Sreelakshmi et al. The latest State of Forests report, however, puts the current distribution at 9 sq. km.
Multiple causes have been identified as the reason for this steady decline, much of which happened during the period 1986-2018. According to the study, illegal cutting of mangrove trees for fuelwood and fodder, fish and shrimp culture, indiscriminate human encroachment of mangrove areas for developmental activities, conversion of these areas into coconut plantations and for sand dredging are some of them.
The study identifies large infrastructure projects, such as International Container Transshipment Terminal (ICTT) in Vallarpadam and LNG Petronet Terminal and various residential projects in suburban areas to have destroyed large mangrove patches in the industrial hub of Kochi, while sand dredging, shrimp farming and land reclamation to have contributed much to their destruction in the northern Kerala districts of Malappuram and Kannur.
Under the Coastal Regulation Zone (CRZ) notification, mangroves are entitled to the highest protection under CRZ 1A which, if enforced, is enough to protect the remaining mangroves in Kerala. When asked how it is being applied in the state, Suneel Pamidi, member secretary, Kerala Coastal Zone Management Authority said that the mangroves in Kerala enjoy the highest protection as designated by the CRZ notification. He maintained that due diligence has been followed in every case of violation of the notification.
Private ownership
More than 75 percent of the mangrove patches in Kerala lie with private owners and that is proving to be a major obstacle in conservation. “Mangroves need to be brought under the forest department to make conservation effective,” informed S. Sujanapal, a KFRI scientist who was a member of the ecologically fragile land sub-committee set up in 2015 by the Kerala government to prioritise mangroves for long-term conservation. “We tabled a report proposing the idea in 2021. The government had started acquiring mangroves from private owners but the project was stopped for unknown reasons,” he told Mongabay India.
The Wildlife Trust of India initiated a project in 2006 called Kannur Kandal Project (mangrove is kandal in Malayalam) to conserve mangroves in Kannur district that boasts of the largest area of mangroves in the state. In a study, yet to be published by WTI, Kannur’s mangrove patches measure up to 13 sq. km., according to Ramith Meledath, officer-in-charge of the project. “We have secured a little over 35 acres (1.141 sq. km.) of private mangrove patches in Kannur district. Our vision is to secure more to conserve the contiguous patches,” he said.
Private owners see no benefit in holding on to the mangroves. They have to pay land tax, too, on a piece of land they cannot put their money in. “They either do paddy or shrimp cultivation, lease it out to shrimp farmers or sell them,” said Ramith.
Traditionally, both Kaipad (Pokkali in central Kerala) cultivation, a unique paddy farming done in saline wetlands, and small-scale shrimp farming were done alongside mangroves without disturbing one another. Sustainable traditions have given way to commercial farming that demands alterations in land use which is proving dear to the sustenance of the mangroves ecosystem.
In 2014, the government initiated a comprehensive survey of mangroves under ‘Mission Mangrove Kannur’ with the forest department after which 236 ha (2.36 sq km) of mangrove area under various panchayats were declared reserved forest for permanent conservation.
Expanding shrimp farms
The mercurial growth and expansion of shrimp cultivation in Kerala in the last decade has been cited as another reason for the decimation of mangroves. According to Pamidi, however, the CRZ notification does not prohibit the practice if it doesn’t harm the mangroves. Ironically, mangroves and shrimp cultivation require similar habitats but in Kerala, one is causing harm to the other, notes a study published in 2022. The study documented 140 shrimp ponds in 2020 which contribute to a total area of 524.4 ha (5.244 sq km) in Kannur district alone. The Marine Products Export Development Authority (MPEDA) data on tiger shrimp farming for 2020-2021 shows that 2813.85 ha (28.13 sq km) of area is under shrimp farming in Kerala accounting for an annual production of 1128.98 tonnes of tiger shrimps.
“Commercial shrimp farms are expanding. It affects the food security of locals by encroaching the habitats of native fishes, prawns, crabs and molluscs that use mangroves as feeding and nursery grounds,” said Bijith Puthiyaveedu who led the study. He explained that traditional shrimp farming was sustainable but new methods adopted demands cutting mangroves and digging deep ponds that increased water levels, rendering the area unsuitable for future restoration of mangroves.
This story was first published on Mongabay India
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Arathi Menon
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