Photoblog: Mangroves of the Aghanashini: Linking the River, Land and the Sea

This photoblog by Abhay Kanvinde takes us to mangroves of Aghanashini River Estuary in Kumta Taluk of Uttar Kannada, Karnataka. This is a special place as Aghanashini is a free flowing river with good forest cover in its entire catchment. This means that the mangroves get unhindered supply of freshwater as well as nutrients from the riverine system. This has resulted in the highest area under mangroves in Honnavar Forest Division at 169.4 hectares. Forest Department has also planted about 6 sq. kms of mangroves here, which are thriving.

Mangroves are unique tree species which can grow with their root systems in submerged conditions. They are found at river mouths and estuaries and can tolerate various ranges of saline water and also daily rise and fall in water levels.The mangrove community as a whole consists of salt tolerant plants of soft and swampy mud, mostly trees and shrubs, with broad, leathery, evergreen leaves. In some trees roots from the main stem and branches grow vertically down and provide additional support like stilts in an unstable, slippery bottom. In many others, roots protrude into the air like sticks, knobs or loops, or creep in serpentine manner all around the tree, exposed fully during the low tide. These roots are meant for taking in air for respiration, as the water-logged soil is deficient in oxygen. In some trees the seeds germinate while the fruits are still attached to the plant, and green seedlings of varied lengths hang from the parent plants until they achieve appropriate length, specific to the species, drop vertically down into the soft mud. This nature of certain mangroves to ‘give birth’ to live seedlings instead of shedding their fruits or seeds is known as vivipary. (M D Subash Chandran et al)

IMG-20200320-WA0031 — Mangroves are extremely productive ecosystems that provide numerous goods and services both to the marine environment and people. According to a recent report, these goods and services are conservatively estimated to be worth US$186 million each year. The mean levels of primary productivity of Mangrove forests is close to the average for tropical terrestrial forests. Their leaves and woody matter (detritus) form a key part of the marine food chains that supports fisheries. (https://wwf.panda.org/our_work/oceans/coasts/mangroves/mangrove_importance/) **Photo:** Abhay Kanvinde

Mangroves provide innumerable goods and services to local as well as global communities and their importance to the river, coasts and communities cannot be overstated. In the Aghanashini Estuary, a team from Energy and Wetlands Research Group, Centre for Ecological Sciences, Indian Institute of Sciences has worked over many years understanding the estuary, its functions and processes and its mangroves. This team, led by Dr. M. D. Subash Chandran and Dr. T. V. Ramchandran have come up with report after report based on primary studies about the uniqueness of the system. In this photoblog, we collate some of these reports which have been pivotal in sharpening our understanding about these systems. We profusely thank Dr. Subash Chandran and Dr. TV Ramchandran for their persistent work on the rivers of Karnataka.

The major services provided by Mangroves are:

Protection of coasts and river banks by their roots systems. In many senses, they are a “green wall” or a natural infrastructure against storm surges, tsunamis and erosion impacts.

Fisheries Mangroves are nurseries for not only riverine and estuarine fish, but also of the marine fish stocks as several marine species lay their eggs in this system which is rich in nutrients, calm and protected from predators. From the fisheries point of view the estuaries are considered highly productive systems not only for fishes but also for mollusks, shrimps, crabs etc. The intermediate conditions of the estuary, the presence of high nutrients, inputs coming from the forest clad hills and inflows from the rest of the drainage basin, the detritus fall from the mangroves, and the nutrients brought in by the marine tides make the estuary an exceptionally good centre of biodiversity and productivity. The entangled mass of aerial roots of mangroves rising from swampy substratum abundant in nutrients provides not only food to a variety of organisms but also shelter the juvenile fish from predators, nor can the fisherman cast his net into the swamp due to the obstruction by the root network.
Just the Aghanashini estuary is home to 80 fish species, most of which depend on the mangroves for their survival.
Mackarel Fish drying out in sun in Tadadi Port, Aghanshini Estuary. Mackarel in found in the estuary too in summer months. Marine fish productivity depends of mangroves and estuarine health. Photo: Abhay Kanvinde
Carbon Sequestering: Mangroves sequester atmospheric carbon at phenomenal rates, even higher than tropical rain forests! According to IISc:

Aghanashini estuarine mangrove areas have stored through ages large pool of soil organic carbon, ranging from 187.7 to 607.1 Mg/ha.
• This is several times more than soil carbon even inside the best rain forests of the world.
• Older mangrove areas have more soil carbon than the younger ones.
• Mangrove protection is very critical from the climatic stability point of our planet.
• Any type of dredging or mining activities will result in loss of stored organic carbon in soil, leading to increased carbon dioxide level in atmosphere contributing towards global warming and hence the climate change

Timber, Medicines, Tourism: In Aghanashini estuary, Twigs of mangroves are used for making charcoal and firewood due to high calorific worth. The Aghanashini estuary contributes 31 percent of total mangrove product harvest of Uttar Kannada district, contributing to an income of about 5.4 million Rs/ year
Cultural and Social importance: The Babrulingeshwar Temple on the Masurkurve Island in Kumta has a sacred grove dedicated to mangroves, only one of its kind in the country. The religious life of the villages around Babrulingeshwar revolves around the temple and its festivals.

There are about 11 species of Mangroves found in the Aghanashini Estuary and their location changes according to salinity levels of the water. Exceptionally tall trees over 12 meters (Avicennia officinalis) are found in the sacred grove of Masurkurve in Aghanashini which houses the Babrulingeshwar Temple.