Crawl, Burrow, Swim: Little Champions of the Sundarbans Ecosystem
Photo StoryPublished : Oct 16, 2020Updated : Sep 24, 2023
The largest mangrove delta in the world may be more famous for its apex predators but its small creatures are also important for the ecosystem
Text by: Amrita Das
Photos by: Dhritiman Mukherjee
The largest mangrove delta in the world may be more famous for its apex predators but its small creatures are also important for the ecosystem
The Sundarbans, the world’s largest mangrove delta, covers a vast area of 10,000 sq km in India and Bangladesh. Though its swamp-specialist royal Bengal tigers, intimidating saltwater crocodiles, and stealthy fishing cats are well known, these estuarine forests also harbour numerous little-known small creatures. These aquatic, terrestrial, and intertidal critters work very closely with the mangrove ecosystem and help keep it running efficiently.
Dr Silanjan Bhattacharyya, professor of Zoology, West Bengal State University, calls the mangroves an “amphibious community”, one that supports life both above and underwater. The mangroves form intertidal forests at the edge of land and sea. Their roots are buried in clay-laden soil while their branches and leaves are above water. This aspect of their anatomy allows them to create a self-sustaining and interdependent community with aquatic, terrestrial, and amphibious organisms. Take the garjan (Rhizophora apiculata) mangrove tree as an example. Its multiple roots and rootlets create complex yet efficient webs which, between the tides, are occupied by numerous fish, clusters of snails, and different invertebrates. Such pockets are full of nutrients, and these creatures rely and thrive on these spaces for food and shelter. Mangroves grow in silt-laden oxygen-deprived soil and in turn the holes made by burrowing creatures like crustaceans and worms help aerate these soils. These interdependencies between the mangroves and small creatures contribute to creating the unique intertidal ecosystem of the Sundarbans, says Dr Bhattacharyya.
Crabs are essential to the mangrove ecosystem. They are responsible for aerating the soil, reshuffling layers of clay and sediment, and helping nutrient transfer among those layers. Because of these contributions, they are often called ecosystem engineers. Additionally, they are efficient burrowers who pierce holes and aerate the compact oxygen-starved soil, benefitting the mangroves as well.
Two types of crabs from the Ocypodidae family dominate the tidal creeks of the Sundarbans: fiddler crabs (Uca spp.) and ghost crabs (Ocypode genus). Popping out in various colours, fiddler crabs include different species such as Uca rosea, Uca triangularis, Uca dussumieri, and Uca vocans. Some male fiddlers (right) stand beside their burrow and vigorously wave an enormous claw in an attempt to attract a wandering female. Once a prospective mate is charmed, the male will lead her underground into his burrow.
Hermit crabs are interesting creatures found in this estuarine habitat. They choose empty shells of molluscs to protect themselves from predators. These crabs are detritus eaters and may be seen eating deposits on mangrove roots (above).
While identification of the small creatures of the Sundarbans remains a challenge, this unique intertidal landscape is a perfect place to study the trophic (feeding and nutrition) relationship between organisms. Crabs are often seen cleaning the forest floor as they consume organic matter. Geckos feed on spiders, insects, and other invertebrates. A female lynx spider (Oxyopes sp.) (above left) actively hunts small insects. And insects like grasshoppers, crickets, and locusts are herbivores.
“Very little is known about the small creatures that thrive in the Sundarbans”, says Bhattacharyya. Various components of this mangrove delta make these creatures diverse and complex. Numerous kinds of molluscs inhabit tidal flats and backwater inlets during low tide. When the tide rises, they are seen on tree trunks. These include gastropods such as Telescopium (seen in the background). Amphibious fish like mudskippers (foreground), which belong to the goby family and are potential bio-indicators of mangrove forests and coastal waters, i.e. they reveal the pollution levels of a habitat. These gobies can breathe both underwater and on land. Their tissues can absorb and accumulate traces of pollution emitted from various sources in intertidal environments. Mudskippers can accumulate toxic chemicals in their skin, gills, and digestive system. In the Sundarbans researchers have monitored them to investigate copper, iron, zinc, and lead pollution levels.
The Sundarbans harbours about 37 species of snakes, including one of the most venomous snakes in India — the king cobra. Interestingly, the king cobra here is pale brown with striking black patterns on its body — unlike its siblings in the Western Ghats. The red-tailed pit viper (Trimeresurus erythrurus) (above) is commonly seen in this forest, but the Indian python is a rare sight. Other reptile species found in the Sundarbans include Russell’s vipers, common kraits, and a host of sea snakes like dog-faced water snakes and hook-nosed sea snakes. Snake numbers in the Sundarbans are gradually declining. Because of the number of humans killed by snakebite in the area, retaliatory killing of snakes by villagers is commonplace. The decline of snake numbers is also due to the destruction of their habitat. Awareness campaigns and snake-handling training sessions by local organisations are some of the conservation efforts being undertaken to address this issue.
In the late colonial period, an extensive network of earthen embankments were raised to reclaim intertidal lands by clearing mangroves. As a result, tidal waters weren’t able to enter the dykes and freshwater ponds that were created. In the course of time, villages and human settlements developed on the outskirts of the natural mangrove forests of the Sundarbans where millions of people now live. These manmade ponds are home to unique and diverse populations of frogs. Amphibians like Indian tree frogs and common toads are accustomed to and can be found around such ponds. However, there have been instances when new and unidentified amphibians have been spotted in freshwater areas and deltaic forests. “Some endemicity might develop due to fragmentation of natural habitats. It is highly likely to get a new variant of amphibians in the Sundarbans,” says Bhattacharyya. This image may be one such instance. Varad Giri, who works on the taxonomy and conservation of amphibians and reptiles, says that looking at its slender fingers, muscular hind limbs, and well-developed webbing this is likely to be a skittering frog (Euphlyctis sp.) though it is difficult to conclusively identify it.
is the photo editor at Roundglass Sustain. When not at work, she invests her time travelling and hiking, in creative pursuits, reading and learning a new skill.
is one of India's most prolific wildlife and conservation photographers. His work has been featured in leading publications. He is also a RoundGlass Ambassador, and an RBS Earth Hero awardee.
