Port Blair, May 14: The biodiversity in the tropical islands like Andaman represents humongous array of unique plants and animals that are found exclusively in the islands. This special characteristics of islands flora and fauna across the world is often threatened by introduction of non-native species. Many evidences suggest that the extinction of species due to invasion of non-native species are much faster in the islands than the larger mainland. This is because the island species are often evolved with less predators and less completion for resources; therefore, the island species cannot compete well with the non-native species.

Andaman Islands have seen introduction of many species from mainland India during the British period. A few of these introduced animals have naturalized well in the Islands and invaded various parts of Andaman affecting the unique plants and animals. Particularly, a recent study by Wildlife Institute of India (WII) published in the Journal of Wildlife Science has emphasized the negative impacts of Spotted deer on the mangrove forests in South Andaman Islands. The WII study conducted in the Mahatma Gandhi Marine National Park (MGMNP) and surrounding areas clearly indicated that the presence of Spotted deer caused detrimental impacts on the mangrove forests and reduced their resilience for disturbance. The study compared mangrove vegetation from spotted deer affected areas in MGMNP and control areas unaffected by spotted deer. The study revealed that control sites, free from deer pressure, exhibit higher number of species and trees than herbivory sites, highlighting the adverse effects of deer herbivory on the mangrove ecosystems.

The study found that spotted deer exploited all parts (leaved, bark, roots) of the 25 true mangrove species in South Andaman, further stressing the extent of the impact. Invasive spotted deer herbivory has led to alterations in the vegetation structure and recruitment of young mangrove plants, particularly in mangroves closer to the land than ocean, where accessibility is higher, resulting in shifts in mangrove distribution. The heavy grazing of Spotted deer on seedlings and saplings of mangroves led to formation of vegetation consisting of few mangrove species that are less preferred by Spotted deer like Ceriops tagal and Lumnitzera racemosa.  Therefore, the Spotted deer grazing is converting the mangroves with more species and dense vegetation to mangroves with few species and sparse vegetation. This change in number of species and density of vegetation will likely to reduce the mangrove ecosystem services such as fishery stocks (eg. fish, prawns, crabs etc.) and carbon sequestration potential.    

Dr. Nehru Prabakaran (Scientist, WII) who led the study said that “our study highlighted an urgent need for management and policy-level interventions for the removal or management of invasive spotted deer in the Andaman Islands to safeguard not only mangroves but also the entire island ecosystem. Further, he added, “mangroves are crucial for ensuring the health of marine resources which is important for sustaining the local livelihood in the Andaman Islands. Therefore, complete removal of spotted deer or finding some other solution to the Spotted deer menace in the islands not only will help the island biodiversity to recover but also improve the local livelihood linked to the marine resources”.