Geospatial analysis of the effects of tsunami on coral and mangrove ecosystems of Mayabunder in Andaman Islands, India

Abstract

Majumdar et al.: Effects of tsunami on coral reef and mangrove 1 Geospatial analysis of the effects of tsunami on coral and mangrove ecosystems of Mayabunder in Andaman Islands, India Mangroves and coral reefs are among the major ecosystems of tropical and subtropical coastlines. The Andaman group of islands, situated at the juncture of Bay of Bengal and Indian Ocean, are one of the richest coastal ecosystems of India in terms of biodiversity. Since the tsunami waves of 2004 affected this region severely, the outer fringes as well as inland areas of these islands faced extensive ecological degradation. Mayabunder is one such place of this region, where corals and mangroves had experienced both natural and anthropogenic threat. Considering the notable vulnerability of this coastal environment, the present study aimed to assess the transformations of the coral and mangrove ecosystems at Mayabunder both in pre-tsunami and post-tsunami periods till the present year using multi-temporal satellite imageries and geospatial techniques. Results showed that the areal coverage of healthy living coral reefs was reduced by 466.56 ha (10.42 %) from 1990 to 2000. Afterwards, the coupled ecosystem had experienced serious degradation again during the 2000−2010 phase. The areal coverage of dense mangroves decreased by 47.37%, whereas the area of dead coral covers showed a significant rise of 55.52%. However, partial restoration of both mangroves as well as healthy corals had also been observed here in recent years. It was raised from the extensive field visits and feedbacks from local inhabitants that this restoration initiative could become more effective if a participatory mode of management is adopted.

Distribution of Avicennia spp. in the Andaman and Nicobar Islands with special reference to new distributional reports and post-tsunami colonization patterns

“…The vegetation survey was conducted from 2019 to 2023 during the non-monsoon season of each year (January to May) across the Andaman and Nicobar Islands focusing on the new intertidal zones formed due to coastal uplift (i.e., uplift reef bed and seafloor) and subsidence (i.e., drowned terrestrial zones) (Figure 1). Field sites were selected with the help of previous field experiences of the authors (Nehru and Balasubramanian, 2012, 2018), Google Earth images, and published literature (Majumdar et al ., 2019; Ramakrishnan et al ., 2020; ShivaShankar et al ., 2020). At each selected site, three belt transects perpendicular to the coastline were laid randomly at a minimum distance of 50 m to cover the site heterogeneity.…”

“…km. of mangrove cover and a constant deterioration owing to alteration in the tidal water regime caused by the coastal uplift and subsidence across the ANI's (Nehru and Balasubramanian, 2018; Majumdar et al ., 2019; Ramakrishnan et al ., 2020; ShivaShankar et al ., 2020). The coastal uplift was recorded highest in the West coast of North Andaman (1.35 m); while the highest subsidence was reported from the Southern tip of Great Nicobar Island (2.85 m) (Malik et al ., 2006; Meltzner et al ., 2006).…”