In the wake of a
natural disaster, there is an increased recognition of the role that
“natural barriers” such as coral reefs, mangroves and sand dunes
play in protecting coastlines across the world. Mangroves are unique
ecological communities found along tropical and sub-tropical
shorelines or estuaries that help in safeguarding the resilience of
coastal areas to the threats posed by tropical storms and tsunamis.
While anthropogenic disturbances have been regarded as one of the
principal causes of mangrove loss, natural disasters can be equally fatal.
scientists sampled 34 locations across the Nicobar Islands to assess
the diversity of mangrove species and compared it with the diversity
reported in the past. Of the 34 locations, 22 were sampled for
species abundance and composition. The researchers also sampled new
inter-tidal habitats that are formed on the erstwhile terrestrial
forests after the sinking of the land to understand the natural colonization
the study did report the presence of new successional habitats for
mangroves, the estimated loss of mangrove areas was an astounding
97%, a loss much higher than reported in previous studies. The
researchers found only three sites with surviving patches of
pre-subsidence mangroves for the entire group of islands.
studies that used satellite data less than six months from the
tsunami probably considered the dead standing trees as a mangrove
vegetation. This is evident from the fact that most of the survived
mangrove patches indicated by the earlier studies were actually
habitats with vast stretches of dead trees,” said Prabakaran.
authors reported 20 surviving mangrove species in the Nicobar
Islands, with the highest diversity in the Central Islands. Four
species recorded pre-disturbance were not reported in the current
study indicating local extinctions. However, some species were
recorded in areas where they were never reported earlier.
Successional habitats showed a dominance of two mangrove species
(mainly Rhizophora mucronata and Bruguiera gymnorhiza)
which contributed to the bulk of their abundance.
the fact that there has been a large-scale loss of mangrove habitats,
the study has important implications for mangrove restoration.
“Restoration activities must initially focus on facilitating the
growth of well-adapted species so as to ensure a functioning mangrove
cover,” said Prabakaran, asserting that the zone preferences of
mangrove species should be kept in mind during these restoration
activities. “Further, some of the areas can be left alone from
human interventions to understand the natural recovery process,
providing a comparative evidence to the effectiveness of the
restoration activities in restoring such habitats,” he suggested.
are very few studies that document mangrove succession post natural
disturbances. Species such as Nypa fruticans once common in
southern Nicobar pre-tsunami, has been stripped away by the tsunami
from almost every creek and inter-tidal zone where it used to occur,”
said Vardhan Patankar, scientist at Centre for Wildlife Studies, and
National Centre for Biological Sciences, with several years of
research experience in the Nicobar Islands. “Traditional housing
on Little and Great Nicobar Islands used these leaves as thatch,
thereby stressing the importance of Nypa rejuvenation as a management
intervention,” said Patankar.
are a crucial part of the coastal ecosystems and form the first line of
defense for any natural disturbances. The loss of such habitats by
both anthropogenic and natural causes has significant impacts on the
stability and functionality of these systems.