Abstract:
Mangroves are the major source of blue carbon which store the atmospheric carbon (C) in soil and
biomass. Sampalthivu Lagoon is a part of a complex of wetland that includes pigeon island, a well known tourist destination and hotspot for biodiversity. The study aims to assess the diversity and
structural characters of this lagoon which undergo rapid alternations due to human interventions
and changes of hydrological regime. The seven sites were selected considering the mangrove
distribution. The community structure, biomass and Above-Ground Carbon stock (AGC) were
assessed by laying 3 belt transects perpendicular to the shoreline at each site. The diversity was
estimated using diversity indexes and to compare diversity between sites. The total biomass and
total AGC were estimated using the allometric equations respective to mangrove species. Six true
mangrove species; Excoecaria agallocha, Lumnitzera racemosa, Aegiceras corniculatum, Rhizophora
mucronata, Avicennia marina, and Avicennia officinalis under 5 families and 4 mangrove associate
species were recorded. E.agallocha was the dominant and most important species with high
abundance and high importance value index (IVI) of 185.012. The highest value of Shannon diversity
index (1.46), Simpson index (0.73), Pielou’s evenness index (0.38) and Margalef’s richness index
(1.5417) recorded in site 4 with high species richness and abundance. The lowest Shannon diversity
index (0.75), Simpson index (0.42), and Pielou’s evenness index (0.20) recorded in site 2. The lowest
Margalef’s richness index (0.4809) recorded with low species richness and high abundance.
Hutcheson’s t-test result revealed that, there was a significant difference in diversity between site 2
and 4 (p<0.005). Further, Site 2 and 4 shared lowest Sorensen similarity index (0.36), which exhibit
the unique assemblage of mangroves in each site. R. mucronata were recorded the highest total
biomass (2.98 t ha-1) and AGC value of 1.38 t C ha-1 because of high mean DBH value. The lowest
above ground biomass (0.0178 t ha-1), below ground biomass (0.015 t ha-1), total biomass (0.039 t
ha-1) and AGC (0.0089 t C ha-1) values were recorded in A.corniculatum. The study is the first record
which provides baseline information about biodiversity and structural attributes of mangrove forest
in Sampalthivu lagoon. The structural characters of mangroves and carbon sequestration capacity
are the important tool for future restoration activities. The present study highlights the requirement
of year around study to understand structural and functional dynamics in the mangrove ecosystem.
