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Palk Bay coast diversity study identifies coral, sponge & other marine species

Fifty coral species have been identified in an effort to chalk out the Molecular Diversity of Coral Zooxanthellae of Palk Bay Coast, India.

As the first time in India the Palk Bay region, we initiate to characterize molecular identification of coral-associated zooxanthellae using molecular markers like SSU and LSU region. This type of clade level molecular identification is helpful for coral health assessment and monitoring of coral bleaching status of Palk Bay.

Currently, we characterized 9 species of scleractinian coral-associated zooxanthellae using both SSU and LSU region by bi-directional sequencing method. This work opened up a new path to protect and monitoring coral health status.

The study carried out by Madurai Kamaraj University has identified the corals up to the genus level and has been supported by the Department of Biotechnology. Among these 35 scleractinian corals were studied up to species level.

The study found that of the total 35 species, Acropora digitifera, Acropora gemifera, Favia halicora, Favia speciosa, Goniastrea spp., Montipora digitata, Platygyra daedalia, Platygyra sinensis, Porite slobata and Porites lutea are the dominant species in the Palk Bay. Some other genus found dominant in the Palk Bay region are Porites, Goniastrea, Favites and Favia spp.

Among the areas studied, Mandapam includes Veedhalai, Pamban, Thangachimadam and Sangumal (East Rameswaram) were largely populated with massive, sub-massive corals, boulders, encrusting brain and pillar corals. Olaikuda region showed patches of branching corals and soft corals, sponges in addition to massive and sub-massive corals.

Figure 1 showing the map of study sites in Palk Bay, Southeast coast of India
Figure showing the map of study sites in Palk Bay, Southeast coast of India (Image Source: Google earth)

Unlike 2014 and 2015, very few species of corals were found bleached and the severity of bleaching is less than 15%. Most of the study sites had dense growth of Seaweeds, coralline algae and algal mats over the reefs and adjutant areas as well as broken / rubbles of corals.

The growth of macro algae and algal mats over the coral reefs indicates high load of organic pollution due to anthropogenic pollution, in addition to sedimentation and siltation. The most important disturbances observed in this coastal water are sedimentation and siltation. During Northeast monsoon period, heavy wind batters the coastal area of Palk Bay, which carries heavy load of sediment, this accumulate over the coral reefs and affect the coral growth, lastly it leads to death of corals. Then the enrichment of algae was reported over dead corals. Further the other anthropogenic activities like boat anchoring; boat pulling, caste net operation, drag net operation and monofilament gill net (Chattu valai) were the other disturbances to the Palk Bay reefs. According to health ranking, most of the sampling sites fall under disturbed areas.

The diversity and distribution of sea cucumbers, Holothurians were observed in the coast of Rameswaram. More than 12 to 17 species of sponges were also reported all over the Palk Bay coasts during the study periods and their identification is also under process.

During the early month of August 2016, the average SST was 29.5 to 30.5°C but it rose to 32.3°C during the 2nd week of August 2016. Further the SST declined 27.5°C during December 2016 and then increased to 30.5°C during March 2017.

These variations may be due to intermittent rain in the Palk Bay region. Similar to Sea Surface Temperature (SST), the pH, salinity and dissolved oxygen (DO2) also found significant fluctuations all over the Palk Bay coast in terms of depth and space.

Already molecular identification of nine coral zooxanthellae for small subunit (SSU) and large subunit (LSU) gene sequences were submitted and published in NCBI with appropriate accession numbers, i.e., SSU- KY012762 to KY012770 and LSU – KX512794 to KX512802.

Phylogenetic interpretation of those zooxanthellae of LSU showed that clade “D1″ was common endosymbiont in the corals of Villunditheertham region and Clade ”C” in Sangumaal region. These results were further confirmed by Polymerization Chain Reaction (PCR) Restricted Fragment Length Polymorphism (RFLP) studies of large subunit gene.
The scientists plan to carry out further confirmation through Multilocus sequence analysis and PCR – RFLP analysis of small subunit (SSU) gene.
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