Blooming of microalgae kills coral reefs in Gulf of Mannar

More than 180 colonies have perished, finds survey.

Published - September 21, 2019 12:43 am IST - RAMANATHAPURAM

Dead coral reefs in Shingle Island after the recent blooming of microalgae.

Dead coral reefs in Shingle Island after the recent blooming of microalgae.

Scientists found dead Noctiluca scintillans along the shore in the Mandapam region when they conducted the survey.

The absence of secondary algae in the reef areas of Shingle Island confirmed the recent death of these coral colonies due to the smothering effect of the microalgae while settling, they said.

Acropora, Montipora, Pocillopora, Porites, Favia, Favites and Goniastrea were the worst affected coral genera, they said.

“Mortality was high in Acropora and Montipora colonies in Shingle Island, while the Acropora colony was less affected in Krusadai Island,” they observed.

The impact of the bloom was less in the nearby Krusadai Island, the scientists said. Out of 120 colonies observed at the depth of 0.5-4 metres, only 12 colonies of sizes 10-20 cm were found dead on the shoreward side of the island, they said.

A greenish settlement was seen on coral colonies and other benthic communities including macro algae, coralline algae and sponges, the scientists said. “Because of this disturbance, corals started secreting excessive mucus, causing mucus sheathing,” a scientist added.

Mucus sheathing was also found around Pullivasal, Poomarichan, Manoliputti, Manoli and Hare islands in the Mandapam group but the intensity was comparatively less, Mr. Patterson said, citing the survey. Coral reefs in the Kilakarai region had suffered bleaching when a similar severe bloom was witnessed in October 2008, he added.

During the recent survey, the scientists also found the dissolved oxygen content in the reef area in Shingle and Krusadai islands to be between 1 and 2 ml/l and it was between 3 and 4 ml/l in the other islands of the Mandapam group, he said. As the decomposed microalgae cells released toxic ammonia gas, the chances of ciliate propagation which killed fish eggs were high, he said and suggested regular monitoring. The SDMRI, on its part, had taken up continuous monitoring of reef areas and environmental parameters, he said.

0 / 0
Sign in to unlock member-only benefits!
  • Access 10 free stories every month
  • Save stories to read later
  • Access to comment on every story
  • Sign-up/manage your newsletter subscriptions with a single click
  • Get notified by email for early access to discounts & offers on our products
Sign in


Comments have to be in English, and in full sentences. They cannot be abusive or personal. Please abide by our community guidelines for posting your comments.

We have migrated to a new commenting platform. If you are already a registered user of The Hindu and logged in, you may continue to engage with our articles. If you do not have an account please register and login to post comments. Users can access their older comments by logging into their accounts on Vuukle.