Insects attack Sunderbans mangroves

Krishnendu Mukherjee Times of India 15 Feb 13;

KOLKATA: Two insect species have made a surprise attack on the mangroves of the Sunderbans, wiping out series of Avicennia Alba (locally known as Kalo Bain) plantations in the Unesco World Heritage Site.

What makes environmentalists worried is that Kalo Bain is one of the very few dominant and salt-tolerant species, which acts as a natural bio-shield for the Sunderbans against threats like rising salinity and sea levels.

Members of Nature Environment and Wildlife Society (NEWS), which is working on mangrove plantation and mapping in the Sunderbans, first observed this in September, 2011. "These insects were spotted in the seeds, which flow with the tide. The seeds had both red and black patches, which is not at all their nature," said Ajanta Dey, the project director of NEWS, adding the seeds were sent to the Zoological Survey of India (ZSI) to identity the insects.

ZSI scientist V D Hegde confirmed that two insects, found in the seeds, were identified as Paedurus Fuscipes Curt and Philonthus SP. Sources said these are commonly known as Rove Beetles and are found mostly in southeastern Asia.

By the time this report reached NEWS members in end-2011, almost 80% of the 5 lakh Alba saplings in their nurseries at Sagar, Namkhana and Patharpratima were destroyed in the insect attack.

"As we ventured close to the forests of Ajmalmari and Bharatgarh near Matla, we discovered black and red patches on the full-grown Alba plants, only confirming our fears that it was taking the proportion of an epidemic among these plants," said Biswajit Roy Chowdhury, secretary, NEWS. Their fears were confirmed when the plants released a negligible number of seeds in September,

2012.

However, Tushar Kanjilal, an expert on the Sunderbans, sees no reason to panic at the moment. "There was no documented evidence of this before. We should wait and watch this trend for a while. Locals involved in plantation have reported some unknown disease in these plants to me before," he added.

For mangrove expert Kumud Ranjan Naskar, this problem may be zone-specific. "As far as release of seeds are concerned, it also depends on the water current. If the current is not adequate, seeds won't flow in the water," he added.

According to experts, if the trend is not checked, the unique succession pattern of the mangroves will be disturbed, leaving the forests more vulnerable to the effects of climate change, such as rising salinity and sea level. "Kalo Bain releases a special toxin which forces other local plants like Proterecia and Coractatus downwards a mud flat, making a natural bio-shield of these plants on the mud flats," added Dey.

Of the 84 mangrove species in the Sunderbans, 15 are dominant species and Avicennia Alba, one of the salt-tolerant species, is one of them.

Sunderbans Biosphere Reserve director Pradeep Shukla said he would comment after going through the report. NEWS members have already contacted an NGO, Yagasu, which is working on several livelihood projects in Indonesia, where this mangrove is also known to be a dominant species. But their members are yet to come across any such trend in the Alba plants there.