Study Finds that Marine Meadows Fight Disease

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A nasty attack of typhoid and another of dysentery suffered by a group of divers on a short trip to Indonesia has led to a remarkable scientific breakthrough. The divers were a group of scientists studying coral reefs falling prey to infections.

One of the group started to consider whether the illnesses were connected to the health of the reefs and why some areas seemed rife with pathogens and other areas were disease free.

The researcher from Cornell University, Joleah Lamb, also noticed that reefs near or surrounded by seagrass meadows appeared to be far healthier than those were the meadows had been destroyed.

Seagrasses ring every continent save Antartica and while they may not make the most interesting dive sites, it is widely understood that they play a crucial role as nurseries for a wide range of marine creatures.

However, the study instigated by the researchers from Cornell, and recently published in Science, has revealed they play a crucial role in purging diseases from the ocean.

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Seagrass near a village in the Spermonde Archipelago in Indonesia / Photo Joleah Lamb

Lamb's team sampled waters off four small islands in the Spermonde archipelago, Indonesia. Her study areas included some with seagrass meadows and others without.

She found that the level of Enterococcus bacteria in seagrass areas was just a third of that in areas lacking the underwater meadows. In seagrass-free areas the bacteria were present at 10 times the limit for recreational water set by the US Environmental Protection Agency.

These Indonesian islands lack sanitation systems, but in areas where seagrass meadows flourish, the bacteria seem to be kept in check to some degree.

It is not clear exactly how the seagrass achieves this dramatic purge. One possibility is that the sediment built up by the grasses is locking the pathogens away. Or it could be the aquatic life colonising the seagrass might be involved.

'We’re looking at microbial communities that are on the surface of the seagrass blades,' Lamb said.

Another possibility is that the oxygen released during photosynthesis is toxic for the pathogens. Or it could be that the improvement in water clarity caused by the plants growing allows more ultraviolet light to penetrate the water column which destroys bacteria.

Another benefit of the seagrass meadows it that they appear to make coral more resistant to temperature-induced bleaching. Lamb’s team surveyed 8,000 reef-building corals and found that those next to seagrass beds had half the levels of diseases linked to bleaching than corals without a nearby meadow.

Earlier studies have shown that seagrass meadows also lock up huge amounts of atmosphere-warming carbon and play a key role in regulating ocean temperatures. As much as 20 billion tonnes is believed to currently stored in their leaves.

However, these life enhancing aquatic prairies are under serious threat with nearly a third of the planet's seagrass lost in the past hundred years and recent studies suggesting that these human-induced losses are accelerating. One report suggests the meadows are disappearing at the rate of a football pitch every 30 minutes. 

No longer will you swim over tracts of seagrass during a dive and wish it wasn't there!






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