Mangroves are murky, beautiful worlds of shifting margins. They’re neither land nor water. Neither river nor sea. They’re everything at once, yet not any one thing at any time. And these silty fringes of green are more important in the fight against climate change than any other ecosystem.
Mangroves sequester as much as 50 times more carbon than do tropical forests of the same area.
How? They are extremely efficient in transferring the carbon to the soil below — far more than forests which store carbon in living tissue and leaf litter. Because the carbon in mangroves is transferred to the soil, it stays sequestered for far longer and is not all is released when the plant dies. (Conservation International’s Marine Climate Change director, Dr. Emily Pidgeon’s paper, via Mongabay)
Says Pidgeon in that article:
Coastal habitats with vegetation “[contribute] about half of the total carbon sequestration in ocean sediments even though they account for less than 2 percent of the ocean surface,” Pidgeon writes, explaining that much of this is capacity is due to the fact that coastal vegetation usually spreads deeper below ground than it grows above with some plants going as deep as eight meters.
They also slow the inward rush of tides balancing salinity and freshwater so that life may thrive. And thrive life does.
Mangroves are fish and shrimp nurseries. They are also prime habitat for shrimp aquaculture. Forests are cleared and channels snaked through mudflats to supply the crustaceans with warm nutrient-rich coastal waters. Densely packed, these shrimp farms are hot beds of chemicals and pesticides, used by farmers in a bid to keep disease at bay. The practice is decimating mangroves, polluting the water, and destroying vital habitat for fish that local fishermen depend upon.
The carbon footprint of a 100gms of shrimp cocktail is equivalent to burning 90 liters of gasoline — ten times greater than beef grown in deforested Amazonian jungles!
The soaring demand for shrimp from the United States, East Asia, and Europe has bloomed shrimp farms all over Asia. Eager to jump on the demand boat, several countries have invested heavily in shrimp farms. Sri Lanka is one such.
As reported by The Conversation, UK, shrimp farming has destroyed the mangroves of Sri Lanka. Says Mark Huxham, one of the researchers studying the Puttalam area of Sri Lanka:
We looked at satellite imagery from 1992 to 2012, which showed an explosion in prawn farms from less than 40ha in our study area to over 1,100ha (a rise of over 2,700%). This combined with a decline in natural habitats – mangroves lost some 36% of their area over the period. Yet most of these historic ponds are now unproductive or abandoned.
Prawn aquaculture has been likened to slash-and-burn cultivation – find a pristine spot, remove the vegetation and farm it for a few years before moving on. But the analogy is misleadingly benign. Slash-and-burn systems on a small scale can be sustainable, since the cut plots can recover afterwards.
We estimate that nearly 192,000 additional tonnes of carbon have been added to climate change as a result of these land-use changes in Puttalam, Sri Lanka alone.
In addition to being an extremely efficient carbon sink, mangroves are warriors in the battle against rising sea levels. Countries like Sri Lanka, where facing a sea level rise of 3mm a year is not something far in the future, stand to lose much from destroying their mangroves.
An additional issue is the sinking shoreline. In the face of global rising sea levels of more than 3mm a year, healthy mangrove forests are among the best protection since they bind together sediments and even elevate their soils to match the rising tide. Lose them and the chances of coastal subsidence, erosion and storm damage goes up.
In fact, mangroves are such useful ecosystems that destroying them almost never makes sense, even from a narrow economic perspective.
Maybe that is what shook the Sri Lankan government to do the right thing. In May this year, Sri Lanka became the first nation to declare protection for 100% of all their remaining mangroves. Countries like India, Bangladesh (who has the largest unbroken stand of mangroves in the world and desperately needs its protection from storm surges), Thailand, and Indonesia will do well to follow Sri Lanka’s example.
The long scourge of demand for shrimp, though, spreads its tentacles beyond mangroves and across disasters. Worldwide, the commercial shrimp trade has an uber-sinister sub-text. That of human trafficking, slave labor, and rape. This video by The Guardian is graphic in its content but lays out the true horrors that are increasingly plaguing global fishing.