Coastal habitats may sequester 50 times more carbon than tropical forests by area

Jeremy Hance, mongabay.com 16 Nov 09;

Highly endangered coastal habitats are incredibly effective in sequestering carbon and locking it away in soil, according to a new paper in a report by the IUCN. The paper attests that coastal habitats—such as mangroves, sea grasses, and salt marhses—sequester as much as 50 times the amount of carbon in their soil per hectare as tropical forest.

"The key difference between these coastal habitats and forests is that mangroves, seagrasses and the plants in salt marshes are extremely efficient at burying carbon in the sediment below them where it can stay for centuries or even millennia. Tropical forests are not as effective at transferring carbon into the soil below them, instead storing most carbon in the living plants and litter," explains the paper's author and Conservation International’s Marine Climate Change Director, Dr. Emily Pidgeon. "But coastal ecosystems keep sequestering large amounts of carbon throughout their life cycle. Equally, the majority of carbon stays locked away in the soil rather than the plant, so only a relatively small amount is released when the plant dies."

This capacity for coastal environments to lock away carbon for thousands of years has largely been ignored in accounts of the global carbon cycle, according to the paper, even though the amount of carbon they are responsible for storing is very high.

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.

According to Pidgeon, salt marshes, mangroves, and seagrasses store ten times more carbon in their soils per hectare than temperate forests and fifty times more than tropical forests.

"The simple implication of this is that the longterm sequestration of carbon by one square kilometer of mangrove area is equivalent to that occurring in fifty square kilometers of tropical forest. Hence, while relatively small in area, coastal habitats are extremely valuable for their longterm carbon sequestration capacity," Pidgeon writes in the paper.

Pidgeon believes that even these remarkable figures may be underestimations, since the accumulation rates do not take into account tidal pumps that move carbon from coastal environments into the open ocean. No studies have yet determined just how much of an affect these tidal pumps have on the carbon cycle.

However, according to Pidgeon, these findings should not diminish the importance of preserving forests in mitigating climate change.

"The sheer size of the world’s forests makes them essential for carbon sequestration. However, the immense carbon sequestration capacity of these coastal habitats has been almost completely ignored and may also be a vital component in global efforts to mitigate climate change," she says.

Yet, coastal habitats are vanishing with incredible speed. According to the paper, 20 percent of mangroves have been lost in the past thirty years. In total, seagrasses have lost 29 percent of their historical distribution. These ecosystems are being converted for agriculture, aquaculture (such as shrimp farming), development, and tourism. The massive and continuing conversion of these ecosystems is having a big impact on our planet.

"The total annual loss of mangroves and seagrasses has the longterm carbon sequestration capacity of a tropical forest area similar to the annual deforestation rate in the Amazon," writes Pidgeon.

Coastal environments are not just important for carbon sequestration. Mangroves provide a number of vital ecosystem services, according to Pidgeon, such as protection from extreme weather and natural disasters like tsunamis and important habitat for natural fish nurseries, providing an important source of food for local communities.

"Not only do these ecosystems help us to remove carbon from the atmosphere, but they are also very important as an adaptation tool to help some of the world’s most vulnerable people to avoid the worst impacts of climate change," writes Pidgeon. "It is imperative that we take steps to protect them immediately."

CITATION: Emily Pidgeon. Carbon Sequestration by Coastal Marine Habitats: Important Missing Sinks. The Management of Natural Coastal Carbon Sinks. (PDF) IUCN. 2009.

Ocean Carbon Central to Climate Challenge
IUCN 17 Nov 09;

World leaders should recognize the immense potential of the ocean to reduce global warming by capturing carbon, if we are to avoid a serious climate crisis.

That’s the advice of a ground-breaking IUCN partnership report, The Management of Natural Coastal Carbon Sinks, launched today at the climate change and protected area summit in Granada, Spain. The first in-depth study revealing the latest science of marine ecosystems, such as seagrass meadows, mangroves and salt marshes, shows that they have a much greater capacity to progressively trap carbon than land carbon sinks, such as forests.

“The current loss of two-thirds of seagrass meadows and 50 percent of mangrove forests due to human activities, has severely threatened their carbon storage capacity and is comparable to that of the annual decline in the Amazon forests,” says Dan Laffoley, Marine Vice-Chair of IUCN’s World Commission on Protected Areas and lead author of the report. “Urgent international action is needed to ensure that coastal marine ecosystems are fully recognized as critical carbon sinks and properly managed and protected.”

The IUCN report, supported by Natural England, The Lighthouse Foundation and UNEP, and compiled by leading scientists in this field, provides the latest evidence of the ocean’s ability to store carbon and the role each of these marine ecosystems play in reducing the negative effects of climate change. It offers specific policy guidelines about how to include management of marine carbon sinks in international and national reduction strategies.

“While there have been a lot of discussions about major carbon sinks on land such as forests, we have not heard much about the missing sinks of carbon in the oceans. The marine world not only regulates our climate, supplies essential goods and services, but also helps us tackle climate change,” says Carl Gustaf Lundin, Head of IUCN Global Marine Programme. “Decision-makers at national and international level will have to look at policies and financing mechanisms for protection and management of our oceans, and this report is the best starting point.”

The potential of mangroves, salt marshes and sea grass meadows to store carbon can be ensured through a number of management approaches such as Marine Protected Areas, Marine Spatial Planning, area-based fisheries management techniques, regulated coastal development and ecosystem restoration, according to the report.