In Praise of Mangroves

Today is World Wetlands Day, which commemorates the day in 1971 that the Convention on Wetlands was adopted in the Iranian city of Ramsar (hence the List of Wetlands of International Importance or Ramsar sites), which to this day remains the only international treaty devoted to a single ecosystem type. Through the Ramsar Convention, over 476,000 acres of wetland have been protected.1 Since 1997, February 2 has been devoted to raising awareness of the importance of wetlands.

As all the wetlands at our research site, Peam Krasoap Wildlife Sanctuary (PKWS) are coastal mangroves, we’re focusing on their importance and role in the wider biome to mark the day.

Mangroves: an overview

“The value of mangroves has been hugely overlooked. Mangroves are incredibly valuable, left standing,” the words of senior marine scientist with The Nature Conservancy and lead author of the UNEP commissioned World Atlas of Mangroves, Mark Spalding.

As Earth Watch observes: “the stilt-like mangrove is an unlikely superhero.” But as we shall see, mangroves have a vital role to play in maintaining coastal ecological health,2 as well as in reduction of disaster risk3, which is the theme of World Wetlands Day 2017 (WWD17). “WWD17 will focus on how wetlands can be protected, restored, and managed effectively to help absorb the shocks of natural disasters,”4 the International Union for Conservation of Nature (IUCN) reports. This follows a UN Water estimate that 90% of all natural hazards are water-related.5

This animation from the Mangrove Action Project illustrates the growing importance of mangroves to the health of the planet:

What’s a Mangrove?

Mangroves are salt-water tolerant shrubs and trees that grow in shallow, tropical coastal waters,” states one official World Wetlands Day document.

‘Mangrove’ can refer to the mangrove habitat, just as the term ‘rainforest’ is a designation based on plant types. The habitat may also be called a ‘tidal forest’ or a ‘mangrove forest’.6

Go inside a mangrove forest with this video from the Khaled bin Sultan Living Oceans Foundation, a “non-profit environmental science organization and ocean research foundation established to help preserve, protect and restore the world’s oceans and aquatic resources through researcheducation, and outreach.”

Where are mangroves found?

Forming dense forests, they are found along many tropical and subtropical coasts, from South America to Asia, from Africa to New Zealand, in 123 countries and territories in total, with an estimated cover of over 150,000km² globally.7

Global mangrove distribution map taken from Mangrove Watch Ltd. (2013) http://www.mangrovewatch.org.au/index.php?

Mangrove species are divided into two global hemispheres: the Atlantic East Pacific (AEP) covering west Africa and the Americas, and the Indo West Pacific (IWP), which covers east Africa and the Asia-Pacific, which contains the most diverse mangrove flora.8

Cambodia’s mangroves are concentrated in the Indo-Malesia subregion of the IWP.

What makes mangroves special?

Amongst the planet’s most complex ecosystems, mangrove forests “flourish where most plants perish”, growing in conditions of searing heat, low-oxygen soils and frequent saltwater inundation.9

The loss of natural wetland area (estimated to be in excess of 64% since 190010) has resulted in a loss of many of the benefits associated with wetlands (see below). Estimates of the value of these lost services stand at around $7.2 trillion per year for tidal marshes and mangroves.11

Despite their priceless biodiversity and valuable ecosystem services, mangroves are in rapid decline, threatened with drainage for agriculture, degradation, pollution, and destruction at an alarming pace,” according to a World Wetlands Day media release by the IUCN.

For an infographic on the multiple values of mangroves see here.

Why are mangroves important?

See a short summary video from the Mangrove Action Project below:

Biodiversity

Wetlands are some of the most productive habitats on the planet, which often support high densities of animals, including mammals, birds, fish and invertebrates.12

The nutrients available from mangrove leaves and roots nourish plankton, algae, fish and shellfish, with mangrove forests’ stilt and prop root systems acting as nurseries.

Mangroves at Peam Krasop Wildlife Sanctuary where we work are no exception (see a brief video of PKWS here).

Water Filtration and Purification

The UNEP’s Coastal Ecosystem-Based Adaptation page for Mangrove Conservation and Restoration lists that, amongst additional benefits for biodiversity which may result from mangrove conservation and restoration, “mangroves filter and trap sediment from run-off and river water before it reaches adjacent ecosystems, reducing the turbidity of the water and allowing essential light to reach ecosystems.” Concluding that, “mangroves therefore contribute to the survival of these adjacent ecosystems and the species they support.”13 The World Atlas of Mangroves estimates that mangrove related species in Southeast Asia support 30% of fish catch, rising to almost 100% for shrimp catch.14

Mangroves filter catchment runoff, prompting some to dub them the “kidneys” of the coast. This filtration helps to reduce shoreline erosion. For a brief explanation of how mangroves filter coastal water, see this video below:

Urban centres near mangroves benefit from this in practical ways; according to the WWF, some cities have made savings of $3-8 billion in new wastewater treatment plants by purchasing and preserving $1.5 billion in wetlands around reservoirs.

Organizations such as the Biomimicry Institute, which “empowers people to create nature-inspired solutions for a healthy planet” are supporting efforts to research, recreate and harness mangrove-like technology to transform salty water into potable water. For more on biomimicry of mangroves’ filtration, see our technology section here.

Reduction of disaster risk (for a summary see here)

Mangrove roots bind the shoreline, and prevent coastal erosion.15 Forests act as bulwarks to storm winds and incoming waves16 17 associated with extreme weather events, the frequency of which is expected to increase due to human-induced climate change.

A 2014 review of all existing research into the role of mangroves in coastal protection described how a 100 metre wide belt of mangrove can reduce wave heights by 13-66%, and up to 100% where mangroves reach 500 metres or more in width.18

According to the Ramsar Convention, Each kilometer of mangrove forest can reduce a storm surge by 50cm, blunting the impact of cyclones/hurricanes and tsunamis,” Healthy wetlands can absorb some of the shock caused by extreme weather events, cushioning the damage in local communities. Evidence points to mangroves having mitigated the impact of the 2004 Indian Ocean tsunami by reducing the destructive energy of water which flowed inland.19

The island town of Silonay in the Philippines provides an even more dramatic example. In 2009, the town was identified by scientists from Conservation International as among the areas most vulnerable to climate change impacts within the Verde Island passage.20 “But the scientists also explained that the town’s residents also had an unprecedented opportunity: to protect its serendipitous mangroves to help protect themselves.”

They were proved right: when Typhoon Haiyan (the strongest tropical cyclone to make landfall anywhere in the world) passed over Silonay in 2013, the mangroves kept Haiyan’s waves at bay; the town didn’t flood, unlike elsewhere in the Philipines where Haiyan devastated communities, claiming 6,000 lives, and displacing 4 million people.21

The short documentary below shows the island of Koh Klang in the Krabi river estuary in Southern Thailand, where mangroves have depleted greatly in the last 50 years, how people have been affected, and  what is being done to restore these habitats to secure a more sustainable future.

There is also evidence that mangroves support soil stabilization and sediment capture, and further, that they are able to build up soil levels vertically (accrete) through formation of layers of peat.22

This in turn means that under the right conditions, mangroves may keep up with sea level rise.23 Additional evidence has found that mangroves act as a refuge for corals from ocean acidification.24

Absorbing excess water from floods, dispersing tidal surges associated with these events and storing water during droughts,25 mangroves can help strengthen people and nature’s resilience to disaster impacts.26

To see how mangroves can  contribute to risk reduction in different settings see here.

Climate change

Mangroves’ ability to trap organic sediment and thus store carbon explains why mangroves are increasingly referred to as ‘blue carbon’ sinks. Moreover, as mangroves age, they store proportionally more carbon in their biomass because of higher productivity.30 Where data is available, they have been shown to capture up to six times more carbon per hectare than undisturbed rainforests.31

Mangrove forests are the ultimate illustration of why humans need nature,” says Mark Spalding, lead author of the World Atlas of Mangroves and senior marine scientist with The Nature Conservancy. He continues that the importance of mangroves’ “natural coastal defenses… will only grow as sea level rise becomes a reality around the world.”32

Threats to Mangroves

Mangroves and tidal saltmarshes are amongst the most endangered marine wetland habitats worldwide.” That’s according to Mangrove Watch, a monitoring program which partners mangrove scientists and community participants the world over. These wetlands are disappearing at up to 2% a year on average,33 with destruction occurring up to four times faster than within the world’s land-based forests, according to the World Atlas of Mangroves report. Consequently, there has been a dramatic loss of ecosystem services from mangroves with vast losses in area and function as remnant patches progressively deteriorate.34

Mangroves in Peam Krasop Wildlife Sanctuary (PKWS)

Overview

Koh Kapik and Associated Islets, (KKAI) is made up of alluvial islands immediately off the mainland of Koh Kong province.

Taken from Ramsar Sites Information Service document

Spanning a total of 12,000ha, of which 60% is located within PKWS (see below), the area was designated as a Ramsar site in mid-1999.

The area is characterized by “substantial tracts of intact mangrove forest”, much of it inundated during the spring tides only. The relatively-intact mangroves mean that the area contributes significantly in the stabilization of the coast against coastal erosion from storm and tidal bore, and furthermore the mangroves are said to have assumed increased importance in providing nursery and feeding grounds for various invertebrate species since the substantial removal of mangrove forests in nearby Thailand.35

Ecology

The inflow from two major rivers, Prek Koh Pao in the North, and Prek Khlang Yai/Stung Kep in the South is essential for maintenance of the site’s brackish-water character, which supports an assemblage of brackish-water plankton and fish populations, the food base for the majority of birds which use the site. The estuary-mangrove system plays a critical role as a nursery ground and nutrient resort for the adjacent coastal fish populations, supporting very valuable fisheries which provide the main income for coastal fishermen communities.36

Species in PKWS mangroves

Overview

Criteria applied to the designation of KKAI as a Ramsar site included its special value to endemic plant or animal species.

Fauna

Of the eight IUCN red-listed mammal species identified by locals in 2009 village surveys, (in An Dara et al 2009), three were recorded within PKWS during the brief 2015 CBC Fishing Cat survey, in addition to: Hog Deer, Asian Water Monitor, Leopard Cat, Large-Spotted Civet, Asian Mongoose, Smooth-Coated Otters and of course, Fishing Cat!37

The following significant birds species have been recorded in Koh Kapik and Associated Islets : Nordmann’s or Spotted Greenshank, Green Peafowl, both Endangered, and Sarus Crane, now listed Vulnerable.

Flora

Of over 50 mangrove species found in Asia, 37 species are present in Cambodia. PWKS represents a mangrove ecosystem of: Brownlowia tersa, Sonneratia ovata, which are both Near Threatened; Rhizophora stylosa, Rhizophora mucronata, Rhizophora apiculata, all Least Concern, backed by Lumnitzera littorea, Lumnitzera racemosa, both Least Concern and Phoenix paludosa, (Mangrove Date Palm), which is Near Threatened. The current population trends of all these species are decreasing across their geographic range.

Within PKWS, local Cambodian coral experts have identified 56 different types of hard and soft corals38 amongst the 600 hectares around Koh Kong province.

The below video explains the symbiotic relationship between coral reefs and coastal mangroves:

Mangrove management

As World Atlas of Mangroves author Mark Spalding points out, mangroves can be restored.39 Although mangrove management requires a degree of specialised knowledge and equipment, as the UNEP’s page on Coastal Ecosystem-Based Adaptation states,“many aspects of conservation and restoration can be implemented at the community level40, for example in re-planting activities.”

In the below video Lecturer in Environmental Marine Biology at the University of Hull, UK, Dr Magnus Johnson explains how mangrove seedlings naturally establish themselves:

“Why are mangroves so important? How are they under threat? And what can we do to help protect them? This short video  sets out to answer those questions, using photographs from all around the tropics, encouraging participation and help spread awareness of the mangrove forest.” – Mangrove Action Project

The national World Wetlands Day event in 2013 included the planting of over 200 kg of grass and more than 500 mangrove seedlings in PKWS and Peam Krasop beach where erosion was reported.

The event drew in 650 participants, including national and provincial government ministers, representatives from the Ministry of Environment and IUCN Cambodia office, University students from Phnom Penh, local students from nearby primary and secondary schools and members of communities.

Kong Kim Sreng (whose 2003 survey yielded the only camera-trap photo of a Fishing Cat in Cambodia previous to the 2015 CBC Fishing Cat survey), then Senior Programme coordinator for IUCN Cambodia, now Director of Terrestrial Protected Area Conservation at the Ministry of Environment, reiterated the importance of wetlands and water, speaking of water as analogous to the body’s blood and wetlands to blood vessels.41

International Organisations working to restore mangroves

The Mangrove Action Project partners with “mangrove forest communities, grassroots NGOs, researchers, and local governments to conserve and restore mangrove forests and related coastal ecosystems, while promoting community-based sustainable management of coastal resources.” See a summary of their activities here and a video about their award winning Community-Based Ecological Mangrove Restoration (CBEMR) model below:

For more on mangrove recovery and restoration see here.

Mangroves and the Cambodian Fishing Cat Project

The success of community-led vegetation planting depends on local commitment; awareness-raising campaigns may assist in promoting local efforts to protect mangroves.42 In time, it’s likely that the Project’s activities will include habitat restoration and re-wilding, which we hope may instill a sense of community ownership and responsibility for natural resource management.

Want to help?

Aside from work on the ground, or supporting organisations which work to protect mangroves, one of the single most important things you can do to help mangroves as an individual is by being an ecologically responsible consumer: choose your seafood wisely. Although no longer widely practiced in PKWS, elsewhere in the world huge tracts of mangrove forest have been lost to shrimp aquaculture. This video from the Mangrove Action Project explains:

In this video people in southern Thailand’s Trang Province explain why they won’t raise shrimp, but will instead continue to conserve their mangroves as they have done since 1984.

You can help the cause of Fishing Cats and their mangrove habitat in Cambodia by donating to the Project here.

 

Or donate to the cause of other species in the mangroves, for example, consider making a donation to our newest partner, Wildlife Alliance, especially to their campaign to provide an enrichment waterfall within their Otter enclosure at their wildlife rescue centre, Phnom Tamao.

They currently have a lively family of Smooth-coated Otters and Pursat, the only Hairy-nosed Otter in captivity in the world.

Phnom Tamao Wildlife Rescue Center

To lighten up your Friday, here is Pursat the Hairy-nosed Otter fetching his dinner and checking out his new rope toy! He is likely the only one in captivity in the world and it is wonderful to watch his movement in the water!

If suitable habitat is found with sufficient protections, these otters may one day be released back into the wild.

Stay tuned for forthcoming blogs about Wildlife Alliance and all the superb work that they do.


Footnotes

1“Wetlands.” WWF. World Wildlife Fund, 2017. Retrieved from http://www.worldwildlife.org/habitats/wetlands Accessed on 2 February 2017.

2Mangrove Watch Ltd. (2013) Global Mangroves: Mangroves – Kidneys Of The Coast. Retrieved from http://www.mangrovewatch.org.au/index.php? Accessed on 1 February 2017.

3Wetlands International. “What are Wetlands?” Retrieved from https://www.wetlands.org/wetlands/what-are-wetlands/ Accessed on 1 February 2017.

4IUCN (2017) World Wetlands Day: “Bolstering resilience and collaboration to reduce disaster risk” (26 January 2017 media release) Retrieved from http://www.iucnredlist.org/news/world-wetlands-day-bolstering-resilience-and-collaboration-to-reduce-disaster-risk Accessed on 1 February 2017.

5United Nations, World Water Assessment Programme (WWAP) Managing Water under Uncertainty and Risk:

World Water Development Report (12 March 2012). Available from http://www.unesco.org/new/en/natural-sciences/environment/water/wwap/wwdr/wwdr4-2012/

6Mangrove Watch Ltd. (2013) Mangroves Defined, retrieved from http://www.mangrovewatch.org.au/index.php?option=com_content&view=category&layout=blog&id=52&Itemid=300137 Accessed on 1 February 2017.

7Spalding M, McIvor A, Tonneijck FH, Tol S and van Eijk P (2014) Mangroves for coastal defence. Guidelines for coastal managers & policy makers. (Wetlands International and The Nature Conservancy)

8Mangrove Watch Ltd. (2013) Global Mangroves: Mangroves – Kidneys Of The Coast. Retrieved from http://www.mangrovewatch.org.au/index.php?option=com_content&view=section&layout=blog&id=21&Itemid=300245 Accessed on 1 February 2017.

10Davidson Nick C. (2014) How much wetland has the world lost? Long-term and recent trends in global wetland area. Marine and Freshwater Research 65, 934-941. Retrieved from http://dx.doi.org/10.1071/MF14173 Accessed on 2 February 2017.

11IUCN (2017) World Wetlands Day: Bolstering resilience and collaboration to reduce disaster risk (26 January 2017 media release) Retrieved from http://www.iucnredlist.org/news/world-wetlands-day-bolstering-resilience-and-collaboration-to-reduce-disaster-risk Accessed on 1 February 2017.

12“Wetlands.” WWF. World Wildlife Fund, 2017. Retrieved from http://www.worldwildlife.org/habitats/wetlands Accessed on 2 February 2017.

13Gillis, L. G., Bouma, T. J., Jones, C. G., Van Katwijk, M. M., Nagelkerken, I., Jeuken, C. J. L., … & Ziegler, A. D. (2014). Potential for landscape-scale positive interactions among tropical marine ecosystems. Marine Ecology Progress Series, 503, 289-303.

14United Nations Environment Programme (14 July 2010), “Mangroves Report Reveals Threats & Opportunities to Global Economy & the Planet”. Retrieved from

http://voices.nationalgeographic.com/2010/07/14/atlas_of_mangroves/ Accessed on 2 February 2017

15Mazda, Y., Magi, M., Ikeda, Y., Kurokawa, T., & Asano, T. (2006). Wave reduction in a mangrove forest dominated by Sonneratia sp. Wetlands Ecology and Management, 14(4), 365-378.

16Zhang, K., Liu, H., Li, Y., Xu, H., Shen, J., Rhome, J., & Smith, T. J. (2012). The role of mangroves in attenuating storm surges. Estuarine, Coastal and Shelf Science, 102, 11-23.

17Gedan, K. B., Kirwan, M. L., Wolanski, E., Barbier, E. B., & Silliman, B. R. (2011). The present and future role of coastal wetland vegetation in protecting shorelines: answering recent challenges to the paradigm. Climatic Change, 106(1), 7-29.

18Spalding M, McIvor A, Tonneijck FH, Tol S and van Eijk P (2014) Mangroves for coastal defence. Guidelines for coastal managers & policy makers. (Wetlands International and The Nature Conservancy)

19Spalding M, McIvor A, Tonneijck FH, Tol S and van Eijk P (2014) Mangroves for coastal defence. Guidelines for coastal managers & policy makers. (Wetlands International and The Nature Conservancy)

20Bergen, M., Conservational International, “The Giving Trees: How an accidental forest saved a village from a storm for the ages” Retrieved from http://stories.conservation.org/the-giving-trees?_ga=1.44208932.1071165183.1469672971 Accessed on 2 February.

21UNHCR (7 November 2014) “1-year on from Typhoon Haiyan, thousands of people still rebuilding lives.” Retrieved from http://www.unhcr.org/545c9cda6.html Accessed on 2 February 2017.

22Lee, S. Y., Primavera, J. H., Dahdouh‐Guebas, F., McKee, K., Bosire, J. O., Cannicci, S., … & Mendelssohn, I. (2014). Ecological role and services of tropical mangrove ecosystems: a reassessment. Global Ecology and Biogeography, 23(7), 726-743.

23McKee, K. L., Cahoon, D. R., & Feller, I. C. (2007). Caribbean mangroves adjust to rising sea level through biotic controls on change in soil elevation. Global Ecology and Biogeography, 16(5), 545-556.

24Yates, K. K., Rogers, C. S., Herlan, J. J., Brooks, G. R., Smiley, N. A., & Larson, R. A. (2014). Diverse coral communities in mangrove habitats suggest a novel refuge from climate change. Biogeosciences, 4321.

25IUCN (2017) World Wetlands Day: Bolstering resilience and collaboration to reduce disaster risk (26 January 2017 media release) Retrieved from http://www.iucnredlist.org/news/world-wetlands-day-bolstering-resilience-and-collaboration-to-reduce-disaster-risk Accessed on 1 February 2017.

26IUCN (2017) World Wetlands Day: Bolstering resilience and collaboration to reduce disaster risk (26 January 2017 media release) Retrieved from http://www.iucnredlist.org/news/world-wetlands-day-bolstering-resilience-and-collaboration-to-reduce-disaster-risk Accessed on 1 February 2017.

27Scholander, P. F. (1968), How Mangroves Desalinate Seawater. Physiologia Plantarum, 21: 251–261. Retrieved from doi:10.1111/j.1399-3054.1968.tb07248.x Accessed 2 February 2017.

28Attenborough, D., Salisbury, M., Nightingale, N., Haynes, I., Elsbury, M., Payne, J., & Olive, S. (1995). The private life of plants. BBC.

29Waisel, Y., Eshel, A. and Agami, M. (1986), Salt balance of leaves of the mangrove Avicennia marina. Physiologia Plantarum, 67: 67–72. doi:10.1111/j.1399-3054.1986.tb01264.x

30Kristensen, E., Bouillon, S., Dittmar, T., & Marchand, C. (2008). Organic carbon dynamics in mangrove ecosystems: a review. Aquatic Botany, 89(2), 201-219.

32United Nations Enviroment Programme (14 July 2010), “Mangroves Report Reveals Threats & Opportunities to Global Economy & the Planet”. Retrieved from

http://voices.nationalgeographic.com/2010/07/14/atlas_of_mangroves/ Accessed on 2 February 2017

33Mangrove Watch Ltd. (2013) Global Mangroves: Mangroves – Kidneys Of The Coast. Retrieved from http://www.mangrovewatch.org.au/index.php? Accessed on 1 February 2017.

34Mangrove Watch Ltd. (2013) Global Mangroves: Mangroves – Kidneys Of The Coast. Retrieved from http://www.mangrovewatch.org.au/index.php? Accessed on 1 February 2017.

35Ramsar Convention (8 July 1999) Cambodia becomes the 116th Contracting Party

36Ramsar Convention Information Sheet on Ramsar Wetlands (RIS): KH998RIS (2009-2012 version) Available from http://www.ramsar.org/ris/key_ris_index.htm.

37Ramsar Convention Information Sheet on Ramsar Wetlands (RIS): KH998RIS (2009-2012 version) Available from http://www.ramsar.org/ris/key_ris_index.htm.

38Ramsar Convention Information Sheet on Ramsar Wetlands (RIS): KH998RIS (2009-2012 version) Available from http://www.ramsar.org/ris/key_ris_index.htm

39Maxwell Braun, D. (July 14, 2010) Taking stock of mangroves, thin frontlines of diversity, National Geographic Society. Retrieved from http://voices.nationalgeographic.com/2010/07/14/on_the_front_lines_of_mangrove/ Accessed on 2 February 2017.

40Zhu, X., Linham, M. M., & Nicholls, R. J. (2010). Technologies for climate change adaptation-Coastal erosion and flooding.

41Bou, V. (2013) Report of World Wetlands Day 2013 in Cambodia (Ramsar Convention and BirdLife International Cambodia) Retrieved from http://www.ramsar.org/sites/default/files/documents/pdf/wwd/13/PDF_reports/WWD2013_Cambodia.pdf Accessed on 1 February 2017.

42Zhu, X., Linham, M. M., & Nicholls, R. J. (2010). Technologies for climate change adaptation-Coastal erosion and flooding.

References

Braun, D.M (14 July 2010), “ ‘Atlas of Mangroves’ highlights global loss of tidal forests”, National Geographic Society. Retrieved from

http://voices.nationalgeographic.com/2010/07/14/atlas_of_mangroves/ Accessed on 2 February 2017

IUCN (2017) World Wetlands Day: Bolstering resilience and collaboration to reduce disaster risk (26 January 2017 media release) Retrieved from http://www.iucnredlist.org/news/world-wetlands-day-bolstering-resilience-and-collaboration-to-reduce-disaster-risk Accessed on 1 February 2017.

Ramsar Convention on Wetlands (2016) Five wetlands that help us cope with extreme weather events. Retrieved from http://www.worldwetlandsday.org/documents/10184/164097/WWD17_Handout_engl1_HR2_desktop+print+.pdf/d8e8728b-3ed7-4686-a174-9ebe02d047bd Accessed on 2 February 2017.

United National Environment Programme (19 July 2010), “CNN: Mangroves disappearing faster than land-based forests, THE ENVIRONMENT IN THE NEWS: UNEP and the Executive Director in the News. Retrieved from http://www.unep.org/cpi/briefs/2010July19.doc Accessed on 2 February 2017.

World Fish (2013) Coral Triangle Atlas. Retrieved from http://archive.constantcontact.com/fs113/1108454596610/archive/1112616022074.html Accessed on 2 February 2017.

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