Frontiers in Ecology and the Environment
paper. “To address this challenge, we
scaled the atmospheric carbon emissions
from mangrove deforestation down to the
level of an individual consumer.”
The study was conducted on 30 rela-
tively undisturbed mangrove forests and
21 adjacent shrimp ponds or cattle pas-
tures. The sites were in Costa Rica, the
Dominican Republic, Honduras, Indonesia,
and Mexico. Shrimp ponds were sampled
in all countries except Mexico, where the
predominant land use was conversion to
cattle pastures.
On the basis of measurements from
these locations, “we determined that
mangrove conversion results in GHG
[greenhouse
gas]
emissions
ranging
between 1,067 and 3,003 megagrams of
carbon dioxide equivalent per hectare,”
says Kauffman.
The decline in carbon storage from man-
grove conversion to shrimp ponds or cat-
tle pastures exceeded the researchers’
original estimates.
Mangroves represent less than 1% of
the world’s tropical forests, scientists have
found, but their degradation accounts
for as much as 12% of the greenhouse
gas emissions that come from tropical
deforestation.
INSIDE A MANGROVE FOREST
Enter a mangrove forest. In this dark
water world, trees with twisted limbs live
double lives—one foot on land, the other
in the sea.
Some
80
species
of
mangroves,
also called mangals, thrive in saline
coastal habitats in the tropics and sub-
tropics. All take root in waterlogged
soils where slow-moving currents allow
sediment to accumulate.
Red, black, and white mangrove trees,
along with buttonwoods, may grow along
the same shoreline. Where these species
are found together, each stakes out a spot.
Red mangroves are closest to the sea’s
edge; their prop roots extend into the
water from branches above. The roots
capture sediment, stabilizing the shore.
Farther inland are black mangroves with
pneumatophores pointing upward from
the soil. Pneumatophores supply oxygen
in otherwise anaerobic sediments.
White mangroves, with no special root
adaptations, are found in the interior man-
grove forest, followed by buttonwoods in
the upland transition area.
These forests-of-the-tide collectively
cover a worldwide area of 53,190 km2
in 118 nations—about 0.6% of all tropical
forests. And that number is dropping.
Rates of mangrove deforestation over
the past three decades have been dra-
matic, says Kauffman. “Mangroves are
disappearing at the rate of about 1% per
year.” In places such as Southeast Asia,
mangrove conversion to shrimp ponds
is the greatest cause of these intertidal
forests’ decline.
MANGROVES: TOP ECOSYSTEM
SERVICES PROVIDERS
Mangroves provide ecosystem services
worth up to $57,000 USD per hectare
per year and collectively sustain more
than 100 million people, according to the
United Nations Environment Programme
report The Importance of Mangroves:
A Call to Action.
The report estimates that deforestation
of the world’s mangroves results in annual
economic damages of up to $42 billion.
From top to bottom: (1) Denuded mangrove forest in Madagascar. (2) Shrimp harvested from
an Indonesian shrimp farm. (3) Shrimp pond in Brazil. Courtesy of J. Boone Kauffman, Oregon
State University
Oceanography | September 2017
Oceanography | September 2017