Article on mangrove ecosystems in the Yucatan

Copyright 2013 Paul Belz

Kate and I knew jaguars hunted in this forest at night while crocodiles darted through Ria Celestun. Today’s darkness didn’t scare us; it was noon, and a mangrove tunnel shielded us from the pounding December sun. Red mangroves stood above this Ria Celestun tributary on arched legs that made them resemble long bodied insects. Black and white trees, farther up the riverbank showed leaves and roots covered with bright salt crystals. The tributary’s water was rust colored by tannin from the trees’ bark. The only sound came from our guide’s pole as he pushed the canoe through this watery maze.

Jose, who shared his first name with us, is a member of Maglares de Dzinitun. This cooperative of local residents strives to restore mangrove habitats along Ria Celestun, and to educate visitors about this work. Our Spanish and Jose’s English were both fairly minimal, but we communicated by repeating and clarifying our statements, gesturing dramatically, and laughing loudly.

“I don’t like Cancun,” Jose said. “My friends like the music there, but the air is dirty, and it’s crowded. Celestun is quiet with good air.” He mimicked a loud cough, and we all giggled as we deeply breathed the clean forest air.

Ria Celestun National Park includes 1480 square miles, or 3500 square kilometers of protected habitat in Mexico’s Campeche and Yucatán States, 50 miles east of the city of Merida. In Mexico, the Spanish word ‘rio’ refers to a river that only flows towards the ocean. A ‘ria’, like Celestun means an estuary where the powerful tide can push saltwater up the river’s course.

Salt tolerant mangrove trees thrive along estuaries and coastlines across the globe. They are found 25 degrees latitude north and south of the equator. Mangroves have several strategies for dealing with estuaries’ salt content. Red mangroves’ arched roots lift them above the oxygen poor Ria Celestun. The trees pump positively charged magnesium ions towards the roots to repel positive sodium ions. The roots’ relatively low water concentration allows water to flow into them while the salt is pushed away.

Black mangroves grow in soggy soil a little higher on the riverbank. These trees grow spongy pneumatophores, structures that transport oxygen to their roots. Red mangroves absorb salt water, but excrete salt from their roots and leaves. White mangroves thrive still higher on the bank where oxygen is abundant. They excrete salt from leaves and roots, like red mangroves.

The three species’ seeds help place them in their habitats. Black mangroves’ large seeds have difficulty moving far from the river; this factor keeps them close to the water. Red mangroves middle sized seeds settle a little above the river, while white mangroves’ small seeds reach the riverbank’s upper limits.

After a slow, quiet ride through the tunnel, our tributary reached Ria Celestun. Sunshine hit us like bright, hot rain. This wide river, whose banks were lined with mangroves, widened as it approached the Gulf of Mexico. Flocks of White pelicans flew high; their feathers were ivory in the persistent light. Thin, graceful magnificent frigate birds circled and plunged towards the water. Great and snowy egrets stood frozen; their quick necks darted quickie when fish approached. Cormorants roosted on wood posts, spreading their ebony wings to let them dry. Gulls shared their space. A green heron greeted us with its “Kyow!” and a woodpecker with a rapid “rat-tat-a-tat.”

Mangrove forests buffer coastlines and human communities from hurricanes and other tropical storms. The trees stabilize riverbanks while their thick roots catch silt that can clog coral reefs. The roots also trap nutrients, including their own fallen leaves that feed invertebrates. Fish feast on these creatures at high tides; they support populations of birds and mammals, including people. Ria Celestun is home to many invertebrate species, 70 fish, more than 20 mammals and 116 birds. At least 15 avian species nest here, including flamingos.

Jose tied the canoe to a post, and we climbed onto a dock. He pointed at tan manta rays that flattened themselves to hide on the river’s bottom. We held a violin crab that he caught, observing its long front claw that resembled a violinist’s arms. Jose smiled as he explained how the male crab waves these appendages to attract a mate. The trail took us past a tall, twisted termite colony, and an armadillo’s burrow.

We found an electric cart at the forest’s edge, and Jose encouraged us to drive it through an area where young mangroves lined the banks. Mangroves are endangered by runoff containing agricultural pesticides and other toxins. People cut them to provide areas for farms and salt evaporation ponds. Irrigation changes stream flows and the salt concentration, hurting aquatic species. Jose pointed to the young saplings in this area, and mentioned that the area should be forested again one day.

“We’re doing this for ourselves, our children and the world.” Jose said. May they succeed!


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