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Costa Rica’s Mysterious Mangroves – A Treasured and Exotic Habitat

by Richard Garrigues

In the nebulous zone between high and low tide, where freshwater meets saltwater and the ground is neither liquid nor solid, grow the mangroves.

Inhabitants of inter-tidal zones throughout the tropics and subtropics, mangroves are a most curious collection of plants. It is easy to make the erroneous assumption that the different kinds of mangrove trees are closely related species adapted to the unique conditions in which they grow. Even their English common names (red mangrove, black mangrove, white mangrove, buttonwood mangrove, etc.) lend to the idea that these are merely different species of the same plant family, as if they were maples or oaks.

In reality, the mangroves are a wonderful example of convergent evolution—a situation in which totally unrelated organisms have evolved certain similarities simply because those are the characteristics best suited for making use of a particular resource. And in this case the resource is a place where a plant might grow if it can overcome the two major difficulties faced by mangroves: the salinity of the sea water which saturates the ground they grow in and the absence of oxygen in that same saturated mud.

In Costa Rica there are seven species of mangrove trees from four very different plant families: the red mangroves (Rhizophora mangle and R. harrisonii, Rhizophoraceae), the black mangroves (Avicennia germinans and A. bicolor, Verbenaceae), the tea mangrove (Pelliciera rhizophorae, Theaceae), the white mangrove (Laguncularia racemosa, Combretaceae), and the buttonwood mangrove (Conocarpus erectus, Combretaceae). In Costa Rica, any and all of these plants are called mangle (man-gley) and the association in which they grow a manglar.

Of the mangroves found in Costa Rica, the red mangrove is the most easily recognized with its striking aerial prop roots, which often branch one or more times before reaching the ground. The primary function of these roots is not to support the tree but to aid in the aeration of the plant’s sap system.

The black mangrove, and to some extent the white mangrove, cope with the lack of air in the mucky substrate by developing vertical extensions from their roots which stick above the soil level and (at low tide) accomplish oxygen exchange. The tea mangrove has pronounced buttresses which act as aerators. The buttonwood mangrove effectively avoids this problem by growing on the back edges or higher ground within a mangrove swamp, thus reducing the likelihood of having the soil around its roots supersaturated except at extreme high tides.

Mangroves have developed various ways to deal with the problem of high salt concentrations in the water around them. Some species secrete salt from their roots and/or leaves. Pacific coast black mangroves can be observed in the dry season with salt crystals along the outer edges of their leaves (secretion of salt through the leaves happens throughout the year, but is not usually observed in the rainy season because the rain washes off the salt).

In some mangroves, such as the red mangrove, salt is stored in the older leaves which soon fall off the tree. And in other species, it appears that salt is simply tolerated in much higher levels than is common in most plants.

As a result of the rather severe conditions where mangroves grow, there is not much plant diversity. Correspondingly, the animal life associated with mangroves is not nearly as diverse as it is in other lowland habitats in Costa Rica. Nevertheless, what mangrove swamps may lack in numbers of species they make up for with numbers of individuals.

At certain times of the year the tops of mangrove trees are filled with nesting birds. In the Tempisque River, the Isla de Pájaros, or Bird Island, is an impressive example of this phenomenon. Each year hundreds of Wood Storks, Roseate Spoonbills, Anhingas, and Neotropical Cormorants reproduce on this protected patch of mid-river mangroves.

In the mangrove of Damas Island you will find White Faced Monkey which many a visitor will have a close encounter. But please, do not feed the monkeys.

Part of the reason for the concentration of nesting and roosting birds in the mangroves could be that it serves as a sanctuary from terrestrial and climbing predators. The bases of the trees are under water almost nearly of the time and even when they are exposed by receding tides, the soft mud that surrounds them is a deterrent to many creatures.

Below the water’s surface in areas where mangroves grow one can find a high diversity of life forms. Among the mangrove’s root systems many marine organisms live or spend a portion of their lives. Such creatures include algae, corals, barnacles, sponges, oysters, crabs, lobsters, shrimps, octopi, and fishes. The importance of mangroves to the health of the marine ecosystem is immeasurable.

Unfortunately, in Costa Rica and the rest of the world, mangrove forests are being destroyed and their sites converted to fish pens, rice paddies, salt-drying ponds, cattle pasture, tourist developments and human settlements. Mangrove wood makes good fuel and excellent charcoal, but over-harvesting has contributed to their demise. Additionally, the red mangrove is an important source of tannin (used in processing leather), but the stripping of the bark to get the tannin kills the individual trees.

All mangroves in Costa Rica are protected by law, but there is not always someone around to enforce the law. Nevertheless, there are still large areas of mangroves lining estuaries and mouths of rivers and streams along the Pacific coast of Costa Rica. Mangrove development is not as common on the Caribbean coast, because there is little variation in the height of the tides, but one area where some very tall red mangroves can be seen is along the extensive canal system between Limón and Tortuguero.

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Ten Reasons Not to Feed the Monkeys

You might find feeding the monkeys (and other wild animals) to be a thrilling experience, but you are not doing the monkeys a favor. In fact, you are actually harming them. Here’s why:

1.Monkeys are highly susceptible to diseases from human hands. They can die from bacteria transferred off your hand that has no ill effect on you.
2.Migration to human-populated areas to be fed increases the risk of dog attacks and road accidents.
3.Irregular feeding leads to an aggressive behavior towards humans and other species.
4.Contrary to the stereotype, bananas are not the preferred food of monkeys in the wild. Bananas, especially those containing pesticides, can be upsetting to the monkeys’ delicate digestive system and cause serious dental problems that can lead to eventual death.
5.Feeding creates a dangerous dependency on humans that diminishes the monkeys’ survival abilities.
6.Feeding interferes with the monkeys’ natural habits and upsets the balance of their lifestyle centered on eating wild fruits, seeds, small animals, and insects.
7.Contact with humans facilitates poaching and the trade in illegal wildlife.
8.Pregnant females who are fed nothing but bananas during their pregnancy will not give birth to healthy infants. The babies will be malnourished, or never develop to term, and die before birth.
9.Monkeys need to travel an average of 17 kilometers each day to be in good physical condition. If they know that food is available in a particular location, they will not leave that area.
10.Not only do we pass on diseases to animals when we feed them by hand, but they can pass diseases to us as well.

The monkeys do not realize any of this. Now YOU do. Don’t facilitate the extinction of one of Nature’s most amazing creatures for your own pleasure or financial gain. Please help save the monkeys by reporting anyone feeding the monkeys: 777-2592. If you are feeding the monkeys, you now know why you should stop. If you don’t stop we owe it to the monkeys to publish your name with the local media.

Text Courtesy of Jennifer Rice PhD
President
Kids Saving The Rainforest
Tel. 506.777.2592 Fax 506.777.1954
contact@kidssavingtherainforest.org
http://www.kidssavingtherainforest.org

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