Tamarindo Mangrove

September 11, 2010

The mangrove swamp is a wetland – submerged only at high tide – and its placement between the shore and the coral reef in tropical areas makes it a crucial part of the ecology of the coral reef itself – hence its placement in this section otherwise dealing with oceanic habitats.
There are 3 common types of mangroves in Tamarindo’s estuary: the Red Mangrove (Rhizophora mangle), the Black Mangrove (Avicennia germinans) and the White Mangrove (Laguncularia racemosa).
Each of them has its own unique way of dealing with high salt concentrations.

Closest to the water – in fact in the water at high tide – are the red mangroves.
The roots of the red mangrove are distinctive, with long arching aerial prop roots that help anchor the plant in the sediment. The roots of the red mangrove are able to obtain water from the ocean by pumping magnesium ions into the root. The high concentration of magnesium in the root creates a high osmotic potential, and this in turn attracts water in from the surrounding seawater.

Next inland, usually above the high tides, are the black mangroves. These trees deal with salt by excreting it onto the leaves; also, like the red mangroves, the roots of the black mangrove are metabolically very active. Unlike the red mangrove which actively excludes ocean salts from entering at the root, the black mangrove allows the salt to enter but excretes it on the surface of the roots and the leaves. You can often find salt crystals on the leaves of the black mangrove.

Furthest inland are the white mangroves. Neither aerial prop roots or pneumatophores are usually visible (but either may be present if conditions warrant; the pneumatophores take the form of peg roots). Like the black mangrove, the white mangrove excretes salts on the leaf surface.

The scientific names for the mangroves differ greatly (Rhizophora mangle, Avicennia germinans, Laguncularia racemosa) because the word “mangrove” indicates an ecological rather than a taxonomical grouping.
However, when we speak of mangroves we are speaking of tropical, salt-tolerant trees that grow along the shore. Hence, the 3 species of mangrove mentioned all hail from different genera and are not closely related to each other.

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