Working in the Mangroves

Tuesday Nov. 9 was our first day in the mangroves at a site called Cristobal (see photos in separate post).  We walked through a narrow Rhizophora (red mangrove) fringe zone of taller trees with large prop roots hanging into the channel, then into a vast area of dwarf Rhizophora trees. Despite their small size, these are fairly old trees. Their age can be estimated by counting leaf scars on the stem, with one scar equivalent to 12-18 months of growth (see photo). The leaves at the top of the branch are 2-3 years worth, and the lowermost leaves might be in the process of becoming senescent and eventually dropping off. Leaf litter is all over the base of the trees and is a major component of the peat formed by the organic matter of the mangrove. Peat consists of mangrove roots, dropped leaves, and dead wood, which decompose over time.  At Cristobal, the trees have well-developed root systems, making the peat more solid and easy to walk on without sinking.  We were experiencing a high spring tide cycle so the water never dropped below 8 inches (got higher actually) all day.

At all of these sites we are studying three sets of trees, which have been treated with N or P fertilizer, or nothing for control (this is to determine which nutrients are most common in the environment and which may be “limiting.”  We are also looking for ways in which animals such as crabs, insects, spiders, etc. use the mangrove tree as their habitat. Crabs (several species) eat leaves and take them into their burrows. Other insects eat leaves and burrow into the wood.  We will look at wood samples to see what has been living inside. We collected water from below the surface of the peat to test for salinity below ground.

A family in dugout canoes approached us as we were getting ready to leave the boat for our day in the mangroves.  The father wanted to help us by cutting a path for us through the trees. We talked to them for a while but we didn’t take him up on his offer.  Preserving the trees is essential. Mangroves are of great ecological importance in the marine ecosystem and affect all kinds of life outside them, even the presence of economically important fish species. If mangroves are cut down and eliminated, the fish that live in the roots for protection while they are still too small to go out into open water will have no place to hide.  Fish species have gone extinct locally in cases where mangroves were taken out. Every link in an ecosystem’s chain is important to all the other links. If links are destroyed, the ecosystem can’t function. Something to think about….

Links to check out – www.stri.si.edu to see the Smithsonian Tropical Research Institute (look for the Bocas del Toro Page).

To see excellent photos of a mangrove in Belize go to http://www.serc.si.edu/labs/animal_plant_interaction/Trail/VirtualTour.html