Recently, I took an early morning boat ride through one of the most interesting and important biological zones on earth. The tropical rains and centrally located mountain ranges of Costa Rica generate a multitude of rivers running to both the Pacific and Atlantic Oceans. If conditions are just right, where these meet the sea a wonderful world of mangrove forests and estuaries forms.
I’ve been among the mangroves during the day and evening hours, and they are fascinating at that time, but early morning is when we find most activity. Roosting birds start their breakfast hunt. Multitudes of crustaceans scurry to see what goodies the night tide has washed in. Monkeys clamor about, searching for fresh blossoms to munch. Insects embark on their daily quest for food. Everyone is up and active with daybreak to accomplish their chores before the tropical sun rises too far into the bright, equatorial sky.
A ride through a mangrove forest with a sharp-eyed guide reveals more animal life than one can comfortably imagine. Water birds abound, sitting on branches overhanging the water. White ibis, roseate spoonbills, egrets and green herons are common. Muscovy ducks stop here on their migrations. The soft morning light reveals termite tunnels leading up tree trunks to giant, high-altitude nests. Red land crabs and lizards scamper on intertwined aerial roots of red mangroves. It’s too early to see the larger reptiles. The turtles and crocodiles will be out to catch the sun’s warming rays when they begin to pierce the thick canopy overhead.
The mangrove is very highly salt-tolerant. Over millions of years it has developed special methods for surviving in the salt-rich environment of the world’s shorelines. Generally, it is found in protected, brackish water, such as where rivers meet the sea or in bays, where it has a chance to take root and develop.
Mangrove forests and estuaries serve several important functions. They protect land from erosion, and animals from predators. Providing safe areas for spawning and nurseries, mangroves are breeding grounds for many marine species and water birds, whose young grow up among their tangled roots. They filter sediment and pollution. Acting as "kidneys," the densely growing mangroves purify water by trapping silt and run-off nutrients. They provide barriers against damaging storm surges and floods.
The canopy closes in on us as we probe further upstream. The water looks muddy—thanks to the recent rains. Most of that mud will stay here, trapped by the labyrinth of mangroves, and slowly build up the area. Over time, it will fill in and become firm, dry land, and the mangroves will migrate into open water, continuing the building process.
Mangrove forests grow within the boundaries of at least ten of Costa Rica’s national parks and reserves. Others exist on privately owned land. Six types of mangroves are known to grow along the Pacific coast, but the red mangrove, with its mesh of impenetrable aerial roots, is the most common. It exists here along with a few other salt-tolerant species, standing as the land’s first line of defense against the raging of angry seas. It is a haven for the fragile beginnings of life.
Costa Rica means "rich coast." If Christopher Columbus had known about ecology, his name for this country surely would have referred to the wealth of life and promise found in our mangrove forests.
Updated on January 20, 1996 by M. L. Smith