MANGROVES IN THE YUCATAN

The word "mangroves" refers to a special community of plants and animals occurring in tropical areas that are inundated permanently or occasionally with saltwater. You find them intermittently along all the Yucatan's coasts and surrounding islands. Few ecosystems are as rich in species and shear numbers of living things, and are so important to the broader ecological community as mangroves.

However, mangroves are also very fragile. They are vulnerable to hurricanes, and human drainage programs and "development." In fact two of the four main woody mangrove species -- Red Mangrove and Black Mangrove -- are regarded as threatened.

Below we describe the four woody species considered to comprise the main vegetative element of the mangrove community. Usually those trees reach 10 to 30 feet tall, but sometimes you find much larger specimens -- up to 80 feet tall for Red Mangrove.

THE YUCATAN'S FOUR MANGROVE SPECIES

In this part of the world usually we think of four different species of shrubs or small trees as constituting our mangrove swamps. Often it's said that, in terms of water depth and salinity, the four species arrange themselves like this:

deepest water & saltiest soil                                                     driest & least salty
RED MANGROVE --> BLACK MANGROVE --> WHITE MANGROVE  --> BUTTONWOOD
In Spanish: mangle rojo --> mangle prieto --> mangle blanco   --> botoncillo

Here are the Yucatan's four mangrove species:

• Red Mangrove, Rhizophora mangle, of the Mangrove Family -- a threatened species. At the picture at the right shows, this species is easy to identify because the bottom part of its trunk branches profusely into numerous leafless "stilt roots" or "prop roots" that arch broadly in the air before entering water. Stilt roots provide the plant with stability in the loose mud and gather oxygen for underground parts. The airborne roots of one Red Mangrove intertwine with the next forming impenetrable thickets. Shellfish colonize the roots and fish and many other kinds of creature hide among them. The roots gather mud and build up the land. Red Mangrove is one of the most ecologically important woody plants I know. Red Mangrove's leaves grow up to 5 inches long, and the tree can grow up to 80 feeet tall in Mexico's tropics, though usually they are much smaller.

• Black Mangrove, Avicennia nitida, of the Verbena Family-- a threatened species -- is easy to identify because from its widely spreading, belowground roots hundreds of slender, gray-brown, pencil-like items emerge vertically from the mud to about a foot high -- as shown at the right. These are called pneumatophores and they collect oxygen for the submerged roots. Black Mangrove grows higher above the low-tide mark than Red  and White Mangroves, so you often see Black Mangrove pneumatophores emerging from mud, not water. Black Mangrove's leaves, reaching only about 3 inches long and therefore somewhat smaller than the   other mangroves leaves, are hairy below. The 4-lobed flowers are white, up to half an inch long. The fruit is a compressed, 2-valved, 1-seeded capsule up to about 1.5 inches long and an inch wide. Here in the tropics Black Mangrove can grow up to 70 feet tall.

• White Mangrove, Laguncularia racemosa, also of the Combretum Family, produces half-inch-long, reddish brown, 10-ribbed, leather, cigar-stump-shaped fruits. The ones on the left side of the picture at the right are immature and therefore still green. White Mangrove's leaves, which are up to 3 inches long, have rounded or notched tips. Notice the leaves' rather long, roundish petioles jutting from the stem almost at right angles. Also maybe you can see at the top of the petioles -- especially of the top leaves in the photo -- "bumps," which are glands. Apparently these glands help the plant rid itself of excess salt. White Mangrove may grow up to 60 feet tall in Mexico's tropical regions.

• Buttonwood or Button-mangrove, Conocarpus erecta, of the Combretum Family, lives even higher above the low-tide mark, often on seldom inundated, not-too-salty ground. Unlike the three other species considered to be mangroves, Buttonwood has alternate leaves, which are pointed, and grow up to 4 inches long. As its picture at the right shows, its fruits cluster consists of spherical, brown, pea-sized, conelike heads. Under ideal conditions Buttonwood can grow to 60 feet tall, though usually it is considerably lower.

MANGROVES ANCHOR THE SOIL

Mangroves occupy an exceptionally vulnerable part of the coastal ecosystem: That part of the land ranging from that which is just below the low tide mark, to that just above the high-tide mark. Most of the time this land quietly bakes and simmers beneath the tropical sun, but when storms come -- especially hurricanes -- the mangrove species hold the land together.

Without them the storm surge would reach far deeper inland. Without them, barrier islands might be completely scoured away.

They also maintain water quality and clarity, filter pollutants and build the land by trapping sediments originating farther ashore.

MANGROVES PROTECT WILDLIFE

The mangroves' tangle of roots -- such as the typical, fairly impenetrable tangle of Red Mangrove aerial roots shown at the right -- provide protected nursery areas for shrimp and other crustaceans, mollusks, and fishes. Thus they are critical for the commercial and recreational fishing industries. Huge numbers of migratory birds occupy the mangroves.

The Yucatan's mangroves often provide safe sites for breeding colonies of such wading birds as egrets, herons and boat-billed herons. Also they are home to species such interesting species as Clapper Rail, Rufous-necked Wood-rail, Mangrove Cuckoo, the kingfishers, and Mangrove Warbler.