Mangroves

Abstract
Your small boat glides forward, nosing between dense stands of mangrove trees that rise up from dark, salty water. Their shade is a welcome relief from the hot tropical sun, and as your eyes adjust, you see small fish between the roots.

Mangroves are not found naturally in San Diego, but they are common throughout the tropics along sandy shores. The nearest mangroves are in Mexico (including Baja California, the Pacific coast and the Caribbean) and at their northern limits in Texas and Florida.

What is a mangrove? Mangroves are trees that foster a great diversity of animal and plant life and support forestry and fisheries. They're often found in developing countries. They are threatened by conversion of the forest into urban areas and aquaculture ponds.

They thrive where many land plants struggle, along the border between land and sea. Mangroves are related to rain forest trees, but they can survive swampy conditions by growing aerial roots, which reach above the water to collect oxygen, and having waxy leaves that sweat away salt.

The environment they support is highly productive and species-rich. For example, more than 400 animal species have been documented in the mangroves of Bangladesh. Oysters, algae, barnacles, tubeworms and sponges cover a tangle of tree roots beneath the water's surface.

The upper branches are busy with monkeys and scurrying beetles, while birds flit between blooms.

These unique forests have fascinated naturalists and repelled explorers since ancient times, from Pliny the Elder's scholarly descriptions in the year 23 to Captain Cook's complaints of biting ants in 1770.

Modern scientists are investigating the details of how fisheries rely on mangroves. We know that mangrove forests act as nurseries for juvenile fish and provide a refuge from predators. Nearly half the diet of juvenile shrimp in mangrove forests consists of rotting leaves and branches. In addition to commercially harvested fish and shrimp, many less-well-known plants and animals depend on mangroves during critical stages of their lives.

As a hybrid between terrestrial and marine ecosystems, the mangrove forest plays an important role in exchanges between them. The forest is affected by human activities in both realms. In urban areas, mangrove forests are often drained to create dry land for development, similar to the modification of salt marshes in California.

In rural areas, large tracts of mangrove forest are often flooded to create ponds for shrimp aquaculture, with long-term consequences for the landscape.

Shrimp have been artificially cultured in small ponds within mangroves for centuries in China and throughout Asia. This allows most of the natural forest to remain undisturbed. However, as demand for cultured shrimp has grown, so has the processes' infringement on the forest. During the 1980s, the international shrimp trade emerged as the highest-value fishery in the world, according to a study by the United Nations.

It is still unclear how increasing pressure on mangrove resources from the shrimp trade can be balanced with intrinsic value of the forest and local forestry needs. However, increasing awareness of the reliance of this fishery on healthy coastal ecosystems can only help. If you don't mind the mosquitoes and the mud, you can raise your awareness firsthand by paddling through a mangrove forest.

The text of the above article originally appeared in the San Diego Union-Tribune on Sep 11, 2002.
Copyright SAN DIEGO UNION TRIBUNE PUBLISHING COMPANY Sep 11, 2002.

Useful websites

Ocean Oasis, Baja California  Field Guide and Teacher's guide
Mangroves in Costa Rica
Mangroves of Singapore
Habitat 14 Terrestrial mangroves
NAGA  Community project to safeguard fish stocks by planting mangroves in Malaysia
Mangroves worldwide and in New Caledonia
Traditional uses of mangroves
Marine Protected Areas in Australia: Mangroves

Unusual treehouse:

Mangroves provide homes to many creatures

Article by Margot Stiles