MANGROVE CRABS

Mangrove forests are wonderful places full of strange creatures adapted to this wet and muddy environment. There are two species of crab that live in this habitat with different but equally fascinating life styles. Fiddler crabs feed by sifting through the soft mud for bits of decaying organic matter, spitting out the inedible components and swallowing the edible material. Male fiddler crabs are easily recognized by their one greatly enlarged claw, which is used both for displaying to attract females, and in combat with other males. During times of peak mating, the forest is alive with gaiety as the little males beckon to females with this claw. Sometimes one male will run up to another and begin pounding him on the head, chasing him down into the safety of his burrow. Usually, females seem oblivious to all these frantic attempts to woo them, for most of the time they just wander around stuffing food into their mouths. If a male approaches too closely, she will even dart into her own burrow to hide.
Found commonly along the African coast, a species of Sesarmid crab feeds on fallen leaves, and is especially sensitive to vibrations. They can detect a leaf falling on the mud while hidden within their burrows. These mangrove leaf crabs can sometimes be seen scurrying out to grab a newly fallen leaf within seconds of it hitting the ground, and then rushing back to their burrows with their nutritious prize. Indeed, great battles often ensue as these crabs fight each other for a scarce morsel. These crabs are easily recognized by their large size, and their equal-sized orange-red claws.

MUD SKIPPERS

The first fish may have crawled onto land during Devonian times (350 million years ago) and probably did so, in response to drying swamps. This required that two problems must be overcome. How to move without the support of water and how to obtain oxygen from air rather than water. The mud skipper, another interesting denizen of the mangroves, has solved both these problems. Their generic name Periopthalmus (Latin=round eyes) was given because their eyes are perched on the top of the head and can be moved independently of each other. This gives the fish virtually 360 degree vision. Mudskippers can often be seen skittering over the mud searching for insects and small crustaceans to eat. Their front, upper (pectoral) fins are quite muscular and function rather like primitive legs, while their front lower (pelvic) fins are modified into a sucker disc. The sucker enables them to cling to the roots and trunks of the mangrove trees. This fish is able to survive out of water because its gills are housed within an enlarged cavity which contains both water and air. The tissue within the cavity can absorb oxygen from the air as long as it remains moist, so it functions like a kind of primitive lung. The mudskipper must return periodically to the sea, however, to replenish the water in its gill chamber.