Mangrove fauna

Mangroves and mudflats provide important breeding and feeding habitats for resident and migratory shore birds. In Sarawak, the proposed Pulau Bruit National Park is being gazetted to protect one of the most important sites for migratory birds in Eastern Asia. Mudflats associated with mangroves are very important for resident and migrating shore birds and several areas in Borneo are protected specifically for birdlife. The large, fish-eating Brahminy kite (Haliastur indus) and the White-bellied sea eagle (Haliaeetus leocogaster) are commonly seen over large rivers and mangrove areas while arboreal mammals especially flying foxes (Pteropus) and fruitbats (Macroglossus) dominate the terrestrial component of the mangrove fauna.

The cave nectar bats (Eonycteris spelaea) fly long distances from inland caves to feed on Sonneratia nectar when the durian (Durio spp) is not in flower.

Proboscis monkeys Nasalis larvatus, are found in undisturbed mangrove areas along the major rivers: Mahakam, Berau (E. Kalimantan), Bako NP & Samunsan WS (Sarawak) and Menumbuk river (Sabah). The Proboscis monkey is a herbivore endemic to Borneo and feeds extensively on the young leaves of Sonneratia and Avicennia although groups also feed on other leaves and fruits, both in mangroves and in other swamp and riverine forests. The fact that Proboscis monkeys move to sleep in trees beside waterways every night has made them easy targets for hunters. This has combined with major losses of coastal habitat to lead to severe population declines and the species is considered to be severely endangered.

The Long-tailed macaques Macaca fascicularis can be seen in many areas foraging at low tide but the Silver Leaf monkey Presbytis cristata which is another herbivore feeding entirely on leaves with some flowers and seeds, is a much shier animal so is rarely seen on the river banks or mangrove edges. Other mangrove species which are protected include estuarine crocodiles (Crocodylus porosus), monitor lizards (Varanus) and otters (Lutra and Aonyx spp).

The invertebrate fauna of the mangroves is dominated by Sesarmid and Grapsid crabs, and the smaller fiddler crabs (Uca sp.). Various species of Uca are adapted to feed on different sizes of particles and the different species live in overlapping zones. Research has shown that their presence or absence may be indicative of pollutants or toxic substances in the substrate, as the crabs feed by filtering the sand particles for organic matter. Indeed, certain species have been shown to be sensitive to various pollutants including certain heavy metals. Little is known about their distribution in the region; 5 Uca species have been recorded in Sarawak (C. Huet, 2000 - MSc thesis ).

Mudskippers (Pteropthalmus sp.) are also abundant, especially at the mangrove edge and on soft mudflats. The blood cockle Anadara granosa is common on the harder sediments of the mid-littoral zone, and is harvested commercially in large numbers.

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