bivalves are represented by only a few species, with the genus Enigmonia being dominant in many intertidal regions of the island.
At Tatawori estuary in Bintuni Bay, the mangrove fauna is dominated by gastro-pods and crabs with densities of >120 individuals/m2 of each group, with biomass averaging 10 g DW/m2 (Erftemeijer et al. 1989). The gastropods on the seaward forest edge are dominated by Melampus, but Nerita spp. and Littorina spp. dominate the forest, foraging on algae and detritus on mangrove roots and tree trunks. As in mangroves throughout the Indo-Pacific, the cosmopolitan species Telescopium telescopium dominates the high intertidal areas, scraping detritus and algae off substrata. Ocypodid and grapsid crabs dominate the crustacean fauna in the bay with Uca species being most ubiquitous, followed by species of Sesarma.
About one-half of the world’s 60 Uca species are found in Indonesia, with these species exhibiting complex niche patterns to maintain high species diversity compared to other invertebrates (Susetiono 1989). These zonation patterns are the result of niche partitioning of sediment by grain size and organic content. The crabs feed on detritus and microbes attached to the sediment particles using specialized feeding maxillipeds that are unique to each species. In Papua, most of the mangrove species found throughout the rest of Indonesia probably occur, but only Uca dussumieri dussumieri, U. vocans vocans, U. coarctata coarctata, U. lactea annulipes, and U. seismeela have been recorded in Papuan mangrove forests thus far (Moosa and Aswandy 1983).
The most commercially important crab, Scylla serrata, is a large carnivorous scavenger that lives in deep burrows within the forest floor and along river banks throughout Indonesia. It exhibits some color plasticity, being dark green in the western archipelago and dark brown in Papua. This species inhabits mangroves throughout its adult life, but females migrate to spawn in waters offshore. Megalopa (crab larvae) move into mangrove waters and by post-larval stage they are sedentary and grow to adulthood in mangrove environments. No quantitative ecological studies are available for the benthic fauna of Papua. Extensive species lists of gastropods, scaphopods, bivalves, and crabs exist for other Indonesian forests and can be found in Tomascik et al. (1997, Chapter 19). Table 5.4.5 summarizes the molluscan species recorded thus far in Papua.
The faunal distribution of the mangroves may be considered within four categories (Cragg 1983): permanent residents; animals that also occur in adjacent forest; animals that are strictly estuarine and marine; and animals that spend their early stages in mangroves. Among the permanent residents are the mudskipper (Periophthalmus spp.), the Mud Lobster (Thalassina anomala), the Mud Crab (Scylla serrata), as well as numerous species of isopods (Ceratolana papuae, Bruce 1995) and brachyuran and sesarmid crabs (Paracleistostoma laciniatum, Baruna trigranulum, Rahayu and Ng 2003; Perisesarma foresti and Perisesarma cricotus, Rahayu and Davie 2002) endemic to New Guinea and the other islands of Indonesia. There are also many other as yet described species that occupy restricted niches in the mangroves of Papua. A variety of wood-boring bivalves (family Teredinidae) are also specialized for life in mangrove wood. Specialist mangrove fauna generally exhibit clear zonation patterns usually in relation to frequency of tidal inundation and salinity (Cook, Currey, and Sarsam 1985; Cragg and Aruga 1987).
Animals that occur in both mangrove and neighboring terrestrial forests and swamps are within the second category, and this fauna includes mostly insects, birds, and mammals. These include water rats, bandicoots, bush pigs, wallabies, sugar gliders, possums, bats, and birds such as the Magpie Goose, cassowary, and Brush Turkey (Appendix 8.3). One of the most complex ecological relationships in this category is that between Philidris ants and epiphytic myrmecophytes, Hydnophytum moseleyanum, in mangrove forests in northern New Guinea (Maeyama and Matsumoto 2000). Both Philidris ants and the epiphyte are common throughout the forests of New Guinea, also occupying mangrove trees. The relationship is mutualistic. The epiphyte gets sustenance by absorbing nutrients from the detritus stored inside tree cavities by the ants, and the ants obtain honeydew secreted by scale insects attracted to the shoot tips of the host mangrove tree.
The third category, strictly estuarine and marine organisms, enter mangrove creeks and waterways on the rising tide and depart as tides recede. Fish are the predominant animals in this category. As Haines (1983) describes for the Purari delta, few fish species are confined to any one zone but many species are confined to a range of zones with species of the same or closely related genera replacing each other along salinity gradients. Some species are wide ranging, such as the Archer Fish (Toxotes chatareus). The Saltwater Crocodile (Crocodilus porosus) lives only in the seaward limits within waterways, while the Freshwater Crocodile (Crocodilus novaeguineae) occurs in river waters upstream.
Some marine invertebrates, such as the penaeid prawns (Table 5.4.6) and the Giant Freshwater Prawn (Macrobrachium rosenbergii), use the mangroves as nursery grounds during their early life stages. The most abundant and widespread species of commercial importance is the Banana Prawn (Penaeus merguiensis). This species is more abundant in regions of high salinity but it exhibits the life cycle typical of all penaeids. During the first stage, planktonic post-larvae settle in estuaries where they feed and grow until adolescence. An oceanic stage begins when the prawns emigrate from the estuaries to coastal waters where, after a period of growth to adulthood, they move into deeper waters to spawn. Penaeus merguiensis, Metapenaeus demani, and Metapenaeus eborancensis spawn in waters 10–20 meters deep, whereas other species such as Metapenaeus ensis and Penaeus semisulcatus spawn in waters up to 60 m deep. The larvae then move shoreward via currents, initially settling in the headwaters of mangrove-lined creeks and waterways. Juveniles and adults congregate in these river mouths before migrating out to sea. The cycle is continuous throughout the year.
Food Web Dynamics
Although little if any information exists on the trophic ecology of New Guinea mangroves, it is assumed that the dynamics of food webs in Papuan mangroves are similar to those in other tropical mangroves. Mangrove links with coastal fisheries have received a lot of attention, but the food webs of mangroves are mostly detritus-based, with most trophic activity focused on interactions among fauna either directly or indirectly through consumption of tree material such as leaves, flowers, propagules, wood, bark, and roots (Robertson, Alongi, and Boto 1992).
Direct grazing on mangrove tissue, mainly by insects and arboreal crabs, generally constitutes a small proportion of energy flow. More recently, evidence of the trophic importance of algal food resources in mangrove ecosystems has emerged, demonstrating that a number of key faunal groups depend on phytoplankton, benthic microalgae, or macroalgae growing on above-ground roots and other tree parts, for food. From a nutritional perspective, algae are a better food than detritus derived from mangrove trees because of easier digestion and relatively higher nitrogen content.
Various species of mammals, insects, and birds permanently or temporarily reside in some mangrove canopies. The feeding ecology of mangrove-associated birds is fairly well understood. Bird communities can be spatially and trophically complex and include up to eight feeding guilds: granivores, frugivores, piscivores, aerial hawkers, and hovering, gleaning, fly catching, and bark-foraging insectivores (Kathiresan and Bingham 2001).
On and beneath the forest floor, crabs are generally the keystone group driving food webs. Sesarmid crabs (Grapsidae) are the most conspicuous organisms, but fiddler crabs (Ocypodidae) are also abundant, being highly efficient consumers of benthic microalgae. Recent work throughout the world has shown that large proportions of leaf and other litter deposited on the forest floor is consumed or hidden underground by crabs (Kathiresan and Bingham 2001). This pathway has profound effects on energy and carbon flow within mangrove forests, as the quantities of material available for export from forests are reduced, and the cycling of nutrients to support forest primary production is enhanced. Material that is consumed or hidden by crabs underground must eventually be decomposed by microbial communities in the sediments.
The
