Ecology of Indonesian Papua Part Two. Andrew J. Marshall
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but the modified light attenuation method gives the most reasonable estimate of total production, while litter fall plus incremental growth can give reasonable estimates of above-ground production (and excluding below-ground root production). The modified light attenuation method is most reasonable because it measures total net fixed carbon production and incorporates the most robust assumptions based on tree physiology and carbon balance. A number of recent studies have measured above-ground production using allometry (relationships of tree weight to stem diameter) coupled with litter fall or leaf turnover (Duarte et al. 1999; Coulter et al. 2001; Ross et al. 2001; Sherman, Fahey, and Martinez 2003).
The estimates of net primary production made using the modified light attenuation method include below-ground production but there is currently no clear understanding of how carbon is allocated to different parts of the tree. As pointed out by Clough (1998), it is not yet possible to construct a robust model of carbon balance for mangrove trees because of the lack of empirical data and the difficulty of measuring root processes and respiration of woody parts. However, some preliminary carbon data for mangroves suggest that roughly half of carbon incorporated into the tree is respired, an estimate that is in agreement with similar estimates for terrestrial trees (Barnes et al. 1998).
If we accept the data obtained using the modified light attenuation method as the most comprehensive estimate of net primary productivity of mangroves, the average rate of net primary production in New Guinea and surroundings (Table 5.4.3) is 51 tons dry weight per ha per yr. There is considerable range between values, but the figures do suggest that mangroves are significant primary producers. This is supported by empirical measurements of rates of leaf photosynthesis in mangroves (Clough and Sim 1989). Measuring gas exchange characteristics and water use efficiency for various mangrove species located on the Era, Wapo, and Ivi rivers along the Gulf of Papua, Galley Reach, and Motupore Island, Clough and Sim (1989) measured the most rapid rates of carbon dioxide uptake, stomatal conductance, and water-use efficiency yet measured. These high rates of CO 2 as-similation and other physiological attributes are a reflection of favorable climatic conditions.
Plotting all available data on mangrove productivity against latitude (Figure 5.4.6) gives a significant negative relationship, indicating that mangrove production declines away from the equator, mirroring the latitudinal decline in mangrove biomass (Figure 5.4.5) and litter fall (Saenger and Snedaker 1993). These graphs show that the mangroves of Papua are well placed geographically and climatically to grow to immense size and are as productive as any other tropical forests in the world.
Fauna
Mangrove forests in Papua support a wide diversity of biota, ranging in size from bacteria to crocodiles, and like most mangroves, house species originating from both land and sea. The fauna of the Papuan mangroves is poorly known. Most information comes from faunal surveys along the southern coast of Papua New Guinea and the west coast of Papua. Generally, there is a high level of similarity between the northern Australian and Papuan faunas (Macnae 1968); differences in species recorded are likely due to the lack of surveys in New Guinea rather than any real biogeographical anomalies.
Figure 5.4.6. Latitudinal changes in net primary production measured using a modified light interception method.
Source: Data from Gong, Ong, and Wong (1991); Gong, Ong, and Clough (1992); Atmadja and Soerojo (1991); Robertson, Daniel, and Dixon (1991); Sukardjo (1995); Clough, Ong, and Gong (1997); Clough (1998); Alongi and Dixon (2000); Alongi, Tirendi, and Clough (2000); Alongi et al. (2004).
The most comprehensive studies of the mangrove fauna of the island have been conducted in the Purari and Fly river deltas bordering the Gulf of Papua (White and White 1976; Liem and Haines 1977; Bayley 1980; Cragg 1983; Liem 1983; Pernetta 1983). The mangrove-associated fish fauna of Bintuni Bay in Papua has also been surveyed (Ecology Team 1984; Erftemeijer et al. 1989), but most of the species lists reflect attention to species of commercial or subsistence use and must be considered incomplete.
Of the mangrove vertebrates, 30 species of reptiles, 12 species of amphibians, 250 species of birds, 50 species of mammals, and 195 species of fish have been recorded on the island thus far (Appendix 8.3). Mangrove invertebrates have not been as well investigated, with the exception of commercially valuable groups, such as crabs and shrimps. The best described groups include the mollusks and insects, the most conspicuous of the latter being the Anopheles mosquito which is the vector for malaria and filariasis.
The mangrove forests of Papua support a rich molluscan and crustacean fauna consisting of approximately 95 and 80 species, respectively (Kartawinata et al. 1979; Sabar, Djajasamita, and Budiman 1979; Kastoro et al. 1991). Numerically, gastropods are the dominant group of mollusks, with Littorina scabra frequently found at the seaward margin in large numbers, with Monodonta labio a co-occurring species (Soemodihardjo 1987). In comparison, 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