ReviewThe habitat function of mangroves for terrestrial and marine fauna: A review
Introduction
Mangroves are predominantly intertidal habitats that occur worldwide in the (sub) tropics along sheltered and shallow-water coastlines. The prop-roots and pneumatophores of mangrove trees extend into the intertidal and subtidal where they become a rare feature: hard substrata in an otherwise soft sediment environment (Ellison and Farnsworth, 1992). As such, mangrove roots become home to terrestrial as well as marine plants, algae, invertebrates and vertebrates. Mangroves form a habitat for a wide variety of species, some occurring in high densities. They are productive habitats and may support coastal fisheries for prawns and fishes (Manson et al., 2005). Mangroves are also important to humans for a variety of reasons, including aquaculture, agriculture, forestry, protection against shoreline erosion, as a source of fire-wood and building material, and other local subsistence use (Hogarth, 1999, Walters et al., 2008). Worldwide, loss of mangroves has been significant in recent decades, although in some regions of the world mangroves still occur as very extensive forests (Spalding, 1998, Alongi, 2002). They suffer from direct impacts such as cutting and pollution, as well as from hidden impacts such as changes in inland freshwater management (Dahdouh-Guebas et al., 2005), and are often regarded as unpleasant environments with little intrinsic value.
Animals found within mangrove environments include a variety of taxa, many of which are vulnerable or threatened as a result of human activities in the coastal zone. Determining the value of mangroves and other estuarine habitats for these animals requires knowledge of their life history, physiology and ecology as they interact across the dynamic mosaic of available habitats. Evidence suggests that mangroves are important to these species, but a lack of research is a major impediment to an evaluation of their mangrove dependency. A challenge for future research is separating the roles of mangroves from those of estuaries and other shallow-water habitats, to help determine the appropriate temporal and spatial scales for habitat protection (see Manson et al., 2005). Estuarine habitats have been recognised as important drivers of nearshore fish productivity. Worldwide, about 30% of all commercial fish species are mangrove-dependent (Naylor et al., 2000), producing an annual catch of almost 30 million tonnes in 2002 (FAO, 2004). Of all ecosystems, estuaries have the highest value per hectare (Costanza et al., 1997), making it significant for subsistence in many coastal communities. In Bragança (N-Brazil), for example, 68% of the cash income is primarily derived from mangrove crabs and fish (Glaser, 2003).
Recent and extensive reviews on mangroves as habitats for terrestrial and marine fauna include Hogarth (1999), Kathiresan and Bingham (2001), and Qasim and Kathiresan (2005). Studies related to the linkages between mangroves and coastal fish populations and fisheries, and new insights relating to the debate on the degree to which mangrove litter fuels the mangrove food web, form an important body of work published since these reviews; hence there is the need for a more up-to-date review. The current review summarises the available data on mangroves as a habitat for terrestrial and marine fauna, with special reference to the interlinkages with adjacent habitats and the importance of litter in the mangrove food web. We focus on the main groups of animals found in the mangrove habitat: sponges, various groups of meiofauna and macrofauna (epifauna and infauna), prawns, insects, fishes (bony fishes and elasmobranchs), amphibians, reptiles, and birds, accepting that a review of the complete fauna would be too far-reaching for this special issue, and that some mangrove fauna are not discussed here. These include less-well studied taxa like zooplankton (e.g., Mohan and Sreenivas, 1998, Ferrari et al., 2003, Krumme and Liang, 2004), tunicates (e.g., Carballo, 2000, Goodbody, 2003, Rocha et al., 2005), and mammals such as bats (Bordignon, 2006), buffalo (Dahdouh-Guebas et al., 2006), deer (Barrett and Stiling, 2006), dolphins (Smith et al., 2006), flying foxes (Moore, 2002), manatees (Spiegelberger and Ganslosser, 2005), marsupials (Fernandes et al., 2006), otters (Angelici et al., 2005), primates (Nijman, 2000), rabbits (Forys and Humphrey, 1996), raccoons (Cuaron et al., 2004), and tigers (Gopal and Chauhan, 2006).
Section snippets
Diversity and distribution of sponges
Sponges occurring on mangrove roots are conspicuous because they often have large sizes (±50 cm in diameter or more) and brilliant colours (e.g., Rützler and Feller, 1996, Diaz et al., 2004). Although some encrusting mangrove sponges can survive above the water line for many hours during a tidal cycle (Barnes, 1999), the aquiferous system of larger sponges will collapse when emerged for periods longer than 4 h (Rützler, 1995). Considering the typical zonation of mangrove habitats (Nybakken, 1997
Diversity and distribution of meiofauna
In mangroves a distinct ‘phytal’ meiofauna (generally defined as animals passing through a 1.0 or 0.5 mm sieve but retained on a 63 μm mesh), often dominated by acari, inhabits hard substrata such as prop-roots and pneumatophores (Proches et al., 2001, Bartsch, 2003). The focus of the majority of studies of meiofauna in mangroves, however, is on communities living in sediment or on decomposing leaves. Within mangrove sediments, as in most estuarine habitats, meiofauna are the numerically dominant
Mangroves as habitats for macrofauna
Mangroves are inhabited by a variety of benthic invertebrates, such as brachyuran crabs, gastropods, bivalves, hermit crabs, barnacles, sponges, tunicates, polychaetes and sipunculids. Mangrove invertebrates often show marked zonation patterns, and colonise a variety of specific micro-environments. While some species dwell on the sediment surface or reside in burrows, others live on pneumatophores and lower tree trunks or prop-roots, burrow in decaying wood, or can even be found in the tree
Mangroves as habitats for prawns
Dall et al. (1990) classified penaeid prawn life cycles into four different types according to the environments in which the adults spawned and the postlarvae settled. Adults of two of these types both spawn offshore, and their larvae move inshore where the postlarvae settle in their preferred nursery grounds, either estuarine or nearshore habitats. The postlarvae develop into juveniles which spend between 6 and 20 weeks in the nursery ground before emigrating offshore (Haywood and Staples, 1993
Mangroves as habitats for insects
The global distribution of mangroves has been divided into two biogeographical hemispheres, the Indo-West Pacific and the Atlantic-East Pacific (Duke, 1992). The former ranges from the east coast of Africa to Asia, Australia and the western Pacific islands, while the latter includes the eastern Pacific islands, the coasts of the American continent and the African west coast. Insect diversity in the mangroves of the Indo-West Pacific is thought to be higher than in the Atlantic-East Pacific as a
Mangroves as habitats for elasmobranchs
The number of elasmobranch species recorded from fresh or estuarine waters is at least 171 species, representing 68 genera and 34 families, with the greatest diversity occurring along the rapidly developing tropical coastlines of South America, West Africa, and Southeast Asia. Of the 171 elasmobranch species, more than 50% occur in estuaries (Martin, 2005).
Estuaries are used by various species of euryhaline and obligate freshwater elasmobranchs, but their life history and ecology, including
Diversity and distribution of fishes
The Indo-West Pacific region, stretching from the east coast of Africa through South and Southeast Asia to Australia and the Central Pacific, has the highest diversity of fishes in the world (at least 600 species in mangrove systems) (Blaber, 2000). The high diversity decreases latitudinally away from the equatorial core area (sensu Blaber, 2000) in Southeast Asia, but larger subtropical mangrove systems still contain at least 100 species. Many species occur throughout this region, while others
Importance of mangrove litter
The idea that mangroves provide a trophic link with the abundant faunal communities within the mangrove ecosystem and in adjacent habitats has been a longstanding issue in the literature and was first proposed by the classical work of Odum and Heald (1972) in their ‘outwelling hypothesis’. Odum and Heald suggested that the high productivity of mangroves is partially exported to the aquatic environment, providing an important food source for secondary consumers and thereby supporting adjacent
The role of mangroves and estuaries in relation to fisheries
Over the last four decades, many studies have demonstrated a strong relationship between mangrove presence and fish catch (Turner, 1977, Yáñez-Arancibia, 1985, Pauly and Ingles, 1986, Lee, 2004, Manson et al., 2005, Meynecke et al., 2007), with fishery catch being influenced by the relative abundance of mangroves in a region. Correlations have also been found between the extent (area or linear extent) of mangroves and the catches of prawns (particularly banana prawns) in the fisheries adjacent
Mangroves as habitats for amphibians and reptiles
Several independent evolutionary lines of reptiles and amphibians have successfully colonised, and are variously dependent on, mangrove ecosystems. These include frogs, marine and freshwater turtles, crocodilians, lizards, and marine and terrestrial snakes.
Mangroves as habitats for birds
Mangrove habitats play host to a moderate number of bird species around the globe. Most diverse are the Queensland mangroves of Australia which host 186 bird species (Noske, 1996). Other counts are 135 in Peninsular Malaysia (Nisbet, 1968), 125 in Guinea-Bissau, West Africa (Altenburg and van Spanje, 1989), 104 in north-western Australia (Noske, 1996), 94 in Surinam (Haverschmidt, 1965), and 84 in Trinidad (Ffrench, 1966). The forests are strongly zoned with few tree species and a sparse
Acknowledgements
I.N. was funded by a Vidi grant from the Dutch Organisation for Scientific Research (NWO). S.B. was funded by a postdoctoral mandate from the Research Foundation Flanders (FWO-Vlaanderen). J.-O.M. was funded by the Australian government and Griffith University postgraduate scholarships. H.M.P. was funded by an Australian Postgraduate Award (Industry) grant and the University of Queensland. P.J.S. was funded by the UK Natural Environment Research Council. This is Centre for Wetland Ecology
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