The habitat function of mangroves for terrestrial and marine fauna: A review

Study Number:

27

Author:

I. Nagelkerken, S.J.M. Blaber, S. Bouillon, P. Green, M. Haywood, L.G. Kirton, J.-O. Meynecke, J. Pawlik i, H.M. Penrose, A. Sasekumar & P.J. Somerfield

Abstract:

Mangroves are defined by the presence of trees that mainly occur in the intertidal zone, between land and sea, in the (sub) tropics. The intertidal zone is characterised by highly variable environmental factors, such as temperature, sedimentation and tidal currents. The aerial roots of mangroves partly stabilise this environment and provide a substratum on which many species of plants and animals live. Above the water, the mangrove trees and canopy provide important habitat for a wide range of species. These include birds, insects, mammals and reptiles. Below the water, the mangrove roots are overgrown by epibionts such as tunicates, sponges, algae, and bivalves. The soft substratum in the mangroves forms habitat for various infaunal and epifaunal species, while the space between roots provides shelter and food for motile fauna such as prawns, crabs and fishes. Mangrove litter is transformed into detritus, which partly supports the mangrove food web. Plankton, epiphytic algae and microphytobenthos also form an important basis for the mangrove food web. Due to the high abundance of food and shelter, and low predation pressure, mangroves form an ideal habitat for a variety of animal species, during part or all of their life cycles. As such, mangroves may function as nursery habitats for (commercially important) crab, prawn and fish species, and support offshore fish populations and fisheries. Evidence for linkages between mangroves and offshore habitats by animal migrations is still scarce, but highly needed for management and conservation purposes. Here, we firstly reviewed the habitat function of mangroves by common taxa of terrestrial and marine animals. Secondly, we reviewed the literature with regard to the degree of interlinkage between mangroves and adjacent habitats, a research area which has received increasing attention in the last decade. Finally, we reviewed current insights into the degree to which mangrove litter fuels the mangrove food web, since this has been the subject of longstanding debate.

Main Results and Conclusions:

[ only regarding “Mangroves as drivers of nearshore fishery production” section of the article ]

• Based on the spawning cycle of many fish species that live near mangrove habitat: “mangroves could function as an important link in the chain of habitats that provide complementary resources and benefits, e.g., as nursery areas for fish, prawns and crabs (Sheridan and Hays, 2003; Crona and Ronnback, 2005), with spatial complexity at a scale that provides refuge to small prey, and abundant food for commercial species at certain stages in their life cycle (Chong et al., 1990)”(171).
• Fish production is proportionally related to the area of mangrove habitat: “Most of the analyses in these studies” – 27 studies were examined for this section of the review – “have resulted in positive correlations, assuming that the area of mangroves or tidal wetland habitat directly translates to the catch of commercial fisheries (Manson et al., 2005; Meynecke et al., 2007). Estimates of the amount of commercial catch explained by the presence of mangroves or estuaries range from 20 to 90% (Fig. 1). The most common variables used were mangrove area, followed by linear extent and intertidal area or estuarine size”(172).
• Data from certain articles suggest that certain species rely on a combination of mangrove and seagrass bed habitat rather than mangrove habitat alone to ensure species health (Robertson and Blaber, 1992; Nagelkerken et al., 2001; Dorenbosch et al., 2006a,b; Jelbart et al., 2007), while other articles stress the importance of mangrove habitat for ontogentic fish movements (Rooker and Dennis, 1991; Nagelkerken et al., 2000c; Nagelkerken and van der Velde, 2002, 2003; Eggleston et al., 2004; Lugendo et al., 2005)” (172-173).
• A main conclusion from the review indicated that it is extremely difficult to make generalizations about mangrove habitat because different fish species have varying dependence on mangrove habitat.

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