INTRODUCTION

Tropical coastal areas are often categorized into three major systems: coral reefs, seagrass beds and mangroves. All three systems often occur in close proximity (Fig. 3.1)and a number of habitats are represented within each (e.g. patterns of habitat zonation in coral reefs: Sheppard, 1982). Many physical and ecological processes transcend individual habitats with some particularly striking examples among the three principal systems. A well-known example is the trapping of riverine sediments in estuarine mangroves that might otherwise discharge onto reefs and cause coral mortality through sedimentation (Pannier, 1979; Torres et al., 2001). Other examples of abiotic linkages include the runoff of cool, low-salinity water from precipitation (Andreéfoueët et al., 2002) and the discharge of hot water from relatively calm lagoons, both of which can cause coral bleaching (reviewed in Glynn, 1993).

Ecological linkages among habitats include the migration of organisms on either an ontogenetic or diurnal basis. Many snappers (Family Lutjanidae), grunts (Haemulidae) and parrotfish (Scaridae) species, for example, undertake ontogenetic shifts in habitat use from seagrass beds or mangroves to their adult coral reef habitat (McFarland et al., 1985; Lindeman et al., 1998; de la Morinieère et al., 2002; Mumby et al., 2004a). Grunts also undertake diurnal migrations from their night-time foraging habitat of seagrass beds to their daytime resting habitat on coral reefs (Ogden and Ehrlich, 1977; Burke, 1995).