On the Benefits of Using Both Dual Frequency Side Scan Sonar and Optical Signatures for the Discrimination of Coral Reef Benthic Communities

Abstract

The importance of coral reef ecosystems is well established (McManus and Noordeloos, 1998). The threats to these highly diverse and endangered communities are well known and a large number of reports document the dramatic effects of climate change and particularly global seawater warming, coastal development, pollution, and impacts from tourism, overfishing, and coral mining on them (Grigg & Dollar, 1990; Holden & LeDrew, 1998; Lough, 2000; Buddemeier, 2002; Knowlton, 2001; Sheppard, 2003). To protect these ecosystems the extent of their degradation must be documented through large scale mapping programmes, and inventories of existing coral reef areas are particularly important (Riegl & Purkis, 2005; Mora et al., 2006). Such programmes are essential so that the health of these ecosystems can be assessed and local and global changes over time can be detected (Holden & LeDrew, 1998). Seagrass beds are also recognized as playing a pivotal role in coastal ecosystems. They are crucial to the maintenance of estuarine biodiversity, the sustainability of many commercial fisheries, for stabilizing and enriching sediments and providing an important food resource and spawning areas for many marine organisms (Powis & Robinson, 1980; Bell & Pollard, 1989, Dekker et al., 2006). Unprecedented declines in seagrass beds have occurred in temperate and tropical meadows throughout the world; their global decline highlights the need for monitoring programmes to manage their conservation and sustainable use (Short & Wyllie-Echeverria, 1996; Ward et al., 1997). Coral reefs, seagrass, and macroalgal habitats are commonly found in association with, and in close proximity to each other, and are linked by many pathways such as sediment deposition mechanisms, the primary productivity cycle, and the migration of many fish species (Mumby, 1997). Due to their nutritional biology and photosynthetic requirements, coral reefs generally exist in clear tropical waters and this makes them highly suited for optical remote sensing (Mumby, 1997; Green et al., 2000). Although less confined to them, macroalgal and seagrass habitats are also found in such environments. Under stress, both coral and seagrass ecosystems may retreat and become replaced by macroalgal or less productive and biologically diverse sedimentary or bare rocky habitats. Such O pe n A cc es s D at ab as e w w w .in te ch w eb .o rg