Progress in Physical Geography http://ppg.sagepub.com/ Progress in the use of remote sensing for coral reef biodiversity studies Anders Knudby, Ellsworth LeDrew and Candace Newman Progress in Physical Geography 2007 31: 421 DOI: 10.1177/0309133307081292 The online version of this article can be found at: http://ppg.sagepub.com/content/31/4/421 Published by: http://www.sagepublications.com Additional services and information for Progress in Physical Geography can be found at: Email Alerts: http://ppg.sagepub.com/cgi/alerts Subscriptions: http://ppg.sagepub.com/subscriptions Reprints: http://www.sagepub.com/journalsReprints.nav Permissions: http://www.sagepub.com/journalsPermissions.nav Citations: http://ppg.sagepub.com/content/31/4/421.refs.html >> Version of Record - Aug 29, 2007 What is This? Downloaded from ppg.sagepub.com at SIMON FRASER LIBRARY on August 15, 2013 Progress in Physical Geography 31(4) (2007) pp. 421–434 Ã Progress in the use of remote sensing for coral reef biodiversity studies Anders Knudby,* Ellsworth LeDrew and Candace Newman Department of Geography, University of Waterloo, 200 University Avenue West, Waterloo, Ontario, N2L3G1, Canada Abstract: Coral reefs are hotspots of marine biodiversity, and their global decline is a threat to our natural heritage. Conservation management of these precious ecosystems relies on accurate and up-to-date information about ecosystem health and the distribution of species and habitats, but such information can be costly to gather and interpret in the fi eld. Remote sensing has proven capable of collecting information on geomorphologic zones and substrate types for coral reef environments, and is cost-effective when information is needed for large areas. Remote sensing-based mapping of coral habitat variables known to infl uence biodiversity has only recently been undertaken and new sensors and improved data processing show great potential in this area. This paper reviews coral reef biodiversity, the infl uence of habitat variables on its local spatial distribution, and the potential for remote sensing to produce maps of these habitat variables, thus indirectly mapping coral reef biodiversity and fulfi lling information needs of coral reef managers. Key words: coral reefs, fi sh biodiversity, habitat characteristics, lidar, remote sensing, rugosity. I Introduction and coral diseases at the local scale to world- Coral reefs are the most biodiverse marine wide ocean warming, acidifi cation, and sea- ecosystems on the planet, estimated to level rise. Most of these threats are expected harbour nearly one million species globally to worsen their impact in the coming decades (Reaka-Kudla, 1997: 93). They can be places (Hoegh-Guldberg, 1999; Kleypas et al., 1999; of extraordinary beauty, and are essential Pittock, 1999), leaving an uncertain future for to the livelihoods of people who depend on coral reefs. The decline of coral reefs, both them for food, coastal protection, tourism- past and projected, is of much more than aca- based income and more (Birkeland, 1997: 2). demic interest; it is a serious threat to global However, the health of coral reefs is declining biodiversity, an important part of our natural at a global scale (Wilkinson, 2004: 7), and heritage. the threats that have precipitated this decline Because of the complexity of coral reef range from overfi shing, nutrient enrichment ecosystems and the multitude of threats, *Author for correspondence. Email: [email protected] © 2007 SAGE Publications DOI: 10.1177/0309133307081292 Downloaded from ppg.sagepub.com at SIMON FRASER LIBRARY on August 15, 2013 422 Progress in Physical Geography 31(4) identification of the important threats and II Coral reef biodiversity the necessary management for a given reef Although reefs have been a recurrent phe- is diffi cult. Nevertheless, the global area of nomenon throughout the history of life on coral reef under some form of management Earth, modern coral reefs only developed in is growing, and so is the need for information the Triassic (Newell, 1972). The evolution on which to base management measures of the Symbiodinium group of dinofl agellates (Wilkinson, 2004: 1). A manager of a protected and their incorporation into scleractinian area needs assessments of various aspects corals produced the symbiotic organisms that of reef health, which provide both a basis are still the primary reef-building organisms from which zonation plans and management (Webb, 1998). Important groups of fauna regulations can be developed, and a baseline evolved thereafter, notably sea urchins, reef from which changes can be assessed. fi shes and currently widespread coral genera Reef health is an intangible concept, and is such as Acropora, Porites and Pocillopora typically mapped and monitored using a num- (Wood, 1998). Today, despite covering only ber of proxies. Live coral cover is often used for between 0.1% and 0.5% of the total area of practical reasons (Mumby et al., 2004b), and the oceans (Moberg and Folke, 1999), coral so is diversity or abundance of ecologically reefs harbour more species than any other important or vulnerable species (Hodgson marine ecosystem (Dubinsky, 1990: 251; et al., 2004). However, owing to the diffi culties Reaka-Kudla, 1997: 93). The largest groups and expense associated with conducting ex- of known coral reef species are fishes and tensive fi eld surveys under water, spatially sponges, the reef-building organisms them- distributed data of the appropriate type and selves being relatively few in number. Com- detail are rarely available. Remote sensing prehensive species lists do not exist for any technologies have therefore been used to map reef area of the world (Paulay, 1997); it is coral reefs since the early days of Landsat apparent that only a fraction of the existing (Smith et al., 1975), and research into the use fauna has been described, and it is likely that of remote sensing technology continues with small cryptic species outnumber the num- the advent of new sensors and data processing erous described fi shes and sponges (Moran methods (Kutser et al., 2006). Classifi cation of and Reaka, 1988). broad substrate types is now routinely possible Coral reefs are generally limited to shal- in clear and shallow water, and water depth low and clear water with a mean water can be derived from a variety of data sources temperature of 18°C or higher, and are thus with varying accuracy. The interference of the largely confi ned to the tropics (Yonge, 1940). water column, however, continues to pose Although reefs exist wherever conditions problems for classifi cation accuracy, and so do permit, there is profound variation in the the similarities in spectral signatures between number of different species that make up the important substrate types. New technologies reef fauna in different parts of the world. At show promise for mapping aspects of coral a regional scale, three factors have had a large reef health beyond substrate types, including infl uence on today’s biogeographic patterns. water quality and reef structural complexity, First, the current distribution of land masses thus providing complementary information and oceans has resulted in upwelling at the for mapping of coral reef biodiversity. In this eastern margins of the two major oceans, paper we aim to review coral reef biodiversity the Atlantic and the Indo-Pacific, and the and its spatial distribution, the infl uence of dominant equatorial currents running east habitat characteristics on biodiversity, and to west (Veron, 1995: 99). Cold nutrient- remote sensing approaches to mapping coral rich water from upwelling is detrimental to reef habitats, with a focus on mapping habitat reef growth, and western margins of oceans variables known to infl uence biodiversity. therefore house larger reef areas than eastern Downloaded from ppg.sagepub.com at SIMON FRASER LIBRARY on August 15, 2013 Anders Knudby et al.: Remote sensing for coral reef biodiversity studies 423 margins (Hubbard, 1997: 52). Second, the across taxonomic groups. This tends to be closing of the Isthmus of Panama separated the case for fish rather than plants (Ward the Atlantic and Pacifi c oceans between 3.1 et al., 1999) or coral (Beger et al., 2003), which and 3.5 million years ago (Coates and Obando, is unfortunate because fi sh are not directly 1996), which resulted in different species now mappable using remote sensing. Fortunately, being present on either side of the Isthmus. distinguishable habitat categories such as reef, Third, the large area of shallow tropical seas in seagrass and sand can predict biodiversity the Indo-West Pacifi c has resulted in greater equally well or better than fi sh, and are more biodiversity of coral reef fauna here than in easily mappable (Ward et al., 1999). any other of the recognized biogeographic regions: the Western Atlantic, Eastern Pacifi c III Habitats as indicators of coral reef and Eastern Atlantic, in order of decreasing biodiversity biodiversity (Briggs, 1999; Bellwood and As noted, several environmental variables Hughes, 2001). Within the Western Pacifi c, have been shown to infl uence the biodiversity the species richness of scleractinian corals of a given habitat. Mapping such habitat themselves is greatest in the coral triangle, variables could indicate the likely spatial formed by Indonesia, the Philippines and distribution of biodiversity at a local scale and New Guinea, with more than 450 described. suggest priority areas for conservation, at least Species richness gradually declines towards for the species for which habitat-biodiversity the Indian Ocean or the Pacifi c (Veron, 1995: relationships have been identifi ed. A survey of 140). A similar biogeographic pattern is found the literature relating biodiversity and habitat for reef fi shes (Bellwood and Hughes, 2001; variables yields a complex picture. Studies Bellwood and Wainwright, 2002), and for all have focused on a variety of taxonomic or other taxa for which data are available (Paulay, functional groups, have employed different 1997: 303). measures of biodiversity, and have measured At smaller spatial scales, communities different habitat variables in different ways.