An Investigation of Seagrass Patterns at Alphonse Atoll, Seychelles: Linking Structure to Function in Marine Landscapes
(2009)
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The idea of landscapes as shifting patch mosaics, structured by a range of biological and physical stochastic forces, is well suited to shallow tropical environments, where seagrass patches lie within a matrix of soft sediments or rocky substrates. The interaction of wave fields and tidal currents with carbonate sediment transport can result in linear morphologies of reef flat material with alternating sand tongues and seagrass beds. Patch-level metrics capture phenomena such as linearity in one variable, which can be evaluated over a gradient of predictable environmental change. Interrogating the statistical properties of patch ensembles enables the links between observed structures and the processes that govern them to be empirically investigated. This study demonstrates how habitat maps derived from remotely sensed Compact Airborne Spectrographic Imager (CASI) data can be used to investigate critical controls of landscape mosaics through the application of geostatistical techniques to Alphonse Atoll, Seychelles.
Landscape ecology is characterised by the empirical investigation of the structure and function of land surface features (Forman and Godron 1986), with particular regard to spatial heterogeneity on biotic and abiotic processes (Risser et al. 1984). The broad scale of a landscape implies that internal processes can be observed across a spectrum of spatial scales, by dividing landscapes into patches, providing a tool
for the representation of reality that can be readily understood. Patch-level metrics capture a feature of interest in one variable, which can then be evaluated over a gradient of predictable environmental change. In this way, ecologists are able to quantify and empirically link structure and function at the landscape scale.
Four key requirements for seagrasses are a marine environment, adequate rooting substrate, sufficient immersion in seawater and illumination to maintain growth (Hemminga and Duarte 2000). Seagrass
landscapes are composed of seagrasses (marine angiosperms) and unvegetated sediments. Studies of seagrass dynamics at the landscape scale have generally focused on mapping historical change in distribution and cover over time, doing little to link observed structures to underlying processes driving change. Across a gradient of increasing
hydrodynamic activity, seagrass beds form patterns that range from continuous meadows to widely dispersed, discrete patches (Fonseca and Bell 1998). Terrestrial landscape ecologists have developed paradigms on island biogeography and fragmentation that have not crossed over to marine landscapes, which have traditionally focused on patch dynamics (Fonseca and Bell 2006). Sub-littoral landscapes are
often viewed as a shifting biological mosaic of multistate systems structured by competition, grazing and predation. Such a viewpoint argues for a shift in focus, from the individual patch to the statistical
properties of the entire ensemble. Landscape ecology techniques have emerged as a useful means of investigating functional drivers, such as the influence of wave exposure on community composition (Turner et al. 1999) and the relative influence of internal and external drivers (Fonseca et al. 2008)…
