Abstract
1. Structural complexity is a key factor in ecology, often positively linked to biodiversity and carrying capacity of habitats. However, defining quantitatively the ecological role of structural complexity remains a challenge, mainly due to its unclear definition and lack of accurate measurement tools and indices. The most common structural complexity indices used in ecological studies are the Rugosity index and Fractal Dimension. However, these indices cannot appraise, or overlook certain complexity indications that may play important ecological roles, such as the different characteristics of structural elements or different spatial scales of structural complexity. 2. This study attempts to tackle these challenges by: 1. examining a new method for structural complexity measurement (Point-Intercept Contour or PIC), which may allow calculation of different complexity indices; 2. measuring structural complexity on different spatial scales, each of which may affect or reflect on different ecological factors; and 3. comparing three different indices of structural complexity (i.e., Rugosity index, Coefficient of Variation and Neighbor's Distance) at different spatial scales, in natural reefs in the Philippines. 3. The PIC method has proven to be easy to perform, provides informative data about structural complexity elements, and enables the calculation of all three indices on different spatial scales. 4. The different spatial scales revealed different patterns among sites that emphasize the importance of considering spatial scaling when expressing different ecological aspects that may indicate reef health. 5. The three indices showed similar general trends, with some differences between scales that reveal some advantages and some drawbacks to each index. 6. The study demonstrates the importance of structural complexity at different spatial scales, and suggests a series of considerations for the use of relevant methods and indices with emphasis on an inexpensive, facile tool for quantitative structural complexity measurements.
Highlights
The goal of the current study is to explore a novel measurement method which can be applied on different spatial scales and examined via the implementation of different structural complexity indices
We introduce and test a new measurement tool, the “Point-Intercept Contour (PIC),” which allows the calculation of different complexity indices on different spatial scales
Large Scale A significant difference was found between the sites
Summary
Structural complexity is a key factor in ecology (e.g., Russ, 1980; August, 1983; Gilinsky, 1984; McCoy and Bell, 1991; Tews et al, 2004; Hardiman et al, 2011; Harborne et al, 2012; Graham et al, 2015). Kovalenko et al (2012) describe complexity as “one of the most important factors structuring biotic assemblages.” Numerous studies have shown a strong correlation betweenStructural Complexity in Coral Reefs structural complexity and species richness and diversity in both terrestrial (e.g., MacArthur and MacArthur, 1961; Karr and Roth, 1971) and marine environments (e.g., Kohn, 1967; Jeffries, 1993; Lingo and Szedlmayer, 2006; Moore and Hovel, 2010).Coral reefs offer a frequently referenced example of a structurally complex ecosystem, and their high structural complexity is recognized as important in accounting for its high species richness (Friedlander and Parrish, 1998; Gratwicke and Speight, 2005b). Determining the exact ecological role of structural complexity, and harnessing it as a potential factor in coral-reef monitoring and management plans, remains a challenge, mainly due to its unclear definition and the limitations of available measurement tools. The need for an improved heuristic definition and for better tools for the evaluation of structural complexity can be demonstrated by its diverse synonymous terms (e.g., habitat complexity, architectural complexity, topographic complexity, habitat heterogeneity, habitat diversity, substratum heterogeneity, spatial heterogeneity, and substratum irregularity; Gilinsky, 1984; Carleton and Sammarco, 1987; Connell and Jones, 1991; Thomas and Atkinson, 1997; Lapointe and Bourget, 1999; Tews et al, 2004; Sleeman et al, 2005; Alvarez-Filip et al, 2009), as well as the diverse definitions and measurement methods (e.g., McElhinny et al, 2005; Graham and Nash, 2013)
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