To characterise the size and geometry of coral reefs on a global scale.
Global.
Present.
Coral reefs.
We process the Allen Coral Atlas database of shallow-water tropical reefs to obtain a comprehensive and unprecedented inventory of coral reefs worldwide. We analyse different macroecological and morphological patterns, including size distribution, the area-perimeter relationship, inter-reef distance distribution, and the fractal dimension of individual reefs and coral provinces.
We identified a total of 1,579,772 individual reefs worldwide (> 1000 m2), extending over a total of 52,423 km2 of ocean area with mean and median sizes of 3.32 and 0.3 ha, respectively. We unravelled three universal laws that are common to all coral reef provinces: the size-frequency distribution and the inter-reef distance distribution follow power laws with an exponent of 1.8 and 2.33, respectively. At the same time, the area-perimeter relationship conforms to a power-law with an exponent of 1.26. Furthermore, we demonstrate that coral reefs develop fractal patterns characterised by a perimeter fractal dimension of and a surface fractal dimension of . Our analysis suggests that coral reefs tend to evolve from simple rounded filled shapes to more complex, elongated and less compact forms, developing into fractal structures with a consistent surface fractal dimension and an increasing perimeter fractal dimension as they grow.
Coral reefs display intricate fractal-like geometries and exhibit universal macroecological patterns, largely independent of their geographical location. The universality of the observed patterns suggests that these features possibly stem from the highly conserved interactions of biological, physical and chemical processes. Over geological scales, these processes lead to reef landscape patterns common among all provinces, providing new information relevant to reef growth modelling.