Abstract
Coral reefs hosts nearly 25% of all marine species and provide food sources for half a billion people worldwide while only a very small percentage have been surveyed. Advances in technology and processing along with affordable underwater cameras and Internet availability gives us the possibility to provide tools and softwares to survey entire coral reefs. Holistic ecological analyses of corals require not only the community view (10s to 100s of meters), but also the single colony analysis as well as corallite identification. As corals are three-dimensional, classical approaches to determine percent cover and structural complexity across spatial scales are inefficient, time-consuming and limited to experts. Here we propose an end-to-end approach to estimate these parameters using low-cost equipment (GoPro, Canon) and freeware (123D Catch, Meshmixer and Netfabb), allowing every community to participate in surveys and monitoring of their coral ecosystem. We demonstrate our approach on 9 species of underwater colonies in ranging size and morphology. 3D models of underwater colonies, fresh samples and bleached skeletons with high quality texture mapping and detailed topographic morphology were produced, and Surface Area and Volume measurements (parameters widely used for ecological and coral health studies) were calculated and analysed. Moreover, we integrated collected sample models with micro-photogrammetry models of individual corallites to aid identification and colony and polyp scale analysis.
Highlights
It has been estimated that coral reefs support an approximate 25% of all marine life, and as a consequence, they are a significant food source for half a billion people worldwide [1]
A total of 10 coral colonies from 10 species and 5 growth forms were imaged in situ and sampled for 3D modelling and Surface Area (SA) and V calculations The growth forms consisted of 4 massive corals (Gardineroseris planulata, Porites lutea, P. lobata and Platygyra daedalea) (Fig 2), 3 branched corals (Acropora sp. 1, Acropora sp. 2, Pocillopora damicornis) and 1 branched tabular coral (Acropora hyacinthus) (Fig 3), 1 encrusting coral (Diploastrea heliopora) (Fig 4A) and 1 foliose coral Echinopora lamellosa) (Fig 4B)
An uncomplicated workflow for generating these sets was created so these techniques can be conveniently taught to non-specialists in coral research or computer science, so there is the possibility that these datasets can be generated for surveying and monitoring on a larger scale
Summary
It has been estimated that coral reefs support an approximate 25% of all marine life, and as a consequence, they are a significant food source for half a billion people worldwide [1]. The total economic value of these valuable organisms ranges from US$ 100,000 to US$ 600,000 per square kilometre per year [2]. They are crucial in supporting human life, but they are fragile and currently under serious hazard [3]. The decline in coral reef populations has been observed in recent decades, and it has been noted that up to 70% of the world's reefs are endangered or destroyed, partly by environmental stress but mostly due to human activity [4, 5].
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