Measuring coral size-frequency distribution using stereo video technology, a comparison with in situ measurements
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Coral colony size-frequency distribution data offer valuable information about the ecological status of coral reefs. Such data are usually collected by divers in situ, but stereo video is being increasingly used for monitoring benthic marine communities and may be used to collect size information for coral colonies. This study compared the size-frequency distributions of coral colonies obtained by divers measuring colonies ‘in situ’ with digital video imagery collected using stereo video and later processed using computer software. The size-frequency distributions of the two methods were similar for corymbose colonies, although distributions were different for massive, branching and all colonies combined. The differences are mainly driven by greater abundance of colonies >50 cm and fewer colonies <10 cm recorded when using the in situ method. The stereo video method detected 93 % of marked colonies >5 cm and was able to record measurements on 87 % of the colonies detected. However, stereo video only detected 57 % of marked colonies <5 cm, suggesting that this method may be unsuitable for assessing abundance of coral recruits. Estimates of colony size made with the stereo video were smaller than the in situ technique for all growth forms, particularly for massive morphologies. Despite differences in size distributions, community assessments, which incorporated genera, growth forms and size, were similar between the two techniques. Stereo video is suitable for monitoring coral community demographics and provided data similar to in situ measure for corymbose corals, but the ability to accurately measure massive and branching coral morphologies appeared to decline with increasing colony size.
KeywordsCoral size-frequency distribution Stereo video Digital imaging techniques Reef monitoring Coral population demographics
We would like to thank the staff in the Marine Science Program of the Department of Parks and Wildlife for allowing data collection to complete this work and for providing technical assistance. This project was funded as part of the Dredging Audit and Surveillance Program by the Gorgon Joint Venture as part of the environmental offsets. The Gorgon project is a joint venture of the Australian subsidiaries of Chevron, Exxon Mobil, Shell, Osaka Gas, Tokyo Gas and Chubu Electric Power. Special thanks to those on the GMER field trip who assisted with logistics and data collection.
Compliance with ethical standards
This study is funded by the Chevron-operated Gorgon Project’s State Environmental Offsets Program and is administered by the Department of Parks and Wildlife. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. This article does not contain any studies with human participants or animals performed by any of the authors.
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