Methods and measurement variance for field estimations of coral colony planar area using underwater photographs and semi-automated image

TitleMethods and measurement variance for field estimations of coral colony planar area using underwater photographs and semi-automated image
Publication TypeJournal Article
Year of Publication2015
AuthorsNeal B.P, Lin T.H, Winter R.N, Treibitz T., Beijbom O., Kriegman D., Kline DI, Mitchell B.G
JournalEnvironmental Monitoring and Assessment
Volume187
Date Published2015/08
Type of ArticleArticle
ISBN Number0167-6369
Accession NumberWOS:000358782300015
Keywordsacropora; calculate; Colony growth; Colony size; coral reefs; decline; growth; Image segmentation; measurements; ocean acidification; Planar area; population-structure; propagation; reef; Size structure; surface-area; tomography
Abstract

Size and growth rates for individual colonies are some of the most essential descriptive parameters for understanding coral communities, which are currently experiencing worldwide declines in health and extent. Accurately measuring coral colony size and changes over multiple years can reveal demographic, growth, or mortality patterns often not apparent from shortterm observations and can expose environmental stress responses that may take years to manifest. Describing community size structure can reveal population dynamics patterns, such as periods of failed recruitment or patterns of colony fission, which have implications for the future sustainability of these ecosystems. However, rapidly and non-invasively measuring coral colony sizes in situ remains a difficult task, as three-dimensional underwater digital reconstruction methods are currently not practical for large numbers of colonies. Twodimensional (2D) planar area measurements from projection of underwater photographs are a practical size proxy, although this method presents operational difficulties in obtaining well-controlled photographs in the highly rugose environment of the coral reef, and requires extensive time for image processing. Here, we present and test the measurement variance for a method of making rapid planar area estimates of small to medium-sized coral colonies using a lightweight monopod image-framing system and a custom semiautomated image segmentation analysis program. This method demonstrated a coefficient of variation of 2.26 % for repeated measurements in realistic ocean conditions, a level of error appropriate for rapid, inexpensive field studies of coral size structure, inferring change in colony size over time, or measuring bleaching or disease extent of large numbers of individual colonies.

DOI10.1007/s10661-015-4690-4
Short TitleEnviron. Monit. Assess.
Student Publication: 
No
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