Methods and measurement variance for field estimations of coral colony planar area using underwater photographs and semi-automated image segmentation
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 short-term 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. Two-dimensional (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 semi-automated 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.
KeywordsCoral reefs Colony size Colony growth Size structure Planar area Image segmentation
This study was supported by a funding from National Science Foundation Cyber Enabled Discovery and Innovation Award # 0941760. We wish to thank the Smithsonian Tropical Research Institute and the staff of the Bocas del Toro field station.
- Bongiorni, L., Shafir, S., Angel, D., & Rinkevich, B. (2003). Survival, growth and gonad development of two hermatypic corals subjected to in situ fish-farm nutrient enrichment (Vol. 253). Oldendorf, Allemagne:Inter-Research.Google Scholar
- Bythell, J., Pan, P., & Lee, J. (2001). Three-dimensional morphometric measurements of reef corals using underwater photogrammetry techniques. Coral Reefs, 20(3), 193–199.Google Scholar
- Cesar, H., Burke, L., & Pet-Soede, L. (2003). The economics of worldwide coral reef degradation.Google Scholar
- Gulshan, V., Rother, C., Criminisi, A., Blake, A., & Zisserman, A. Geodesic star convexity for interactive image segmentation. In Computer Vision and Pattern Recognition (CVPR), 2010 I.E. Conference on, 2010 (pp. 3129–3136): IEEE.Google Scholar
- Herlan, J., & Lirman, D. Development of a coral nursery program for the threatened coral Acropora cervicornis in Florida. In Proc 11th Int Coral Reef Symp, 2008 (Vol. 24, pp. 1244–1247).Google Scholar
- Hill, J., & Wilkinson, C. (2004). Methods for ecological monitoring of coral reefs, a resource for managers. Australian Institute of Marine Science.Google Scholar
- Hughes, T. P. (1984). Population dynamics based on individual size rather than age: a general model with a reef coral example. American Naturalist, 123, 778–795.Google Scholar
- Jones, A. M., Cantin, N. E., Berkelmans, R., Sinclair, B., & Negri, A. P. (2008). A 3D modeling method to calculate the surface areas of coral branches. Coral Reefs, 27(3), 521–526.Google Scholar
- Laforsch, C., Christoph, E., Glaser, C., Naumann, M., Wild, C., & Niggl, W. (2008). A precise and non-destructive method to calculate the surface area in living scleractinian corals using X-ray computed tomography and 3D modeling. Coral Reefs, 27(4), 811–820. doi: 10.1007/s00338-008-0405-4.CrossRefGoogle Scholar
- Lirman, D., Schopmeyer, S., Galvan, V., Drury, C., Baker, A. C., & Baums, I. B. (2014). Growth dynamics of the threatened Caribbean staghorn coral Acropora cervicornis: influence of host genotype, symbiont identity, colony size, and environmental setting. PloS One. doi: 10.1371/journal.pone.0107253.Google Scholar
- Stimson, J., & Kinzie, R. A. (1991). The temporal pattern and rate of release of zooxanthellae from the reef coral Pocillopora damicornis (Linnaeus) under nitrogen-enrichment and control conditions. Journal of Experimental Marine Biology and Ecology, 153(1), 63–74. doi: 10.1016/s0022-0981(05)80006-1.CrossRefGoogle Scholar
- Veal, C. J., Holmes, G., Nunez, M., Hoegh-Guldberg, O., & Osborn, J. (2010). A comparative study of methods for surface area and three- dimensional shape measurement of coral skeletons. Limnology and Oceanography: Methods, 8, 241–253.Google Scholar