Ecological monitoring programs depend on the robust estimation of descriptive parameters. Percent cover, gleaned from transects sampled with video imagery, is a popular benthic ecology descriptor often estimated using point counting, an image-based method for identifying substrate types beneath random points. We tested the hypothesis that the number of points needed to robustly estimate benthic cover in video imagery transects depends on cover itself, predicting that lower cover will require more points/frame to be accurately estimated. While this point may seem obvious to the statistically inclined, the justification of point density has been largely ignored in the literature. We examined the statistical behavior of point count estimates using computer-simulated 20？m-long transects patterned after data from a Bahamian reef. The minimum number of points necessary to insure accurate percent cover estimation, the Optimal Point Count (OPC), is a function of mean percent cover and spatial heterogeneity of the benthic community. More points are required to characterize reefs with lower cover and more homogeneously distributed coral colonies. These results show that careful consideration must be given to sampling design and data analysis prior to attempting to estimate benthic cover, especially in the context of long-term monitoring of degrading coral reef ecosystems. 1. Introduction A common problem while working in ecological characterization and monitoring programs is how to effectively test and optimize methods and experimental designs. Live percent cover is a widely used ecological descriptor in marine conservation biology and large-scale monitoring projects (e.g., [1–4]) and has been a key parameter in the quantification of coral reef degradation over large spatial scales (e.g., [5–7]). Using point count to analyze video transects and photoquadrats is an efficient way to estimate percent cover and monitor large areas, because it allows copious amounts of data to be collected while minimizing underwater time, and provides a permanent record of the benthic community [8, 9]. Substrate types underlying randomly assigned points are identified. Percent cover is then estimated as a ratio of the number of points overlaying a substrate type to the total number of points. The number of points to be used per unit area (point density and the unit area being an image frame from a video transect) is crucial to obtaining a robust estimate of percent cover, and initial statistical tests should be performed to establish the point density that will provide adequate
References
[1]
H. Sweatman, “Long-term monitoring of the Great Barrier Reef,” Status Report 2, Australian Institute of Marine Science, Townsville, Australia, 1997.
[2]
J. Porter, V. Kosmynin, K. Patterson, et al., “Detection of coral reef change by the Florida keys coral reef monitoring project,” in The Everglades, Florida Bay, and Coral Reefs of the Florida Keys: An Ecosystem Sourcebook, J. Porter and K. Porter, Eds., pp. 749–769, CRC Press, Boca Raton, Fla, USA, 2002.
[3]
J. Lang, “Status of Coral Reefs in the western Atlantic: results of initial surveys, Atlantic and Gulf Rapid Assessment (AGGRA) Program,” Tech. Rep. 496, Atoll Research Bulletin, 2003.
[4]
E. Brown, E. Cox, P. Jokiel et al., “Development of benthic sampling methods for the Coral Reef Assessment and Monitoring Program (CRAMP) in Hawai'i,” Pacific Science, vol. 58, no. 2, pp. 145–158, 2004.
[5]
T. A. Gardner, I. M. C？té, J. A. Gill, A. Grant, and A. R. Watkinson, “Long-term region-wide declines in Caribbean corals,” Science, vol. 301, no. 5635, pp. 958–960, 2003.
[6]
J. F. Bruno and E. R. Selig, “Regional decline of coral cover in the Indo-Pacific: timing, extent, and subregional comparisons,” PLoS ONE, vol. 2, no. 8, article e711, 2007.
[7]
C. R. Wilkinson, Status of Coral Reef of the World: 2004, Global Coral Reef Monitoring Network and Australian Institute of Marine Science, Townsville, Australia, 2004.
[8]
R. B. Aronson, P. J. Edmunds, W. F. Precht, D. W. Swanson, and D. R. Levitan, “Large-scale, long-term monitoring of Caribbean coral reefs: simple, quick, inexpensive techniques,” Atoll Research Bulletin, vol. 415–425, no. 421, pp. 1–19, 1994.
[9]
L. B. Preskitt, P. S. Vroom, and C. M. Smith, “A rapid ecological assessment (REA) quantitative survey method for benthic algae using photoquadrats with scuba,” Pacific Science, vol. 58, no. 2, pp. 201–209, 2004.
[10]
B. Riegl, R. P. Moyer, B. K. Walker, K. Kohler, D. Gilliam, and R. E. Dodge, “A tale of germs, storms, and bombs: geomorphology and coral assemblage structure at Vieques (Puerto Rico) compared to St. Croix (U.S. Virgin Islands),” Journal of Coastal Research, vol. 24, no. 4, pp. 1008–1021, 2008.
[11]
P. A. Kramer, “Synthesis of coral reef health indicators for the western Atlantic: results of the AGRRA program (1997–2000),” Atoll Research Bulletin, no. 496, pp. 1–58, 2003.
[12]
E. Pante, Temporal variation in a Bahamian patch reef community: the decline of Rainbow Gardens Reef, M.S. thesis, College of Charleston, Charleston, SC, USA, 2005.
[13]
P. Dumas, A. Bertaud, C. Peignon, M. Léopold, and D. Pelletier, “A “quick and clean” photographic method for the description of coral reef habitats,” Journal of Experimental Marine Biology and Ecology, vol. 368, no. 2, pp. 161–168, 2009.
[14]
J. Guinan, A. J. Grehan, M. F. J. Dolan, and C. Brown, “Quantifying relationships between video observations of cold-water coral cover and seafloor features in Rockall Trough, west of Ireland,” Marine Ecology Progress Series, vol. 375, pp. 125–138, 2009.
[15]
J. Hill and C. R. Wilkinson, Methods for Ecological Monitoring of Coral Reefs : A Resource for Managers, Australian Institute of Marine Science, Townsville, Queensland, Australia, 2004.
[16]
K. E. Kohler and S. M. Gill, “Coral point count with excel extensions (CPCe): a visual basic program for the determination of coral and substrate coverage using random point count methodology,” Computers and Geosciences, vol. 32, no. 9, pp. 1259–1269, 2006.
[17]
R Development Core Team, “R: a language and environment for statistical computing,” R Foundation for Statistical Computing, Vienna, Austria, ISBN 3-900051-07-0, 2011, http://www.R-project.org/.
[18]
A. King, Digital analysis of a patch reef community: Rainbow Gardens Reef, Lee Stocking Island, Exuma Cays, Bahamas, M.S. thesis, College of Charleston, Charleston, SC, USA, 1995.
[19]
E. Pante, A. King, and P. Dustan, “Short-term decline of a Bahamian patch reef coral community: Rainbow Gardens Reef 1991–2004,” Hydrobiologia, vol. 596, no. 1, pp. 121–132, 2008.
[20]
B. S. Rowlingson and P. J. Diggle, “Splancs: spatial point pattern analysis code in S-plus,” Computers and Geosciences, vol. 19, no. 5, pp. 627–655, 1993.
[21]
R. Sokal and F. Rohlf, Biometry, W. H. Freeman and Compagny, New York, NY, USA, 3rd edition, 1995.
[22]
T. J. Done, “Phase shifts in coral reef communities and their ecological significance,” Hydrobiologia, vol. 247, no. 1–3, pp. 121–132, 1992.
[23]
T. P. Hughes, “Catastrophes, phase shifts, and large-scale degradation of a Caribbean coral reef,” Science, vol. 265, no. 5178, pp. 1547–1551, 1994.
[24]
R. B. Aronson, W. F. Precht, T. J. T. Murdoch, and M. L. Robbart, “Long-term persistence of coral assemblages on the Flower Garden Banks, Northwestern Gulf of Mexico: implications for science and management,” Gulf of Mexico Science, vol. 23, no. 1, pp. 84–94, 2005.
[25]
M. Risk and A. Risk, “Reef surveys as an aid in management,” in Proceedings of the 8th International Coral Reef Symposium, H. A. Lessios and I. G. Macintyre, Eds., vol. 2, pp. 1471–1474, Smithsonian Tropical Research Institute, Panama, 1997.
[26]
R. B. Aronson and W. F. Precht, “Conservation, precaution, and Caribbean reefs,” Coral Reefs, vol. 25, no. 3, pp. 441–450, 2006.
[27]
P. S. Vroom, K. N. Page, K. A. Peyton, and J. K. Kukea-Shultz, “Spatial heterogeneity of benthic community assemblages with an emphasis on reef algae at French Frigate Shoals, Northwestern Hawai'ian Islands,” Coral Reefs, vol. 24, no. 4, pp. 574–581, 2005.
[28]
E. Pante, M. Adjeroud, P. Dustan, L. Penin, and M. Schrimm, “Spatial patterns of benthic invertebrate assemblages within atoll lagoons: importance of habitat heterogeneity and considerations for marine protected area design in French Polynesia,” Aquatic Living Resources, vol. 19, no. 3, pp. 207–217, 2006.
[29]
L. Alvarez-Filip, N. K. Dulvy, J. A. Gill, I. M. C？té, and A. R. Watkinson, “Flattening of Caribbean coral reefs: region-wide declines in architectural complexity,” Proceedings of the Royal Society B, vol. 276, no. 1669, pp. 3019–3025, 2009.
