The Government of Guam's Long-term Coral Reef Monitoring Program, coordinated through the Guam Coastal Management Program until October 2013 and now coordinated through the University of Guam Marine Laboratory, involves the collection of data for a suite of coral reef ecosystem health parameters at several high priority reef sites around the island of Guam. Various coral reef surveys are carried out on an annual or biennial basis along the seaward slope between 7 and 15 m depth in the Tumon Bay Marine Preserve, East Agana Bay, the Piti Bomb Holes Marine Preserve, the Achang Reef Flat Marine Preserve, and the eastern side of the Cocos Barrier Reef (Cocos-East). Data collection is also carried out on a less frequent basis along the seaward slope (5-8 m) in Fouha Bay and along the reef margin (1-2 m) and slope (2-15 m) of Western Shoals, in Apra Harbor. The surveys, which are conducted by University of Guam Marine Lab and NOAA PIRO biologists at numerous permanent and non-permanent sampling stations within each site, currently include benthic photo transects, quadrat surveys for coral colony size and condition, stationary point count fish surveys, macroinvertebrate belt transects, and chain-length rugosity surveys. The data products described herein document the status and trends for benthic cover and composition at the monitoring sites mentioned above. Benthic cover and coral and algal generic diversity are currently assessed using digital photo transects. The still images provide a permanent record of the transects and are quantitatively analyzed using Coral Point Count with Excel extensions (CPCe; Kohler and Gill, 2006) point sampling software to obtain benthic cover estimates. Power analyses support the methodological approach, whereby statistically sound benthic cover estimates can be successfully derived. Benthic percent cover is calculated at the sampling station level (= one 25 m transect) for data derived from benthic images. Benthic percent cover has been derived from images collected at sites during surveys from 2010 through 2012 and quality control has been completed for these data. Additionally, benthic cover data has also been derived from images collected at sites during surveys in 2014, but quality control has not yet been completed for these , and analysis of images collected during 2015 surveys is currently underway. Surveys were not carried out in 2013.
The benthic cover data are collected as part of the Guam Long-term Coral Reef Monitoring Program, which documents a number of important parameters related to ecosystem health. These parameters are grouped into three categories: water quality, benthic habitat, and associated biological communities; the benthic cover data provide information about the benthic habitats at specific sites around Guam. Many of these parameters are indicators of stressors, and significant changes in these parameters will likely raise concern and possibly trigger management actions. Data collected for these indicators provide important information about the resilience of high priority reef areas around Guam. Monitoring these parameters allows resource managers to evaluate the effectiveness of specific management strategies, and inform the development of new management actions.
Benthic cover data have been generated from benthic photos captured since 2010 (with the noted exceptions below) in: Tumon Bay in 2010 (10 permanent and 10 non-permanent stations), 2012 (12 permanent and 9 non-permanent stations), 2014 (12 permanent and 4 non-permanent stations), and 2015 (12 permanent and 10 non-permanent stations). East Agana Bay in 2010 (10 permanent and 10 non-permanent stations), 2012 (10 permanent stations), and 2014 (10 permanent stations). Western Shoals in 2011 (11 permanent and 12 non-permanent stations); and Piti in 2012 (10 permanent and 10 non-permanent stations) and 2014 (10 permanent and 2 non-permanent stations). Surveys were not conducted in 2013. Benthic images collected during surveys in 2014 have been analyzed, but quality control is still on-going for these data, and images collected during 2015 surveys are currently being analyzed.
Ground Condition
Please cite the University of Guam Marine Laboratory when using data collected after October 2013 and the Guam Coastal Management Program when using data collected prior to October 2013 (Guam Coastal Management Program, Bureau of Statistics and Plans, Government of Guam)
Marine Laboratory - University of Guam
e-mail preferred
University of Guam Marine Laboratory, NOAA Pacific Islands Regional Office, and Guam Coastal Management Program.
Data sets derived from image analysis are highly reliable within the stipulated taxonomic context. Photo analysts undergo a training period during which they analyze images from several stations in the presence of the monitoring program coordinator. The total number of images analyzed during the training period varies according to the prior experience level of the trainee.
Quality control is carried out by the monitoring program coordinator or the full-time technical support staff and involves reviewing all images for at least 25% of the total number of sampling stations for each monitoring site. If a significant number of misidentifications are encountered the original photo analyst is asked to undergo additional training and then re-analyze the images; alternatively, the monitoring program coordinator or technical support staff will re-analyze all the images for the site(s) in question. The benthic cover data derived from photo transects collected at the Tumon and East Agana sites in 2010 and the Western Shoals site in 2011 were explored in multivariate space using the statistical software package PRIMER and the PERMANOVA add-on. The exploration of the benthic cover data in multivariate space allowed for the visualization of the spatial structure of the data and the exploration of the possible influence of environmental factors on this spatial structure. This preliminary data exploration also assisted in determining if the benthic community remained relatively homogeneous across the monitoring sites or strata as original delineated, and whether or not the site boundaries should be adjusted, subdivided into two or more strata, or if certain sampling stations should be abandoned. Univariate power analyses using the R software program were carried out separately on total coral cover for sampling stations from different strata or other sampling station groupings. Multivariate power analyses were carried out in order to examine the ability of the sampling regime to adequately capture the overall character of the benthic communities.
The data set derived from the image analysis is only as good as the images themselves; poor images with low contrast, inappropriate white balance, or out of focus may have to be discarded. Therefore, percent cover estimates for some sites may derive from differing number of points between sites. Although the analysis process is statistically robust to allow for differing n (points) between sites the users should be aware of this limitation. Between 2010 and 2012, benthic photos were captured every 0.5 meters along either side of the transect tape. Overlapping did not appear to be an issue for most of the images collected between 2010 and 2012; however, significant overlapping of images for the Piti site in 2012 was observed and was addressed by analyzing only every other image. In order to avoid overlapping images, photos were taken every 1 meter beginning in 2014. Image quality has improved over time with the availability of digital cameras capable of capturing higher resolution images and with more advanced functionality. A Canon PowerShot A720 IS digital camera (8 Megapixel sensor; 3264x2448 pixel image resolution) was used between 2010 and 2011, a Nikon Coolpix 36300 (16 Megapixel sensor; 4608x3456 pixel image resolution) was used for most sampling stations in 2012; and a Canon PowerShot ELPH 300 HS (12 Megapixel sensor; 4000x3000 pixel image resolution) was used for a limited number of sampling stations in 2012. The lower resolution PowerShot A720 was again used in 2014 due to the loss of the newer, higher resolution Nikon Coolpix and PowerShot ELPH cameras. Beginning in 2015 a Sony Cybershot RX-100 (20 Megapixel sensor; 5472x3648 pixel image resolution) has been used. The higher image resolution achieved by the more recent cameras allows for greater taxonomic resolution during image analysis, and likely allows for greater accuracy in the identification of benthic features, particularly for features, such as turf algae, crustose coralline algae, and small corals, that can be difficult to discern at lower resolutions. For photos analyzed since 2014, a total of 16 points (random stratified using a 4 x 4 grid) are used to analyze each image in CPCe; prior to 2014 a total of 25 points (random stratified using a 5 x 5 grid) were used to analyze each image in CPCe. Due to time constraints, for most sampling stations only images collected along the left side of the transect were analyzed and underwent quality control. Benthic percent cover has been derived from imagery collected during surveys in 2010 through 2014. Survey imagery collected in 2014 have been analyzed, but quality control is on-going, and imagery collected in 2015 are currently being analyzed (as of the publication date of this record).
At the start of a benthic survey, one of the divers begins the photo transect and captures non-overlapping digital photos every 0.5 meters along the left side of a 25-meter transect and then returns along the right side of the transect (for a total of 50 images). Currently, a 20 megapixel Sony Cybershot RX-100 digital point and shoot camera mounted on a PVC frame is used to obtain the images. The camera is positioned on the PVC frame such that a 50 centimeter by 50 centimeter quadrat at the base of the frame is visible within each image. As mentioned above, different, lower resolution cameras were used prior to 2015. Percent cover is estimated from quantitative analysis of the benthic still images using Coral Point Count with Excel extensions (CPCe; Kohler and Gill, 2006), a software application developed by Nova Southeastern University’s National Coral Reef Institute. Prior to analysis using CPCe, images are catalogued, color-corrected and renamed using standard naming conventions. A copy of the original, uncorrected image is preserved. Images are opened within the CPCe program and the area for image analysis is set based on the extent of the PVC frame. Initially, each frame was analyzed using 25 random points stratified with a 5 x 5 grid. After conducting a series of tests using various combinations of images and points in an effort to maximize accuracy while minimizing effort, is was determined that 16 random points stratified using a 4 x 4 grid would provide the desired accuracy and efficiency. The use of 16 points per frame began with the 2014 images. The benthic feature falling directly underneath each point is identified to the lowest taxonomic level possible. The taxonomic level can be divided into four tiers: Tier 1 (function group-broad-e.g., hard coral, soft coral, macroalgae, turf algae, etc.); Tier 2 (functional group-specific-e.g., Hard Coral = massive, branching, foliose, encrusting, etc.; Macroalgae = fleshy erect macroalgae, adherent macroalgae); Tier 3 (genus-e.g., Hard Coral = Acropora, Montipora, Pocillopora, etc.; Macroalgae = Padina, Dictyota, Dictosphaeria, etc.); and Tier 4 (species and species-groups- Hard Coral = Porites rus, massive Porites spp., etc.). Hard corals are identified to genus or species for the vast majority of points and only on rare occasion are they identified at the Tier 2 or Tier 1 level. A "note" is added to points that fall on recently dead or diseased corals; the note indicates the likely cause of the mortality or the name of the disease. However, a note is only provided if the point falls directly on an area of recently dead tissue or disease activity. If a point falls precisely on the border between two benthic categories (e.g., coral-algae), the benthic category occupying the greatest area within symbol (circle wrapping the cross-hairs) is classified. Additionally, if the two benthic categories occupy equal space within the symbol, the benthos falling on the top left quadrant within the point symbol is classified. The category Shadow is used when the point falls on an area that is dark and the nature of the benthos cannot be assessed due to diminished light. The categories Tape and Frame are used when the point falls on a transect line/tape measure or photo quadrat frame. Percent cover is calculated at the sampling station level.
While every effort has been made to ensure that these data are accurate and reliable within the limits of the current state of the art, the University of Guam Marine Laboratory and the Guam Coastal Management Program cannot assume liability for any damages caused by errors or omissions in the data, nor as a result of the failure of the data to function on a particular system. The University of Guam Marine Laboratory and the Guam Coastal Management Program make no warranty, expressed or implied, nor does the fact of distribution constitute such a warranty.
Contact the Monitoring Program Coordinator at the University of Guam Marine Laboratory for more information. Data are available in xls (Microsoft Excel worksheet) or csv (comma-separated values) format
