STATION SPECIES
INVENTORY (SSI)
Counts of stony coral species (Milleporina and Scleractinia) present
in each station provide data on stony coral species richness (S).
Two observers conduct simultaneous timed (15 min) inventories wihtin the
roughly 22 X 2 m stations and enter the data on underwater data
sheets. Each observer records all stony coral taxa and fire corals
and enumerates long-spined urchins (Diadema antillarum)
within the station boundaries. After recording the data, observers
compare (5 min) data underwater and confirm species recorded by only one
observer. Taxonomic differences are addressed. Data sheets
are verified aboard the vessel and forwarded to FMRI for data entry and
processing. This method facilitates data collection with broad
spatial coverage at optimal expenditure of time and labor.
Disease/Conditions
During the timed species count, if any species within a station
exhibits specific signs of either bleaching or disease (black band,
white complex and other), the appropriate code letter is entered for the
species on the data sheet.
Videography
All sampling through 1999 was conducted with a Sony CCD-VX3 with
full automatic settings and artificial lights (two 50 watt) at 40 cm
above the benthos. Beginning in 2000, the project upgraded to
digital video filming all sites with a Sony TRV 900. A convergent
laser light system indicates distance from the reef surface for
filming. The videographer films a clapperboard prior to beginning
each transect. A complete record of date and location of each film
segment is recorded. Filming is conducted at a constant speed of
about 4 m/minute yielding approximately 9,000 frames per transect.
Images for all transects are framegrabbed, written to and archived on
CD-ROM.
Image Analyses
Camera settings are optimized for quality of individual
frames. Although approximately 9,000 frames of videos are
collected for each transect, only 120 frames of imagery are digitized
for analysis. CRMP video analysis uses only captured still
imagery. Percent cover analysis is predicted on selecting video
frames that abut, with minimal overlap between images. At the
filming distance of 40cm above the reef surface, the field of view is
40cm square. About 60 abutting frames are required to capture a 20
meter transect in 40 cm segments. Therefore, of the original 120
digitized images, each trained analyst selects a subset of about 60
abutting frames. Image analysis is conducted using a custom
software application PointCount for coral reefs. When the analyst
opens each image, the software inserts ten random points over the
image. Selected benthic taxa (stony coral, octocoral, zoanthid,
sponge, seagrass, and macroalgae) and substrate are identified under
each point. The software has a "point and click" feature
that feeds the identification data into a backend spreadsheet.
After all images are analyzed, the data is converted to an ASCII file
for Quality Assurance and entry into the master ACCESS data set.
Statistical Analyses
In addition to the descriptive methods of organizing and summarizing
the data, hypothesis testing was performed to analyze the percent cover,
species richness, and disease/condition data. The decision to
reject or not to reject the null hypothesis that there is no significant
difference in the data for certain years is based on the minimum
detectable difference for different significance levels and
powers.
VIDEO DATA
To ensure at least 90% similarity between point assessments of the
observers, the Bray-Curtis dissimilarity measure was performed.
Each species was assigned a coefficient of dissimilarity based on the
interobserver data files. In addition to the three principal
investigators, the point assessments of three additional observers were
included. The list of species in a station was reviewed, and if
necessary, the rare (below 5% contribution) species were combined into a
category "other" until the sum of the coefficients of the
species present became less than 10%. |