International Journal of Marine Science, 2016, Vol.6, No.21, 1-20
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Figure 5. The mean percent cover of benthic substrata at Birthday and Acer 24 reefs. Benthic substrate information was collected
during the summer (August) and winter (February) from 2011-2012 along 30m transects (n=6). Error bars represent 95% confidence
intervals.
3.2 Abiotic Characteristics
Principal component analysis (PCA) was applied to winter and summer subsets of the WQMP dataset to identify
factors that may be associated with stress during these periods and influence the coral communities of inshore and
offshore reefs. During winter months (January and February) 55% of the variation between sites was accounted
for by three components (Figure 8). Variation along principal component 1 (22.9%) was influenced by water
chemistry attributes. Total organic nitrogen (TON) ordinated sites negatively while the inorganic nutrients
ammonium and silicate ordinated sites positively along this axis. These three variables did not vary significantly
by region or location, however the marginal assurance in variation associated with silicate (ANOVA; p = 0.0652)
provides a potential difference between inshore and offshore reefs during winter months. Along principal
component 2 (19.2%), variation between sites was dictated by nitrate, soluble reactive phosphorus (SRP),
chlorophyll a (Chl a), and total organic carbon (TOC). Nitrate was significantly greater at eastern sites than
western sites and independent of location (ANOVA; p = 0.0062), while SRP, Chl a, and TOC remained
statistically similar across regions and locations. The variation along principal component 3 (13.1%) was dictated
by the variation in the physical characteristics turbidity and temperature. Turbidity was significantly greater at
western sites regardless of location (ANOVA; p = 0.0113), while SWT was not significantly different for either
region or location. Additionally, during winter months, greater variation in SWT was observed at inshore reefs
(18-29ºC) than on offshore reefs (20-25ºC).
Plotting each of these components against one another resulted in regional ordination (Figure 8). With the
exception of Rock Key, the western most sites West Washerwoman, Eastern Sambo, Cliff Green, Western Head
and Sand Key, oriented away from eastern sites: Looe Key, Sombrero Reef, Dustan Rocks and Western Turtle
Shoal. Variation in SWT, turbidity, and TOC appear responsible for the observed region dependent ordination
