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Halodule spring 210 0.00 - 5.00 0.52 ± 0.86
fall 210 0.00 - 5.00 0.63 ± 1.02 22482.5 0.710
Halophila sp. spring 210 0.00 - 2.50 0.02 ± 0.19
fall 210 0.00 - 3.00 0.10 ± 0.44 23141.5 0.056
Syringodium spring 210 0.00 - 5.00 1.36 ± 1.41
fall 210 0.00 - 5.00 1.37 ± 1.49 21996.5 0.965
Thalassia spring 210 0.00 - 5.00 0.68 ± 1.09
fall 210 0.00 - 5.00 0.59 ± 1.00 21999 0.965
Red Algae spring 210 0.00 - 3.98 0.83 ± 0.81
fall 210 0.00 - 3.00 0.21 ± 0.44 8781.5 0.000
Green Algae spring 210 0.00 - 1.50 0.10 ± 0.26
fall 210 0.00 - 2.67 0.21 ± 0.43 26497 0.000
Brown Algae spring 210 0.00 - 1.67 0.06 ± 0.22
fall 210 0.00 - 0.75 0.03 ± 0.11 21671 0.571
Calcareous Algae spring 210 0.00 - 2.83 0.22 ± 0.40
fall 210 0.00 - 2.50 0.38 ± 0.51 25708.5 0.002
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Figure 6A.
Figure 6B.
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Figure 6C.
Figures 6A-C. Mean seasonal seagrass species cover-densities; A) Syringodium, B)
Thalassia, C) Halodule, measured in the Port of Miami basin across the 2005-2011
sampling period with 95% CI error bars.
Figure 7. The annual mean average seagrass canopy height measured in the Port of
Miami basin across the 2005-2011 sampling period with 95% CI error bars.
38
Kruskal Wallis H-tests showed no significant variations in seagrass coverdensities between the seven sampling years, (p > 0.05); however, there was significant
annual effect on canopy height for Syringodium, Halodule, and the average canopy height
(Table 6). Thalassia canopy height tended to fluctuate over the years, F6 = 11.717, p =
0.069 (Figure 9). Since Halophila sp. canopy heights were measured at only 6% of the
sample sites and they are relatively short grasses, no further analysis was done for this
group. No major change was documented in seagrass cover-density (Figure 8), but
canopy height did show some significant variations between collection years (Figure 9
and Figure 10). Algae cover-densities showed an annual effect for calcareous (F6 =
17.925, p = 0.006) and brown algae groups (F6 = 27.992, p < 0.000), but not in red or
green algae (Table 6). Significant changes between years for brown algae can be
attributed to the low occurrence of species within the group (Figure 11).
Table 6. Kruskal Wallis test of differences in seagrass canopy height (cm) and vegetation
cover-densities (#/m2
) among years (2005-2011).
Vegetation Canopy Height and Cover-Density Measurements
among Collection Years (1-7) Kruskal-Wallis
Measure N range mean +/- SD F df Sig.
Canopy Height
Average Seagrass 383 1-101.2 29.96 ± 16.97 15.623 6 0.016
Halodule 196 4-44 16.59 ± 8.2 12.984 6 0.043
Halophila sp. 25 1-7 3.57 ± 2.12 3.285 6 0.772
Syringodium 275 7-101.2 38.55 ± 16.29 17.167 6 0.009
Thalassia 203 3-61.2 27.6 ± 11.3 11.717 6 0.069
Cover-Density
Halodule 420 0-5 0.58 ± 0.94 4.078 6 0.666
Halophila sp. 420 0-4.5 0.07 ± 0.41 7.216 6 0.301
Syringodium 420 0-5 1.37 ± 1.45 4.800 6 0.570
Thalassia 420 0-5 0.63 ± 1.05 9.841 6 0.131
Red Algae 420 0-3.98 0.52 ± 0.72 6.397 6 0.380
Green Algae 420 0-2.67 0.16 ± 0.36 9.802 6 0.133
Brown Algae 420 0-1.67 0.04 ± 0.17 27.992 6 0.000
Calcareous Algae 420 0-2.83 0.30 ± 0.46 17.925 6 0.006
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Figure 8. Mean annual seagrass species cover-densities (Syringodium, Thalassia,
Halodule, and Halophila sp.) measured in the Port of Miami basin across the 2005-2011
sampling period with 95% CI error bars.
Figure 9. Mean annual seagrass species canopy heights (Syringodium, Thalassia, and
Halodule) measured in the Port of Miami basin across the 2005-2011 sampling period
with 95% CI error bars.
40
Figure 10. The annual mean average seagrass canopy height measured in the Port of
Miami basin across the 2005-2011 sampling period with 95% CI error bars.
Figure 11. Mean annual algae group cover-densities (#/m2
) (red, calcareous, green, and
brown) measured in the Port of Miami basin across the 2005-2011 sampling period with
95% CI error bars.
41
The seagrass community varied across the POM basin (see Figure 3). Results
from the Kruskal Wallis H-tests showed spatial effects on the average seagrass canopy
height, all seagrass cover-densities, and on green and calcareous algae cover-densities, p
< 0.05 (Table 7). Red and brown algae cover-densities showed no significant variation
between the thirty sample sites within the POM basin at p > 0.05. Seagrass distribution
within the POM basin can be attributed to habitat differences due to location within the
basin (Table 15, Appendix 3). Sample sites located in the shallow, protected areas yielded
the tallest average canopy heights and the highest seagrass cover-densities. Locations
within channels had some of the shorter average canopy heights and the lowest seagrass
cover-densities (Table 8, Appendix 4 and Appendix 5).
Table 7. Kruskal Wallis test on average seagrass canopy height (cm) and vegetation
cover-densities (#/m2
) between collection sites (1-30) within the Port of Miami basin.
Vegetation Cover-Density Measurements between
Collection Sites (1-30) Kruskal-Wallis
Measure N range mean +/- SD F df Sig.
Canopy Height
Average Seagrass 383 1-101.2 29.96 ± 16.97 140.925 29 0.000
Cover-Density
Halodule 420 0-5 0.58 ± 0.94 71.182 29 0.000
Halophila sp. 420 0-4.5 0.07 ± 0.41 56.575 29 0.002
Syringodium 420 0-5 1.37 ± 1.45 144.831 29 0.000
Thalassia 420 0-5 0.63 ± 1.05 113.669 29 0.000
Red Algae 420 0-3.98 0.52 ± 0.72 23.898 29 0.734
Green Algae 420 0-2.67 0.16 ± 0.36 66.363 29 0.000
Brown Algae 420 0-1.67 0.04 ± 0.17 27.799 29 0.529