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for conventional and environmental variables. D. Models evaluating seagrass canopy height
adjusted for conventional, environmental and habitat (algae) variables. *Significance = p <
0.05.
Model Set 5A-D Model 5-A Model 5-B
2005-2011 N  SE p N  SE p
Average
Canopy Height
Year 420 1.527 0.425 <0.001 *
Season 2.641 1.704 0.122
Water Depth 418 -0.054 0.012 <0.001 *
Sediment Depth 0.033 0.010 0.002 *
Turbidity -1.619 0.508 0.002 *
Surface
Temperature 2.365 1.396 0.091
Bottom
Temperature -2.380 1.395 0.089
Surface Salinity 0.489 0.412 0.236
Bottom Salinity -1.847 0.581 0.002 *
Model 5-C Model 5-D
Year 418 1.497 0.477 0.002 * Year 418 1.184 0.460 0.010 *
Season -0.153 3.270 0.963 Season 1.275 3.125 0.683
Water Depth -0.051 0.012 <0.001 * Water Depth -0.044 0.012 <0.001 *
Sediment Depth 0.039 0.010 <0.001 * Sediment Depth 0.031 0.010 0.002 *
Turbidity -0.723 0.578 0.212 Turbidity -0.442 0.554 0.426
Surface
Temperature 2.336 1.415 0.100
Surface
Temperature 1.849 1.349 0.171
Bottom
Temperature -2.442 1.554 0.117
Bottom
Temperature -0.873 1.500 0.561
Surface Salinity 0.383 0.409 0.350 Surface Salinity 0.460 0.389 0.238
Bottom Salinity -1.862 0.609 0.002 * Bottom Salinity -1.840 0.578 0.002 *
Red Algae 7.153 1.185 <0.001 *
Green Algae -0.806 2.363 0.733
Brown Algae 6.842 4.641 0.141
Calcareous Algae -5.354 1.811 0.003 *
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4.0 Discussion
This study set out to determine whether there were any effects of natural and
anthropological change evident in the Port of Miami basin seagrass habitat. Some trends
and patterns were detected in the basin. South Florida experiences seasonal and annual
weather variation (Sutula et al. 2003) and the POM basin is impacted by shipping and a
large coastal human population (Caccia and Boyer 2005; CDMP 2011; FDH 2012). The
seagrass habitats in the POM basin are susceptible to many anthropogenic disturbances
due to the continued development in the area. The distribution and growth of submerged
aquatic vegetation (i.e. seagrass and algae) within an estuarine environment are
controlled by a combination of factors. Decreases in seagrass populations have been
attributed to environmental change (e.g. changes in water clarity, light attenuation and
salinity) and anthropogenic-induced damage to the habitat particularly the introduction of
pollutants, coastal development, dredge and fill activities, and motor vessel damage
(Littler et al. 1989; Sargent et al. 1995; Hall et al. 1999).
4.1 Habitat Patterns of Benthic Vegetation
The Port of Miami basin, within the North Biscayne Bay region, is designated as a
tall-canopy mixed seagrass habitat within South Florida (Robblee and Browder 2012) and
is dominated by three principal species of seagrass found in South Florida (S. filiforme, T.
testudinum, and H. wrightii) and several of the algae characteristic of South Florida
seagrass beds. Over half the sample sites within the basin contained a mixture of all three
of these seagrass species along with associated algae (Table 3). Algae are important
secondary habitat builders within the POM basin. From the four algae types, red and
calcareous-green algae were most abundant and green and brown algae were the least
abundant groups observed (Figure 11).
Spatial patterns of the three principle seagrasses and associated algae observed in
the basin are most likely dictated by habitat conditions (Figure 3). The average canopy
height and the seagrass and algae coverage-densities were generally greater in the
shallower and protected sites versus the deeper, busy channel sites. Among the FIAN
seven collection years (2005-2011), the three main seagrasses species showed no
significant variation in their cover-density (Figure 8, Appendix 1). In contrast, the
average seagrass canopy height did experience larger changes across the sample years
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(Figure 10, Appendix 2). This could be due to slightly greater cover-densities of the
taller grass species like Syringodium and Thalassia (Figure 1) during certain years.
Calcareous and brown algae cover-density did exhibit variation among the study years
(Figure 11). Brown algae variation can most likely be attributed to the low occurrence of
these species within the basin. Red and green algae, both abundant, did not exhibit
significant change in cover-density across the collections (Figure 11).
Seasonal differences in seagrass and algae distribution were expected in South
Florida coastal waters (Phillips 1960; Moffler and Durako 1982; Dineen 2001; Robblee
and Browder 2012). The three principle seagrasses in this study displayed no significant
change in cover-density or occurrence between seasons (spring and fall) (see Table 5).
However, Syringodium and Halodule canopy heights as well as the overall average
seagrass canopy height did exhibit seasonality within the POM basin (Table 5). Although
not significant, seagrass occurrence was just marginally higher in the fall collections.
Significant seasonality was observed in some of the algae groups. Generally, densities of
red and brown algae are higher in the spring (dry season) than in the fall (wet season) and
the cover-densities of green and calcareous algae are higher in the fall than in the spring
in the POM basin (Table 5). Red algae showed the greatest variation between sampling
seasons. The seasonal differences seen between the algae groups may be explained by the
greater occurrence of algae found in the spring collections (Appendix 4).
Most seagrass species exhibit seasonality in both growth and biomass. The three
major seagrasses monitored are all dioecious plants (Moffler and Durako 1987) and can
grow by sexual and asexual reproduction. Because of the seasonal nature of flowering in
seagrasses, water temperature is suggested to play an influential role in controlling floral
development as well as subsequent flower density and seed production (Phillips 1960;
Moffler and Durako 1982). In Florida, flowering in S. filiforme and H. wrightii is rare, so
Phillips (1960) speculated that most production occurs through vegetative growth,
rhizome elongation and new branch growth. New shoot production is reported to be
abundant throughout the year for S. filiforme and H. wrightii, except in the coldest winter
months (Phillips 1960). In Florida, T. testudinum undergoes seasonal fluctuations in