Trends in Seagrass Abundance and
Density, and Water Quality near the
Ft DeSoto Circulation Project
Ft DeSoto 1942 and Future Bridge Location
Ft DeSotoBridge Location
Circulation Re-established at Bridge
Circulation Re-established at Bridge
Possible Benefits to Nearby Seagrass
Boca Ciega Bay Transects
General Description
• BCB-10 is located in South
Mullet Key Bayou.
• The transect extends
northeast 150m from the
mangrove shoreline towards
the boat channel.
• The depth ranged from
30cm-140cm.
• The sediment composition
was sandy mud.
• The seagrass bed was a
mixture of Halodule and
Thalassia.
• The condition of the
seagrass varied from fair to
good .
• Green marks - coverage
• Red marks – density and wq
Seagrass Species
175
Seagrass Species
175
170
169
160
151
150
140
130
120
110
102
100
90
80
78
75
70
60
Seagrass Species
170
169
160
151
150
140
130
120
110
102
100
90
80
78
75
Halophila
70
Syringodium
Thalassia
60
Halodule
50
Thalassia
Halophila
50
Syringodium
25
15
3
2
1
0
B r a u n -B la n q u e t R a n k
Halodule
25
15
3
2
1
0
B r a u n - B la n q u e t R a n k
Seagrass Coverage – Braun Blanquet
1999
5
4
3
2
1
0
2000
5
4
3
2
1
0
175
175
170
169
160
151
150
140
130
120
110
102
100
90
80
78
75
70
Seagrass Species
170
169
160
151
150
140
130
120
110
102
100
90
80
78
75
Halophila
70
Halophila
60
Thalassia
50
Syringodium
60
Syringodium
Thalassia
25
15
3
2
1
0
B r a u n -B la n q u e t R a n k
Halodule
50
Halodule
25
15
3
2
1
0
B r a u n - B la n q u e t R a n k
Seagrass Coverage – Braun Blanquet
2001
5
4
3
2
1
0
Seagrass Species
2002
5
4
3
2
1
0
175
175
170
169
160
151
150
140
130
120
110
102
100
90
80
78
75
70
Seagrass Species
170
169
160
151
150
140
130
120
110
102
100
90
80
78
75
Halophila
70
Halophila
60
Thalassia
50
Syringodium
60
Syringodium
Thalassia
25
15
3
2
1
0
B r a u n - B la n q u e t R a n k
Halodule
50
Halodule
25
15
3
2
1
0
B r a u n -B la n q u e t R a n k
Seagrass Coverage – Braun Blanquet
2003
5
4
3
2
1
0
Seagrass Species
2004
5
4
3
2
1
0
Seagrass Coverage – Braun Blanquet
B r a u n - B la n q u e t R a n k
Seagrass Species
Halodule
Syringodium
Thalassia
Halophila
2005
5
4
3
2
B r a u n - B la n q u e t R a n k
Seagrass Species
Halodule
Syringodium
Thalassia
Halophila
175
170
169
160
151
150
140
130
120
110
102
100
90
80
78
75
70
60
50
25
15
3
2
1
0
1
0
2006
Distance Along Transect (m)
175
170
169
160
151
150
140
130
120
110
102
100
90
80
78
75
70
60
50
25
15
3
2
1
0
5
4
3
2
1
0
Canopy Height
BCB-10 Canopy Height
60
Halodule
Canopy Height (cm)
50
Thalassia
40
30
20
10
0
1996
1998
2000
2002
Year
2004
2006
2008
Shoot Density, Mid-bed and Edge of Bed
BCB-10 Shoot Density
2000
Halodule
1800
Thalassia
Mean Density per m2
1600
1400
1200
1000
800
600
400
200
0
1996
1998
2000
2002
Year
2004
2006
2008
Possible Water Quality Benefits
Chlorophyll-a Trend at BCB-10 Transect
Average Chlorophyll-a Along Transect BCB 10
Chlorophyll-a Pg/L
30
25
20
15
10
5
0
10/28/95
7/24/98
4/19/01
1/14/04
Date
10/10/06
7/6/09
Mullet Key Bayou Chlorophyll-a Trend
Chlorophyll-a in Mullet Bayou North of Transect BCB 10
Chlorophyll-a mg/L
30
25
20
15
10
5
0
10/28/95
7/24/98
4/19/01
Date
1/14/04
10/10/06
7/6/09
Summary
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BCB-10 varied in species composition and abundance while maintaining a stable
seagrass bed.
Data indicate that the edge of bed is consistent at 150m throughout the monitoring
program.
In 1998 the prominent seagrass was Halodule.
In 1999-2000, Thalassia increased in abundance becoming the prominent seagrass.
By 2001, Halodule and Thalassia were both prominent species along the transect.
The abundance of both seagrasses decreased in 2002, and then increased slightly
through 2003-2004.
The abundance of the Halodule increased drastically in 2005-2006.
In November 2004, the Fort De Soto Recirculation Project restored the connection
between the east and west side of the causeway. Improved circulation may have
contributed to the increase in seagrass abundance along the transect.
The epibiont density was light to heavy consisting of attached algae, polycheates,
and barnacles.
The canopy height ranged from 15cm-35cm with Thalassia consistently higher than
the Halodule.
Shoot density for Thalassia ranged from 25-200 shoots (per m2) with a decreasing
density trend.
Shoot density for Halodule ranged from 25-1600 shoots (per m2) with a doubling in
density from 2004-2006.