Recent Changes in Macroalgal Distribution and Abundance in Florida Bay:
An Initial Analysis of FHAP Macroalgal Data
J. Brooke Landry1, Michael, J Durako1, Manuel Merello2, and Margaret O. Hall2
1
The University of North Carolina at Wilmington
Center for Marine Science
Wilmington, NC 28409
2
Florida Marine Research Institute
Florida Fish and Wildlife Commission
St. Petersburg, FL 33701
The Fisheries Habitat Assessment Program (FHAP), initiated in 1995, has
produced an extensive database of distribution and abundance information
regarding both seagrasses and macroalgae. To date, a thorough analysis of the
macroalgal data has not been completed. The objective here is to provide an initial
assessment of the abundance and distribution of three macroalgal species found in
the Florida Bay.
Sampling for FHAP is conducted biannually, during spring and fall. Ten basins,
chosen to represent a range of conditions and gradients in Florida Bay, have been
partitioned into approximately 30-35 tesselated hexagonal grid cells. During each
sample period, sampling station locations are randomly chosen from within each
cell, for a total of about 330 stations. This type of sampling design results in
systematic random sampling, it scales the sampling effort to the size of the basin,
and it is well-suited for interpolation (i.e., kriging) and mapping of the data.
At each station, both seagrass and macroalgal cover is visually quantified within
four, haphazardly-located 0.25m2 quadrats using a modified Braun-Blanquet
frequency/abundance scale, in which a value of .1 is solitary, .5 is sparse, 1 is
numerous, but <5% cover, 2 is from 5-25% cover, 3 is 25-50% cover, 4 is 50-75%
cover, and 5 is 75-100% cover. Seagrass and macroalgal distribution and
abundance are estimated using a contouring and 3D mapping program (Surfer 8).
The geostatystical gridding method of kriging is used to express the trends in the
Braun-Blanquet data. A linear variogram model is used to calculate all grid node
values. Planar areas for each cover class are calculated by the area differences
among cut (positive) and fill (negative) volumes of the kriged grids using the grid
volume command in Surfer. A dimension-less estimate of the total abundance of a
species within a basin is then obtained by multiplying the planar area for each
cover class by the cover class midpoint and adding the resulting values together.
A representative from each of the three major Divisions of algae has been chosen
for this initial analysis. The abundance and distribution of Batophora
(Chlorophyta), Sargassum (Phaeophyta), and the drift reds (primarily Laurencia)
(Rhodophyta), in the spring of 1995, 1999, and 2002, have been computed using
the methods described above.
In 1995, Batophora was observed in seven of the ten basins, in abundance ranging
from sparse to numerous. In Johnson Key, Rabbit Key and Rankin Lake, the more
north-western basins, no Batophora was found. Sargassum was observed in
seven of the ten basins, ranging in abundance from sparse to numerous. No
Sargassum was found in Johnson Key, Rabbit Key and Twin Key. Drift reds were
found in abundances from sparse to numerous in all but one basin, Rabbit Key
Basin.
In 1999, Batophora increased in both abundance and distribution, occurring in
nine of the ten basins, Johnson Key being the only basin in which this genus was
not found. Sargassum, however, decreased in abundance and distribution,
occurring in sparse abundance in three of the ten basins. Eagle Key, Calusa Key,
and Rankin Lake were the only basins in which this genus was observed. The drift
reds were more widely distributed, occurring in all ten basins, and showed a
significant shift in abundance to the more western basins, although the total
relative abundance was slightly less than in 1995
In 2002, Batophora exhibited a great increase in distribution, occurring in all ten
basins in a greater abundance, though still having the least cover in Rankin Lake.
Sargassum increased in distribution again, occurring in six of the ten basins. It
was not observed in Blackwater Sound, Madeira Bay, Twin Key or Rabbit Key
basins. The drift reds increased in abundance from 1999 to 2002 and maintained
distribution throughout the ten FHAP basins.
Figure 1 shows a high variability of both abundance and distribution for each
algae for each year in each individual basin, from Blackwater Sound, the easternmost basin sampled, to Johnson Key Basin, the western-most basin sampled.
Figure 2 clearly shows, at the Bay scale, that Batophora increased from 1995 to
1999 and from 1999 to 2002. Sargassum initially decreased from 1995 to 1999
but then increased to almost its original abundance in 2002. Drift Reds showed
little change from 1995 to 1999 but increased from 1999 to 2002. The overall
trend observed from both figures is a high variability in abundance at the basin
scale but a general increase in macroalgal abundance at the Bay scale since 1995.
Financial support was provided by the United States Geological Survey
(#98HQAG2186) and Everglades National Park.
Figure 1. Relative total abundances (dimension-less, see methods) of Batophora,
Sargassum, and the Drift Reds in each FHAP basin.
Blackw ater
Whipray Key
50
40
30
20
10
0
50
40
30
20
10
0
Bat
Sar
Bat
DR
Eagle Key
Sar
DR
Rankin Lake
50
40
30
20
10
0
50
40
30
20
10
0
Bat
Sar
Bat
DR
Calusa Key
Sar
DR
Tw in Key
50
40
30
20
10
0
50
40
30
20
10
0
Bat
Sar
Bat
DR
Sar
DR
Rabbit Key
Crane Key
50
40
30
20
10
0
50
40
30
20
10
0
Bat
Sar
Bat
DR
Sar
DR
Johnson Key
Madiera Bay
50
40
30
20
10
0
50
40
30
20
10
0
Bat
Sar
DR
Bat
Sar
DR
Figure 2. Relative total abundances of Batophora (Bat), Sargassum (Sar), and the
Drift Reds (DR) in ten Florida Bay basins during spring 1995, 1999, and 2002.
FHAP Basins Total
200
150
1995
100
1999
50
2002
0
Bat
Sar
DR