MACROALGAE OF CHARLOTTE HARBOR
Betty Staugler, Florida Sea Grant Marine Agent - Charlotte County UF/IFAS Extension
Macroalgae are large species of algae often referred to as
seaweeds. When not attached to the sediments they are
commonly called drift algae.
Macroalgae are different from
seagrasses, and other common
plants such as grasses, scrubs and
trees, that have vascular tissues to
transport water and nutrients
(much like veins and arteries
transport blood in humans)
throughout the plant. Vascular
plants also have true roots, stems
and leaves.
Macroalgae do not have these
vascular tissues, instead water and
nutrients are absorbed directly
across their surfaces.
Macroalgae, like all plants
photosynthesize. That is they
convert sunlight energy into usable
chemical energy, specifically
carbohydrates such as sugars. The
carbohydrates are stored in or
used by the plant and then
transferred to other organisms as
the plant is consumed.
wavelengths of sunlight penetrate further down in the water
and thus make it possible for red algae to carry out photosynthesis in deep or dark waters. Common red species found in
the Harbor include Gracilaria, Hypnea and Acanthophora. All
of these are similar in appearance.
Gracilaria—FSG Image
Acanthophora—FSG Image
There are three types of
macroalgae, which are distinguished from one another by the
different types of photosynthetic
pigments found in their cells;
green algae (Chlorophyta), brown
algae (Phaeophyta), and red algae
(Rhodophyta).
The most commonly seen
macroalgae In Charlotte Harbor
Ulva—FSG Image
are red algae. Worldwide red
algae comprise about 6,000
species and make up the second largest group of algae. Red
algae get their red color from pigments called phycoerythrins
that absorb blue light and reflect red light. The blue
EAS-050513-005
Less common in the Harbor, but
most abundant worldwide are
green algae. Approximately 7,000
species are known worldwide. In
Charlotte Harbor the green algae
typically seen include Ulva and
Caulerpa. Ulva also known as sea
lettuce looks much like pieces of
saran wrap. Caulerpa is an
attached algae that is either
feathery or strap like and looks like
it could be a seagrass.
Brown algae are far less abundant
in the Harbor. The species I see
most frequently is Sargassum.
Most Sargassum is planktonic
meaning they drift in the water
column but the one I frequently
see in the Harbor is attached.
Although little Sargassum is seen in
the upper Harbor, at times it is
locally abundant near the mouth of
the Caloosahatchee River.
Sargassum have small berry like
bladders that are gas filled and
help with buoyancy.
In many coastal waters macroalgae
abundance has increased in recent
decades due to nutrient
enrichment. Periodically, I receive
phone calls and emails from
boaters and anglers who are
concerned that macroalgae
abundance is on the rise in
Charlotte Harbor too. There are
certainly seasonal patterns that give rise to more macroalgae.
Whether we are experiencing an increasing trend or seasonal
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MACROALGAE
May 5, 2013
patterns is unclear but something that will need to be
addressed in the future.
As nutrient levels in coastal
environments change so do the
plants species. All plants require
light, water and nutrients to grow.
Studies have shown that seagrasses
generally dominate in waters with
low nutrients and high light
availability. In contrast, macroalgae
(and microscopic microalgae) tend
to dominate where there is less
light and more nutrients.
Because macroalgae (and
microalgae) are better able to make
use of low light levels than are
seagrasses they have competitive
edge when nutrient levels increase.
This is because seagrasses are
rooted to the substrate and as such
are subject to shading effects of
unattached macroalgae covering
them. When seagrasses are
shaded their ability to photosynthesize is reduced and ultimately their
growing season is shortened.
Studies indicate that nitrogen is generally the nutrient that
seems to control macroalgae
growth rates throughout the year.
However phosphorus alone, or at
certain times of the year, both
nitrogen and phosphorus together
may be important. To complicate
this, different species of
macroalgae can be limited by
nitrogen or by phosphorus in the
same estuary.
Caulerpa—FDEP Image
Air Bladder
Sargassum—FSG Image
One of the biggest challenges when
nutrient levels increase is
identifying where the increase is
coming from. Regular water
monitoring programs cannot get to
that detail without including some
sophisticated and often costly
sampling. In recent years a few
studies have been conducted in
southwest Florida estuaries and
coastal waters to identify the
species of macroalgae present and
to determine what nutrient
sources (fertilizers, sewage, etc.)
macroalgae were utilizing.
Determining what nutrient sources
So, one could expect as nutrient
are contributing to macroalgae
levels increase, seagrasses which
growth will enable resource
are slow growing, to be replaced by
managers to implement corrective
macroalgae, which are fast growing.
action hopefully before major
If nutrients continue to increase
shifts in plant species occur.
macroalgae will be replace by even
faster growing microalgae
Of course in the end it’s important
(microscopic algae). From an
to note that simply seeing
ecosystem perspective, the shift
macroalgae is not cause for
from seagrass to microalgae could
concern. In fact as primary
Macroalgae and seagrass—
have cascading impacts as animals
producers (photosynthesizers) they
Smithsonian Image (Ft. Pierce Website)
dependent upon seagrass for food
do serve an important role,
and shelter, spotted seatrout for instance, are replaced by less
particularly in winter months when seagrass growth is
desirable species such as jellyfish.
naturally slowed. The key is keeping our bays and estuaries
healthy to ensure a healthy balance in
Sources:
macroalgae and seagrass abundance.
Valiela I. et al. 1997. Macroalgal blooms in shallow estuaries: Controls and ecophysiological
and ecosystem consequences. Limnol Oceanogr, 42(5, Part 2): 1105-1118.
Milbrandt E. et al. 2010. Bioavailability and sources of nutrients and the linkages to red drift
algae. Final report to Florida Gulf Coast University, 188 pp.
BETTY STAUGLER
Florida Sea Grant Marine Agent
[email protected]
CHARLOTTE COUNTY UF/IFAS EXTENSION
25550 Harbor View Road, Suite 3 - Port Charlotte, Florida 33980
941.764.4340 - 941.764.4343 (fax) - http://charlotte.ifas.ufl.edu