Species of Florida's Seagrasses:
Turtle Grass (Thalassia testudinum)
Turtle grass is the most common of seagrasses off the coast of Florida and throughout the
Caribbean. It also occurs in Bermuda, and south from the Gulf of Mexico to Venezuela. The grass
blades are flat and ribbon-like, growing to 14 inches (35.5 cm) long and ½ inch (10 mm) wide.
These blades have 9-15 parallel veins each, and are densely colonized by epiphytes. These long,
broad blades distinguish it from other species of seagrasses. There are two to five blades per
rhizome node. These rhizomes may be as deep as 10 inches (25 cm) below the substrate surface.
Turtle grass typically occurs from the low tide level to depths of approximately 30 feet (10 m) on
sand and rubble-covered bottoms. Turtle grass grows in extensive meadows throughout its range.
The common name "turtle grass" refers to green sea turtles (Chelonia mydas) that graze on large
fields of this seagrass.
Manatee Grass (Syringodium filiforme)
Occurring throughout most of Florida’s estuaries, manatee grass is the second most common
seagrass in Florida waters. It is also found in Bermuda, the Bahamas, and throughout the Gulf of
Mexico and the Caribbean. Manatee grass, along with turtle grass, is found in tropical coastal
waters with salinities of 20-36 parts per thousand (ppt). The blades of this seagrass are cylindrical
with two to four blades arising from each rhizome node. These blades can reach lengths of 20
inches (50 cm) in some locations. Roots of this seagrass barely go below the substrate surface. It
commonly occurs growing with other species of seagrasses or alone, in small patches.
Commonly referred to as manatee grass, it is a favorite food of the manatee.
Shoal Grass (Halodule wrightii)
Shoal grass colonizes disturbed areas where conditions are too harsh for turtle and manatee
seagrasses to occur. This seagrass ranges from North Carolina, south along the Atlantic and Gulf
of Mexico coasts, to the Caribbean. It is also found off of portions of South America, northwestern
Africa, Indian Ocean, and the west coast of Mexico. Although shoal grass commonly occurs in
estuarine waters with salinities of 10-25 parts per thousand, it also forms dense patches in high
salinity areas exposed to wave energy or in tidal flats. The blades are clustered from a single node
on the rhizome, with notched blade tips. The flat, narrow blades grow to maximum lengths of 4-6
inches (10-15 cm) and widths of only .08-.11 inches (2-3 mm).
Johnson’s Seagrass (Halophila johnsonii)
Johnson’s seagrass was first recognized as a separate species in the Indian River Lagoon in
1980. It was named in honor of J. Seward Johnson Sr., the founder of Harbor Branch
Oceanographic Institution in Ft. Pierce, Florida. The National Marine Fisheries Service considers
the Johnson’s seagrass to be a threatened species under the Endangered Species Act, due to its
limited distribution. Its distribution ranges from central Biscayne Bay (north of Virginia Key) to
Sebastian Inlet. Johnson's seagrass has been documented within flood-tidal deltas, muddy
basins, sandy shoals, and near canals, tolerating fluctuations of salinity and water clarity. Johnson’
s seagrass has paired leaves originating from a single rhizome node. Measuring 0.04-0.12 inches
(1-3 mm) wide and 4-8 inches (10-20 cm) in length, the blades are light green with a brown midrib
and veins. This seagrass was added to the list of threatened species under the Endangered
Species Act on September 14, 1998. As protected by the ESA, the recovery plan for the Johnson’s
seagrass is currently being developed. Management plans are now in place for the Indian River
Lagoon, Biscayne Bay, and Loxahatchee River Aquatic Preserves.
Paddle Grass (Halophila decipiens)
This seagrass occurs on the continental shelf near the Indian River Lagoon, the Gulf of Mexico, the
Caribbean and the Indo-West Pacific. The paddle grass resembles Johnson’s seagrass, but is
distinguishable by a finely serrated leaf margin and a paddle-shaped green blade terminating with
a rounded tip. The two, opposite, blades measure 0.5-1.0 inches (10-25 mm) long and 0.12-0.23
inches (3-6 mm) wide, extending directly from nodes on the rhizome. Rhizomes creep through soft
substrates, forming patches of paddle grass in shallow waters.
Star Grass (Halophila engelmanni)
Star grass occurs in Florida, the Bahamas, Texas, and the West Indies, growing on sandy or
muddy bottoms at depths to 130 feet (40 m). The 0.5-1.2 inch (10-30 mm) long blades are
clustered in groups of 4-8, arranged in a star-like whorl. Each cluster has two scale leaves at the
base as well as a second pair halfway up the leaf stem. The smooth, flat blades have distinct
midribs and veins and fine-toothed edges.
Widgeon Grass (Ruppia maritima)
Although widgeon grass is not a true seagrass, it grows in both fresh and brackish aquatic
environments. It is widely distributed worldwide in temperate and subtropical regions. In North
America, widgeon grass is found along the Atlantic coast from Newfoundland south to Texas. The
blades are wider at the base of the stem, arising alternately from the sheath and tapering to long
pointed tips. This grass is often confused with shoal grass in low salinity locations. Forming
extensive meadows in subtidal areas with exposure to intense sun, widgeon grass is able to
tolerate some dessication. Since it does not occur in full-strength seawater, it is not considered a
true seagrass. However, the widgeon grass does provide food and refuge for a variety of
organisms, similar to the function of the true seagrasses.
- Turtle Grass
- Manatee Grass
- Shoal Grass
- Johnson's Seagrass
- Paddle Grass
- Star Grass
- Widgeon Grass
Turtle Grass (Thalassia testudinum)
Turtle grass is the most common of seagrasses off the coast of Florida and throughout the
Caribbean. It also occurs in Bermuda, and south from the Gulf of Mexico to Venezuela. The grass
blades are flat and ribbon-like, growing to 14 inches (35.5 cm) long and ½ inch (10 mm) wide.
These blades have 9-15 parallel veins each, and are densely colonized by epiphytes. These long,
broad blades distinguish it from other species of seagrasses. There are two to five blades per
rhizome node. These rhizomes may be as deep as 10 inches (25 cm) below the substrate surface.
Turtle grass typically occurs from the low tide level to depths of approximately 30 feet (10 m) on
sand and rubble-covered bottoms. Turtle grass grows in extensive meadows throughout its range.
The common name "turtle grass" refers to green sea turtles (Chelonia mydas) that graze on large
fields of this seagrass.
Manatee Grass (Syringodium filiforme)
Occurring throughout most of Florida’s estuaries, manatee grass is the second most common
seagrass in Florida waters. It is also found in Bermuda, the Bahamas, and throughout the Gulf of
Mexico and the Caribbean. Manatee grass, along with turtle grass, is found in tropical coastal
waters with salinities of 20-36 parts per thousand (ppt). The blades of this seagrass are cylindrical
with two to four blades arising from each rhizome node. These blades can reach lengths of 20
inches (50 cm) in some locations. Roots of this seagrass barely go below the substrate surface. It
commonly occurs growing with other species of seagrasses or alone, in small patches.
Commonly referred to as manatee grass, it is a favorite food of the manatee.
Shoal Grass (Halodule wrightii)
Shoal grass colonizes disturbed areas where conditions are too harsh for turtle and manatee
seagrasses to occur. This seagrass ranges from North Carolina, south along the Atlantic and Gulf
of Mexico coasts, to the Caribbean. It is also found off of portions of South America, northwestern
Africa, Indian Ocean, and the west coast of Mexico. Although shoal grass commonly occurs in
estuarine waters with salinities of 10-25 parts per thousand, it also forms dense patches in high
salinity areas exposed to wave energy or in tidal flats. The blades are clustered from a single node
on the rhizome, with notched blade tips. The flat, narrow blades grow to maximum lengths of 4-6
inches (10-15 cm) and widths of only .08-.11 inches (2-3 mm).
Johnson’s Seagrass (Halophila johnsonii)
Johnson’s seagrass was first recognized as a separate species in the Indian River Lagoon in
1980. It was named in honor of J. Seward Johnson Sr., the founder of Harbor Branch
Oceanographic Institution in Ft. Pierce, Florida. The National Marine Fisheries Service considers
the Johnson’s seagrass to be a threatened species under the Endangered Species Act, due to its
limited distribution. Its distribution ranges from central Biscayne Bay (north of Virginia Key) to
Sebastian Inlet. Johnson's seagrass has been documented within flood-tidal deltas, muddy
basins, sandy shoals, and near canals, tolerating fluctuations of salinity and water clarity. Johnson’
s seagrass has paired leaves originating from a single rhizome node. Measuring 0.04-0.12 inches
(1-3 mm) wide and 4-8 inches (10-20 cm) in length, the blades are light green with a brown midrib
and veins. This seagrass was added to the list of threatened species under the Endangered
Species Act on September 14, 1998. As protected by the ESA, the recovery plan for the Johnson’s
seagrass is currently being developed. Management plans are now in place for the Indian River
Lagoon, Biscayne Bay, and Loxahatchee River Aquatic Preserves.
Paddle Grass (Halophila decipiens)
This seagrass occurs on the continental shelf near the Indian River Lagoon, the Gulf of Mexico, the
Caribbean and the Indo-West Pacific. The paddle grass resembles Johnson’s seagrass, but is
distinguishable by a finely serrated leaf margin and a paddle-shaped green blade terminating with
a rounded tip. The two, opposite, blades measure 0.5-1.0 inches (10-25 mm) long and 0.12-0.23
inches (3-6 mm) wide, extending directly from nodes on the rhizome. Rhizomes creep through soft
substrates, forming patches of paddle grass in shallow waters.
Star Grass (Halophila engelmanni)
Star grass occurs in Florida, the Bahamas, Texas, and the West Indies, growing on sandy or
muddy bottoms at depths to 130 feet (40 m). The 0.5-1.2 inch (10-30 mm) long blades are
clustered in groups of 4-8, arranged in a star-like whorl. Each cluster has two scale leaves at the
base as well as a second pair halfway up the leaf stem. The smooth, flat blades have distinct
midribs and veins and fine-toothed edges.
Widgeon Grass (Ruppia maritima)
Although widgeon grass is not a true seagrass, it grows in both fresh and brackish aquatic
environments. It is widely distributed worldwide in temperate and subtropical regions. In North
America, widgeon grass is found along the Atlantic coast from Newfoundland south to Texas. The
blades are wider at the base of the stem, arising alternately from the sheath and tapering to long
pointed tips. This grass is often confused with shoal grass in low salinity locations. Forming
extensive meadows in subtidal areas with exposure to intense sun, widgeon grass is able to
tolerate some dessication. Since it does not occur in full-strength seawater, it is not considered a
true seagrass. However, the widgeon grass does provide food and refuge for a variety of
organisms, similar to the function of the true seagrasses.
Species of Florida's Seagrasses
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