What are seagrasses?
Just below the water’s surface you’ll find underwater flowering
plants growing in the Lake Worth Lagoon and the Intracoastal Waterway. These
highly productive and ecologically important plants....
- create habitats that provide a nursery area for juvenile finfish and shellfish
with commercial and recreational fishing value
- increase water clarity by capturing sediments with their roots
- provide a great spot for tiny plant and animal organisms to attach
- provide a direct food source for endangered manatees and green sea turtles;
birds also use the seagrass beds as regular feeding grounds
While seagrass does provide a valuable food source for manatees and sea turtles,
it may be more important to the food web when it decomposes. Dead, decaying
plant matter forms the base of the food chain and is an important food source
for crustaceans, worms, mollusks, and mullet.
What seagrasses are found in the Lake Worth Lagoon and Intracoastal
Waterway?
- Turtle Grass – Thalassia testudinum
- Manatee Grass – Syringodium filiforme
- Shoal Grass – Halodule wrightii
- Paddle Grass – Halophila decipiens
- Johnson’s Grass – Halophila johnsonii
- Star Grass – Halophila engelmanni
View photos of these species at the Florida
Museum of Natural History.
Quick Facts - Lake Worth Lagoon Seagrasses
- Seagrass beds cover at least 1,688 acres or almost 22% of Lagoon (2007 aerial
mapping estimates).
- The seagrass coverage varies throughout the Lagoon, with more seagrass found
in the north end than in the central or southern end.
- 65% of the seagrasses are in the north (Little Lake Worth just north
of PGA Blvd to Flagler Memorial Bridge)
- 12% of the seagrasses are in the central (Flagler Memorial Bridge to
Lake Ave Bridge)
- 23% of the seagrasses are in the south (Lake Ave Bridge to Ocean Ave.
Bridge in Boynton Beach.)
- The Lake Worth Lagoon contains the largest known beds of Johnson’s
seagrass (Halophila johnsonii), the first marine plant species to
be listed under the Endangered Species Act.
Lake Worth Lagoon Seagrass Trends
- Palm Beach County Environmental Resources Management has conducted seagrass
monitoring since the year 2000. Nine imaginary lines drawn through the Lagoon
called transects help biologists monitor seagrass beds along the lines over
time.
- Seven years of surveys have shown fluctuations in seagrass cover with no
obvious pattern of increase or decrease – until the hurricanes of 2004
(Charley, Frances, and Jeanne). In June 2005, monitoring results revealed
a major decrease in seagrass cover in most areas of the Lagoon. The loss was
likely caused by an increased amount of sediment in the water which is a result
of increased stormwater runoff from areas directly adjacent to the Lagoon.
Hurricanes also increased freshwater discharges from Lake Okeechobee and the
West Palm Beach Canal (C-51), and bottom sediment resuspensed from wave action.
- 2007 and 2008 monitoring efforts suggest that the seagrass beds have returned
to conditions previously observed before the storms and have even increased
in both density and coverage. The width of the grass beds often extended further
from the shore and set new all-time records at several locations, including
one transect where seagrasses extended all the way to (and into) the Intracoastal
Waterway channel.
- The 2007 aerial mapping estimates a slight increase of 42 acres over the
2001 estimate of 1,646 acres. A 58 acre decrease of seagrass cover in the
northern segment, a 9 acre increase in the central segment, and a 91 acre
increase in the southern segment was observed.
What are the major threats to Seagrass?
- shading from structures, such as docks and moored vessels
- physical damage from boat propellers
- dredging/filling activities, which result in removal or burial of seagrasses
and increased sediment in the water column reducing clarity.
- coastal development and shoreline protection, including seawalls, groins,
and jetties, which refracts wave energy away from the shoreline. Wave energy
can cause erosion and increase currents, harming seagrasses
- excessive nutrients, such as nitrogen and phosphorus, which allow algae
and other non-desirable species thrive and "out-compete" seagrasses.
Where can I find more information?
Coastal Resources
