- Bacteria and Fungi
Bacteria and Fungi
Bacteria and fungi are responsible for the decomposition of dead seagrass blades. Microfauna and meiofauna
colonize the dead seagrass blades, feeding on the bacteria and fungi as well as on the dissolved organic
matter released from the decomposing blades. These dissolved organics also support phytoplankton and
zooplankton which in turn provide prey for organisms further up the food web.
Lacking a firm substrate for attachment, seagrass beds contain benthic macroalgae attached to sediments,
rocky outcroppings, and the seagrasses themselves. Calcareous algae lives among the seagrasses,
producing calcium carbonate which eventually becomes incorporated into the surrounding sediments. Drift
algae form large unattached masses along the sea bottom and drift about with any water movement.
Red algae and brown algae are also common within seagrass habitats. In addition to calcareous algae, the
majority of drifting algal masses are species of red algae.
Seagrasses dramatically increase the surface area of the habitat for the attachment of epiphytes. On turtle
grass (Thalassia testudinum) alone, over 100 species of epiphytic algae have been documented. Epiphytes
cover seagrass blades more at the tips than toward the bases in order to receive more sunlight than those
lower on the blade. These epiphytes reduce seagrass growth due to shading. Epiphytes, along with the
seagrass blades, eventually become part of the detritus.
Invertebrate fauna living in seagrass habitats represents a diverse group. Seagrasses provide a rich source of
food for invertebrates, primarily in the form of epiphytes.
Epibenthic organisms reside on the surface of the bottom sediments. Some epibenthic invertebrates feed on
both the epiphytes living on the seagrass blades as well as the blades themselves, such as the queen conch
(Strombus gigas). Other epibenthic species, including the Bahamian starfish (Oreaster reticulatus) and
various gastropods, feed on infaunal organisms found living within the sediments. Feeding on detritus,
epiphytes, and seagrass blades are various sea urchins that move from nearby reefs to feed in the
seagrasses at night. Another echinoderm, the sea cucumber (Holothuria floridana), moves slowly along the
surface of the sediments ingesting sand grains and algae. Pink shrimp (Paneaus duorarum) and juvenile
spiny lobsters (Panulirus argus) find refuge among the blades of seagrasses.
Epiphytic organisms, dominated by gastropods, are common throughout turtle and shoal grass habitats.
These include anemones, bryozoans, and sponges, suspension feeders that live attached to the blades of
seagrass. Without the dramatic increase in surface area provided by the seagrasses, the diversity of epiphytic
organisms would be much lower.
Throughout shallow turtle grass communities, small patches of stony corals are common. As water depth
increases, sponges become more common and may be found growing among the seagrasses or attached to
dead coral skeletons.
Although not obvious, infauna communities thrive within the sediments of seagrass beds. The rigid pen shell
(Atrina rigida), along with many other bivalve molluscs, is a common filter feeder found within the sediments of
many seagrass beds.
Seagrass beds provide nursery areas and feeding grounds for many species of fish, including those of
commercial and sportfishing value. These habitats are also the home to many resident species.
Year-round residents are typically small in size and cryptic. The emerald clingfish (Acyrtops beryllina) is a tiny
epiphytic fish only found associated with turtle grass. Common year-round resident fish of south Florida
seagrass habitats include the pipefishes (Syngnatus spp.), seahorses (Hippocampus spp.), and the inshore
lizardfish (Synodus foetens). Parrotfish (Sparisoma spp.) reside in the clear waters of the Florida Keys, feeding
directly on blades of seagrass. Sharptail eels (Myrichthys breviceps) and young moray eels (Gymnothorax spp.)
forage in seagrass beds for mollusks and other prey.
Seasonal residents are fishes that spend part of their life cycle in seagrass beds, mainly as a nursery area for
spawning and/or juvenile development. The spotted seatrout (Cynoscion nebulosus) and silver perch
(Bairdiella chrysura) are among seasonal residents that are common as juveniles in seagrasses. Other
seasonal species include pigfish (Orthopristis chrysoptera), blue-striped grunt (Haemulon scirus), French
grunt (H. flavolineatum), ceasar grunt (H. carbonarium) and the tomtate (H. aurolineatum).
Coral reef fishes often utilize seagrasses as nurseries. Juveniles of the ocean surgeonfish (Acanthurus
bahianus) and the doctorfish (A. chirurgus) are commonly observed residing among seagrasses. The spotted
goatfish (Pseudupeneus maculatus), yellow goatfish (Mulloidicthys martinicus), gag grouper (Mycteroperca
microlepis), gray snapper (Lutjanus griseus), spotted seatrout (Cynoscion nebulosus), and southern flounder
(Paralichthys lethostigma) also occur as juveniles in seagrass habitats. The bucktooth parrotfish (Sparisoma
radians), redtail parrotfish (S. chrysopterum) and the emerald parrotfish (Nicholsina usta) all reside in
seagrass beds as juveniles as well as immature adults.
A commercially valuable group of fishes, the snappers, are common throughout south Florida’s seagrass
habitats. These include the gray snapper (Lutjanus griseus), lane snapper (L. synagris), schoolmaster (L.
apodus), mutton snapper (L. analis), dog snapper (L. jocu), and yellowtail snapper (Ocyurus chrysurus).
White grunts (Haemulon plumeri) are abundant in the turtle grass beds of south Florida, while other grunts
such as the porkfish (Anisotremus virginicus) rarely occur in these habitats. Other species of grunts are
present as juveniles in these waters.
Seagrass beds of south Florida include large numbers of reef fishes when the beds are adjacent to coral
reefs. Fishes find shelter on the reef during the day, moving to seagrass beds at night to forage. Grunts and
gray snappers (Lutjanus griseus) live diurnally on the reefs and feed nocturnally over seagrasses. Other
nocturnal visitors include hardhead catfish (Arius felis), fantail mullet (Mugil gyrans), Atlantic thread herring
(Opisthonema oglinum), scaled sardine (Harengula jaguana), silver perch (Bairdiella chrysura), and ladyfish
(Elops sarus). On the other hand, species occurring over seagrasses only during the day include jenny
mojarra (Eucinostomus gula), pinfish (Lagodon rhomboides), and flathead mullet (Mugil cephalus). Offshore
migrants such as nurse sharks (Ginglymostoma cirratum), smalltooth sawfishes (Pristis pectinata), southern
stingrays (Dasyatis americana), and Atlantic stingrays (Dasyatis sabina) visit seagrass habitats in search of
Several species of sea turtles reside in the waters of the Gulf of Mexico and Caribbean, including the green sea
turtle (Chelonia mydas). The main food of this sea turtle is Thalassia testudinum, commonly referred to as
turtle grass. The American crocodile (Crocodylus acutus) occurs in the shallow waters of Florida Bay and the
northern Florida Keys. Although it is unknown to what extent the crocodile utilizes seagrasses, they are known
to feed in these areas.
Large numbers of birds utilize seagrass beds, especially wading birds searching for food. The three common
feeding modes of birds are waders, swimmers, and plungers.
The great egret (Casmeroidus albus), reddish egret (Egretta rufescens), and little blue heron (Egretta caerulae)
are among the wading birds that frequent seagrass beds in search of food.
Double-crested cormorants (Phalacrocorax auritus) pursue fishes throughout the water column. Other
swimming birds include the white pelican (Pelecanus erythrorhynchos) and red-breasted merganser (Mergus
Brown pelicans (Pelecanus occidentalis) fly over seagrass beds in search of prey. Once a fish is spotted, the
pelican plunges into the water using its pouch-like bill to scoop its prey. Ospreys (Pandion haliaetus) and
southern bald eagles (Haliaeetus leucocephalus leucocephalus) seize prey from the water surface with their
Seagrasses also provide excellent foraging for large wading birds such as herons.
Manatees (Trichechus manatus) and bottlenose dolphins (Tursiops truncatus) feed within the waters over
seagrass habitats of Florida. Manatees are primarily tropical in distribution, however in Florida waters,
manatees are found in shallow seagrass meadows or in spring-fed warm water rivers during the cool winter
months. They feed on aquatic vegetation including seagrasses.
The bottlenose dolphin (Tursiops truncatus) is the most common marine mammal in this region, feeding over
seagrass beds, even in waters less than 3 feet (1 m) in depth. They feed primarily on large fish, squid, and
Florida Keys National Marine Sanctuary
Life in the Seagrasses