Growth pattern of Amathia alternata,
an erect, branching bryozoan. Drawing by J. Winston, courtesy of American
of Natural History.
Used with permission.
Amathia alternata Lamouroux,
A. alternata is an arborescent
bryozoan that forms upright, bushy, heavily branched colonies. Zooids are
yellow to brown in color with a tubular shape measuring approximately 0.56 X
0.15 mm. Zooids are arranged in paired double rows along the stolons. Rows
of zooids may either lie straight on the stolon, or twist as much as 90°
around it. Zooids of successive internodes are arranged at 180°
angles to each other. The lophophore bears 8 tentacles and measures 0.302 mm
Other Taxonomic Groupings:
Potentially Misidentified Species:
A. alternata has been confused with Amathia
convoluta (Maturo), 1957.
II. HABITAT AND
A. alternata occurs from Cape Hatteras south
to Florida, the Gulf of Mexico, and possibly the Caribbean.
Within the Indian River Lagoon, A. alternata
has been collected from the Sebastian Inlet area. Coastally, it has been
collected at Walton Rocks and Seminole Shores. Offshore it was collected from
Capron Shoals (Winston 1982, 1995).
III. LIFE HISTORY AND POPULATION BIOLOGY
Age, Size, Lifespan:
Zooids are tubular in shape and measure 0.56 X 0.15
mm. The lophophore has 8 tentacles and measures approximately 0.302 mm in
diameter. Colonies collected from the Atlantic coast of Florida, and from the
IRL did not attain the larger sizes of up to 30 cm observed on the Gulf coast
and described by Shier (1964 in Winston 1982).
A. alternata occurs year-round in Florida
waters, but is most common during the winter (Winston 1982). Winston (1995)
found it to be one of the most abundant winter species in the Indian River
The embryology of A. alternata is unknown.
IV. PHYSICAL TOLERANCES
A. alternata in the western Atlantic is
distributed throughout warm, subtropical waters and is thus considered to be eurythermal.
This species is generally collected in areas where
salinity exceeds 30 ‰ (Winston 1982, 1995).
V. COMMUNITY ECOLOGY
A. alternata, like all bryozoans, is a
suspension feeder. Each individual zooid in a colony has 8 ciliated tentacles
that are extended to filter phytoplankton less than 0.045 mm in size (about
1/1800 of an inch) from the water column. Bullivant (1967; 1968) showed that
the average individual zooid in a colony can clear 8.8 ml of water per day.
Typical habitat for ectoprocts in the Indian River
Lagoon include seagrasses, drift algae, oyster reef, dock, pilings, breakwaters,
and man-made debris (Winston 1995). A. alternata was commonly found
attached to shells, beach rocks and rock overhangs. In the seagrass flats around
Sebastian Inlet, it was also commonly found entangled in the Rhodophyte Solieria
VI. SPECIAL STATUS
Seagrasses as well as floating macroalgae, provide
support for bryozoan colonies. In turn, bryozoans provide habitat for many
species of juvenile fishes and their invertebrate prey such as polychaete worms,
amphipods and copepods (Winston 1995). Bryozoans are also found in association
with other species that act as support structures: mangrove roots, oyster beds,
Benefit in IRL:
Bryozoans are ecologically important in the Indian
River Lagoon due to their feeding method. As suspension feeders, they act as
living filters in the marine environment. For example, Winston (1995) reported
that bryozoan colonies located in 1 square meter of seagrass bed could
potentially filter and recirculate an average of 48,000 gallons of seawater per
Report by: K. Hill, Smithsonian Marine
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Page last updated: July 25, 2001