Synonymy:
None
Other Taxonomic Groupings:
Suborder: Carnosa
Superfamily: Vesicularioidea
II. HABITAT AND
DISTRIBUTION
Regional Occurrence:
B. gracilis is
most likely cosmopolitan in shallow water (Winston 1982). In the western
Atlantic, its range extends from Greenland south to Brazil.
IRL Distribution:
B. gracilis is
widely distributed throughout the Indian River Lagoon and along the Florida
coast.
III. LIFE HISTORY AND POPULATION BIOLOGY
Age, Size, Lifespan:
Individual zooids of live specimens taken from the
IRL measured 0.38 - 0.80 mm in length (Average: 0.6 mm), and 0.9 - 0.14 mm in
width (Winston 1982). The lophophore bears 8 tentacles and measures
approximately 0.315 mm in diameter.
Abundance:
Winston (1982) reported this species as the most
common ctenostome in the IRL. It is collected year-round at coastal sites, and
from December through June at IRL sites. Colonies having embryos are observed in
March.
Locomotion:
Sessile
Embryology:
Eggs are brooded internally in B. gracilis,
usually in zooids whose polypides have degenerated. Embryos are peach colored
(Winston 1982).
IV. PHYSICAL TOLERANCES
Temperature:
B. gracilis is considered to be
eurythermal.
Salinity:
B. gracilis has
been collected in areas of the IRL where salinity was below 30‰ and is
generally considered to be euryhaline (Winston 1995).
V. COMMUNITY ECOLOGY
Trophic Mode:
B. gracilis,
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.
Both the polypide and the body wall of B. gracilis
are highly flexible. With the polypide retracted, the zooid is compressed
against the substratum; with the polypide expanded, the zooid elongates and
rises to a vertical or diagonal position with respect to the substratum. B.
gracilis holds its tentacles straight while feeding. The polypides slowly
scan the water column in a circular motion in search of appropriately sized
particulates. Adjacent lophophore in this species are well separated. Polypides
of neighboring zooids may occasionally touch each other while scanning, but they
will quickly withdraw.
Habitats:
Typical habitat for ectoprocts in the Indian River
Lagoon include seagrasses, drift algae, oyster reef, dock, pilings, breakwaters,
and man-made debris (Winston 1995). In the IRL, B. gracilis was found
primarily on seagrasses, but also on wood, dead shells, and aluminum cans.
Coastally, it was found on algae, dead shells, hydroids and on other bryozoans.
Associated Species:
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, mussels,
etc.
VI. SPECIAL STATUS
Special Status:
None.
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 day.
Economic Importance:
None.
Report by: K. Hill,
Smithsonian Marine Station
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irl_webmaster@si.edu
Page last updated: July 25, 2001
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