Other Taxonomic Groupings
B. gracilis colonies are generally pale yellow to tan in color and form tangled masses
in hydroids, algae, seagrasses, or other substrata (Winston 1982). Zooids
are tubular in shape and are attached basally to the stolon where they are
arranged either alone, in pairs, or in clumps. Stolon width measures
approximately 0.05 mm in diameter. Individual zooids differ in size
depending on whether the lophophore is extended or not, measuring
approximately 0.6 mm X 0.12 mm while expanded. Retracted zooids are shorter
and are generally observed to be flattened against the substratum. The
lophophore is not pigmented and measures approximately 0.315 mm in diameter.
It bears 8 tentacles and shows a great deal of flexibility while actively
feeding (Winston 1978).
HABITAT AND DISTRIBUTION
B. gracilis is most likely cosmopolitan in shallow water (Winston 1982). In the western Atlantic, its range extends from Greenland south to Brazil.
B. gracilis is
widely distributed throughout the Indian River Lagoon and along the Florida
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.
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
Eggs are brooded internally in B. gracilis,
usually in zooids whose polypides have degenerated. Embryos are peach colored
B. gracilis is considered to be eurythermal.
B. gracilis has
been collected in areas of the IRL where salinity was below 30‰ and is
generally considered to be euryhaline (Winston 1995).
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.
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.
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,
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.
Winston JE. 1978. Polypide morphology and feeding behavior in marine ectoprocts. Bull Mar Sci 28: 1-31.
Winston JE. 1982. Marine bryozoans (Ectoprocta) of the Indian River area (Florida). Bull Amer Mus
Nat Hist 173: 99-176.
Winston JE. 1995. Ectoproct diversity of the Indian River coastal lagoon. Bull Mar Sci 57: 84-93.