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Species Name:    Bowerbankia gracilis
Common Name:                       (None)

 

I.  TAXONOMY

Kingdom Phylum/Division: Class: Order: Family: Genus:
Animalia Ectoprocta Gymnolaemata Ctenostomata Vesiculariidae Bowerbankia


Colony of Bowerbankia gracilis.  Note individual zooids have extended their lophophores for feeding.  Photo courtesy 
of J. Winston.



Detail of Bowerbankia gracilis showing  zooids with and without fully extended lophophores.  Drawing by J. Winston.  Courtesy of American Museum of Natural History.  Used with permission.
Species Name:
Bowerbankia gracilis Leidy, 1855

Common Name:
None

Species Description:
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).


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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Page last updated: July 25,  2001