Species Description: B. imbricata colonies have a creeping or somewhat upright and bushy growth pattern, with zooids forming clusters along a thick stolon which measures approximately 0.23 mm in diameter.
Zooids are vase-shaped or subcylindrical. Individual functional zooids measure approximately 0.38 X 0.17 mm, while degenerated zooids measure 0.38 X 0.19 mm. Zooids and stolons of living colonies are studded with small, star-shaped black pigments. The polypide and lophophore are not pigmented. The lophophore measures approximately 0.246 in diameter, and bears 10 tentacles. Both the body wall and the lophophore are somewhat flexible to enhance scanning while feeding.
Potentially Misidentified Species: B. imbricata in the Indian River Lagoon could be confused with B. pustulosa, a related bryozoan. In overall morphology, zooid clusters of B. imbricata have largely been described as non-helical; however, in IRL specimens, zooids of this species did form a partial helix around the stolon (Winston 1982). They thus resemble the overall morphology of B. pustulosa. These species can be differentiated base on the number of tentacles present: B. imbricata has 10 tentacles, while B. pustulosa has 8 tentacles.
Regional Occurrence: In the western Atlantic, B. imbricata has been reported from cool water areas north of Florida; however, it is also known from warm water areas in the Mediterranean and the Red Sea.
IRL Distribution: B. imbricata has been collected from the IRL at the Sebastian Inlet grass flats, and coastally at the Ft. Pierce breakwater. It is likely to have a wider distribution within the lagoon, but as yet, no documentation exists.
Age, Size, Lifespan: Functional zooids measure approximately 0.38 X 0.17 mm. Degenerated zooids measure 0.38 X 0.19 mm. Stolon diameter is approximately 0.23 mm in diameter. Lophophore diameter averages 0.246 mm.
Abundance: B. imbricata was collected from March to September in the IRL. Little information on its abundance exists.
Embryology: The embryology of B. imbricata is unknown.
Temperature: B. imbricata is a eurythermal species known from both temperate and sub-tropical waters.
Trophic Mode: B. imbricata, like all bryozoans, is a suspension feeder. Each individual zooid in a colony has 10 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. imbricata 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. imbricata holds its tentacles straight while feeding. The polypides slowly scan the water column in a circular motion in search of appropriately sized particulates. Adjacent lophophores 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).
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. At Sebastian Inlet, B. imbricata is commonly found in association with algae, especially Solieria tenera, a common Rhodophyte. However, at other IRL and coastal locations, B. imbricata is found attached to the undersides of rocks and ledges, and in holes in worm-reef (Phragmatopoma spp.) mounds (Winston 1982).
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. 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.