II. HABITAT AND
Z. verticillatum is widely distributed in
warm temperate and tropical waters in the western Atlantic and the Caribbean.
Z. verticillatum has the greatest biomass of
any bryozoan species in the IRL, and develops large populations throughout the
summer. It is possible that this species, due to its ability to filter
particulates from large volumes of water, contributes to the overall health of
the IRL ecosystem.
III. LIFE HISTORY AND POPULATION BIOLOGY
Age, Size, Lifespan:
Colonies in the IRL can reach 1 meter or more in
length within 6 – 8 months (Winston 1995). Stolons generally measure 0.5 mm in
diameter, individual zooids measure 0.4 – 0.6 mm, and tentacles of individual
zooids measure approximately 0.3 mm in diameter. In Florida, colonies grow well
from April through late September. They die back with the onset of decreasing
water temperatures in fall, but enough fragments overwinter that new growth
begins in spring.
Seasonality in the IRL plays a major role in the
abundance of any bryozoan species. Typically, bryozoans are most abundant from
October to May. Zoobotryon verticillatum is highly abundant, and has the
greatest biomass of any bryozoan in the IRL.
Z. verticillatum is a member of the Order
Ctenostomata that broods its embryos.
IV. PHYSICAL TOLERANCES
Z. verticillatum grows best at water
temperatures above 22 ° C. Colonies in the IRL tend
to die back with the first fall cold fronts that begin to lower lagoon water
Z. verticillatum is considered to be
euryhaline. However, it is typically found in its greatest abundance where salinity is above 30 ‰.
V. COMMUNITY ECOLOGY
Z. verticillatum, 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. This
figure, multiplied by an approximate count of the number of individual zooids in
1 square meter (m2) of seagrass beds yields an average of 184,728
liters (48,613 gallons) of water filtered per day.
It is highly unlikely that many organisms feed
directly on Z. verticillatum as colonies produce bromo-alkaloids, a class
of chemical compounds related to drugs like nicotine, morphine, and cocaine
(Sato and Fenical 1983). These secondary metabolites are likely to protect
zooids in the colony by discouraging predation, preventing settlement of other
organisms, and preventing bacteria or viruses from invading. Only a few species
of nudibranch mollusks are known to feed directly on Z.
Typical habitat for ectoprocts in the Indian River
Lagoon include seagrasses, drift algae, oyster reef, dock, pilings, breakwaters,
and man-made debris (Winston 1995). Z. verticillatum is typically found
in fouling, seagrass and mangrove habitats within the IRL.
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,
VI. SPECIAL STATUS
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 Station
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Page last updated: July 25, 2001