Photographer: Eugene van der Pijll Source: www.commons.wikimedia.org Copyright: public domain
Membranipora membranacea grows as a colony composed of microscopic individuals known as zooids. They inhabit tiny boxlike compartments, which together make up the flexible silver-white patches of the bryozoan. Species in the genus Membranipora tend to grow in a circular pattern that can exceed a diameter of 3 inches and they may merge with other patches with the oldest member of the colony is in the center. Colonies can become very large, covering extensive areas of kelp forests.
As pictured above, the lacy crust bryozoan grows on kelp and when it invades a kelp forest, it forms thick crusts on kelp blades. These blades are highly prone to breaking during storms, which causes an overall decline in kelp density. What could make the Atlantic coast kelp more susceptible is that the kelp has no natural defenses against this invasive bryozoan. Also, some studies have shown that the kelp is more palatable to invertebrates if it is covered with the bryozoans. Because kelp forests are an important source of food and shelter for many marine organisms, any loss of kelp can have a major negative impact on the marine environment. The lacy crust bryozoan is also known to crowd out native bryozoans and other epiphytes, and reduced sea urchin populations have been reported in kelp forests where M. membranacea has invaded.
Membranipora membranacea is capable of reproducing sexually via broadcast spawning in the spring and summer. It can also reproduce asexually by budding new zooids. Being a filter-feeder this animal sieves phytoplankton from seawater with a ring of tentacles called a lophophore. Egg production occurs once a year in the spring; the planktotrophic larvae are free swimming, feeding on zooplankton and phytoplankton, even other larvae. In the late summer and early autumn, the larvae then settle on kelp fronds and begin forming colonies.
Membranipora membranacea first appeared off the coast of Maine in 1987; means of introduction is not specifically known but it is thought to have come by ballast water or as a fouling organism on a boat. Now it is present along the Northeastern Atlantic coast from Nova Scotia to Connecticut.
Northeast European Atlantic including: Baltic Sea, English Channel, and Mediterranean Sea.; also, the North Pacific from Alaska to Baja California.
U.S. Habitat: Shallow sub-tidal zones of temperate seas where kelp and other macro-algae grow.
U.S. Present: Coastal bays of CT, MA, ME, NH and RI
As is the problem with marine invasives, there are no real management protocols besides diving and physically removing the bryozoans from the kelp. The physical removal of the invasive invertebrate is so for little results it in turn has little effect on population management. Some nudibranchs (sea slugs) have been found to be predators of these bryozoans, but almost no studies have been performed to see if the nudibranchs are successful bio-controls. What is known is Membranipora membranacea grows quickly (several mm/day) in response to predation from sea slugs and in order to maintain its position on the kelp frond. Prolific growth is favored by fast flowing water which provides food and oxygen. Future research needs to occur so this bryozoan can remain contained in and eventually be eradicated from the Northeastern Atlantic coast of the United States.
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