''Membranipora membranacea'' is a very widely distributed species of marine

bryozoa Bryozoa (also known as the Polyzoa, Ectoprocta or commonly as moss animals) are a phylum of simple, aquatic animal, aquatic invertebrate animals, nearly all living in sedentary Colony (biology), colonies. Typically about long, they have a spe ...

n known from the

Atlantic The Atlantic Ocean is the second largest of the world's five oceanic divisions, with an area of about . It covers approximately 17% of Earth's surface and about 24% of its water surface area. During the Age of Discovery, it was known for se ...

and

Pacific The Pacific Ocean is the largest and deepest of Earth's five oceanic divisions. It extends from the Arctic Ocean in the north to the Southern Ocean, or, depending on the definition, to Antarctica in the south, and is bounded by the cont ...

Oceans, usually in temperate zone environments. This bryozoan is a colonial organism characterized by a thin, mat-like encrustation, white to gray in color. It may be known colloquially as the coffin box, sea-mat or lacy crust bryozoan and is often abundantly found encrusting seaweeds, particularly kelps.Barnes, R.D. (1982). Coasts and Estuaries pp 114-115. Hodder & Staughton, London.

Distribution

Northeast Atlantic including the Baltic Sea, English Channel, Mediterranean Sea and North Sea. Also native to the North Pacific coastline of North America from Alaska to California.De Haas, W. and F. Knorr (1966). Marine Life pp 212-213. Burke, London.North, W.J. (1976). Underwater California pp 161. University of California Press. The species was first recorded on the Atlantic coastline of the U.S. in 1987 in the Gulf of Maine.Lambert, W.J., P.S. Levin and J. Berman (1992). Changes in the structure of a New England (USA) kelp bed: the effects of an introduced species? Marine Ecology Progress Series 88:303-307. In Canada's Atlantic coast, it was first observed in Nova Scotia during the early 1990s, and had reached Newfoundland and Labrador by 2002. It now commonly occurs along the Northwest Atlantic from Long Island Sound to northern Newfoundland (island), Newfoundland, including coastal Quebec, New Brunswick, and Prince Edward Island.

Morphology and physiology

''Membranipora membranacea'' colonies consist of individual organisms called zooids, each with a chitinous exoskeleton which is secreted by the Epidermis (zoology), epidermis.Barnes, R.D. (1974). Invertebrate Zoology, 3rd ed. Saunders, Philadelphia, PA:695-712. This exoskeleton, hardened with calcium carbonate, is known as the zooecium, which not only serves to protect the internal structures of the organism, but also keeps the individual permanently attached to the substrate and neighboring zooids.Wilmoth, J.H. (1967). Biology of invertebrata. Prentice-Hall, Englewood Cliffs, NJ:381-384. Zooids within a colony can communicate via pores in their interconnecting walls, through which Coelom#Coelomic fluid, coelomic fluid can be exchanged. The internal, living portion of the zooid is known as the polypide, whose walls are formed by the outer epidermis and inner peritoneum. The lophophore, a ring of ciliated tentacles, protrudes from the polypide to feed.De Burgh, M.E. and P.V. Fankboner (1978). A nutritional association between the bull kelp Nereocystis luetkeana and its epizooic bryozoan ''Membranipora membranacea''. Oikos 31(1):69-72. When not feeding, the lophophore retracts into the polypide through the tentacular sheath. The lophophore is controlled by the zooid's nervous system, which consists of a ganglion at the lophophore base. This ganglion is responsible for motor and sensory impulses to and from the lophophore, as well as the epithelium and digestive tract. The lophophore retractor is the muscle which controls the movement of the lophophore. This species does not have the ovicells or avicularium seen in most other members of this phylum.

Natural history

Life cycle

''Membranipora membranacea'' begins its life cycle as a plankton-feeding larva, triangular in shape. After several weeks, the larva attach to a substrate and undergo metamorphosis.Harvell, C.D., H. Caswell and P. Simpson (1990). Density effects in a colonial monoculture: experimental studies with a marine bryozoan (''Membranipora membranacea'' L.). Oecologia 82(2):227-237. The larvae typically settle on their preferred substrates in May, and then the colony undergoes growth, punctuated equilibrium, stasis and reproduction, shrinkage, and senescence around September, except in regions where temperature allows them to persist further into the winter. The presence of conspecifics may cause a colony to stop growing and begin stasis and reproduction early. The presence of predators also reduces growth of a colony.

Reproduction

Colonies of ''M. membranacea'' are protandrous sequential hermaphrodites, where colonies transition from male to female reproductive stages, allowing fertilization to occur between colonies or within colonies. Fertilization takes places in the coelomic fluid of female colonies, and the eggs are released through an opening in the lophophore known as the coelomophore. Reproduction or growth of the colony can also take place by budding in a radial pattern from the first established zooid, the ancestrula.

Ecology

Habitat

''M. membranacea'' prefers shallow marine habitats between the mid intertidal to the shallow sublittoral. It may also be found in brackish water. It is typically found attached in colonies to seaweed, shells, or artificial substrates.

Feeding

''M. membranacea'' can eat food particles such as bacteria, flagellates, diatoms, and other small, planktonic organisms by extracting them from the water with their lophophore. They can also supplement their diet with dissolved organic nutrients through the absorptive epidermis.

Predation

Nudibranchs or sea slugs are the primary predators of ''M. membranacea''. To defend themselves against these predators, the ''M. membranacea'' produce chitinous spines which protrude from the corners of the zooid. These spines make it difficult for the nudibranchs to access the polypide of the zooid. However, the energy and resources needed to produce the spines may result in decreased growth and reproduction of the colony.Yoshioka, P.M. (1982). Predator induced polymorphism in the bryozoan ''Membranipora membranacea'' (L.). Journal of Experimental Marine Biology and Ecology 61(3):233-242.

Ecological significance

''M. membranacea'' has become an invasive species in many places, and is believed to have a potentially negative impact on marine ecosystems by limiting the ability of seaweeds to reproduce, specifically by interfering with spore release from the kelp blade. The colonies of this bryozoan are also known to interrupt nutrient uptake by seaweed.Saier, B. and A. S. Chapman (2004). Crusts of the alien bryozoan ''Membranipora membranacea'' can negatively impact spore output from native kelps (''Laminaria longicruris''). Botanica Marina 47(4): 265-271. ''M. membranacea'' also decreases density and size of kelp plants within kelp beds by increasing tissue loss and blade breakage.Hepburn, C.D., C.L. Hurd and R.D. Frew (2006). Colony structure and seasonal differences in light and nitrogen modify the impact of sessile epifauna on the giant kelp ''Macrocystis pyrifera'' (L.) C Agardh. Hydrobiologia 560:373-384. Additionally, ''M. membranacea'' also affects photosynthetic processes in kelp, since their encrustations may result in reduced concentrations of the primary and accessory pigments in the kelp blade tissue.

References

{{Authority control Cheilostomatida Fauna of the Atlantic Ocean Bryozoans of the Pacific Ocean Taxa named by Carl Linnaeus Animals described in 1767