Membranipora membranacea is a very widely distributed species of marine bryozoan known from the Atlantic and Pacific 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.
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. The species was first recorded on the Atlantic coastline of the U.S. in 1987 in the Gulf of Maine. In Canada's Atlantic coast, it was first observed in Nova Scotia during the early 1990s, and had reached Newfoundland and Labrador by 2002. 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. Zooids within a colony can communicate via pores in their interconnecting walls, through which coelomic fluid can be exchanged. 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. The larvae typically settle on their preferred substrates in May, and then the colony undergoes growth, stasis and reproduction, shrinkage, and senescence around September, except in regions where temperature allows them to persist further into the winter.
Ecological significance
thumb|M. membranacea on a kelp blade
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.
M. membranacea also decreases density and size of kelp plants within kelp beds 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.