Membranipora membranacea
Encyclopedia
Membranipora membranacea is a very widely distributed species of marine bryozoa
n 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 sea-mat or lacy crust bryozoan and is often abundantly found encrusting seaweeds, particularly kelp
s.
, English Channel
, Mediterranean Sea
and North Sea
. Also native to the North Pacific coastline of North America
from Alaska
to California
. First recorded on the Atlantic coastline of the U.S. in 1987 in the Gulf of Maine
, it now commonly occurs along the Northwest Atlantic from Long Island Sound
to northern Newfoundland
.
s, each with a chitinous exoskeleton which is secreted by the epidermis
. 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.
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. When not feeding, the lophophore retracts into the polypide through the tentacular sheath. The lophophore is controlled by the zooids 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.
Unlike most byrozoans, this species does not have the ovicells or avicularia
often seen in other members of this phylum.
. 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. 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.
in a radial pattern from the first established zooid, the ancestrula.
, 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.
s or seas 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 also results in decreased growth and reproduction of the colony.
in many places, and is believed to have a potentially negative impact on marine ecosystems by limiting the ability of the 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 by increasing tissue loss and blade breakage.
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.
Bryozoa
The Bryozoa, also known as Ectoprocta or commonly as moss animals, are a phylum of aquatic invertebrate animals. Typically about long, they are filter feeders that sieve food particles out of the water using a retractable lophophore, a "crown" of tentacles lined with cilia...
n known from the Atlantic and Pacific Oceans, usually in temperate
Temperate
In geography, temperate or tepid latitudes of the globe lie between the tropics and the polar circles. The changes in these regions between summer and winter are generally relatively moderate, rather than extreme hot or cold...
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 sea-mat or lacy crust bryozoan and is often abundantly found encrusting seaweeds, particularly kelp
Kelp
Kelps are large seaweeds belonging to the brown algae in the order Laminariales. There are about 30 different genera....
s.
Distribution
Northeast Atlantic including the Baltic SeaBaltic Sea
The Baltic Sea is a brackish mediterranean sea located in Northern Europe, from 53°N to 66°N latitude and from 20°E to 26°E longitude. It is bounded by the Scandinavian Peninsula, the mainland of Europe, and the Danish islands. It drains into the Kattegat by way of the Øresund, the Great Belt and...
, English Channel
English Channel
The English Channel , often referred to simply as the Channel, is an arm of the Atlantic Ocean that separates southern England from northern France, and joins the North Sea to the Atlantic. It is about long and varies in width from at its widest to in the Strait of Dover...
, Mediterranean Sea
Mediterranean Sea
The Mediterranean Sea is a sea connected to the Atlantic Ocean surrounded by the Mediterranean region and almost completely enclosed by land: on the north by Anatolia and Europe, on the south by North Africa, and on the east by the Levant...
and North Sea
North Sea
In the southwest, beyond the Straits of Dover, the North Sea becomes the English Channel connecting to the Atlantic Ocean. In the east, it connects to the Baltic Sea via the Skagerrak and Kattegat, narrow straits that separate Denmark from Norway and Sweden respectively...
. Also native to the North Pacific coastline of North America
North America
North America is a continent wholly within the Northern Hemisphere and almost wholly within the Western Hemisphere. It is also considered a northern subcontinent of the Americas...
from Alaska
Alaska
Alaska is the largest state in the United States by area. It is situated in the northwest extremity of the North American continent, with Canada to the east, the Arctic Ocean to the north, and the Pacific Ocean to the west and south, with Russia further west across the Bering Strait...
to California
California
California is a state located on the West Coast of the United States. It is by far the most populous U.S. state, and the third-largest by land area...
. First recorded on the Atlantic coastline of the U.S. in 1987 in the Gulf of Maine
Gulf of Maine
The Gulf of Maine is a large gulf of the Atlantic Ocean on the east coast of North America.It is delineated by Cape Cod at the eastern tip of Massachusetts in the southwest and Cape Sable at the southern tip of Nova Scotia in the northeast. It includes the entire coastlines of the U.S...
, it now commonly occurs along the Northwest Atlantic from Long Island Sound
Long Island Sound
Long Island Sound is an estuary of the Atlantic Ocean, located in the United States between Connecticut to the north and Long Island, New York to the south. The mouth of the Connecticut River at Old Saybrook, Connecticut, empties into the sound. On its western end the sound is bounded by the Bronx...
to northern Newfoundland
Newfoundland and Labrador
Newfoundland and Labrador is the easternmost province of Canada. Situated in the country's Atlantic region, it incorporates the island of Newfoundland and mainland Labrador with a combined area of . As of April 2011, the province's estimated population is 508,400...
.
Morphology and Physiology
Membranipora membranacea colonies consist of individual organisms called zooidZooid
A zooid or zoöid is a single animal that is part of a colonial animal. The zooids can either be directly connected by tissue or share a common exoskeleton...
s, each with a chitinous exoskeleton which is secreted by the epidermis
Epidermis
Epidermis may refer to:* Epidermis , in plants, the outermost layer of cells covering the leaves and young parts of a plant* Epidermis , the outermost layer of the skin of a human...
. This exoskeleton, hardened with calcium carbonate
Calcium carbonate
Calcium carbonate is a chemical compound with the formula CaCO3. It is a common substance found in rocks in all parts of the world, and is the main component of shells of marine organisms, snails, coal balls, pearls, and eggshells. Calcium carbonate is the active ingredient in agricultural lime,...
, 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.
The internal, living portion of the zooid is known as the polypide
Polypide
The polypide in bryozoans encompasses most of the organs and tissues of each individual zooid. This includes the tentacles, tentacle sheath, U-shaped digestive tract, musculature and nerve cells. It is housed in the zooidal skeleton, which in cyclostomes is tubular and in cheilostomes is box-shaped....
, whose walls are formed by the outer epidermis and inner peritoneum
Peritoneum
The peritoneum is the serous membrane that forms the lining of the abdominal cavity or the coelom — it covers most of the intra-abdominal organs — in amniotes and some invertebrates...
. The lophophore
Lophophore
The lophophore is a characteristic feeding organ possessed by four major groups of animals: the Brachiopoda, Bryozoa, Entoprocta, and Phoronida. All lophophores are found in aquatic organisms.-Characteristics:...
, a ring of ciliated tentacles, protrudes from the polypide to feed. When not feeding, the lophophore retracts into the polypide through the tentacular sheath. The lophophore is controlled by the zooids nervous system, which consists of a ganglion
Ganglion
In anatomy, a ganglion is a biological tissue mass, most commonly a mass of nerve cell bodies. Cells found in a ganglion are called ganglion cells, though this term is also sometimes used to refer specifically to retinal ganglion cells....
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.
Unlike most byrozoans, this species does not have the ovicells or avicularia
Avicularia
Avicularia is a genus of the family Theraphosidae containing various species of tarantulas. The genus is native to tropical South America. Each species in the genus has very distinguishable pink foot pads....
often seen in other members of this phylum.
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 metamorphosisMetamorphosis
Metamorphosis is a biological process by which an animal physically develops after birth or hatching, involving a conspicuous and relatively abrupt change in the animal's body structure through cell growth and differentiation...
. The larvae typically settle on their preferred substrates in May, and then the colony undergoes growth, stasis
Stasis
The term stasis may refer to* A state of stability, in which all forces are equal and opposing, therefore they cancel out each other....
and reproduction, shrinkage, and senescence
Senescence
Senescence or biological aging is the change in the biology of an organism as it ages after its maturity. Such changes range from those affecting its cells and their function to those affecting the whole organism...
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 buddingBudding
Budding is a form of asexual reproduction in which a new organism grows on another one. The new organism remains attached as it grows, separating from the parent organism only when it is mature. Since the reproduction is asexual, the newly created organism is a clone and is genetically identical...
in a radial pattern from the first established zooid, the ancestrula.
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 bacteriaBacteria
Bacteria are a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria have a wide range of shapes, ranging from spheres to rods and spirals...
, 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
NudibranchNudibranch
A nudibranch is a member of what is now a taxonomic clade, and what was previously a suborder, of soft-bodied, marine gastropod mollusks which shed their shell after their larval stage. They are noted for their often extraordinary colors and striking forms...
s or seas 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 also results in decreased growth and reproduction of the colony.
Ecological significance
M. membranacea has become an invasive speciesInvasive species
"Invasive species", or invasive exotics, is a nomenclature term and categorization phrase used for flora and fauna, and for specific restoration-preservation processes in native habitats, with several definitions....
in many places, and is believed to have a potentially negative impact on marine ecosystems by limiting the ability of the 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 by increasing tissue loss and blade breakage.
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.