Overview

Comprehensive Description

General Description

A very common and conspicuous bryozoan throughout Britain and North America’s Pacific coast. Colonies form white or light grey encrusting sheets on algal substrates, with short tubercules or spines protruding from the zooids. Colonies can become very large, covering extensive areas of kelp fronds. Colonies are found from the lower intertidal down to the limit of the kelp forests

M. membranacea is recognised an invasive bryozoan species and can have serious ecological impacts on kelp forests.

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Description

 This epiphytic bryozoan forms encrusting lacy mat-like colonies of very small, rectangular autozooids, 0.42 x 0.13 mm, with tubercules or short spines in the corners. Each zooid has lateral calcified walls that contain ventral uncalcified bands providing flexibility. A frontal membrane completely roofs the space between the supporting side walls with a lophophore (feeding tentacles) visible within. Tower zooids may also be present; where the frontal membrane projects upwards in a columnar way.Colonies may vary in size. 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 favoured by fast flowing water which provides food and oxygen. Egg production occurs once a year in the spring; the larva (cyphonautes) is planktotrophic and is the most abundant and largest coastal larva in Britain between June and August. The larva settles in late summer-early autumn.
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Biology/Natural History: Bryozoans start from a single individual zooid (an ancestrula) which repeatedly reproduces asexually to form a colony. In this species, the oldest individual is in the middle. Colonies of this species usually begin to be noticeable in late spring and grow through summer into fall. By fall they may form extensive crusts on the kelp and many colonies have merged with one another. In many bryozoans there are various types of zooids but in this species there is only one type of zooid which serves for feeding, for reproduction, and for defense. The colony appears to be a simultaneous hermaphrodite, or male zooids may develop first. They do not brood their young. Eggs are fertilized then released, and quickly develop into cyphonautes larvae which may feed and develop as plankton for several months. The larvae settle when they encounter kelp such as Laminaria or water with an excess of potassium ions. The small white nudibranch Doridella steinbergae may be found living and feeding on these colonies but it blends in so well it is difficult to see. Other predators include sea urchins and the nudibranch Corambe pacifica (pale translucent gray with a central yellowish patch and marginal yellow lines, up to 1 cm long, nearly as wide as long, with a deep notch in back). Colonies which have recently been attacked by nudibranchs may grow large chitonous spines, especially on the peripheral zooids.

This species appears to be able to feed at higher water flow velocities than some other species can (Pratt, 2008). They frequently encrust the brown kelp Nereocystis luetkeana, and the larvae show a strong preference to settling on that alga over the red alga Mazzaella splendens (Matson et al., 2010). The Matson et al. article includes online several videos showing larval settlement in flow.

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This bryozoan frequently grows as thin, flat white crusts on large kelp. The zooids are small rectangular boxlike structures. Most of the frontal of the zooid is membranous instead of calcified, and they have an operculum. They have no distinct spines, though there are knoblike or small spinelike protuberances on the margins between zooids (photo) (and see the note below). They have no avicularia or vibracula. The side walls between zooids are thin and not heavily calcified (photo), though they may be slightly serrated. Colonies are often nearly circular and usually nearly white. The individual zooids are little calcified and almost clear.
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Description

This bryozoan forms lacy patches on kelp fronds. The individual zooids have transparent tops allowing the colour of the kelp to show through. Each zooid is rectangular.
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Distribution

Leeft enkel op bruinwieren. In België aangespoeld op knotswier, riemwiervoetjes en Laminaria. Alle gereviseerde kolonies in de collectie van het KBIN bleken andere soorten te zijn! Bijgevolg kan M. membranacea niet als inheems in België beschouwd worden. Kwam (komt?) in de Oosterschelde voor van Colijnsplaat tot Yerseke (Faasse & De Blauwe, 2004). Spoelt langs de gehele kust van Nederland aan op zeewier (Lacourt (1978), de Ruijter (2007, 2008)).
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Membranipora membranacea komt voor als uitgebreide kolonies op bladeren van Laminaria en kleinere kolonies op Fucus serratus
  • De Blauwe, H. (2009). Mosdiertjes van de Zuidelijke Bocht van de Noordzee. Determinatiewerk voor België en Nederland. Uitgave Vlaams Instituut voor de Zee, Oostende: 464pp.
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M. membranacea is native to the North Pacific, but occurs throughout the temperate NE Atlantic and Pacific. Populations have established along the coasts of Nova Scotia, New Brunswick, Newfoundland and the Gulf of Maine. M.membranacea is present on all British coasts and is the most commonly occurring bryozoan in Scotland. This species is the only member of its genus in British waters.

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National Distribution

United States

Origin: Native

Regularity: Regularly occurring

Currently: Present

Confidence: Confident

Type of Residency: Year-round

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Global Range: Native to Europe and Pacific coast of North America from Alaska to Baja California. Introduced to the Gulf of Maine on the Atlantic coast of North America (Berman et. al., 1992).

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Geographical Range: All world temperate zones. In the Eastern Pacific, from Alaska to Baja California. It is apparently not native in the North Atlantic.

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Physical Description

Morphology

Colonies form extensive, lacey sheets on algal substrates. Zooids are rectangular with tubercules (spines) protruding from the corners. The lateral walls of the zooids are calcified, but incorporate two vertical uncalcified bands which provide flexibility to colony as the aglal substrate moves in the waves. Large chitonous spines are produced rapidly in response to waterborne cues from the trophically specialised nudibranch, Doridella steinberae.

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Size

Zooids are typically 0.42 by 0.13mm

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Diagnostic Description

Description

De kolonie vormt een uitgebreide, leerachtige bedekking op bruinwieren. Zoïden rechthoekig, met knobbeltjes of korte stekels, waarvan de top niet verkalkt is, op de hoeken. Het membraan bedekt het gehele frontale vlak. Kolonie flexibel, zodat ze zich kan vasthechten aan zeewier zoals Laminaria, zonder te breken als de bladeren bewegen in de golven. « Torenzoïden » waar het frontale membraan opwaarts gericht is als een buis, kunnen aanwezig zijn. Polypide met ongeveer 17 tentakels.
  • De Blauwe, H. (2009). Mosdiertjes van de Zuidelijke Bocht van de Noordzee. Determinatiewerk voor België en Nederland. Uitgave Vlaams Instituut voor de Zee, Oostende: 464pp.
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Look Alikes

M.membranacea bears a superficial resemblance to Electra pilosa, which has a similar colony form and colour. M. membranacea can be distinguished by its rectangular zooids, compared to the rounded zooids of E.pilosa. Zooids of E.pilosa also have a characteristic large central spine.

Species of Membranipora are easily confused with those of the related genus Conopeum. Membranipora species may be distinguished by the presence of a twinned ancestrula (the founding zooid), compared to the single ancestrula of Conopeum species. However, the ancestrula region is frequently missing from colonies, making this character insufficient to distinguish species. Conopeum reticulum has thicker calcification than Membranipora species. C. reticulum may also be distinguished from other littoral and sublittoral species in the same family by the presence of paired triangular chambers (kenozooids) at the end of each zooid.


Conopeum and Membranipora species also differ in their ecology. M. membranacea is the only species of its genus to occur in British waters, where it forms extensive colonies, normally on Laminaria. Membranipora tuberculata, which colonises Sargassum, and Membranipora tenuis, a tropical species, are, on rare occasions, washed up on south-western shores of the UK. Both of the British species of Conopeum colonise hard substrata or estuarine plants, but would not be expected to occur on marine algae.

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How to Distinguish from Similar Species: Although Conopeum reticulatum also grows as thin, flat crusts with rectangular zooids and no avicularia, the walls between zooecia are heavily calcified and granular. The California spiral-tufted bryozoan, Bugula californica, may also grow on kelp blades but it does not form a crust.
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Ecology

Habitat

M. membranacea most commonly grows on kelp from the lower shore down to the lower limit of the kelp forests. It may also colonise Fucus species in rock pools. Common on sheltered rocky shores, colonies will grow best in areas of fast flowing water or high tidal influx.

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Depth range based on 268 specimens in 1 taxon.
Water temperature and chemistry ranges based on 34 samples.

Environmental ranges
  Depth range (m): 0 - 2900
  Temperature range (°C): 10.151 - 12.348
  Nitrate (umol/L): 4.729 - 7.362
  Salinity (PPS): 31.893 - 35.363
  Oxygen (ml/l): 6.095 - 6.665
  Phosphate (umol/l): 0.335 - 0.943
  Silicate (umol/l): 2.311 - 15.658

Graphical representation

Depth range (m): 0 - 2900

Temperature range (°C): 10.151 - 12.348

Nitrate (umol/L): 4.729 - 7.362

Salinity (PPS): 31.893 - 35.363

Oxygen (ml/l): 6.095 - 6.665

Phosphate (umol/l): 0.335 - 0.943

Silicate (umol/l): 2.311 - 15.658
 
Note: this information has not been validated. Check this *note*. Your feedback is most welcome.

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Comments: Kelps and seaweeds occurring in shallow water and along the lowtide line. Most common on Laminaria SPP. kelp hosts and more abundant in exposed versus protected kelp bed sights (Berman et.al., 1992).

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 Encrusting colonies are typically found on marine algae e.g. Laminaria digitata and Laminaria hyperborea. Occasionally small colonies can be found on Fucus serratus and in rock pools. Found on the lower shore to shallow water.
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Depth Range: Intertidal to shallow subtidal

Habitat: Usually on kelp fronds. May also be on floats or rocks.

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Typically on kelp, especially Laminaria hyperborea in the shallow sublittoral. Colonies grow towards the base of the kelp frond, as this is where the kelp grows from and therefore the colony does not all get shed when the kelp blades are shortened by winter storms.
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Migration

Non-Migrant: No. All populations of this species make significant seasonal migrations.

Locally Migrant: No. No populations of this species make local extended movements (generally less than 200 km) at particular times of the year (e.g., to breeding or wintering grounds, to hibernation sites).

Locally Migrant: No. No populations of this species make annual migrations of over 200 km.

Intoduced to the North American Atlantic coast via ballast water from Pacific coast and/or European ships (Berman et.al., 1992).

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Trophic Strategy

Like all bryozoans, M. mebranacea is a suspension feeder. It feeds on small phytoplankton using ciliated tentacles of the lophophore. 

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Associations

Plant / epiphyte
Membranipora membranacea grows on frond of Laminaria
Other: major host/prey

Plant / epiphyte
Membranipora membranacea grows on Fucus serratus
Other: unusual host/prey

Plant / epiphyte
Membranipora membranacea grows on Seaweeds
Other: sole host/prey

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M. membranacea is commonly predated on by nudibranchs including Polycera quadrillineata and Doridella steinberae.

Colonies attach to shallow sub-tidal seaweeds, particularly on the fronds of kelp (Laminaria digitata and Laminaria hyperborean in the UK, Ecklonia, Macrocystis, and Saccharina longicruris elsewhere). Smaller colonies also form on Fucus serratus.

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General Ecology

Laminaria SPP. of kelp are by far the most common host plant on the Atlantic coast. Kelps covered with M. MEMBRANACEA are apparently more likely to fracture during rough waters created by storms (Berman et.al., 1992). Presence of this invader has contributed significantly to defoliation of Laminaria kelp beds at Cape Neddick Maine (Lambert, 1992).

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Life History and Behavior

Life Cycle

Embryos develop from early spring to early summer. Planktonic larvae are long-lived. They feed and grow throughout summer, and in some cases continue to November. Settlement occurs from summer and peaks in early autumn (September-October), after which larvae metamorphose into a twinned ancestrula (the founding zooid). The ancestrula buds asexually to form young colonies which are approximately circular. Growth is perennial and will occur throughout spring and summer. The colony will tend to grow towards the youngest part of algal substrates at the base.

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Reproduction

Sexually-produced embryos develop once a year, in early spring. Breeding continues through the early summer. The larvae of M.membrancea are planktonic cyphonautes larvae which feed and grow up to 0.6 mm in height and 0.8 mm across the base. Larvae are triangular in shape and laterally compressed. They are common in coastal plankton from February to November, and are especially abundant between June and August.

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Molecular Biology and Genetics

Molecular Biology

Barcode data: Membranipora membranacea

The following is a representative barcode sequence, the centroid of all available sequences for this species.


There are 62 barcode sequences available from BOLD and GenBank.  Below is a sequence of the barcode region Cytochrome oxidase subunit 1 (COI or COX1) from a member of the species.  See the BOLD taxonomy browser for more complete information about this specimen and other sequences.

ACTCTATATTTTTTATTTGGACTTTGAGCCGGGATAGTTGGAAGAGGTTTA---AGAGCGTTAATCCGAGTGGAGCTCAGACAACCCGGCAGTTTATTGGGGAAT---GACCAGTTGTATAATGTTATTGTAACAGCTCATGCTTTTGTTATGATTTTCTTTATGGTTATGCCTGTTATAATTGGGGGTTTTGGTAACTGACTCGTTCCTTTAATG---CTAGGAGTGCCTGATATGGCATTTCCTCGGTTAAATAATATGAGGTTTTGACTTTTACCTCCTGCTTTATTATTATTGCTTATGTCTTCTATAGTAGAATCAGGAGCGGGGACGGGATGAACTGTTTATCCCCCTTTGTCCTCTAATATTGCACATGGGGGAGGTTCCGTTGATTTA---GCTATCTTCTCTCTCCACCTTGCAGGTGTATCTTCTATTTTAGGAGCAATTAATTTTATAACAACAATTGCCAACATACGTAATAGAAAGATTTCTTTTGAGCGTATTAGAATGCTTTGCTGATCAATTTTCATTACAGCTTTATTATTATTACTCTCTCTCCCTGTACTAGCAGGA---GCTATTACTATGCTTCTCACGGATCGTAATTTGAATACTTCTTTCTTTGATCCAGCTGGAGGGGGAGATCCTATCCTTTATCAACATCTA
-- end --

Download FASTA File
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Statistics of barcoding coverage: Membranipora membranacea

Barcode of Life Data Systems (BOLDS) Stats
Public Records: 62
Specimens with Barcodes: 62
Species With Barcodes: 1
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Conservation

Conservation Status

National NatureServe Conservation Status

United States

Rounded National Status Rank: NNR - Unranked

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NatureServe Conservation Status

Rounded Global Status Rank: GNR - Not Yet Ranked

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Relevance to Humans and Ecosystems

Risks

Risk Statement

The species is recognised as invasive throughout Europe and the NW Atlantic. The presence of M. membranacea colonies on kelp reduces the algae’s survival, and can exacerbate the natural seasonal declines of kelp beds in autumn. Colonised kelp tends to become brittle and may be more prone to breakage during periods of intense wave action.  Defloliation of kelp beds by M. membranacea facilitates the introduction and establishment of opportunistic green algae and hence alters the habitat of ecologically and economically important species such as sea urchins and lobsters.

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Wikipedia

Membranipora membranacea

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 sea-mat or lacy crust bryozoan and is often abundantly found encrusting seaweeds, particularly kelps.[1]

Distribution[edit]

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.[2][3] First recorded on the Atlantic coastline of the U.S. in 1987 in the Gulf of Maine,[4] it now commonly occurs along the Northwest Atlantic from Long Island Sound to northern Newfoundland.

Morphology and physiology[edit]

Membranipora membranacea colonies consist of individual organisms called zooids, each with a chitinous exoskeleton which is secreted by the epidermis.[5] 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.[6] Zooids within a colony can communicate via pores in their interconnecting walls, through which coelomic fluid can be exchanged.[5]

The internal, living portion of the zooid is known as the polypide, whose walls are formed by the outer epidermis and inner peritoneum.[6] The lophophore, a ring of ciliated tentacles, protrudes from the polypide to feed.[7] 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.[6]

Unlike most byrozoans, this species does not have the ovicells or avicularia often seen in other members of this phylum.

Natural History[edit]

Life Cycle[edit]

Membranipora membranacea begins its life cycle as a plankton-feeding larva, triangular in shape.[5] After several weeks, the larva attach to a substrate and undergo metamorphosis.[8] 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.[8] The presence of conspecifics may cause a colony to stop growing and begin stasis and reproduction early.[8] The presence of predators also reduces growth of a colony.

Reproduction[edit]

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.[8] 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.[5] Reproduction or growth of the colony can also take place by budding in a radial pattern from the first established zooid, the ancestrula.[5]

Ecology[edit]

Habitat[edit]

M. membranacea prefers shallow marine habitats between the mid intertidal to the shallow sublittoral. It may also be found in brackish water.[1] It is typically found attached in colonies to seaweed, shells, or artificial substrates.[6]

Feeding[edit]

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.[7] They can also supplement their diet with dissolved organic nutrients through the absorptive epidermis.[7]

Predation[edit]

Nudibranchs 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.[9]

Ecological significance[edit]

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 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.[10]

M. membranacea also decreases density and size of kelp plants within kelp beds[4] by increasing tissue loss and blade breakage.[11] 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.[11]

References[edit]

  1. ^ a b Barnes, R.D. (1982). Coasts and Estuaries pp 114-115. Hodder & Staughton, London.
  2. ^ De Haas, W. and F. Knorr (1966). Marine Life pp 212-213. Burke, London.
  3. ^ North, W.J. (1976). Underwater California pp 161. University of California Press. ISBN 0-520-03025-7
  4. ^ a b 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.
  5. ^ a b c d e Barnes, R.D. (1974). Invertebrate Zoology, 3rd ed. Saunders, Philadelphia, PA:695-712.
  6. ^ a b c d Wilmoth, J.H. (1967). Biology of invertebrata. Prentice-Hall, Englewood Cliffs, NJ:381-384.
  7. ^ a b c 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.
  8. ^ a b c d 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.
  9. ^ Yoshioka, P.M. (1982). Predator induced polymorphism in the bryozoan Membranipora membranacea (L.). Journal of Experimental Marine Biology and Ecology 61(3):233-242.
  10. ^ 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.
  11. ^ a b 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.
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