Membranipora membranacea (Linnaeus, 1767) Common name(s): Kelp encrusting bryozoan, Lacy crust bryozoan, Kelp lace bryozoan, Encrusting bryozoan
Synonyms:  Flustra membranacea
Phylum Bryozoa (Ectoprocta) Class Gymnolaemata Order Cheilostomata Suborder Anasca Family Aeteidae
	Membranipora membranacea bryozoans on a Nereocystis float and blades.
	(Photo by: Dave Cowles, July 2007)

Note:  There are at least three Membranipora species which have been commonly identified on kelp along our coast:  M. membranacea, M. tuberculata, and M. villosa. M. tuberculata and M. villosa have spines while M. membranacea does not.  However,  grazing by nudibranchs is now known to induce spines on M. membranacea and it is possible that the two other species are simply M. membranacea which has had spines induced by grazing.  Others say that M. membranacea is an Atlantic species and the species here is M. villosa.

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.

Geographical Range:  All world temperate zones.  In the Eastern Pacific, from Alaska to Baja California.

Depth Range:  Intertidal to shallow subtidal

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

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).

References:

General References:
  Harbo, 1999
  Johnson and Snook, 1955
  Kozloff, 1993
  McConnaughey and McConnaughey, 1985
  O'Clair and O'Clair, 1998
  Ricketts et al., 1985

Scientific Articles:
Pratt, Marney C., 2008.  Living where the flow is right:  How flow affects feeding in bryozoans.  Integrative and Comparative Biology 48:6 pp 808-822
 

Web sites:

General Notes and Observations:  Locations, abundances, unusual behaviors:

A closer view of one of the colonies shows the lacelike latticework of the boxlike zooecia.

This closer view of the same colony as above shows the small spines present around some of the zooids.  Perhaps this colony has been attacked by nudibranchs lately.

This closeup view of a colony wrapped around a tiny Nereocystis stipe shows the feeding zooids with their lophophores extended in the feeding position.

Here is a closer view of the lophophores.