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Membranipora membranacea
Welcome to the Membranipora membranacea information page. Just click on the topic of interest from the contents menu or scroll down to
find out all about Membranipora in Nova Scotia.
1. Membranipora membranacea. What is it?
Membranipora is a surface growing bryozoan (on both live organisms and other substrata) that often grows on kelp. Bryozoans form colonies of very small (less than 1mm across) animals called zooids (small filter feeding units). A single colony can consist of thousands of individual zooids. In the case of Membranipora growing on kelp, the colonial zooids attach themselves to the blades and secrete a protective limestone covering which forms a tough, stiff crust over the flexible, rubbery surface of the kelp blade. Kelp blades that are heavily encrusted with Membranipora, become brittle and more susceptible to breakage during storm surge (see Ecological Implications).
2. How to Identify Membranipora
The encrusting colonies of Membranipora appear as a white lace-like coating on kelp fronds. This lacey structure will often appear as patches of varying sizes on a kelp blade. When densities of Membranipora are high enough the entire blade and much of the stipe can be covered by one or more colonies.
3. Quick Reference ID Key:
- Encrusts kelps plants
- White Color
- Lacey, net-like structure
- Patches from a centimeter in diameter to a solid sheet covering the entire frond
4. History and Vectors of Spread: The World and Nova Scotia
Membranipora can be found in temperate oceans of both the Northern and Southern Hemispheres. It occurs in parts of Europe as well as on both coasts of North America. Its first appearance on the Atlantic coast of North America was on the kelp Laminaria saccharina at the Isles of Shoal in the Gulf of Maine in 1987 (Lambert 1992). Within three years of this introduction Membranipora became the dominant kelp epiphyte off the coasts of New Hampshire and Maine. It has since spread both north and south along the coast.
Vectors responsible for the worldwide spread of Membranipora are most likely ship fouling and ballast water.
5. Present Known Distribution in Nova Scotia
The exact distribution of Membranipora in Nova Scotia is unknown. It does however occur throughout areas sampled by a SCUBA survey to determine the extent of Codium
(see Present Known Distribution in Nova Scotia for Codium)
6. Ecological Implications for the Coast of Nova Scotia
While Membranipora does seem to overgrow native epiphytes of kelp for space on kelp fronds, its effect on these epiphtyes is likely minimal because they are more common on other algal hosts (Berman et al 1992). Its greatest impact on the subtidal ecosystem has been the loss of kelp due to frond breakage as a result of heavy encrustations of this byozoan. During periods of increased wave surge, encrusted blades are far more prone to break off. In some areas this has lead to the removal of entire kelp beds. Kelp is a source of both habitat and food for a number of important marine species, and its removal will undoubtably have an impact on these species.
While Membranipora by itself has the ability to alter the subtidal ecosytems it invades, in most cases this alteration would be temporary, with kelp returning when Membranipora densities fall. However the occurance of Membranipora in Nova Scotia has corresponded to the invasion of the subtidal by Codium fragile ssp. tomentosoides (see the Codium page). In areas where the kelp bed has been reduced or removed by Membranipora, Codium has established itself, preventing kelp from returning. Thus, by working together, Membranipora and Codium have brought about what may be long-lasting change in the subtidal ecosystem of Nova Scotia that could have negative effects on biodiversity and commercial resource use.
7. Ecology of Membranipora membranacea
Membranipora grows on most types of macroalgae. It feeds on phytoplankton that it traps with a protruding tentacle. The main predators of Membranipora are some species of
nudibranchs (sea slugs), such as Onchidoris sp, and Palio dubia and Doridella steinbergae which may keep the bryozoan from encrusting entire fronds of kelp. At present there is
little information on the potential for nudibranchs to control Membranipora populations in Nova Scotia.
8. Reproduction in Membranipora
Membranipora reproduces both sexually and asexually. Asexual reproduction is used to expand an existing colony through the budding of new zooids. This is how it rapidly spreads over the kelps surface. Membranipora also produces eggs (one generation per year), normally during the spring and summer, which are shed into the ocean. These eggs develop into larvae and spend several weeks floating freely in the ocean before attaching to a substrate in late summer, early fall.
An interesting characteristic of Membranipora is its apparent ability to detect the youngest part of the algal frond to which it is attached and grow towards it. This behavior is likely an adaptation to the fact that fronds are lost mostly at their oldest, distal edges. However, exactly how Membranipora detects the youngest part of the frond is still unknown.
9. References and Further Reading
References:
Berman J., Harris L., Lambert W., Buttrick M., and Dufresne M. 1992. Recent invasions of the Gulf of Maine: three contrasting ecological histories. Conservation Biology. 6:no. 3,
435-441.
Lambert W.J., Levin P.S., and Berman J. 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.
Further Reading:
Ryland J.S. 1970. Bryozoans. Hutchinson and Co, London.
10. Photo Gallery
Coming Soon!!
11. Acknowledgements
All photos on this website were provided by and the property of Dr. R.E. Scheibling.
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