An ecological study of Electra posidoniae Gautier, 1954 (Cheilostomata, Anasca), a bryozoan epiphyte found solely on the seagrass Posidonia oceanica (L.) Delile, 1813


  • Gilles Lepoint Oceanology, Centre MARE, University of Liège
  • Olivier Mouchette, Centre MARE, University of Liège
  • Corine Pelaprat STARESO (STAtion de REcherches Sous-marines et Océanographiques), Calvi, Corse
  • Sylvie Gobert Oceanology, Centre MARE, University of Liège



biofouling, bryozoan, seagrass, stable isotopes, Neptune grass, NW Mediterranean


The bryozoan Electra posidoniae Gautier is found solely on the leaves of the Neptune grass Posidonia oceanica (L.) Delile, dominating the leaf epifauna of this seagrass. Epiphytes of marine angiosperms (or seagrasses) often play an important role in ecosystem functioning, for example as food web suppliers. As dysfunction of the epiphytic component is often implied in human-induced seagrass decline, it is important to understand the dynamics and life traits of this community in pristine areas. This study involved the monthly assessment of colonization dynamics, biomass seasonality, and diet composition through measurements of stable isotopes, in E. posidoniae at a depth of 10 m in the Revellata Bay (Corsica, Mediterranean Sea). Ancestrulae (i.e. colony founders) appeared towards the end of winter and were very selective in their settlement position along the leaves of P. oceanica. A maximum of 100,000 colonies per square meter was recorded. Colonies of E. posidoniae dominated the epiphytic community biomass in early spring, but were overtaken by epiphytic algae in June. Food shortage could be involved in this reduction in dominance. Although stable isotope ratios of C, N and S showed that this suspension feeder mainly relies on the water column for its food, other food sources such as re-suspended epiphytic diatoms could be important in late spring (i.e. after the phytoplanktonic bloom). Additionally, a contribution of seagrass phytodetritus to the diet of this species cannot be excluded. The species was almost absent in winter, raising the question of its recruitment in spring. This study confirms the quantitative importance of this species in the seagrass meadow and explores its role in the relationship between the water column and this seagrass ecosystem.


Alcoverro T, Perez M & Romero J (2004). Importance of within-shoot epiphyte distribution for the carbon budget of seagrasses: the example of Posidonia oceanica. Botanica Marina, 47: 307-312.

Balata D, Piazzi L, Nesti U, Bulleri F & Bertocci I (2010). Effects of enhanced loads of nutrients on epiphytes on leaves and rhizomes of Posidonia oceanica. Journal of Sea Research, 63: 173-179.

Boero F, Chessa L, Chimenz C & Fresi E (1985). The zonation of epiphytic hydroids on the leaves of some Posidonia oceanica (L.) Delile beds in the central Mediterranean. Pubblicazione della Stazione Zoologica di Napoli I : Marine Ecology, 6: 27-33.

Borowitzka MA, Lavery PS & van Keulen M (2006). Epiphytes of seagrasses. In: Larkum AWD, Orth RJ, Duarte CM (eds). Seagrasses: Biology, Ecology and Conservation, Springer, Berlin: 441-461.

Bracken M (2004). Invertebrate-mediated nutrient loading increases growth of an intertidal macroalga. Journal of Phycology, 40: 1032-1041.

Cebrian J & Lartigue J (2004). Patterns of herbivory and decomposition in aquatic and terrestrial ecosystems. Ecological Monographs, 74: 237-259

Cebrian J, Enriquez S, Fortes M, Agawin N, Vermaat JE, Duarte CM (1999). Epiphyte accrual on Posidonia oceanica (L.) Delile leaves: implications for light absorption. Botanica Marina, 42: 123-128.

Cocito S, Lombardi C, Ciuffardi F & Gambi MC (2012). Colonization of Bryozoa on seagrass Posidonia oceanica ‘mimics’: Biodiversity and recruitment pattern over time. Marine Biodiversity, 42: 189-201.

Coma R & Ribes M (2003). Seasonal energetic constraints in Mediterranean benthic suspension feeders: effects at different levels of ecological organization. Oikos, 101: 205-215.

Connolly RM & Schlacher TA (2013). Sample acidification significantly alters stable isotope ratios of sulfur in aquatic plants and animals. Marine Ecology Progress Series, 493: 1-8.

Dalla Via J, Sturmbauer C, Schonweger G, Sotz E, Mathekowitsch S, Stifter M, Rieger R (1998). Light gradients and meadow structure in Posidonia oceanica: ecomorphological and functional correlates. Marine Ecology Progress Series, 163: 267-278.

Dauby P, Bale AJ, Bloomer N, Canon C, Ling RD, Norro A, Robertson JE, Simon A, Théate J-M, Watson AJ, Fankignoulle M (1995). Particle fluxes over a Mediterranean seagrass bed: a one year case study. Marine Ecology Progress Series, 126: 233-246.

De Stefano M, Marino D & Mazzella L (2000). Marine taxa of i on leaves of Posidonia oceanica, including a new species and two new varieties. European Journal of Phycology, 35: 225-242.

Gacia E, Duarte CM & Middelburg JJ (2002). Carbon and nutrient deposition in a Mediterranean seagrass (Posidonia oceanica) meadow. Limnology and Oceanography, 47: 23-32.

Gacia E, Costalago D, Prado P, Piorno D & Tomas F (2009). Mesograzers in Posidonia oceanica meadows: an update of data on gastropod-epiphyte-seagrass interactions. Botanica Marina, 52: 439-447.

Gautier YV (1961). Recherches écologiques sur les bryozoaires Chilostomes en Méditerrannée occidentale. Thèse de Doctorat, Université de Marseille, Marseille.

Hayward PJ (1975). Observations on the bryozoan epiphytes of Posidonia oceanica from the island of Chios (Aegean Sea). In: Pouyet S (ed), Bryozoa, Presse de l’Université Claude Bernard, Lyon: 347-356.

Jacquemart J & Demoulin V (2008). Comparison of the epiphytic macroflora of Posidonia oceanica leaves in different meadows of the western Mediterranean. Flora Mediterranea, 18: 393-420.

Lemmens JWTJ, Clapin G, Lavery PS & Cary J (1996). Filtering capacity of seagrass meadows and other habitats of Cockburn Sound, Western Australia. Marine Ecology Progress Series, 143: 187-200.

Lepoint G, Havelange S, Gobert S & Bouquegneau JM (1999). Fauna vs flora contribution to the leaf epiphytes biomass in a Posidonia oceanica seagrass bed (Revellata Bay, Corsica). Hydrobiologia, 394: 63-67.

Lepoint G, Nyssen F, Gobert S, Dauby P & Bouquegneau JM (2000). Relative impact of a seagrass bed and its adjacent epilithic algal community in consumer diets. Marine Biology, 136: 513-518.

Lepoint G, Dauby P, Fontaine M, Bouquegneau JM & Gobert S (2003). Carbon and nitrogen isotopic ratios of the seagrass Posidonia oceanica: Depth-related variations. Botanica Marina, 46: 555-561.

Lepoint G, Gobert S, Dauby P & Bouquegneau JM (2004). Contributions of benthic and planktonic primary producers to nitrate and ammonium uptake fluxes in a nutrient-poor shallow coastal area (Corsica, NW Mediterranean). Journal of Experimental Marine Biology and Ecology, 302: 107-122.

Lepoint G, Balancier B & Gobert S (2014). Seasonal and depth-related biodiversity of leaf epiphytic Cheilostome Bryozoa in a Mediterranean Posidonia oceanica meadow. Cahiers de Biologie Marine, 55: 57-67.

Lisbjerg D & Petersen JK (2000). Clearance capacity of Electra bellula (Bryozoa) in seagrass meadows of Western Australia. Journal of Experimental Marine Biology and Ecology, 244: 285-296.

Mabrouk L, Hamza A, Ben Brahim M & Bradai MN (2011). Temporal and depth distribution of microepiphytes on Posidonia oceanica (L.) Delile leaves in a meadow off Tunisia. Marine Ecology, 32: 148-161.

Mateo MA, Cebrian J, Dunton K & Mutchler T (2006). Carbon Flux in Seagrasses. In: Larkum AWD, Orth RJ, Duarte CM (eds). Seagrasses: Biology, Ecology and Conservation, Springer, Berlin:159-192.

Matricardi G, Montagna P & Pisano E (1991). Settlement and growth strategies of Electra posidoniae Gautier on Posidonia oceanica (L.) Delile. In: Bigey FP (ed), Bryozoaires actuels et fossiles: Bryozoa living and fossil. Nantes (France): 255-262.

Mazzella L, Scipione MB & Buia MC (1989). Spatio-temporal distribution of Algal and Animal communities in a Posidonia oceanica meadow. Pubblicazione della Stazione Zoologica di Napoli I : Marine Ecology, 10: 107-129.

Mazzella L & Russo GF (1989). Grazing effect of two Gibbula species (Mollusca, Archaeogastropoda) on the epiphytic community of Posidonia oceanica leaves. Aquatic Botany, 35: 353-373.

Mazzella L, Buia MC, Gambi MC, Lorenti M, Russo GF, Scipione MB, Zupo V (1992). Plant-animal trophic relationships in the Posidonia oceanica ecosystem of the Mediterranean Sea: a review. In: John DM, Hawkins SJ, Price JH (eds), Plant-Animal Interactions in the Marine Benthos, Clarendon Press, Oxford: 165-187.

McKinney FK & Jackson JBC (1989). Bryozoan Evolution. Unwin Hyman, Boston.

Michel L (2011). Multidisciplinary study of trophic diversity and functional role of amphipod crustaceans associated to Posidonia oceanica meadows. PhD Thesis, University of Liège.

Novak R (1984). A Study in Ultra-Ecology: Microorganisms on the Seagrass Posidonia oceanica (L.) Delile. Pubblicazione de,lla Stazione Zoologica di Napoli I : Marine Ecology 5: 143-190.

Nikulina EA, Hanel R & Schafer P (2007). Cryptic speciation and paraphyly in the cosmopolitan bryozoan Electra pilosa - Impact of the Tethys closing on species evolution. Molecular Phylogenetics and Evolution, 45: 765-776.

Peres J-M & Picard J (1964). Nouveau manuel de bionomie benthique de la mer Méditerranée. Edition revue et augmentée. Publication de la Station Marine d’Endoume, Marseille.

Pinnegar JK & Polunin NVC (1999). Differential fractionation of d13C and d15N among fish tissues: implications for the study of trophic interactions. Functional Ecology, 13: 225-231.

Prado P, Alcoverro T & Romero J (2008). Seasonal response of Posidonia oceanica epiphyte assemblages to nutrient increase. Marine Ecology Progress Series, 359: 89-98.

Sturaro N, Caut S, Gobert S, Bouquegneau J-M & Lepoint G (2010). Trophic diversity of idoteids (Crustacea, Isopoda) inhabiting the Posidonia oceanica litter. Marine Biology, 157: 237-247.

Tomas F, Turon X & Romero J (2005). Effects of herbivores on a Posidonia oceanica seagrass meadow: importance of epiphytes. Marine Ecology Progress Series, 301: 95-107.

Van Der Ben D (1971). Les épiphytes des feuilles de Posidonia oceanica Delile sur les côtes françaises de la Méditerranée. Mémoires de l’Institut Royal des Sciences Naturelles de Belgique, 168: 1-101.

Vermeulen S (2012). Spatial and temporal responses of marine gastropods and biofilms to urban wastewater pollution in a Mediterranean coastal area. PhD Thesis, University of Liège.

Vizzini S (2009). Analysis of the trophic role of Mediterranean seagrasses in marine coastal ecosystems: a review. Botanica Marina, 52: 383-393.




How to Cite

Lepoint, G., Mouchette, O., Pelaprat, C., & Gobert, S. (2020). An ecological study of Electra posidoniae Gautier, 1954 (Cheilostomata, Anasca), a bryozoan epiphyte found solely on the seagrass Posidonia oceanica (L.) Delile, 1813. Belgian Journal of Zoology, 144(1).