DAO 81:231-240 (2008)  -  doi:10.3354/dao01956

Phylogenetic and morphological characterisation of the green algae infesting blue mussel Mytilus edulis in the North and South Atlantic oceans

Francisco Rodríguez1,5, Stephen W. Feist2, Laure Guillou1, Lisbeth S. Harkestad3, Kelly Bateman2, Tristan Renault4, Stein Mortensen3,*

1Station Biologique de Roscoff, UMR 7144 CNRS et Université Pierre et Marie Curie, BP74, 29682 Roscoff, Cedex, France
2Centre for Environment, Fisheries and Aquaculture Science (Cefas), Barrack Road, Weymouth, Dorset DT4 8UB, UK
3Institute of Marine Research, PO Box 1870, Nordnes, 5817 Bergen, Norway
4IFREMER, Laboratoire de Génétique et Pathologie, 17390 La Tremblade, France
5Present address: Centro Oceanográfico de Canarias (IEO), Ctra. San Andrés 45, 38180 S/C Tenerife, Spain
*Corresponding author. Email:

ABSTRACT: Blue mussels Mytilus edulis with shell deformations and green pustules containing parasitic algae were collected at 3 coastal sites (Burøy, Norway; Bockholm, Denmark; Goose Green, Falkland Islands). A comparative study, including mussel histopathology, algal morphology, ultrastructure and phylogenetic position was performed. Green pustules were mainly located in the posterior portion of the mantle and gonad tissues and the posterior adductor muscle. Electron microscopy confirmed the presence of algal cells with similar morphology to Coccomyxa parasitica. Algae were oval shaped with a single nucleus and chloroplast, 1 or 2 mitochondria and a dense granular cytoplasm with a lipid inclusion body, Golgi apparatus and small vesicles. Partial small subunit (SSU) rRNA phylogeny confirmed the inclusion of parasitic algae into the Coccomyxa clade. However, the sequence identity between almost full SSU rRNA sequences of parasitic algae and others in this clade yielded an unexpected result. Green algae from mussels were distant from C. parasitica Culture Collection of Algae and Protozoa (CCAP) strain 216/18 (94% identity), but very similar (99% identity) to C. glaronensis (a lichen endosymbiont) and green endophytes from the tree Ginkgo biloba. The CCAP strain 216/18 was a sister sequence to Nannochloris algae, far from the Coccomyxa clade. These results suggest a misidentification or outgrowth of the original CCAP strain 216/18 by a different ‘Nannochloris-like’ trebouxiophycean organism. In contrast, our sequences directly obtained from infested mussels could represent the true C. parasitica responsible for the green pustules in blue mussels.

KEY WORDS: Blue mussels · Coccomyxa parasitica · Mytilus edulis · Mytilus edulis chilensis · Parasitic alga · Phylogeny

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Cite this article as: Rodríguez F, Feist SW, Guillou L, Harkestad LS, Bateman K, Renault T, Mortensen S (2008) Phylogenetic and morphological characterisation of the green algae infesting blue mussel Mytilus edulis in the North and South Atlantic oceans. Dis Aquat Org 81:231-240

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