title: Free-living stage of the unicellular algae Coccomyxa sp. parasite of the blue mussel (Mytilus edulis): Low-light adaptation, capacity for growth at a very wide salinity range and tolerance to low pH.
abstract: Coccomyxa parasitica and similar, unidentified Coccomyxa species infect the soft tissues of many bivalve species, giving them a conspicuous green coloration and leading to mantle and shell deformities. Very little information exists regarding the ecophysiology of parasitic Coccomyxa sp. and this limits our ability to understand how it can achieve its unusual life history. In the present study, the growth of Coccomyxa sp. Metis-sur-mer (KJ372210) in liquid culture was investigated. Coccomyxa sp. maximum growth rate was 0.75day-1(equivalent to a doubling time of 22h), growth saturated at ∼100μmol quanta m-2s-1and was still ∼20% of maximum at 13μmol quanta m-2s-1, the lowest photosynthetically available radiation (PAR) intensity tested. Coccomyxa sp. showed a very wide tolerance to salinity, with growth rate practically invariable over the salinity range 15-35. Even in natural spring water enriched with f/2 media, the growth rate was nearly half of maximum. Unlike the closely related acid-tolerant Coccomyxa sp. CPCC 508, Coccomyxa sp. Metis-sur-mer could not grow in acidic waters. Considering the ability of Coccomyxa sp. to achieve a high growth rate at low irradiance and its relative insensitivity to the prevailing salinity, it is somewhat surprising it has not yet infected bivalves at a larger scale worldwide.
authors.affiliation: Institut des sciences de la mer de Rimouski (ISMER), Université du Québec à Rimouski, Rimouski, Québec G5L 3A1, Canada. Electronic address: claude_belzile@uqar.ca.
authors.forename: Claude
authors.initials: C
authors.lastname: Belzile
authors.affiliation: Institut des sciences de la mer de Rimouski (ISMER), Université du Québec à Rimouski, Rimouski, Québec G5L 3A1, Canada.
authors.forename: Michel
authors.initials: M
authors.lastname: Gosselin
keywords: Euryaline algae; Flow cytometry; Parasitic algae; Photoacclimation; Photoadaptation; St. Lawrence Estuary