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Bibliographie de l'Institut Maurice-Lamontagne

Plantes - Algues vertes / Codium fragile / 

DROUIN, A., C.W. MCKINDSEY, L.E. JOHNSON, 2012. Detecting the impacts of notorious invaders : experiments versus observations in the invasion of eelgrass meadows by the green seaweed Codium fragile. Oecologia, 168: 491-502.

[Résumé disponible seulement en anglais]
Biological invasions can vary in the extent of their effects on indigenous communities but predicting impacts for particular systems remains difficult. In coastal marine ecosystems, the green seaweed Codium fragile ssp. Fragile is a notorious invader with its reputation based on studies conducted largely on rocky shores. The green seaweed has recently invaded soft-bottom eelgrass communities by attaching epiphytically to eelgrass (Zostera marina) rhizomes, thereby creating the potential for disruption of these coastal habitats through competition or disturbance. We investigated the effect of this invader on various aspects of eelgrass performance (shoot density and length, shoot growth, above- and below-ground biomass, carbohydrate storage) using both small-scale manipulative and large-scale observational experiments. Manipulative experiments that varied Codium abundance demonstrated clear negative effects over a 4-month period on shoot density and carbohydrate reserves, but only for high, but realistic, Codium biomass levels. Light levels were much lower under canopies for high and medium density Codium treatments relative to low and control Codium cover treatments, suggesting that shading may influence eelgrass growing under the algal cover. In contrast, these effects were either not detectable or very weak when examined correlatively with field surveys conducted at larger spatial scales, even for sites that had been invaded for over 4 years. It is premature to extend generalizations of Codium’s impact derived from studies in other systems to eelgrass communities; further efforts are required to assess the long-term threats that the alga poses to this ecosystem. This study demonstrates the need to investigate impacts of invasions over multiple scales, especially those that incorporate the temporal and spatial heterogeneity of the invader’s abundance.©2011 Springer

GAGNON, K., C.W. McKINDSEY, L.E. JOHNSON, 2011. Dispersal potential of invasive algae : the determinants of buoyancy in Codium fragile ssp.fragile. Mar. Biol., 158(11): 2449-2458 .

[Résumé disponible seulement en anglais]
The capacity for long-distance dispersal is an important factor in determining the spread of invasive species. For algae, positive buoyancy generally is correlated with increased dispersal potential, and the light environment has been previously identified as a possible determinant of buoyancy in several species. We examined the effect of light intensity on the buoyancy of fragments of the invasive Green Alga Codium fragile ssp. fragile. Under natural and controlled conditions, the buoyancy of samples taken from the thallus tip was higher than those from near the holdfast. Both laboratory and field experiments also showed that buoyancy was dynamic and switched from positive to negative under reduced light intensity, but this change required several days. We also observed seasonal changes in buoyancy, presumably due to natural variations in light intensity, with the buoyancy of fragments washed up on the shore highest in mid-summer. These results show that buoyancy is a dynamic property of the C. fragile ssp. fragile thallus and suggest that buoyant fragments contribute to long-range dispersal and accelerated regional spread of this invader. This finding suggests that dispersal is more likely during conditions of high light intensity and illustrates the need to understand how variations in the natural environment can affect the dispersal potential of invasive species.©2011 Springer