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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 .
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 Codiums 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 invaders abundance.©2011 Springer
DROUIN, A., C.W. MCKINDSEY, L.E. JOHNSON, 2011. Higher abundance and diversity in faunal assemblages with the invasion of Codium fragile ssp. Fragile in eelgrass meadows. Mar. Ecol. Prog. Ser., 424: 105-117 .
The present study examined how species-specific attributes of the invasive alga Codium fragile ssp. Fragile (hereafter Codium) and eelgrass Zostera marina influenced faunal assemblages associated with eelgrass ecosystems in îles de la Madeleine, eastern Canada. Direct association of species with Codium (<1 m) was evaluated and compared to eelgrass faunal assemblages from invaded beds. Potential neighborhood effects (ca. 10 m) were assessed by comparing invertebrates associated with eelgrass in invaded and non-invaded beds. The influence of Codium on more mobile species was evaluated by comparing fish assemblages associated with macrophytes in invaded and non-invaded beds. In addition, speciesarea relationships for low mobility species associated with Codium were contrasted between beds where Codium or eelgrass was the dominant structuring macrophyte. Codium had distinct invertebrate species assemblages, as there was a greater abundance and diversity of invertebrates associated with Codium than with eelgrass, and multivariate assemblage structure differed between macrophyte types. In contrast, no neighborhood patterns were observed as invertebrate assemblages associated with eelgrass did not differ between invaded and non-invaded beds, suggesting that the mechanisms that account for differences between the invertebrate assemblages are a function of the macrophytes nature and operate at small spatial scales. Fish community structure differed between invaded and non-invaded beds, largely due to a greater abundance of 2 fishes, Apeltes quadracus and Tautogolabrus adspersus, in invaded beds. Epifaunal abundance and species richness were positively correlated with Codium thallus biomass, and the abundance relative to biomass correlation was greatest where Codium was the dominant macrophyte. Experimental manipulation of thallus structure to create straight or branched Codium fronds with similar surface area showed that associated invertebrate and gastropod abundance was not influenced by this factor and indicated that factors other than macrostructure complexity influenced the presence of epifauna on the introduced alga. Overall, the present study suggests that the invasion of eelgrass beds by Codium increases faunal density and diversity. However, longer-term effects of Codium invasion in this and other eelgrass ecosystems require further assessment, as the severity of the invasion effects on faunal communities likely depends on the interaction between Codium and eelgrass.©2011 Inter-Research
DROUIN, A., C.W. McKINDSEY, 2007. QBRAT v2 assessment : Codium fragile ssp. tomentosoides in the Gulf of St. Lawrence as a case study ; Evaluation de QBRAT v2 : etude de cas pour Codium fragile ssp. tomentosoides dans le golfe du Saint-Laurent. DFO, Canadian Science Advisory Secretariat, Research Document ; MPO, Secrétariat canadien de consultation scientifique, Document de recherche, 2007/007, 28 p .
The green macroalgae Codium fragile ssp. tomentosoides (herafter, Codium) is native to Japan and has invaded water in eastern Canada. This study evaluated the risk associated with the spread of Codium fragile ssp. tomentosoides in the Gulf of St. Lawrence. Several specific objectives were thus addressed: 1) to review and synthesize the available literature on the ecology and impacts of Codium; 2) to seek the judgement of Codium experts with respect to dispersal vectors, critical habitat attributes, and probabilities and magnitudes of environmental, economic and social impacts related to the establishment of Codium by soliciting participation using a survey; 3) to evaluate the use of an Analytic Hierarchy Process (AHP) to interpret the expert judgements; 4) to do a risk assessment of Codium in the Gulf of St. Lawrence; and 5) to evaluate the utility of using the Quantitative Risk Assessment Tool (QBRAT v2) framework and software by using the Codium risk assessment as a case study. Qualitative analysis of the literature review and the survey results suggest that Codium is quite likely to continue its expansion in the Gulf of St. Lawrence and is likely to cause damage to various components. Spread by plants or plant fragments were considered the greatest single vector for the spread of Codium. With respect to natural processes, spread by propagules was considered to be much less important. Expert judgements suggest that the most important anthropogenic vector for Codium spread is the translocation of infested objects. The presence of artificial structures and biofouling on ships were considered the next most important anthropogenic vectors whereas recreational and commercial boating and ballast water were considered to be less important. The most important criteria for habitat suitability were factors associated with substrate quality (wave exposure, area of available habitat, and substrate type) and mean water temperature. Expert judgements suggest that two of the four environmental criteria (biodiversity and trophic interactions) are considered at high risk from Codium invasion. Economic criteria were judged to be at moderate risk and social criteria at moderate or negligible risk. The AHP was quite efficient for summarizing the expert judgements and describing the error associated with the judgements for each criterion and was thus good for organizing qualitative data quantitatively. The risk assessment using the QBRAT framework showed that the Gulf of St. Lawrence is at high risk from Codium and that most of that risk was associated with further spread of the alga within the area. Future runs of QBRAT for Codium should be done for ecological, economic and social criteria separately to provide the most precise information for management purposes. The use of QBRAT v2 allowed novice users to focus their research to research to acquire all the information needed to run the risk assessment and made choices more objective. The use of the AHP combined with QBRAT v2 gave the user the ability to well define values for different criteria as well as their associated error structure. Several specific recommendations about QBRAT are made.
DROUIN, A., P. SIROIS, P. ARCHAMBAULT, 2006. Structure des communautés dinvertébrés et des espèces damphibiens dans des lacs avec et sans omble de fontaine (Salvelinus fontinalis) en forêt boréale. Rapp. tech. can. sci. halieut. aquat., 2628, 40 p .
The influence of stocking fishless lakes on the biological integrity and diversity is unknow. The objective was to compare the structure of invertebrate communities and amphibian species between lakes with and without fish. Zooplanktonic, nektonic, benthic communities and amphibians were sampled in five fishless lakes as well as in five lakes containing allopatric populations of brook trout (Salvelinus fontinalis). The structure of invertebrate communities and amphibian species were analysed according to univariate (abundance, richness, Shannons diversity index, equitability) and multivariate (PERMANOVA, MDS) approaches. Fishless lakes had a greater abundance of zooplanktonic organisms and a greater diversity of amphibians than lakes with fish. The multivariate approach seemed to be more sensitive than the diversity indexes commonly used to illustrate the differences in invertebrate communities between both types of lakes.
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