title: Dynamics of recruitment and establishment of the invasive seaweedCodium fragilewithin an eelgrass habitat.
abstract: Knowledge of the potential distribution (i.e. abundance and spatial extent) of an invasive species is important to estimating its potential impacts on recipient communities. Most previous studies have focused on the potential spatial extent of invasive species populations at regional scales, but little is known on how species successfully recruit and establish at more local scales. In this study, we examined how recruitment of the green algaCodium fragilessp.fragile(hereafterCodium) can vary spatially and the environmental factors associated withCodiumestablishment in eelgrass (Zostera marina) beds. Standardized recruitment blocks (65 blocks in a 720 × 240 m2grid) were used to monitor the number ofCodiumrecruits, juveniles and adults over 2 years. Environmental factors (depth, relative water flow, light and temperature) and attributes of the surrounding macrophyte assemblage (eelgrass density, eelgrass length,Codiumbiomass) were also measured. Recruitment occurred on all blocks or nearby artificial structures (i.e. buoys) and mainly originated from button stages (i.e. female gametes or utricles). Contrary to other studies, the abundance ofCodium(recruits, juveniles and adults) was best predicted by the density of the native canopy-forming species,Z. marina, which highlights a positive interaction between native and non-native canopy-forming species. Seasonal variation in recruitment was observed; it was lower during the summer. Recruitment did not show any distinct spatial pattern (e.g. gradient or patch), but the same spatial pattern of recruitment was observed every sampling date, suggesting that there are "hotspots" for recruitment. In general, the total number ofCodiumfronds observed on a block at the end of the experiment was positively correlated with the cumulative number of recruits. However, recruitment occurred on some blocks but recruits never grew, suggesting that some environmental factors limitCodiumdistribution and abundance in eelgrass beds. Overall, the assessment ofCodiumrecruitment over 2 years showed that the colonization of suitable locations byCodiumwithin seagrass beds may take several years and that some factors may not only limit, but also inhibitCodiumexpansion within eelgrass beds.
authors.affiliation: Demersal and Benthic Sciences Branch, Maurice-Lamontagne Institute, Fisheries and Oceans Canada, PO Box 1000, Mont Joli, QC G5H 3Z4 Canada ; Département de biologie et Québec-Océan, Université Laval, Quebec, QC G1V 0A6 Canada.
authors.forename: Annick
authors.initials: A
authors.lastname: Drouin
authors.affiliation: Demersal and Benthic Sciences Branch, Maurice-Lamontagne Institute, Fisheries and Oceans Canada, PO Box 1000, Mont Joli, QC G5H 3Z4 Canada.
authors.forename: Christopher W
authors.initials: CW
authors.lastname: McKindsey
authors.affiliation: Département de biologie et Québec-Océan, Université Laval, Quebec, QC G1V 0A6 Canada.
authors.forename: Ladd E
authors.initials: LE
authors.lastname: Johnson