Impacts of green tides on flatfish communities and individual performances Emilie Le Luherne, Olivier Le Pape & Elodie Réveillac Flatfish symposia Flatfish ecology – From genomics to ecosystems November 11-16, 2017 Saint Malo, France Impacts of green tides on flatfish – Flatfish symposia – November 16, 2017
Introduction Materials et methods Community scale Individual scale Conclusion Coastal zones and estuaries These systems encompass essential fisheries habitats 44% of the ICES species are dependent on these areas 77% of the commercial landings (Seitz et al., 2014) Life cycle of marine nursery-dependent fish species Emilie Le Luherne Impacts of green tides on flatfish – Flatfish symposia – November 16, 2017
Introduction Materials et methods Community scale Individual scale Conclusion Coastal zones and estuaries These systems encompass essential fisheries habitats 44% of the ICES species are dependent on these areas 77% of the commercial landings (Seitz et al., 2014) Life cycle of marine nursery-dependent fish species Nursery habitats (Beck et al.,2001) Emilie Le Luherne Impacts of green tides on flatfish – Flatfish symposia – November 16, 2017
Introduction Materials et methods Community scale Individual scale Conclusion Coastal zones and estuaries Areas with economical interests (urbanisation, fishery, industry et tourism) Anthropogenic activities threaten these habitats (Lotze et al., 2006; Halpern et al., 2008) Emilie Le Luherne Impacts of green tides on flatfish – Flatfish symposia – November 16, 2017
Introduction Materials et methods Community scale Individual scale Conclusion Coastal zones and estuaries Areas with economical interests (urbanisation, fishery, industry et tourism) Anthropogenic activities threaten these habitats (Lotze et al., 2006; Halpern et al., 2008) Credit : USDA Credit : SIPA (Fletcher, 1996; Merceron et al., 2007) Emilie Le Luherne Impacts of green tides on flatfish – Flatfish symposia – November 16, 2017
Introduction Materials et methods Community scale Individual scale Conclusion Coastal zones and estuaries Areas with economical interests (urbanisation, fishery, industry et tourism) Anthropogenic activities threaten these habitats (Lotze et al., 2006; Halpern et al., 2008) Credit : USDA Green tides Credit : SIPA (Fletcher, 1996; Merceron et al., 2007) Emilie Le Luherne Impacts of green tides on flatfish – Flatfish symposia – November 16, 2017
Introduction Materials et methods Community scale Individual scale Conclusion What are green tides ? Natural phenomenon driven by different seasonal limiting factors (Fletcher, 1996; Merceron et al., 2007) • light • temperature • nutrients (mostly nitrogen) Green tide From CEVA, 1998 Massive proliferation of opportunistic green macroalgae Credit : CEVA Credit : Arirao Emilie Le Luherne Impacts of green tides on flatfish – Flatfish symposia – November 16, 2017
Introduction Materials et methods Community scale Individual scale Conclusion Green tides location In nutrient enriched sublittoral areas with a slight slope and low residual hydrodynamic conditions In the world In Northwestern France more than 80 sites From CEVA, 2011 From Yé, 2011 Credit : fourweekdiary Credit : fourweekdiary Credit : marcelgreen.fr Emilie Le Luherne Impacts of green tides on flatfish – Flatfish symposia – November 16, 2017
Introduction Materials et methods Community scale Individual scale Conclusion Green tides: multiple habitat perturbations Green tides Formation processes (e.g. Fletcher, 1996; Merceron et al., 2007) Emilie Le Luherne Impacts of green tides on flatfish – Flatfish symposia – November 16, 2017
Introduction Materials et methods Community scale Individual scale Conclusion Green tides: multiple habitat perturbations Green tides Physical perturbations habitat structure and complexity Chemical perturbations • [dissolved oxygen] • toxic substances • hydrogen sulfide Trophic perturbations • prey abundance and diversity • access to preys Formation processes (Fletcher, 1996; Raffaelli et al., 1998) (e.g. Fletcher, 1996; Merceron et al., 2007) Emilie Le Luherne Impacts of green tides on flatfish – Flatfish symposia – November 16, 2017
Introduction Materials et methods Community scale Individual scale Conclusion Green tides: multiple habitat perturbations Green tides Intertidal community Physical perturbations habitat structure and complexity Chemical perturbations • [dissolved oxygen] • toxic substances • hydrogen sulfide Trophic perturbations • prey abundance and diversity • access to preys Formation processes (Fletcher, 1996; Raffaelli et al., 1998) (e.g. Fletcher, 1996; Merceron et al., 2007) Emilie Le Luherne Impacts of green tides on flatfish – Flatfish symposia – November 16, 2017
Introduction Materials et methods Community scale Individual scale Conclusion Green tides: multiple habitat perturbations Green tides Intertidal community Physical perturbations habitat structure and complexity Chemical perturbations • [dissolved oxygen] • toxic substances • hydrogen sulfide Trophic perturbations • prey abundance and diversity • access to preys Formation processes (Fletcher, 1996; Raffaelli et al., 1998) (e.g. Fletcher, 1996; Merceron et al., 2007) Studies on the benthic macrofauna • Green tides effect on benthic macrofauna (e.g. Hull, 1987; Norkko & Bonsdorff, 1996a, 1996b) and trophic webs (e.g. Quillien et al., 2015; 2016) • How green tides affects benthic macrofauna (e.g. Magre, 1974; Johnson & Welsh, 1985; Harder et al, 2004) Emilie Le Luherne Impacts of green tides on flatfish – Flatfish symposia – November 16, 2017
Introduction Materials et methods Community scale Individual scale Conclusion Green tides: multiple habitat perturbations Green tides Intertidal community Physical perturbations habitat structure and complexity Chemical perturbations • [dissolved oxygen] • toxic substances • hydrogen sulfide Trophic perturbations • prey abundance and diversity • access to preys Formation processes (Fletcher, 1996; Raffaelli et al., 1998) (e.g. Fletcher, 1996; Merceron et al., 2007) Meta-analysis on the effect of green tides on the entire intertidal community (Lyons et al., 2014) Few studies on ichthyofauna Emilie Le Luherne Impacts of green tides on flatfish – Flatfish symposia – November 16, 2017
Introduction Materials et methods Community scale Individual scale Conclusion Green tides: multiple habitat perturbations Green tides Intertidal community Physical perturbations habitat structure and complexity Chemical perturbations • [dissolved oxygen] • toxic substances • hydrogen sulfide Trophic perturbations • prey abundance and diversity • access to preys Formation processes (Fletcher, 1996; Raffaelli et al., 1998) (e.g. Fletcher, 1996; Merceron et al., 2007) Objective Characterise the effect of green tides on the role of intertidal habitats for flatfish ? Emilie Le Luherne Impacts of green tides on flatfish – Flatfish symposia – November 16, 2017
Introduction Materials et methods Community scale Individual scale Conclusion Part 1 What are the effects of green tides on fish community and especially on flatfish community? Community Part 2 Which physiological processes are implemented by a flatfish species to accomodate the perturbation? Individual Emilie Le Luherne Impacts of green tides on flatfish – Flatfish symposia – November 16, 2017
Introduction Materials et methods Community scale Individual scale Conclusion Study areas Sandy beach Estuarine mudflat N Bay of Saint Brieuc Rance estuary Sandy beach Estuarine mudflat Control Control Impacted Impacted Interannual cover rate < 1% 5 10 50 >75% from CEVA Emilie Le Luherne Impacts of green tides on flatfish – Flatfish symposia – November 16, 2017
Introduction Materials et methods Community scale Individual scale Conclusion Sampling protocol Approach BACI Before/After Control/Impact Control site Impacted site From CEVA, 1998 every 15 days from april to october in 2013 and 2014 Emilie Le Luherne Impacts of green tides on flatfish – Flatfish symposia – November 16, 2017
Introduction Materials et methods Community scale Individual scale Conclusion Sampling protocol Control site Impacted site 6 sampling at each site • Physico-chemical parameters measures (Temperature, Salinity, Dissolved oxygen concentration, pH) and sediment structure • Trawl haul (25 m) using a trawl net Ichthyofauna sampling Measures and Trawling Identification and count samplings Trawl net (juveniles and adults) mesh: 8 mm Total lenght Dorsal Otoliths muscle Emilie Le Luherne Impacts of green tides on flatfish – Flatfish symposia – November 16, 2017
Introduction Materials et methods Community scale Individual scale Conclusion Sampling protocol Control site Impacted site 6 sampling at each site • Physico-chemical parameters measures (Temperature, Salinity, Dissolved oxygen concentration, pH) and sediment structure • Trawl haul (25 m) using a trawl net Ichthyofauna sampling Macroalgae biomass and estimation of each macroalgae morphotype percentage Other macroalgae Filamentous green Expanded blade (e.g. Fucus spp.) macroalgae Ulva spp. Credit : algaeBASE Credit : CEVA Credit : univ-lille1 Emilie Le Luherne Impacts of green tides on flatfish – Flatfish symposia – November 16, 2017
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