title: Interaction strength between different grazers and macroalgae mediated by ocean acidification over warming gradients.
abstract: Since the past century, rising CO2levels have led to global changes (ocean warming and acidification) with subsequent effects on marine ecosystems and organisms. Macroalgae-herbivore interactions have a main role in the regulation of marine community structure (top-down control). Gradients of warming prompt complex non-linear effects on organism metabolism, cascading into altered trophic interactions and community dynamics. However, not much is known on how will acidification and grazer assemblage composition shape these effects. Within this context, we aimed to assess the combined effects of warming gradients and acidification on macroalgae-herbivore interactions, using three cosmopolitan species, abundant in the Iberian Peninsula and closely associated in nature: the amphipod Melita palmata, the gastropod Gibbula umbilicalis, and the green macroalga Ulva rigida. Under two CO2treatments (ΔCO2≃ 450 μatm) across a temperature gradient (13.5, 16.6, 19.9 and 22.1 °C), two mesocosm experiments were performed to assess grazer consumption rates and macroalgae-herbivore interaction, respectively. Warming (Experiment I and II) and acidification (Experiment II) prompted negative effects in grazer's survival and species-specific differences in consumption rates. M. palmata was shown to be the stronger grazer per biomass (but not per capita), and also the most affected by climate stressors. Macroalgae-herbivore interaction strength was markedly shaped by the temperature gradient, while simultaneous acidification lowered thermal optimal threshold. In the near future, warming and acidification are likely to strengthen top-down control, but further increases in disturbances may lead to bottom-up regulated communities. Finally, our results suggest that grazer assemblage composition may modulate future macroalgae-herbivore interactions.
authors.affiliation: Interdisciplinary Centre of Marine and Environmental Research (CIIMAR/CIMAR), University of Porto, Rua dos Bragas 289, 4050-123 Porto, Portugal; MARE - Marine Environmental Science Centre, Laboratório Marítimo da Guia, Faculdade de Ciências da Universidade de Lisboa, Av. Nossa Senhora do Cabo 939, Cascais 2750-374, Portugal. Electronic address: edusilvasampaio@gmail.com.
authors.forename: E
authors.initials: E
authors.lastname: Sampaio
authors.affiliation: Interdisciplinary Centre of Marine and Environmental Research (CIIMAR/CIMAR), University of Porto, Rua dos Bragas 289, 4050-123 Porto, Portugal; Tvärminne Zoological Station, University of Helsinki, Hanko, Finland; Baltic Sea Centre, Stockholm University, Stockholm, Sweden.
authors.forename: I F
authors.initials: IF
authors.lastname: Rodil
authors.affiliation: Interdisciplinary Centre of Marine and Environmental Research (CIIMAR/CIMAR), University of Porto, Rua dos Bragas 289, 4050-123 Porto, Portugal.
authors.forename: F
authors.initials: F
authors.lastname: Vaz-Pinto
authors.affiliation: Interdisciplinary Centre of Marine and Environmental Research (CIIMAR/CIMAR), University of Porto, Rua dos Bragas 289, 4050-123 Porto, Portugal.
authors.forename: A
authors.initials: A
authors.lastname: Fernández
authors.affiliation: Interdisciplinary Centre of Marine and Environmental Research (CIIMAR/CIMAR), University of Porto, Rua dos Bragas 289, 4050-123 Porto, Portugal.
authors.forename: F
authors.initials: F
authors.lastname: Arenas
mesh_terms: D000818:Animals; D002245:Carbon Dioxide; D017753:Ecosystem; D020387:Food Chain; D057232:Global Warming; D060434:Herbivory / Q000502:physiology*; D006863:Hydrogen-Ion Concentration; D009792:Oceans and Seas; D012623:Seawater / Q000737:chemistry*; D012624:Seaweed / Q000502:physiology*
chemical_list: D002245:Carbon Dioxide
keywords: Acidification; Interaction strength; Macroalgae-herbivore interaction; Stressor gradient; Warming