Interaction strength between different grazers and macroalgae mediated by ocean acidification over warming gradients

Abstract

Since the past century, rising CO levels 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 CO treatments (ΔCO ≃ 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.

Cascading effects of climate change on plankton community structure

“…Therefore, we chose levels of experimental warming to represent a predicted warming scenario (4°C) and an extreme warming scenario (8°C). This range of temperature increase has been used in other shallow aquatic ecosystem warming experiments (Sampaio, Rodil, Vaz‐Pinto, Fernandez, & Arenas, ; Tuck, ; Yvon‐durocher, Montoya, Trimmer, & Woodward, ). Mean ocean pH is expected to drop by 0.14–0.35 units from increased CO 2 concentrations over the next century (IPCC, ).…”

“…This range of temperature increase has been used in other shallow aquatic ecosystem warming experiments (Sampaio, Rodil, Vaz-Pinto, Fernandez, & Arenas, 2017;Tuck, 2010;Yvon-durocher, Montoya, Trimmer, & Woodward, 2010). Mean ocean pH is expected to drop by 0.14-0.35 units from increased CO 2 concentrations over the next century (IPCC, 2013).…”

Invasion-mediated effects on marine trophic interactions in a changing climate: positive feedbacks favour kelp persistence

“…The influence of ocean warming on ecosystem dynamics often depends on the extent that such environmental change alters species interactions [8]. For example, plantherbivore interactions may be altered at elevated ocean temperatures, as a result of a mismatch between production and herbivore consumption [28][29][30]. Increasing ocean temperatures enhance respiration, metabolism and grazing activity of herbivores up to their thermal maxima.…”

Warming and temperature variability determine the performance of two invertebrate predators

“…lower and upper tolerance limits), basal metabolic rates increase with increasing temperature until maximal levels 30 . Outside this window, negative performance is mainly a result of limited maximum metabolic rate due to limited oxygen capacity 30 , from where any further drop or rise in temperature will cause severe stress for an individual 31 . Beyond critical temperature limits, metabolic depression or anaerobic energy production occurs, with stress protection mechanisms providing some limited plasticity 30 .…”