Response of macroalgal assemblages from rockpools to climate change: effects of persistent increase in temperature and CO₂

Abstract

Anthropogenically induced global climate change has important implications for marine ecosystems with unprecedented ecological and economic consequences. Climate change will include the simultaneous increase of temperature and CO2 concentration in oceans. However, experimental manipulations of these factors at the community scale are rare. In this study, we used an experimental approach in mesocosms to analyse the combined effects of elevated CO2 and temperature on macroalgal assemblages from intertidal rock pools. Our model systems were synthetic assemblages of varying diversity and understory component and canopy species identity. We used assemblages invaded by the non‐indigenous canopy forming alga Sargassum muticum and assemblages with the native canopy species Cystoseira tamariscifolia. We examined the effects of both climate change factors on several ecosystem functioning variables (i.e. photosynthetic efficiency, productivity, respiration and biomass) and how these effects could be shaped by the diversity and species identity of assemblages. CO2 alone or in combination with temperature affected the performance of macroalgae at both individual and assemblage level. In particular, high CO2 and high temperature (20°C) drastically reduced the biomass of macroalgal assemblages and affected their productivity and respiration rates. The identity of canopy species also played an important role in shaping assemblage responses, whereas species richness did not seem to affect such responses. Species belonging to the same functional effect group responded differently to the same environmental conditions. Data suggested that assemblages invaded with S. muticum might be more resistant in a future scenario of climate change. Thus, in a future scenario of increasing temperature and CO2 concentration, macroalgal assemblages invaded with canopy‐forming species sharing response traits similar to those of S. muticum could be favoured.

Ocean acidification effects on calcifying macroalgae

“…For example, rising temperature due to global warming is a large concern and has received considerable attention in recent decades (Sinutok et al 2011, Olabarria et al 2013. Sinutok et al (2011) found that elevated temperature amplified the negative effects of CO 2 on 2 Halimeda spp.…”

“…Among other temperate coralline algae, reported responses include decreased calcification, growth, MgCO 3 content, total inorganic content and reproduction rates under elevated CO 2 (Martin & Gattuso 2009, Russell et al 2009, Cumani et al 2010, Hofmann et al 2012a, Olabarria et al 2013. In environments impacted by natural seafloor CO 2 vents, benthic and epiphytic crustose coralline algae (CCA) are much lower in abundance compared to unimpacted areas (Hall-Spencer et al 2008, Porzio et al 2011).…”

“…Sinutok et al (2011) found that elevated temperature amplified the negative effects of CO 2 on 2 Halimeda spp. Olabarria et al (2013) reported that the combination of elevated CO 2 and temperature drastically reduced the productivity of both noncalcifiers and calcifiers in macroalgae growing in rock pools. Martin et al (2013) found that calcification in Lithophyllum cabiochae was stimulated by increased temperature under current CO 2 conditions, but the combination of high temperature and CO 2 negatively impacted net calcification rates.…”

Short-term effects of increasing CO2, nitrate and temperature on three Mediterranean macroalgae: biochemical composition

“…Two main approaches have been followed: (1) experimental approaches designed as factorial experiments, incubating macroalgae for days or months at different growth temperatures according to the future predicted scenarios, and evaluating the interactive responses with other variables, such as acidification, UV radiation (UVR), and nutrient availability, amongst others (Baulch et al 2003, Hoppe et al 2008, Porzio et al 2011and (2) field studies of seaweeds growing at their temperature limit for growth and reproduction, while monitoring the temporal and spatial variation of temperature and other variables (Viejo et al 2011, Martínez et al 2012. Most investigations have been conducted on individual species separately, rather than communities (Olabarria et al 2013), although it has been reported that community-level impacts might be less noticeable (Kroeker et al 2010). Moreover, studies on the effect of global climate changes on aquatic organisms have mostly been conducted with 1 or 2 variables, and interactions between multiple factors have scarcely been studied (Franklin & Foster 1997, Gordillo et al 2001, Bischof et al 2006a, Häder et al 2007).…”

Species interactions can shift the response of a maerl bed community to ocean acidification and warming

“…Climate change is likely to strongly alter interactions between macroalgae (e.g. calcifying and noncalcifying macroalgae; Olabarria et al, 2013;Short et al, 2014Short et al, , 2015, interactions between grazers and macroalgae (Poore et al, 2016;Sampaio et al, 2017), and prey-predator dynamics (Asnaghi et al, 2013;Jellison et al, 2016), inducing drastic consequences on the structure and functioning of marine ecosystems (Widdicombe and Spicer, 2008;Hale et al, 2011).…”