Food availability outweighs ocean acidification effects in juvenile Mytilus edulis: laboratory and field experiments

Abstract

Ocean acidification is expected to decrease calcification rates of bivalves. Nevertheless, in many coastal areas high pCO 2 variability is encountered already today. Kiel Fjord (Western Baltic Sea) is a brackish (12-20 g kg À1 ) and CO 2 enriched habitat, but the blue mussel Mytilus edulis dominates the benthic community. In a coupled field and laboratory study we examined the annual pCO 2 variability in this habitat and the combined effects of elevated pCO 2 and food availability on juvenile M. edulis growth and calcification. In the laboratory experiment, mussel growth and calcification were found to chiefly depend on food supply, with only minor impacts of pCO 2 up to 3350 latm. Kiel Fjord was characterized by strong seasonal pCO 2 variability. During summer, maximal pCO 2 values of 2500 latm were observed at the surface and >3000 latm at the bottom. However, the field growth experiment revealed seven times higher growth and calcification rates of M. edulis at a high pCO 2 inner fjord field station (mean pCO 2 ca. 1000 latm) in comparison to a low pCO 2 outer fjord station (ca. 600 latm). In addition, mussels were able to out-compete the barnacle Amphibalanus improvisus at the high pCO 2 site. High mussel productivity at the inner fjord site was enabled by higher particulate organic carbon concentrations. Kiel Fjord is highly impacted by eutrophication, which causes bottom water hypoxia and consequently high seawater pCO 2 . At the same time, elevated nutrient concentrations increase the energy availability for filter feeding organisms such as mussels. Thus, M. edulis can dominate over a seemingly more acidification resistant species such as A. improvisus. We conclude that benthic stages of M. edulis tolerate high ambient pCO 2 when food supply is abundant and that important habitat characteristics such as species interactions and energy availability need to be considered to predict species vulnerability to ocean acidification.

Experimental ocean acidification alters the allocation of metabolic energy

“…The mechanisms underlying the differential energy response to the stress of ocean acidification between fed and unfed larvae require further study but likely are related to different anabolic (growth) and catabolic (starvation) states. The difference in metabolic response between fed and unfed larvae suggests that nutritional and physiological states impact the response to many environmental stressors, including ocean acidification (47). Such increases in metabolic demand have important implications for long-term resistance to starvation of larval forms with minimal energy reserves (48,49).…”

Historical baselines and the future of shell calcification for a foundation species in a changing ocean

“…[10]), food availability [11] and predation pressure [12,13], some of which can interact, either counteracting the effects of changing seawater saturation state [11] or exacerbating them [3]. All of these factors probably contribute to how a species modulates calcification internally (e.g.…”

Effects of CO<sub>2</sub>-driven ocean acidification on early life stages of marine medaka (<i>Oryzias melastigma</i>)

“…A number of studies found that CO 2 -driven acidification had obvious influences on ELS of many marine invertebrates, especially calcified organisms including coral (Doropoulos et al, 2012;Fabricius et al, 2011), coccolithophores (Berry et al, 2002), and mollusk (Kroeker et al, 2013;Thomsen et al, 2013;Waldbusser et al, 2011). OA was predicted to potentially affect individual behaviour such as development, growth, survival, and swimming particularly during the early life stage of marine organisms (Munday et al, 2008).…”