Can variable pH and low oxygen moderate ocean acidification outcomes for mussel larvae?

Abstract

Natural variation and changing climate in coastal oceans subject meroplanktonic organisms to broad ranges of pH and oxygen ([O2 ]) levels. In controlled-laboratory experiments we explored the interactive effects of pH, [O2 ], and semidiurnal pH fluctuations on the survivorship, development, and size of early life stages of two mytilid mussels, Mytilus californianus and M. galloprovincialis. Survivorship of larvae was unaffected by low pH, low [O2 ], or semidiurnal fluctuations for both mytilid species. Low pH (<7.6) resulted in delayed transition from the trochophore to veliger stage, but this effect of low pH was absent when incorporating semidiurnal fluctuations in both species. Also at low pH, larval shells were smaller and had greater variance; this effect was absent when semidiurnal fluctuations of 0.3 units were incorporated at low pH for M. galloprovincialis but not for M. californianus. Low [O2 ] in combination with low pH had no effect on larval development and size, indicating that early life stages of mytilid mussels are largely tolerant to a broad range of [O2 ] reflective of their environment (80-260 μmol kg(-1) ). The role of pH variability should be recognized as an important feature in coastal oceans that has the capacity to modulate the effects of ocean acidification on biological responses.

Hypoxia and acidification in ocean ecosystems: coupled dynamics and effects on marine life

“…It is thus unclear whether pH and DO fluctuations primarily afford temporal relief from stressful conditions, or whether they compound environmental stress by requiring constant physiological adjustments. For larvae of two Californian mytilid mussels, Frieder et al's [31] study suggested the former, showing that constant low pH (7.48-7.51) during 8 days of exposure had a negative effect on development rate, whereas the fluctuating pH treatment (+0.15 pH units) was less detrimental. Keppel [33] recently observed that diel acidification cycles (pH 7.0-7.8 at control DO) severely reduced growth in oyster spat (Crassostrea virginica) only at low salinity conditions, whereas severe hypoxia cycles (0.5-7.2 mg l 21 at control pH) always reduced growth, and combinations of DO Â pH fluctuations elicited additive negative effects.…”

“…Metabolism, survival and activity in adult Baltic blue mussels (Mytilus edulis trossulus) appeared to be robust even to severe acidification ( pH ¼ 7.5 and 7.0) and hypoxia (2.2 mg l 21 ), although the study was limited by short exposures and small sample sizes [30]. Similarly, concurrent low DO (2.8-3.3 mg l 21 ) Â low pH (7.61-7.68) had no effects on early-life survival and veliger size in two mussel species (Mytilus californianus, M. galloprovincialis, individual low DO, low pH treatments were not tested [31]). All three studies [29][30][31] argued that local adaptation of bivalves to regular low DO Â low pH conditions in the Baltic sea or the California upwelling region may partially explain these findings.…”

“…Similarly, concurrent low DO (2.8-3.3 mg l 21 ) Â low pH (7.61-7.68) had no effects on early-life survival and veliger size in two mussel species (Mytilus californianus, M. galloprovincialis, individual low DO, low pH treatments were not tested [31]). All three studies [29][30][31] argued that local adaptation of bivalves to regular low DO Â low pH conditions in the Baltic sea or the California upwelling region may partially explain these findings. In addition, some bivalves undertake anaerobic respiration as DO concentrations decline, an adaptation that may permit greater resistance to the combined effects of low DO and pH [32].…”

Characterizing the vulnerability of intertidal organisms in Olympic National Park to ocean acidification

“…M. californianus dominates the mid intertidal zone at the POA and TAY sites and has a high sensitivity to OA. OA conditions can reduce mussel larval size (Frieder et al, 2014;Kelly et al, 2015) as well as shell strength and thickness (Gaylord et al, 2011), which could have consequences for development time or predator avoidance (Gaylord et al, 2011). A reduction in the percent cover of M. californianus would have major implications for intertidal landscapes (Wootton et al, 2008), as mussels provide biogenic habitat for a diverse community of organisms (Smith et al, 2006).…”

Changing mineralogical properties of shells may help minimize the impact of hypoxia-induced metabolic depression on calcification

“…Since hypoxia can be persistent, or even permanent, as observed in many coastal and marine waters 225 worldwide (Helly and Levin, 2004;Diaz and Rosenberg, 2008), the survival of some calcifying organisms under persistent hypoxia suggests that they may have evolved the capacity to accommodate its impacts on energy metabolism and hence maintain calcification (Mukherjee et al, 2013;Frieder et al ,2014;Nardelli et al, 2014;Keppel et al, 2016). …”