Physiology & physiological ecology
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pH & ocean acidification

  The topic of physiology & physiological ecology is divided into a section on pH & ocean acidification considered here, and sections on CHEMORECEPTION, GAS EXCHANGE & METABOLISM, LOCOMOTION & TENACITY, DIEL SEASONAL & TIDAL RHYTHMS, OSMOTIC REGULATION & SALINITY TOLERANCE, and THERMAL STRESSES presented elsewhere.
Research study 1

A group of California researchers provides details of energy metabolism in developmental stages of porcelain crabs Petrolisthes cinctipes under conditions of ambient pH (7.9) and predicted year 2300 pH (7.6).  Porcelain crabs along the California coast are subject to tidal fluctuations of upwelled waters of varying pH and of tidepool conditions that undergo diel change in pH through cycles of respiration and photosynthesis, and thus represent a good model organism for investigations of this type.  Larvae are reared to metamorphosis over 33d in each seawater pH, then late-stage embryos, zoea I larvae, and newly metamorphosed juveniles are monitored for rate of oxygen consumption and levels of various metabolites.  Overall results are highly variable and reveal no strong and consistent acute effects of exposure to low pH.  The authors photograph of porcelain crab Petrolisthes cinctipesnote some effects relating to nitrogen and C-N  ratios that suggest a possible switch from lipid to protein metabolism under exposure to low pH.  Interestingly, the authors observe that different broods vary in several measurable ways, reflecting genetic differences among them.  The results lead the researchers to suggest that P. cinctipes may have the genetic potential to adapt to future declines in pH in inshore waters.  Carter et al. 2013 J Exp Biol 216: 1412.

NOTE  these include dry mass, total protein & lipids, and carbon-nitrogen ratios (C/N)

Porcelain crab Petrolisthes cinctipes. An easy way to
distinguish this species from the congenor species
is that the former has burgundy-coloured
antennae, while the latter has straw-coloured ones.
Remember: B/C: burgundy/cinctipes; S/E: straw/eriomerus

Research study 2

graph comparing survival of juvenile porcelain crabs Petrolisthes cinctipes in seawater of different pHsIn a companion article to Research Study 1 above, several of the same researchers use essentially the same protocol to investigate pH effects on survival, cardiac performance, energetics and morphology in porcelain crabs Petrolisthes cinctipes reared from eggs through to juvenile.  Survival of larvae over 9d is not affected by pH treatment but, if the treatment period is extended to 40d, then survival of juveniles in the low-pH treatment (7.6) is reduced by about 30% over that in the ambient-pH treatment (7.9; see graph).  Embryos grow significantly more slowly in pH 7.6 than in pH 7.9 conditions.  Embryonic and larval hearts beat  significantly slower in the lower pH treatment.  Just as in the companion study, different broods respond differently to the different pH conditions.  Ceballos-Osuna et al. 2013 J Exp Biol 216: 1405.

NOTE  the authors mention that the intertidal habitat of the crabs may fluctuate between pH 6.9-9.5, so the experimental treatments of 7.9 and 7.6 are well-encompassed within this range

Research study 3

histogram showing effects of pH and salinity, alone and in combination, on oxygen uptake of larvae of porcelain crabs Petrolisthes cinctipesResearchers at Bodega Marine Laboratory, California measure combined stresses of low pH seawater, and high and low salinities on oxygen uptake in larval porcelain crabs Petrolisthes cinctipes.  The larvae are reared for 10d at 14oC in ambient and CO2-treated seawater, then moved into CO2-treated seawaters with 3 salinities: ambient (34‰), low (22‰), and high (40‰).  Results show that neither low pH nor high pH, nor low salinity alone, lead to enhanced oxygen uptake, but low pH combined with either high or low salinity significantly increases oxygen consumption (see histogram).  The interest in the subject relates mainly to the application of multiple stressors not simultaneously, as is commonly done, but sequentially. Miller et al. 2014 PLoS ONE 9 (10): e109167.

NOTE  the rationale for the study is that predicted future climate change will, among other things, include ocean acidification and precipitation-induced runoff events.  Hypersaline conditions are included in the study with the idea that larvae in future acidified waters may also encounter plumes of hypersalinity in stratified coastal condtions

NOTE  pH levels tested are 8.1 and 7.9 based on ambient and future (year 2100) pCO2 levels, respectively, of 385 and 1000µatm

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