title for learn-about sections for chitons in A SNAIL'S ODYSSEY
  Adaptations to intertidal life
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pH & ocean acidification

  This hodge-podge selection of topics relating to intertidal life in chitons includes pH & ocean acidification, considered here, and WAVE EXPOSURE & TENACITY, GAS EXCHANGE, TOLERANCE OF FRESHWATER & OSMOREGULATION and LIGHT, DESICCATION, & TEMPERATURE STRESS, considered in other sections.
 
Research study 1
 

photographs of chitons with shell plates used in ocean-acidification studyRapidly increasing CO2 concentrations in the atmosphere with corresponding pH decreases in the ocean have stimulated research interest in potential future shell degradation in molluscs. To test simulated pH conditions on shell integrity of west-coast chitons, researchers1 from Irish and eastern North American universities expose individuals of 3 species for 10d to control and elevated pCO22 levels in aquarium tanks at Friday Harbor Laboratories, Washington. Before-and-after measurements of cracking strength of both isolated and in vivo shell valves are obtained using a special crushing device. Not surprisingly, given the short exposure time and often variable ruggedness of the shell valves, results show no significant3 effect of elevated pCO2 on fracture strength of the valves. The authors do report a significant species effect, with shell valves of the larger species Katharina tunicata being 2-3-fold more fracture resistant than those of the 2 Mopalia species. The researchers speculate that the differences may relate to degree of wave exposure of the species, but no measurements of wave forces are made in the different habitats, and body size (i.e., valve thickness, see graph) is the more likely correlate. The authors conclude from their study that “…wave exposure may have stronger impacts on adult chitons than changes in ocean chemistry under future climate change” but, really, wave exposure was never tested and a brief 10d exposure to somewhat less basic seawater than normal can scarcely be considered a simulation of "future climate change". Sigwart et al. 2015 Mar Biol 162: 2257. Photographs courtesy the authors.graph comparing fracture strength of shell valves in 3 species of chitons Katharina tunicata, Mopalia muscosa, and M. lignosa

NOTE1 the researchers may be attracted to west-coast waters by the presence of many varied and comparatively large species of chitons. Atlantic species are few in number (6-8 common species in Britain and even fewer on the Atlantic coast of N.A.) and are much smaller in size (1-2cm length in Britain; 2-5cm on the east coast). In comparison, there are more than 3 dozen fairly common west-coast species, ranging from 2-35cm in length

NOTE2 pCO2 levels selected are 400µatm (pH 8.0) and 1550µatm (pH 7.5) at 13oC

NOTE3 the authors expected to find a difference based on results of an earlier study on whelks exposed to similar experimental treatments (see LEARNABOUT/WHELK/whelGrow), but more careful reading of the earlier paper shows that statistical significance was only found with isolated shells, not with shells of living specimens. Moreover, as chiton shell-plates are much better protected than the exposed shell of a whelk, a significant effect of lower pH on them might be even less expected

 
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