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Buffer capacity of the coelomic fluid in echinoderms
Collard, M.; Laitat, K.; Moulin, L.; Catarino, A.I.; Grosjean, P.; Dubois, P. (2013). Buffer capacity of the coelomic fluid in echinoderms. Comp. Biochem. Physiol., Part A Mol. Integr. Physiol. 166(1): 199-206. dx.doi.org/10.1016/j.cbpa.2013.06.002
In: Comparative Biochemistry and Physiology. Part A. Molecular and Integrative Physiology. Elsevier: New York. ISSN 1095-6433, more
Peer reviewed article  

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    VLIZ: Open Repository 279380 [ OMA ]

Keywords
    Asterias rubens Linnaeus, 1758 [WoRMS]; Asteroidea [WoRMS]; Echinodermata [WoRMS]; Echinoidea [WoRMS]; Paracentrotus lividus (Lamarck, 1816) [WoRMS]; Marine
Author keywords
    Acid-base regulation; Asterias rubens; Buffer capacity; Echinoderms;Ocean acidification; Paracentrotus lividus; Sea urchins; Starfish

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Abstract
    The increase in atmospheric CO2 due to anthropogenic activity results in an acidification of the surface waters of the oceans. The impact of these chemical changes depends on the considered organisms. In particular, it depends on the ability of the organism to control the pH of its inner fluids. Among echinoderms, this ability seems to differ significantly according to species or taxa. In the present paper, we investigated the buffer capacity of the coelomic fluid in different echinoderm taxa as well as factors modifying this capacity. Euechinoidea (sea urchins except Cidaroidea) present a very high buffer capacity of the coelomic fluid (from 0.8 to 1.8 mmol kg- 1 SW above that of seawater), while Cidaroidea (other sea urchins), starfish and holothurians have a significantly lower one (from - 0.1 to 0.4 mmol kg- 1 SW compared to seawater). We hypothesize that this is linked to the more efficient gas exchange structures present in the three last taxa, whereas Euechinoidea evolved specific buffer systems to compensate lower gas exchange abilities. The constituents of the buffer capacity and the factors influencing it were investigated in the sea urchin Paracentrotus lividus and the starfish Asterias rubens. Buffer capacity is primarily due to the bicarbonate buffer system of seawater (representing about 63% for sea urchins and 92% for starfish). It is also partly due to coelomocytes present in the coelomic fluid (around 8% for both) and, in P. lividus only, a compound of an apparent size larger than 3 kDa is involved (about 15%). Feeding increased the buffer capacity in P. lividus (to a difference with seawater of about 2.3 mmol kg- 1 SW compared to unfed ones who showed a difference of about 0.5 mmol kg- 1 SW) but not in A. rubens (difference with seawater of about 0.2 for both conditions). In P. lividus, decreased seawater pH induced an increase of the buffer capacity of individuals maintained at pH 7.7 to about twice that of the control individuals and, for those at pH 7.4, about three times. This allowed a partial compensation of the coelomic fluid pH for individuals maintained at pH 7.7 but not for those at pH 7.4.

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