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| Titel |
Physiological basis for high CO2 tolerance in marine ectothermic animals: pre-adaptation through lifestyle and ontogeny? |
| VerfasserIn |
F. Melzner, M. A. Gutowska, M. Langenbuch, S. Dupont, M. Lucassen, M. C. Thorndyke, M. Bleich, H.-O. Pörtner |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1726-4170
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| Digitales Dokument |
URL |
| Erschienen |
In: Biogeosciences ; 6, no. 10 ; Nr. 6, no. 10 (2009-10-30), S.2313-2331 |
| Datensatznummer |
250004047
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| Publikation (Nr.) |
 copernicus.org/bg-6-2313-2009.pdf |
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| Zusammenfassung |
Future ocean acidification has the potential to adversely affect many marine
organisms. A growing body of evidence suggests that many species could
suffer from reduced fertilization success, decreases in larval- and adult
growth rates, reduced calcification rates, and even mortality when being
exposed to near-future levels (year 2100 scenarios) of ocean acidification.
Little research focus is currently placed on those organisms/taxa that
might be less vulnerable to the anticipated changes in ocean chemistry; this
is unfortunate, as the comparison of more vulnerable to more tolerant
physiotypes could provide us with those physiological traits that are
crucial for ecological success in a future ocean. Here, we attempt to
summarize some ontogenetic and lifestyle traits that lead to an increased
tolerance towards high environmental pCO2. In general, marine
ectothermic metazoans with an extensive extracellular fluid volume may be
less vulnerable to future acidification as their cells are already exposed
to much higher pCO2 values (0.1 to 0.4 kPa, ca. 1000 to 3900 μatm)
than those of unicellular organisms and gametes, for which the ocean (0.04 kPa,
ca. 400 μatm) is the extracellular space. A doubling in
environmental pCO2 therefore only represents a 10% change in
extracellular pCO2 in some marine teleosts. High extracellular
pCO2 values are to some degree related to high metabolic rates, as
diffusion gradients need to be high in order to excrete an amount of
CO2 that is directly proportional to the amount of O2 consumed. In
active metazoans, such as teleost fish, cephalopods and many brachyuran
crustaceans, exercise induced increases in metabolic rate require an
efficient ion-regulatory machinery for CO2 excretion and acid-base
regulation, especially when anaerobic metabolism is involved and metabolic
protons leak into the extracellular space. These ion-transport systems,
which are located in highly developed gill epithelia, form the basis for
efficient compensation of pH disturbances during exposure to elevated
environmental pCO2. Compensation of extracellular acid-base status in
turn may be important in avoiding metabolic depression. So far, maintained
"performance" at higher seawater pCO2 (>0.3 to 0.6 kPa) has only been
observed in adults/juveniles of active, high metabolic species with a
powerful ion regulatory apparatus. However, while some of these taxa are
adapted to cope with elevated pCO2 during their regular embryonic
development, gametes, zygotes and early embryonic stages, which lack
specialized ion-regulatory epithelia, may be the true bottleneck for
ecological success – even of the more tolerant taxa.
Our current understanding of which marine animal taxa will be affected
adversely in their physiological and ecological fitness by projected
scenarios of anthropogenic ocean acidification is quite incomplete. While a
growing amount of empirical evidence from CO2 perturbation experiments
suggests that several taxa might react quite sensitively to ocean
acidification, others seem to be surprisingly tolerant. However, there is
little mechanistic understanding on what physiological traits are
responsible for the observed differential sensitivities (see reviews of
Seibel and Walsh, 2003; Pörtner et al., 2004; Fabry et al., 2008;
Pörtner, 2008). This leads us to the first very basic question of how to
define general CO2 tolerance on the species level. |
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