Geoscience Reference
In-Depth Information
Low ocean pH
and high [CO
2
]
ion equilibria
-
Na
+
/H
+
-exchange etc.
Calcification site
Epithelia (gill, gut, kidney)
calcification
-
[
H
+
]
, W
Brain
Chemosensory
Neurons pH
i
CO
2
H
2
O
HCO
3
H
2
O
H
i
+
2 K
+
-
ATP-
ase
H
+
3 Na
+
Adenosine
accumulation
and release
Na
+
-
H
+
Heart
Muscle
HCO
3
Cl
-
-
-
functional
capacity
H
+
-
blood
pigment
Na
+
gene
expression
(
+
or -
)
intracellular space
extracellular space
Tissues
Figure 8.1
Role of extracellular pH (or proton activity, H
+
e
) in modulating and coordinating the rates and capacity of various physiological functions (after
Pörtner 2008). Changes in individual functions (neuronal functions affected by adenosine accumulation in the central nervous system, muscular excitability,
ventilatory rates, metabolic equilibria, protein synthesis rates, calcii cation, ion exchange) integrate into changes in performance and i tness of the whole
organism. Changes in extracellular pH inl uence the rate of pH regulation through Na
+
-dependent proton exchange, and thus the rate of use of
ATP -dependent Na
+
/K
+
-ATPase. Efi cient maintenance of extracellular pH by proton-equivalent ion exchange across epithelia (for example, gill, gut,
and kidney epithelia in marine teleosts) minimizes such disturbing inl uences.
gene expression patterns and the concentrations
of functional proteins, and thereby the capacities
of molecular functions. For example, it is well
established that seasonal temperature l uctuations
can cause acclimatization responses in animals
which involve changes in the gene expression of
key functional proteins. The capacity for such
responses is probably greater in ectotherms from
temperate climate zones than in polar or tropical
climates. In contrast, acclimatization responses
under changing CO
2
levels have scarcely been
investigated and may also vary between organ-
isms from different climate zones. Studies of the
effects of hypercapnia on the transcriptome and
proteome, with a focus on ion and acid-base
regulation, have identii ed long-term compensa-
tory responses in sensitive versus vulnerable spe-
cies (Hofmann and Todgham 2010).
In the following sections we examine to what
extent this general picture applies to nektonic
organisms, particularly i shes and cephalopods. By
dei nition, nektonic organisms comprise those that
swim actively and freely and are generally inde-
pendent of water currents. This implies that their
metabolic and exercise capacities are higher than
those of sessile organisms (Seibel and Drazen 2007).
Active marine taxa that have high metabolic rates
and strong ion regulatory abilities are considered to
be the most tolerant to future changes in seawater
carbonate chemistry (Seibel and Walsh 2003; Pörtner
2008 ; Melzner
et al.
2009a). This poses a challenge to
identify small but relevant levels of sensitivity to
ocean acidii cation, which may become visible only
with concomitant changes in other environmental
factors, such as temperature. The physiological
principles involved are those that have also been
