Geoscience Reference
In-Depth Information
and subtidal burrows, estuarine waters, and tide-
pools, hypercapnia is regularly associated with
hypoxia. Burnett (1997) comments that the nega-
tive correlation between oxygen and pH in estuar-
ies is striking while also noting that pH is not
affected directly by oxygen. Animals consume oxy-
gen, and correspondingly produce a given amount
of CO
2
(the exact ratio predicated on the energy
substrate used to fuel metabolism), thereby reduc-
ing pH in surrounding waters. When O
2
and CO
2
are measured in water sampled at different depths
in a burrow, the negative correlation between these
two gases as highlighted by Burnett (1997) is evi-
dent. We know more about responses to O
2
than to
CO
2
. Therefore it is reasonable to assume (until we
have more CO
2
studies) that the extent to which
organisms are physiologically adapted to hypoxia
may act as a surrogate for physiological tolerance
to hypercapnia. For example, deposit-feeding tha-
lassinidean shrimps (such as
Callianassa
) show bet-
ter adaptation to hypoxia in terms of their
respiratory physiology (namely ventilation and
haemolymph O
2
binding characteristics) than their
i lter-feeding relatives (such as
Upogebia
; Atkinson
and Taylor 2005 ).
is likely to be different from that of their pelagic lar-
vae or settling juveniles. For example, Green
et al.
(2009) showed that early settlement mortality in
bivalves can be signii cantly affected by a reduction
in the aragonite saturation state at the sediment sur-
face. Another consideration is that many infaunal
organisms may actually be living at the very limit of
their CO
2
tolerance, and consequently even a small
change in CO
2
levels could be detrimental to the
long-term survival and functioning of key biotur-
bating species. All of which means that there remains
a pressing need for carefully targeted comparative
studies that will help identify the behaviour and
physiological traits that dei ne an organism's vul-
nerability to ocean acidii cation.
9.8 Acknowledgements
This work is a contribution to the 'European Project
on Ocean Acidii cation' (EPOCA) which received
funding from the European Community's Seventh
Framework Programme (FP7/2007-2013) under
grant agreement no. 211384. S.W. and V.K. acknowl-
edge support from the NERC funded project Oceans
2025. The authors would also like to thank Andreas
Andersson and Brad Seibel for their constructive
comments on an initial draft of this chapter.
9.7 Conclusions
It was initially assumed that, as sediment environ-
ments experience high levels of CO
2
, infaunal organ-
isms may be more tolerant to ocean acidii cation
than those that live on the sediment surface or in the
overlying water column. This assumption was based
on the fact that infaunal organisms appear to have
developed a number of behavioural and physiologi-
cal strategies in order to cope with a fossorial life-
style. However, many of these strategies have been
primarily developed to avoid or withstand periods
of hypoxia or anoxia rather than hypercapnia.
Consequently, before we can assume with any great
coni dence that infaunal organisms are less vulner-
able to elevated CO
2
than their counterparts living
in other habitats, in the same way that they are more
tolerant to hypoxia, more comparative data from a
wide range of taxa and life strategies are needed.
This is particularly the case for the many infaunal
species that rely on a planktonic early life stage, as
the vulnerability of infaunal adults to elevated CO
2
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