Geoscience Reference
In-Depth Information
indicates signii cantly higher calcii cation rates and
marginally higher growth for crustaceans in
low-pH waters, though survival was somewhat
reduced. Kurihara (2008) found lower hatching
success for krill exposed to low-pH waters and
mixed effects on other crustacean taxa. It remains
questionable how krill populations will be affected
by ocean acidii cation, and how the effects, if any,
will inl uence marine biodiversity and food web
function.
Sparingly few studies are available to assess the
effects of ocean acidii cation on gelatinous taxa.
Jellyi sh outbreaks have been reported more com-
monly over the past decades, with several factors
(warming, overi shing, habitat modii cation, eutro-
phication, species introductions) being implicated
( Richardson
et al.
2009 ). Several gelatinous groups
are important elements of open-ocean food webs
from the tropics to the poles, including larvaceans,
chaetognaths, salps, and siphonophores. It remains
unclear how these taxa will respond to ocean
acidii cation.
Meroplankton, taxa that live only part of their
lives (often early life-history phases) in open
waters, are expected to be particularly sensitive to
ocean acidii cation. Recent reviews have shown
generally negative or mixed results concerning the
effects of ocean acidii cation on early life stages
(Dupont
et al.
2010; Kroeker
et al.
2010 ). Kurihara
(2008) reports generally negative effects on eggs,
larvae, and other early phases for a variety of
marine calcii ers. The vulnerability of early life-
history stages can have large effects on population
survival and demography, even though adults are
somewhat unaffected. For some taxa, the develop-
ment and survival of early life stages are impaired,
and in others delayed, but the larvae develop fully
in low-pH waters, albeit more slowly than in con-
trol treatments (Dupont
et al.
2010). Slow develop-
ment can put early life-history phases at prolonged
risk to predators. Although the literature remains
sparse concerning the impacts of ocean acidii ca-
tion or climate-related environmental change on
the survival and development of meroplankton in
general, changing ocean conditions could drive
important changes in the population dynamics of
various species, with indirect effects throughout
marine food webs.
10.6.2 Deep-sea ecosystems
Deep-sea ecosystems may experience some of the
most profound changes in biodiversity and ecosys-
tem function in response to ocean acidii cation.
Dramatic shoaling of the aragonite and calcite satu-
ration boundaries (see Chapter 2) will cause very
large shifts in habitat quality for deep-sea calcii ers.
Aragonite and calcite undersaturation of deep-sea
waters is likely to restrict deep-sea aragonitic corals
(and perhaps many calcitic forms) from much of
their existing bathymetric ranges (Tittensor
et al.
2010). As the saturation states for aragonite (Ω
a
) and
calcite (Ω
c
) drop, it becomes energetically more
costly to precipitate CaCO
3
(Cohen and Holcomb
2009), and where Ω drops below 1, exposed CaCO
3
is subject to dissolution (Hall-Spencer
et al.
2008 ;
Manzello
et al.
2008). Recent surveys of the global
distributions of aragonitic scleractinian corals indi-
cate that few taxa are currently found below the
saturation depth for aragonite (Guinotte
et al.
2006 ).
Lophelia
sp., a common aragonitic deep-sea coral,
has been shown to calcify 30 to 56% more slowly in
waters with pH perturbations 0.15 to 0.3 units lower
than ambient (Maier
et al.
2009 ). Although calcii ca-
tion proceeds even when Ω
a
drops below 1, contin-
ued reductions in CaCO
3
saturation appear very
likely to have an effect on deep-sea corals in the
future. Many other deep-sea corals (e.g. gorgoni-
ans) precipitate less soluble calcite, but could be
affected as the calcite saturation depth rises with
increasing ocean CO
2
.
Changes in the biodiversity of deep-sea corals
are likely to affect the function of deep-sea ecosys-
tems. Deep-sea coral communities are often con-
sidered to be hot spots for biodiversity, with high
species diversity of structure-forming corals (often
dominated by octocorals) as well as many other
taxa associated with the heterogeneous habitat
structure (Roberts
et al.
2006 ). Such communities
are common on many seamounts, which number
upwards of 50 000 worldwide. Impacts on deep-
sea corals could also require long periods for
recovery, even in suitable habitats, considering
the slow growth rates and high longevity of many
species, with ages reaching from decades to centu-
ries (Roberts
et al.
2006 ) or longer ( Roark
et al.
2009 ).
