Biology Reference
In-Depth Information
Fig. 19.5
Variation in pH at CO
2
vents south of Castello d' Aragonese (Ischia Island, Italy) and
abundance of macroalgae. (
a
) Mean pH
s.d. data from stations S1-S3. (
b
) Percent cover of
calcareous (
triangles
) and noncalcareous macroalgae (
circle
). (Modified from Hall-Spencer et al.
2008
, with permission of Macmillan Publishers Limited)
response to OA in coastal seas (Jiang et al.
2010
). However, neither study consid-
ered the consequence of the shift in C:N ratio on ecosystem trophic dynamics.
19.8.2 Community Structure
Natural volcanic CO
2
vents have conditions comparable to the high CO
2
/low pH
conditions progressively developing in oceans through the uptake of fossil-fuel
CO
2
. Hall-Spencer et al. (
2008
) used this natural ecosystem to demonstrate the
effect of OA on biodiversity and ecosystem structure and function. They showed
that organisms such as sea urchins, coralline algae, and stony corals decline in
abundance or completely disappear with decreasing pH close to the vents, while
seagrasses and brown algae benefit from elevated CO
2
availability close to the vent
by increasing their biomass. Percentage cover of calcareous algae dropped from
>
60% outside the vent area (S1, pH
¼
8.14) to zero cover within it (S2-S3,
pH
7.83-6.57), while the reverse was observed with noncalcareous algal cover
(Fig.
19.5
). Macroalgae observed to be resilient to naturally high amounts of
p
CO
2
include
Caulerpa
,
Cladophora
,
Asparagopsis
,
Dictyota,
and
Sargassum
. This study
showed that lowered pH due to OA, even without global warming that is associated
with rise in atmospheric CO
2
, can bring about loss in biodiversity and shift in
ecosystem structure and function (Hall-Spencer et al.
2008
). Recently, Porzio et al.
¼
