Page 21 - climate-change2013

Photo: J.Hall-Spencer
abundance and productivity (Hall-Spencer et al., 2008;
Suggett et al., 2012). P. oceanica is, on the other hand,
highly sensitive to seawater warming, and high mortality
rates may be expected in natural populations with the
rise in annual water temperature.

Effects of sea-level rise

As seen above, the rise in sea-level is generally consid-
ered one of the most significant consequences of cli-
mate warming, yet its effects on biodiversity are poorly
understood.

Observed effects on the endemic coral Cladocora Sea-level rise threatens coastal marshes, sea caves
caespitosa polyps with marks of dissolution of and beaches, which are crucial habitats for many spe-
their skeleton under low pH conditions. cies, such as endangered populations of sea turtles and
Mediterranean monk seals, which use them for breeding
(see page 24). Intertidal bioconstructions such as reefs
in Mediterranean benthic ecosystems. The natural CO built by vermetid molluscs together with coralline algae
2
emissions from these vents provide a range of pH levels (such as the vermetid Dendropoma petraeum and the
that can be used to monitor what benthic ecosystems red alga Neogoniolithon brassica-florida) or rims built
will be like in a high-CO scenario. These studies have slightly above sea-level by the encrusting coralline alga
2
shown that nearby rocky shore communities exposed Lithophyllum byssoides are extremely vulnerable to
to low-pH waters decrease in species number and shift water-level changes and to wave erosion during major
from a calcareous-dominated community structure to storms (Boudouresque, 2004). Vermetid reefs are found
one dominated by uncalcified organisms (Hall-Spencer mostly in the central and southern Mediterranean Sea
et al., 2008). For example, around the Vulcano vents of while rims are widely distributed throughout the Mediter-
Italy, a macroalgae-dominated community decreased ranean (Chemello and Silenzi, 2011) and have been used
in species richness, coverage and reproduction capac- to track past changes in sea-level in the Mediterranean.
ity in a low-pH environment. Likewise, the abundance As these habitats are built from calcium carbonate, sea
of various calcareous organisms such as scleractinian acidification can also affect vermetid and algal calcifi-
corals (Cladocora caespitosa and Balanophyllia euro- cation and have detrimental effects on the organisms’
paea), macroalgae (Lithophyllum incrustans, Corallina growth rate, resulting in local extinction events.
elongata, Padina pavonica and Halimeda tuna), mol-
luscs (Osilinus turbinatus, Patella caerulea and Hexa- Rising sea temperature, sea-level rise and acidity thus
plex trunculus) and sea-urchins (Paracentrotus lividus appear to be associated with various changes in bio-
and Arbacia lixula) was lower under low-pH/more acidic diversity in the Mediterranean (Rodolfo-Metalpa et al.,
conditions (Hall-Spencer et al., 2008; Rodolfo-Metalpa 2010). The synergic effects of different stressors linked
et al., 2011). to global change will probably exacerbate the impact on
the biodiversity and functioning of coastal ecosystems.
Aquarium experiments and transplants in the field into
naturally acidified waters have confirmed some of the
observed negative effects of acidification. For exam-
ple, for the scleractinian corals Cladocora caespitosa
and the alien Oculina patagonica, low-pH conditions
reduced calcification rates by about 30% (Movilla et
al., 2012). Similarly, other species such as the red coral
Corallium rubrum and the coralline alga Lithophyl-
lum cabiochae displayed a significant reduction (by
up to 60%) in skeleton growth and feeding activity or
increased necrosis, respectively, in a low-pH environ-
ment. These and other findings suggest that rich coral-
ligenous communities are likely to be severely affected
by the ongoing acidification. Ocean acidification has
also been shown to have an impact on shellfish growth,
reproduction and structure.
In contrast, a number of species seem to be resistant to
or even to benefit from acidification. For instance, Posi-
donia oceanica meadows seem remarkably tolerant of
low pH levels and several algal species, among them
some aliens (Caulerpa racemosa, Asparagopsis armata
and Dictyota dichotoma), and other species such as
the sea anemone Anemonia viridis can increase their Vermetid platforms at Torre Guaceto MPA, Italy. Photo: M. Otero

MEDITERRANEAN MARINE PROTECTED AREAS AND CLIMATE CHANGE: A GUIDE TO REGIONAL MONITORING AND ADAPTATION OPPORTUNITIES 19