Page 16 - climate-change2013

Impact of climate change

on marine biodiversity

The Mediterranean Sea is considered one of the world`s tions in the field and from different in situ and ex situ
biodiversity hotspots, where the impact of climate experimental settings. In coastal habitats, where most
change together with other anthropogenic pressures Mediterranean MPAs are established, the main stress-
could be most devastating (Lejeusne et al., 2009; Coll ors liable to have an impact on the marine biota are tem-
et al., 2010). perature rise, the acidification of waters and decreasing
oxygen concentration.
Climate change is already affecting its environment,
ecosystems and species in many ways and evidence It is outside the scope of this guide to describe in detail
suggests that the impact will become more severe as all the known impacts on marine biodiversity resulting
climate change continues. Species may no longer be from the changing climate (see reviews by Gambiani et
adapted to the set of environmental conditions where al., 2009; Lejeusne et al., 2009; Calvo et al., 2011; Di
they live and will need to produce adaptive responses Carlo and Otero, 2013). Instead, it presents an overall
fast enough to keep up with the rapid pace of change review illustrated with examples of the most important
(Somero, 2012). Individuals, populations or species may effects that are likely to be monitored (or at least re-
suffer severe mortality events, which ultimately could ported) in MPAs.
result in their local extinction, while others may migrate
adapt to the new conditions. These effects in turn will Changes in native
to more favourable areas or change their physiology to
tion, etc.) and cascading effects, which will propagate species distributions
lead to altered species interactions (predation, competi-
at community and ecosystem levels and may signifi-
cantly alter the structure and function of Mediterranean Shifts in the distribution of marine populations are
marine communities in the future (Hughes et al., 2003; the most commonly reported effects associated with
Doney et al., 2012). changing climate conditions. In the Mediterranean, the
long-term temperature increase has been shown to af-
In addition, species have to cope with additional threats fect the boundaries of biogeographical regions, with
caused by human activities, some of which may act in some warm-water species extending their ranges and
synergy with climate change. The sum of these major colonizing areas where they were previously absent or
disturbances is known as global change. The effects rare (CIESM, 2008). Fish and crustaceans as well as
that the different stressors, and particularly their com- sessile species such as echinoderms, cnidarians and
bination, have on marine organisms are currently poorly algae are shifting their geographical ranges in both lo-
understood. cation and depth, in what seems to be a widespread
phenomenon that already involves about 100 native
Direct effects of changes in ocean temperature and species from primary producers to top predators.
chemistry (mainly rising sea temperature and acidity)
may alter the physiological functioning, behaviour and Warm-water species, more abundant in the southern
population growth of organisms, leading to shifts in the and eastern Mediterranean, where temperatures are
size, structure, spatial range and seasonal abundance higher, are increasing in abundance and extending their
of populations. Other climate-derived stressors, such ranges northwards. For example, the ornate wrasse
as sea-level rise, changes to ocean circulation and mix- Thalassoma pavo increased its population density ten-
ing, or ocean deoxygenation, might also co-occur in fold within less than 5 years of its arrival in the Scan-
time and space, increasing their simultaneous impact dola Marine Reserve (NW Corsica, France) in 1988.
on marine communities. Likewise, an increase in landings of other warm-water

Ocean deoxygenation: the global trend
of decreasing oxygen levels as a result of
ocean warming and increasing stratification

Many studies have revealed the substantial impact that
climate change has on marine ecosystems and the
Mediterranean Sea in particular (Hall-Spencer et al.,
2008; Coma et al., 2009; Garrabou et al., 2009; Azzurro
et al., 2011). Most of these works have focused on the
effects of temperature and the response of organisms
under high CO concentrations, while the diminution of
2
oxygen concentration has received less attention. The
information available at present is based on observa-
Thalassoma pavo. Photo: A. Can - www.alpcan.com

14 COLLECTION