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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

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