Page 38 - climate-change2013

INDICATOR
Mass-mortality events MPA CASE STUDY 4

In recent years, rocky coastal habitats have been badly
hit by several mass-mortality events. The most severe Thriving invasive
reported events affected large areas (more than 1,000
km of coastline) and the populations of some 40 mac- alien species
robenthic species belonging to several different phyla
(sponges, cnidarians, bryozoans, molluscs and ascid- New marine invasions have been recorded in increasing
ians) in the north-western Mediterranean. There have numbers throughout the Mediterranean Sea, including
been reports of similar happenings in other parts of the in many MPAs (Otero et al., 2013). Rising water temper-
Mediterranean. Habitat-forming species, including gor- atures and climate fluctuations, together with the ability
gonians and sponges, have suffered the worst impact of many of these species to tolerate a broader thermal
down to depths of 45 m. range than native species, are partly responsible for
their rapid and successful spread (CIESM, 2008).
In general, these events have been associated with an
anomalous rise in seawater temperatures in late sum- Unfortunately, there are not yet many effective meas-
mer and early autumn. Under these conditions organ- ures for fighting marine invasions, which highlights
isms have suffered from a variety of stressors, includ- the importance of early detection, the development of
ing energetic constraints, physiological stress, reaching rapid response actions and the periodic monitoring of
thermal tolerance limits and development of thermo- sites, especially vulnerable habitats.
dependent pathogens, leading to the observed mortal-
ity events.
PROPOSED MONITORING PROCEDURE
In order to monitor the effects of mass mortalities with-
in MPAs, scuba diving surveys carried out by techni-
cal diving teams, MPA personnel or recreational diving
centres should be conducted in late summer or early
autumn. The surveys should encompass several sites
and the most representative habitats in each MPA. The
species affected during past mass mortalities can be
used a priority list for surveys (see MPA Case Studies Photo: B. Weitzmann
2 & 3). Annual surveys carried out even in years when
there are no apparent signs of mortality are important The invasive red seaweed Asparagopsis armata
probably introduced into the Mediterranean by
to provide a good baseline for assessing subsequent aquaculture disperse with water currents, attached to
impact. Two kinds of survey can be carried out: floating objects.

• Qualitative surveys report on species showing In the Montgrí, Illes Medes i Baix Ter Nature Park (Cata-
clear-cut signs of recent necrosis, such as denud- lan Coast, Spain), surveys for the early detection and
ed skeletons in gorgonians, sponges and sclerac- monitoring of invasive species are conducted every
tinian corals. two years with the assistance of researchers from the
CEAB-CSIC Institute. The monitoring is performed by
• Quantitative surveys report on the degree of im- scuba divers at several stations along the coast and
pact on populations of certain species. During the around the islands, exposed headlands and open-sea
surveys the goal is to observe the state of speci- rocks, from the surface to the maximum depth at sedi-
mens — that is, whether they are healthy or show ment level. The communities and species present are
signs of partial or total mortality — along random identified and their relative abundances are estimated.
transects or within random quadrats, depending The monitoring programme also keeps an eye on the
on the abundance of the targeted species. In or- abundance of alien species such as the algae Aspara-
der to provide a representative impact value, sur- gopsis armata, Womersleyella setacea and Dictyota
veys should include observations on a significant cyanoloma, the coral Oculina patagonica and the cal-
number of specimens (150–300) for each species careous sponge Paraleucilla magna.
at each site. From these surveys the percentage
of affected specimens in each population can be Standard, periodic monitoring of these species pro-
used as the main indicator. vides the foundation for assessing the combined ef-
fects of climate change and invasions as well as any
feasible management response in the MPA environ-
ment.

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