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International Journal of Marine Science 2013, Vol.3, No.43, 352-360
http://ijms.sophiapublisher.com
357
increases the chances of landslides and rock-falls. This
is a very common phenomenon for the Black Sea
shoreline. Discussing this issue we need to remember
that there is a feed-back loop – an increase of every
kind of erosion leads to degradation of vegetation.
And again it is a positive feed-back – a mechanism of
self-acceleration of de-vegetation and coastal erosion
because “A positive feedback loop is self-reinforcing.”
(Meadows, 1999).
Areas adjoining to the tops of the cliffs often are
plowed in the Crimea for an agricultural use, leaving
on the tops of the cliffs only a narrow strip (10-50 m)
of unploughed ground. In many cases this leads to a
huge concentration of the holes of the small rodents
on the unploughed strip. The holes promote to
intensify a process of suffusion, which often leads
to subsidence, rock-fall, and landslides (our
unpublished data).
Coastal soil erosion is also an increase of biogenic
elements input into coastal marine waters; this leads to
a local eutrophication of marine waters and hypoxia or
anoxia in near bottom waters (Arhonditsis et al., 2000;
Boesch et al., 2001; our observations). Negative
consequences of this for biodiversity are well known.
In addition to landslides in the sea, there is at least
long-term increase of marine water turbidity and local
eutrophication with all negative consequences from
this for marine biodiversity. After the rains and storms
there is a sharp increase in turbidity of the marine
areas from the eroded clay cliffs and landslides
(determined visually or on photos, extend from the
coast to the 50-500 m). These areas with sharp
increased turbidity temporally occupy most productive
zone lead to a decrease of primary production in them.
Well developed natural vegetation is one of the best
natural mechanisms of a prevention of coastline
erosion and degradation of marine communities.
3.2 Marine grasses and seaweeds
6 species of marine grasses (
Zostera
– at first) and
different seaweed species occupy the large areas of
seabed along the Black Sea coastline (Kalugina-Gutnik,
1970). Thickets of submerged vegetation (mainly
Cystoseira
and
Zostera
) form the "cushions" in some
parts of the sea that dampens the pounding waves,
protecting the coasts and sea bottom (Zhivago, 1947;
1948; Zenmkovich, 1958; Shadrin, 1998; Sadogursky,
1999). Storms pluck off macroalgae and marine grass
and release them up onto the beaches. Their debris in
supralittoral areas plays a very important role in
regulation of coastline erosion and beach formation
(Zhivago, 1947; 1948; Zenmkovich, 1958). Total mass
of algae or
Zostera
on the beach can be very large - to
1000 kg per 1 m
2
in some parts of the Black Sea
shoreline (Zhivago, 1947; 1948; Shadrin, 1998;
Sadogursky, 1999). Preliminary calculation showed
that 10-15 mln. tons of their biomass are thrown out
into the Black Sea supralittoral by waves every year.
Destruction of 90-95% of total algae and marine grass
biomass produced in the sea occurs in the supralittoral
area (Shadrin, 1998). Degradation of populations of
seaweeds (
Cystoseira
– at first) and marine grasses are
observed in the Black Sea currently (UNDP, 1997;
Sadogursky, 1999; Zaitsev, 2006). On the one hand an
increase of coastal erosion is one of the reasons of
degradation of submerged vegetation, on other hand –
this degradation made input in the increase of
coastline erosion rate. We need to make an accent that
feed-forward and feed-back loops are both positive
3.3 Changes in mollusk shell production for beaches
Mollusk shells contribute to the formation of different
Black Sea beaches; they may constitute more than
70% of all solid particles forming some beaches
(Zenkovich, 1960; Klyukin, 2004; Ivlieva, 2009;
Kosyan et al., 2012b; Shadrin et al., 2012). From this
it is clear that a change in the intensity of the
production of shells and their location on the shore
determines dynamics of a beach by many ways.
The large Asian gastropod mollusk
Rapana venosa
Valenciennes 1846 (Neogastropoda, Muricidae) is
native to the Sea of Japan, Yellow Sea, Bohai Sea, and
the East China Sea to Taiwan. This predator species
has been accidentally introduced to the Black Sea in
30th years of 20 century (Drapkin, 1963; Gomoiu et
al., 2002). It preys mostly on Bivalve mollusks.
During the first years in the Black sea
Rapana
had
eaten the large settlements of
Ostrea edulis,
near the
Caucasus coast (Drapkin, 1963). Before this,
O. edulis
was the main producer of shells for beaches here.
When production of new
Ostrea
shells had stopped, a
gradual degrading of beaches started. After about two
decades the beaches disappeared or decreased with no
natural protection against cliff abrasion present. And
cliff degradation started to accelerate with damages