Status of alien species in the Mediterranean and Black Sea

41
Figure 22 – The Suez Canal (Por, 1978)
The construction of the Aswan High Dam across the Nile River in the 1960s reduced the inflow of
freshwater and nutrient-rich silt from the Nile into the eastern Mediterranean, making conditions there
even more similar to the Red Sea, thus increasing the impact of invasions and facilitating the
occurrence of new ones. The Red and Mediterranean Seas removed a geographic barrier between them,
then the migration began from the Red Sea to the Mediterranean and many Red Sea species
(lessepsian) penetrated to the Mediterranean. As a result, various changes have occurred in the biota of
the Mediterranean. Accordingly, most invasions are of Red Sea species into the Mediterranean, and
only a few in the opposite way (Ben-tuvia, 1966; Avşar, 1999).
Enlargement of the Suez Canal is also a facilitating factor for Lessepisan migrants to settle or pass to
the Mediterranean Sea. The Suez Canal was deepened and widened several times, and now has a
navigational depth of 14.5 m and width of 365 m (see Table 3.1).
Table 3.1 – Dimension of the Suez Canal over the years (Halim, 1990)
Years 1869 1956 1981
Width at sea surface (m) 52 160 365
Width of navigable channel (m) 44 110 190
Total depth (m) 7.8 12 14.5
Cross-sectional area (m 2 ) 304 1 200 3 600