134
The Migrant Biota
The success of these species can be seen also in our case as a result of the time
factor. If we calculate the percentage of the 0.0.3 and 0.0.4 species-the most
distantly spread Lessepsian migrants-as a function of their early or late migrational advance, the results are convincing: from among the species which entered
the Canal in the first period (1.0.0) 33.33% are 0.0.3 and 0.0.4, as compared with
16.36% in the second period (2.0.0), and 20% in the third period (0.0.3). The
situation is similar when we check the percentage of the 0.0.3 and 0.0.4 species in
relation to the period of their a ppearance in the Mediterranean: they are 34.78%
among the 0.1.0 species, only 25.92% among the 0.2.0, and 21.34% among the
0.3.0 species. This too indicates that the spreading of the Lessepsian migrants is a
gradual migrational process in which passive or adventive transport does not play
a significant role; the relatively high euryhalinity of the early settlers of the Canal
might have been beneficial-but at any rate not detrimental-to their further
move into the Mediterranean.
3.6 The Diversity of Lessepsian Migrants
After more than a century of Lessepsian migration, some qualitative aspects
can already be discerned, in addition to the merely quantitative time-distance
aspects.
The great majority of the migrant species belong to a very small number of
major taxa (Table 6). If we distribute the High Probability Lessepsian Migrants
(HPLM species) according to the taxa then from the 128 species, the Crustacea
represent 27.34%, Mollusca 21.09%, and Pis ces 21.09%; the plants, from planktonic algae to the flowering plant Halophila represent 10.93 %, the rest is divided
between only six other phyla (Porifera, Coelenterata, Polychaeta, Bryozoa,
Table 6. Relative importance (%) of the eight main taxa among the migrants
Taxon
HPLM (128 sp.)
LPLM (76 sp.)
HPLM+
LPLM
No.of
No.of
(204 sp.)
species
%
species
%
Total %
Plants
14
10.93
11
14.47
12.25
Porifera
5
3.90
2
2.63
3.43
Polychaeta
9
7.03
14
18.42
11.27
Crustacea (Total)
35
27.34
16
21.05
25.00
Decapoda
23
17.96
8
10.52
15.19
Mollusca (Total)
27
21.09
17
22.36
21.56
Pelecypoda
13
10.15
6
7.89
9.31
Gastropoda
13
10.15
11
14.47
11.76
Bryozoa
4
2.89
3
3.94
3.43
Ascidiacea
4
2.89
3
3.94
3.43
Pis ces
27
21.09
5
6.57
15.68
125
97.06
71
93.38
96.00
The Migrant Biota
The success of these species can be seen also in our case as a result of the time
factor. If we calculate the percentage of the 0.0.3 and 0.0.4 species-the most
distantly spread Lessepsian migrants-as a function of their early or late migrational advance, the results are convincing: from among the species which entered
the Canal in the first period (1.0.0) 33.33% are 0.0.3 and 0.0.4, as compared with
16.36% in the second period (2.0.0), and 20% in the third period (0.0.3). The
situation is similar when we check the percentage of the 0.0.3 and 0.0.4 species in
relation to the period of their a ppearance in the Mediterranean: they are 34.78%
among the 0.1.0 species, only 25.92% among the 0.2.0, and 21.34% among the
0.3.0 species. This too indicates that the spreading of the Lessepsian migrants is a
gradual migrational process in which passive or adventive transport does not play
a significant role; the relatively high euryhalinity of the early settlers of the Canal
might have been beneficial-but at any rate not detrimental-to their further
move into the Mediterranean.
3.6 The Diversity of Lessepsian Migrants
After more than a century of Lessepsian migration, some qualitative aspects
can already be discerned, in addition to the merely quantitative time-distance
aspects.
The great majority of the migrant species belong to a very small number of
major taxa (Table 6). If we distribute the High Probability Lessepsian Migrants
(HPLM species) according to the taxa then from the 128 species, the Crustacea
represent 27.34%, Mollusca 21.09%, and Pis ces 21.09%; the plants, from planktonic algae to the flowering plant Halophila represent 10.93 %, the rest is divided
between only six other phyla (Porifera, Coelenterata, Polychaeta, Bryozoa,
Table 6. Relative importance (%) of the eight main taxa among the migrants
Taxon
HPLM (128 sp.)
LPLM (76 sp.)
HPLM+
LPLM
No.of
No.of
(204 sp.)
species
%
species
%
Total %
Plants
14
10.93
11
14.47
12.25
Porifera
5
3.90
2
2.63
3.43
Polychaeta
9
7.03
14
18.42
11.27
Crustacea (Total)
35
27.34
16
21.05
25.00
Decapoda
23
17.96
8
10.52
15.19
Mollusca (Total)
27
21.09
17
22.36
21.56
Pelecypoda
13
10.15
6
7.89
9.31
Gastropoda
13
10.15
11
14.47
11.76
Bryozoa
4
2.89
3
3.94
3.43
Ascidiacea
4
2.89
3
3.94
3.43
Pis ces
27
21.09
5
6.57
15.68
125
97.06
71
93.38
96.00