Tab. 1: Absolute abundances of Amphistegina lobifera recorded along decreasing depth
levels of the two cores portions (upper and lower), collected in 2018 and 2019.
An alternative age model was developed after observing results of grain-size and
porosity analyses. In both cores, in fact, sediment grain-size and porosity were
remarkably different in the upper and lower parts of cores: the upper portion exhibited
sediments mainly composed of very coarse sands and, in equal proportion, of coarse and
medium sand, while fine and very fine sands and mud were subordinated. Particularly,
the mud fraction had percentages between 5% and 18%. Porosity ranged between 0.42
and 0.59. Mollusc shells occurring in this portion were typically depigmented, eroded
and bio-perforated.
Conversely, sediments from the lower portion of both cores mainly consisted of fine and
very fine sands and mud (60-70%) and were characterised by a dark grey colour,
probably due to hypoxic conditions of the sediments (Fig. 1A-B). This was suggested
by both the smell of hydrogen sulphide present during the core sectioning and the very
high abundance of undecomposed Posidonia oceanica remains, mainly rhizomes well
visible to the naked eye (Fig. 1D), which were missing in the upper core. Porosity was
higher, ranging between 0.52 and 0.74. Sediments from this core portion also contained
abundant mollusc shells with an unusually well-preserved pigmentation and with
unsmoothed, sharp edge fractures.
These differences are consistent with the hypothesis of a sudden depositional event
occurred around cm 25-24 bsf, i.e., around the years 1905-1910.
Discussion and Conclusion
Stochastic events, such as forest fires, ice storms, hurricanes and typhoons, that can
abruptly change local environmental conditions, may be involved in invasion failure,
although this has been rarely documented in the literature (e.g., Carlton & Eldredge,
2009). Our data suggest that an earlier population of the Red Sea foraminifer
Amphistegina lobifera, occurring in Malta’s Marsamxett Harbour at the beginning of the
Upper core
Lower core
from cm
to cm
2018 core 2019 core
from cm
to cm
2018 core 2019 core
0.5
0
1
3.70
3.83
Current invasion
25.5
25
26
0
0
1.5
1
2
2.70
5.99
26.5
26
27
0
0
2.5
2
3
3.96
7.06
27.5
27
28
0
0
3.5
3
4
3.68
4.81
28.5
28
29
0
0.13
Early failed invasion
4.5
4
5
3.40
2.02
29.5
29
30
0
0
5.5
5
6
2.82
2.97
30.5
30
31
0
0
6.5
6
7
1.12
2.31
31.5
31
32
0
0
7.5
7
8
1.40
1.18
32.5
32
33
0
0
8.5
8
9
0.85
1.02
33.5
33
34
0
0
9.5
9
10
0.28
0.38
34.5
34
35
0.28
0
10.5
10
11
0.28
0.26
35.5
35
36
0.57
0
11.5
11
12
0.57
0.65
36.5
36
37
0.28
0
12.5
12
13
0.57
0.39
37.5
37
38
0.14
0
13.5
13
14
0.28
0.38
38.5
38
39
0.57
0
14.5
14
15
0.28
0.39
39.5
39
40
0.28
0
15.5
15
16
0
0
40.5
40
41
0
0
16.5
16
17
0
0.13
41.5
41
42
0
17.5
17
18
0
0
42.5
42
43
0
18.5
18
19
0
0
43.5
43
44
0
19.5
19
20
0
0
44.5
44
45
0
20.5
20
21
0
0
45.5
45
46
0
21.5
21
22
0
0
46.5
46
47
0
22.5
22
23
0
0
47.5
47
48
0
23.5
23
24
0
0
48.5
48
49
0
24.5
24
25
0
0
49.5
49
49,5
0
A. lobifera abundance
(N g
-1
)
A. lobifera abundance
(N g
-1
)
Depth level
(cm bsf)
Depth level
(cm bsf)
2nd Mediterranean Symposium on the Non-Indigenous Species (Genoa, Italy, 22-23 September 2022)
53
levels of the two cores portions (upper and lower), collected in 2018 and 2019.
An alternative age model was developed after observing results of grain-size and
porosity analyses. In both cores, in fact, sediment grain-size and porosity were
remarkably different in the upper and lower parts of cores: the upper portion exhibited
sediments mainly composed of very coarse sands and, in equal proportion, of coarse and
medium sand, while fine and very fine sands and mud were subordinated. Particularly,
the mud fraction had percentages between 5% and 18%. Porosity ranged between 0.42
and 0.59. Mollusc shells occurring in this portion were typically depigmented, eroded
and bio-perforated.
Conversely, sediments from the lower portion of both cores mainly consisted of fine and
very fine sands and mud (60-70%) and were characterised by a dark grey colour,
probably due to hypoxic conditions of the sediments (Fig. 1A-B). This was suggested
by both the smell of hydrogen sulphide present during the core sectioning and the very
high abundance of undecomposed Posidonia oceanica remains, mainly rhizomes well
visible to the naked eye (Fig. 1D), which were missing in the upper core. Porosity was
higher, ranging between 0.52 and 0.74. Sediments from this core portion also contained
abundant mollusc shells with an unusually well-preserved pigmentation and with
unsmoothed, sharp edge fractures.
These differences are consistent with the hypothesis of a sudden depositional event
occurred around cm 25-24 bsf, i.e., around the years 1905-1910.
Discussion and Conclusion
Stochastic events, such as forest fires, ice storms, hurricanes and typhoons, that can
abruptly change local environmental conditions, may be involved in invasion failure,
although this has been rarely documented in the literature (e.g., Carlton & Eldredge,
2009). Our data suggest that an earlier population of the Red Sea foraminifer
Amphistegina lobifera, occurring in Malta’s Marsamxett Harbour at the beginning of the
Upper core
Lower core
from cm
to cm
2018 core 2019 core
from cm
to cm
2018 core 2019 core
0.5
0
1
3.70
3.83
Current invasion
25.5
25
26
0
0
1.5
1
2
2.70
5.99
26.5
26
27
0
0
2.5
2
3
3.96
7.06
27.5
27
28
0
0
3.5
3
4
3.68
4.81
28.5
28
29
0
0.13
Early failed invasion
4.5
4
5
3.40
2.02
29.5
29
30
0
0
5.5
5
6
2.82
2.97
30.5
30
31
0
0
6.5
6
7
1.12
2.31
31.5
31
32
0
0
7.5
7
8
1.40
1.18
32.5
32
33
0
0
8.5
8
9
0.85
1.02
33.5
33
34
0
0
9.5
9
10
0.28
0.38
34.5
34
35
0.28
0
10.5
10
11
0.28
0.26
35.5
35
36
0.57
0
11.5
11
12
0.57
0.65
36.5
36
37
0.28
0
12.5
12
13
0.57
0.39
37.5
37
38
0.14
0
13.5
13
14
0.28
0.38
38.5
38
39
0.57
0
14.5
14
15
0.28
0.39
39.5
39
40
0.28
0
15.5
15
16
0
0
40.5
40
41
0
0
16.5
16
17
0
0.13
41.5
41
42
0
17.5
17
18
0
0
42.5
42
43
0
18.5
18
19
0
0
43.5
43
44
0
19.5
19
20
0
0
44.5
44
45
0
20.5
20
21
0
0
45.5
45
46
0
21.5
21
22
0
0
46.5
46
47
0
22.5
22
23
0
0
47.5
47
48
0
23.5
23
24
0
0
48.5
48
49
0
24.5
24
25
0
0
49.5
49
49,5
0
A. lobifera abundance
(N g
-1
)
A. lobifera abundance
(N g
-1
)
Depth level
(cm bsf)
Depth level
(cm bsf)
2nd Mediterranean Symposium on the Non-Indigenous Species (Genoa, Italy, 22-23 September 2022)
53