1. Introduction
The Mediterranean Sea has become a hotspot for alien species, with an increase of established taxa of 40% the last decade, with approximately 1,000 of non-indigenous species being recorded till the end of 2021 [
1]. Amongst them, fish is the group that attracted the highest attention as their settlement has raised serious concerns because of their short migration rate [
2,
3].The successful establishment into their newly invaded ecosystems could be attributed to their generalist nature [
4,
5], which has fundamental effects on local food web dynamics [
6,
7]. The invasive lionfish
Pterois miles (Bennett 1828) is one of the most successful invaders [
8], with increased predation rates on native fauna, resulting in altered community structure [
9,
10,
11,
12,
13,
14,
15]. Its presence can reduce recruitment of native species, drive declines in populations [
13,
16], and subsequently have serious implications on marine ecosystem functioning [
17].
Since the first documented appearance of
Pterois miles in the Mediterranean Sea [
18], the species has been extremely successful in establishing populations in new marine ecosystems [
19]. Its range is constantly updated in the Mediterranean Sea [
20,
21], confirming its successful introduction and progressive invasion of the basin. Moreover, the biological characteristics of the species [
11] promote its range expansion, which has not been interrupted by eradication programs [
20]. Particularly, lionfifish diet composition has exhibited a large variability among different locations [
22], rendering important location-based diet assessments to better inform local management regimes.
The species exhibits an opportunistic, generalist feeding behaviour, whose diet habits are directly connected to prey availability [
23,
24]. Differences in diet have been reported in the Mediterranean basin, where sampling (spear gun, boat-seining, long lines, video recordings) and identifification approaches (macroscopic examination and visual-video records) revealed that various fish species were among its main prey in Rhodes Island [
25], whereas fish or benthic invertebrates were found in stomachs from Cyprus [
26,
27]. Given that regional differences in its diet are already confirmed, identification of new prey species should be expected with the investigation of its trophic preferences across its invaded geographic range. Therefore, new studies are required to evaluate lionfish diet habits and its effects as a predator of the native fauna. This study aims to provide first-time insights on lionfish diet composition in three study sites in the Aegean Sea (southern Crete, and Kastellorizo and Nysiros islands) and verify the species’ generalist strategy as a consumer across sites and individuals.
4. Discussion
The lionfish
(P. miles) is a scorpaenid fish endemic in the Red Sea and the Gulf of Aqaba, where it preys on a big variety of benthic fishes and decapods [
46,
47]. This study provides a first comparative assessment of its diet composition in three different study areas located in southern Greece (Southern Aegean Sea) and highlights the similarities and differences in its feeding habits. It is, to our knowledge, the first study in Greece to describe the species’ diet composition and feeding patterns at a regional scale and to compare them among different areas.
The diet of
P. miles was dominated either by fish or by decapods, depending on the area. The contribution of other benthic invertebrate groups in the species diet was comparatively low across all areas. At the same time, the lionfish diet composition and the relative contributions of prey varied considerably among study areas. Decapods were by far the primary prey in numerical abundance (95%) and frequency of occurrence (90.3%), followed by fish (4.3% and 16,1%, respectively) in Kastelorizo Island. Conversely, the main prey were fish (82.9% numerical abundance and 56.8% frequency of occurrence respectively), followed by decapods (12.2% numerical abundance and 10.8% frequency of occurrence, respectively) in Nisyros Island. A similar lionfish prey composition was reported by Morris Jr and Akins [
48], who stated that 71.8 % numerical abundance and 61.6% frequency of occurrence of the prey species of lionfish in the Bahamas were teleosts and crustaceans. The dominant presence of these taxa as prey items in lionfish’s diet noted in other studies as well [
14,
22,
25,
49,
50,
51].
Pterois miles seems to behave as a specialist predator in both sites, targeting specific food items. Almost all 71%F and 83%N of its diet comprised of
Plesionika spp. in Kastelorizo Island, whereas in the island of Nisyros, most prey (40.5%F and 63.4%N) were unidentified fish remains, whilst the families Gobidae (5.4%F and 7.3%N) and Labridae (5.4%F and 7.3%N) dominated the identified fish prey (5.4%F and 4.88%N). Additionally, almost all the decapod prey items belonged to caridean shrimp (8.11%F and 9.76%N) in Nisyros Island. Similarly, the diet of
P. miles was composed predominantly of bony fish (78.5%N), with the majority of prey belonging to the family Gobidae, followed by Pomacentridae and Labridae in Rhodes Island,southeastern Aegean Sea, [
25]. Fish prey that belongs to the aforementioned families were also reported in the Caribbean Sea, such as the Mexican Caribbean [
49,
50], Costa Rica [
51], and Puerto Rico [
14]. These findings support the hypothesis that lionfish can be dietary specialists [
17]. Specialization in diet may largely depend on local prey assemblages’ composition and thus, it is more likely to be observed locally [
17,
52].
Fish and decapods were also the main prey categories for the lionfish (%N = 55.3 and 36.8 and %F = 58.9% and 42.5%, respectively) in southern Crete. In this site, the lionfish exhibited a relatively more balanced diet with one noticeable exception. Interestingly, a large proportion of the decapod prey belonged to the family Scyllaridae (26.3%N out of 36.8%N and 28.8%F out of 42.5%F). The specialist behaviour appeared here as well, but at a lesser degree than in Kastelorizo Island. Thus, the lionfish could pose a threat to the endangered Mediterranean slipper lobsters species (Scyllaridae), at least at the local level. Native Mediterranean scorpionfish species may prey on slipper lobsters, but only in one study to our knowledge
S. latus and
S. arctus were both listed amongst the prey items of
S. scrofa [
53].
It is difficult to properly assess the actual fisheries pressure on threatened and/or protected decapods when relying on official data [
54,
55]. The degree of uncertainty increases in species with limited or no commercial value, such as the slipper lobsters of the genus
Scyllarus. The addition of the pressure caused by the lionfish predation along with the uncertainty level of the fisheries pressure, may further reduce
Scyllarus populations.
Native Mediterranean fish species of the Scorpanidae family exhibit several ecological similarities with
P. miles, such as from being a generalist to a specialist strategy at a local level. For instance,
Scorpaena maderensis Valenciennes, 1833 prefers epibenthic crustaceans, [
56] and
Scorpaena loppei Cadenat, 1943 prefers mysids and decapods [
57].. Studies regarding the feeding ecology of
S. porcus, showed similar specialist feeding strategy [
58,
59,
60,
61] and in some cases endangered seahorses species were preyed upon [
62]. However, in all studies investigating the feeding habits of
P. miles, it is suggested that many factors such as prey availability, habitat complexity and season could affect the feeding ecology of the species.
In conclusion, the lionfish is an especially successful generalist, opportunistic, predatory species at a regional scale [
17,
22,
48,
52,
63], and as such it feeds on the most abundant and common prey species [
22]. At the same time, at a local level, it seems to be an equally successful specialist and it could increase the predation mortality of already stressed prey populations, depending on local predator communities [
22]. It can have high ecological impact on native Mediterranean communities [
64], similar to the detrimental impacts on native fish fauna and the food web in the Caribbean ecosystem [
11,
19,
65,
66,
67] and can be a serious threat to endemic, critically endangered [
16,
68,
69], and/or commercially important species [
50].
However, in order to reveal individual- and population-level specializations in lionfish diet and whether these can cause negative effects on native and/or endangered prey populations, robust large-scale studies of the species diet composition in association with prey availability are needed.
Figure 1.
Approximate sampling location of Pterois miles in southern Greece.
Figure 1.
Approximate sampling location of Pterois miles in southern Greece.
Figure 2.
Plots of the expected (mean) number of prey taxa as a function of the cumulative number of P. miles stomachs examined (prey accumulation curves) for the whole dataset and separately for Nisyros, Kastellorizo and Crete.
Figure 2.
Plots of the expected (mean) number of prey taxa as a function of the cumulative number of P. miles stomachs examined (prey accumulation curves) for the whole dataset and separately for Nisyros, Kastellorizo and Crete.
Figure 3.
Variations of the frequency of occurrence (%F) of the P. miles prey groups between areas, sex and size classes, and for the whole dataset. Σε τι αντιστοιχούν τα N, C, K, F, M, U, S, L;.
Figure 3.
Variations of the frequency of occurrence (%F) of the P. miles prey groups between areas, sex and size classes, and for the whole dataset. Σε τι αντιστοιχούν τα N, C, K, F, M, U, S, L;.
Figure 4.
Treemap plots presenting the variations of the relative numerical abundance (%N) of the P. miles prey taxa and groups between areas.
Figure 4.
Treemap plots presenting the variations of the relative numerical abundance (%N) of the P. miles prey taxa and groups between areas.
Figure 5.
nMDS ordination plot of the P. miles stomach samples, colored by area (N = Nisyros Island, K = Kastellorizo Island, C = Crete).
Figure 5.
nMDS ordination plot of the P. miles stomach samples, colored by area (N = Nisyros Island, K = Kastellorizo Island, C = Crete).
Figure 6.
Modified Costello graphical analysis of the P. miles diet for the whole dataset and separately for each area. Relative abundance of prey taxon i (pi) is plotted in the charts against its frequency of occurrence (%F).
Figure 6.
Modified Costello graphical analysis of the P. miles diet for the whole dataset and separately for each area. Relative abundance of prey taxon i (pi) is plotted in the charts against its frequency of occurrence (%F).
Table 1.
Total number of stomachs and percentages of full and empty stomachs (= VI) of P. miles for each area, sex (Female, Male, Unknown) and size class (Small, Large).
Table 1.
Total number of stomachs and percentages of full and empty stomachs (= VI) of P. miles for each area, sex (Female, Male, Unknown) and size class (Small, Large).
Factor |
Levels |
Total |
Full % |
Empty % (= VI) |
Area |
Crete |
73 |
77% |
23% |
|
Kastellorizo |
31 |
84% |
16% |
|
Nisyros |
37 |
62% |
38% |
Sex |
F |
78 |
78% |
22% |
|
M |
15 |
60% |
40% |
|
U |
48 |
73% |
27% |
Size |
S |
68 |
76% |
24% |
|
L |
73 |
73% |
27% |
Grand Total |
|
141 |
74% |
26% |
Table 2.
Mean values of the P. miles repletion index (0/00) for each area, sex and size class.
Table 2.
Mean values of the P. miles repletion index (0/00) for each area, sex and size class.
Sex |
Size |
Nisyros |
Kastellorizo |
Crete |
F |
|
31.83 |
315.07 |
171.12 |
|
S |
27.66 |
294.77 |
210.83 |
|
L |
32.66 |
330.30 |
103.39 |
M |
|
27.19 |
187.33 |
|
|
S |
|
126.32 |
|
|
L |
27.19 |
614.39 |
|
U |
|
96.94 |
230.66 |
83.19 |
|
S |
23.50 |
166.26 |
100.78 |
|
L |
121.42 |
311.17 |
61.20 |
Area |
52.07 |
257.60 |
138.60 |
Table 3.
Results of the one-way SIMPER analysis comparing areas in terms of the P. miles diet composition. The table presents area typifying species and species contributing most to the between areas dissimilarities up to a 90% cut-off value.
Table 3.
Results of the one-way SIMPER analysis comparing areas in terms of the P. miles diet composition. The table presents area typifying species and species contributing most to the between areas dissimilarities up to a 90% cut-off value.
One-way SIMPER analysis |
Group N (Average similarity: 34,59) |
Species |
Av.Abund |
Av.Sim |
Sim/SD |
Contrib% |
Cum.% |
|
fish remains |
0,80 |
32,91 |
0,79 |
95,14 |
95,14 |
|
Group C (Average similarity: 29,05) |
Species |
Av.Abund |
Av.Sim |
Sim/SD |
Contrib% |
Cum.% |
|
fish remains |
0,73 |
27,19 |
0,74 |
93,60 |
93,60 |
|
Group K (Average similarity: 26,60) |
Species |
Av.Abund |
Av.Sim |
Sim/SD |
Contrib% |
Cum.% |
|
Plesionika edwarsii |
0,91 |
15,56 |
0,53 |
58,51 |
58,51 |
|
Plesionika spp. |
0,91 |
9,28 |
0,35 |
34,90 |
93,41 |
|
Groups N & C (Average dissimilarity = 69,17) |
|
Group N |
Group C |
|
|
|
|
Species |
Av.Abund |
Av.Abund |
Av.Diss |
Diss/SD |
Contrib% |
Cum.% |
fish remains |
0,80 |
0,73 |
23,30 |
1,09 |
33,69 |
33,69 |
Caridea |
0,15 |
0,02 |
5,05 |
0,39 |
7,30 |
40,98 |
Scyllarus sp. |
0,00 |
0,13 |
4,02 |
0,35 |
5,81 |
46,80 |
Scyllaridae |
0,00 |
0,14 |
3,89 |
0,37 |
5,63 |
52,42 |
Pterois sp. |
0,09 |
0,00 |
3,53 |
0,30 |
5,10 |
57,52 |
Cumacea |
0,09 |
0,00 |
3,53 |
0,30 |
5,10 |
62,63 |
Gobidae |
0,10 |
0,04 |
2,96 |
0,34 |
4,29 |
66,91 |
Scyllarides latus |
0,00 |
0,12 |
2,89 |
0,29 |
4,18 |
71,09 |
Labridae |
0,10 |
0,00 |
2,79 |
0,29 |
4,04 |
75,13 |
Homola barbata |
0,00 |
0,08 |
2,11 |
0,26 |
3,04 |
78,18 |
Decapoda |
0,04 |
0,00 |
1,76 |
0,21 |
2,55 |
80,73 |
Polychaeta |
0,00 |
0,06 |
1,65 |
0,23 |
2,39 |
83,12 |
Chromis sp. |
0,00 |
0,04 |
1,50 |
0,18 |
2,18 |
85,29 |
Parapenaeus longirostris |
0,00 |
0,04 |
1,29 |
0,18 |
1,87 |
87,16 |
Inachus sp. |
0,00 |
0,04 |
1,19 |
0,18 |
1,72 |
88,88 |
Ostracoda |
0,00 |
0,03 |
0,95 |
0,13 |
1,38 |
90,26 |
Groups N & K (Average dissimilarity = 93,62) |
|
Group N |
Group K |
|
|
|
|
Species |
Av.Abund |
Av.Abund |
Av.Diss |
Diss/SD |
Contrib% |
Cum.% |
Plesionika edwarsii |
0,00 |
0,91 |
26,14 |
0,91 |
27,92 |
27,92 |
Plesionika spp. |
0,00 |
0,91 |
23,09 |
0,71 |
24,67 |
52,59 |
fish remains |
0,80 |
0,21 |
21,39 |
1,12 |
22,84 |
75,43 |
Natantia |
0,00 |
0,27 |
6,06 |
0,40 |
6,48 |
81,91 |
Caridea |
0,15 |
0,00 |
3,72 |
0,37 |
3,97 |
85,88 |
Pterois sp. |
0,09 |
0,00 |
2,86 |
0,29 |
3,06 |
88,94 |
Cumacea |
0,09 |
0,00 |
2,86 |
0,29 |
3,06 |
92,00 |
Groups C & K (Average dissimilarity = 93,68) |
|
Group C |
Group K |
|
|
|
|
Species |
Av.Abund |
Av.Abund |
Av.Diss |
Diss/SD |
Contrib% |
Cum.% |
Plesionika edwarsii |
0,00 |
0,91 |
24,18 |
0,90 |
25,81 |
25,81 |
Plesionika spp. |
0,03 |
0,91 |
21,79 |
0,72 |
23,26 |
49,08 |
fish remains |
0,73 |
0,21 |
19,08 |
1,07 |
20,37 |
69,44 |
Natantia |
0,00 |
0,27 |
5,63 |
0,40 |
6,00 |
75,45 |
Scyllaridae |
0,14 |
0,04 |
3,57 |
0,40 |
3,81 |
79,26 |
Scyllarus sp. |
0,13 |
0,00 |
3,14 |
0,35 |
3,35 |
82,61 |
Scyllarides latus |
0,12 |
0,00 |
2,35 |
0,29 |
2,51 |
85,12 |
Homola barbata |
0,08 |
0,00 |
1,68 |
0,26 |
1,79 |
86,91 |
Polychaeta |
0,06 |
0,00 |
1,33 |
0,23 |
1,42 |
88,33 |
Ostracoda |
0,03 |
0,04 |
1,27 |
0,21 |
1,36 |
89,69 |
Chromis sp. |
0,04 |
0,00 |
1,16 |
0,18 |
1,24 |
90,93 |