multivariate analysis of variance (PERMANOVA), with the fixed predictive factor of
sampling locations, while similarity percentages analysis (SIMPER) was used to reveal
which taxa contributed the most to the sessile community pattern of each marina.
Finally, a non-metric multidimensional scaling analysis (nMDS) was used to depict
spatial patterns in community structures for the studied marinas.
Results
In total, 60 benthic taxa were recorded in the studied marinas, 45 of which were
identified to the species level (or species complex), 12 to genus level and 13 to higher
taxonomic and/or morpho-functional categories. The taxa were classified into
Chlorophyta (4), Rhodophyta (6), Phaeophyta (3), Porifera (12), Cnidaria (4),
Polychaeta (2) Mollusca (7), Crustacea (1), Bryozoa (7) and Ascidiacea (14). The
highest species richness was recorded in HER and RHO marinas (48 and 37 taxa,
respectively) and the lowest in PAT and ZEA (25 and 26 taxa, respectively). Ascidiacea
was the most diverse group with 13 taxa in HER, but only 3 to 5 in the other studied
areas. In terms of coverage, macroalgae (in descending order: Turf-forming algae,
Rhodophyta, Chlorophyta and Ochrophyta) prevailed in all marinas (mean coverage:
60.84%), mainly on vertical substrates, while sciaphilic benthic taxa dominated below
horizontal floating platforms in HER and RHO marinas. Statistical analysis revealed
differences among the examined areas and different dominant taxa. PERMANOVA
showed that there were significant differences (p-value < 0.05) among the four sampling
locations (also in pairwise comparisons). SIMPER revealed the similarity of samples
within the marinas with 39.94% in RHO, 41.88% in HER, 45.53% in ZEA and 46.69%
in PAT. Different taxa combinations contributed to the similarity in every site with
Turf-forming algae contributing more than 25% in each area. The nMDS analysis
revealed a scattered pattern with no distinct grouping for the quadrats of different
studied areas, despite the significant differences among them (Fig. 2).
In total, four (7%) sessile CRY and eight (13%) sessile NIS were recorded in the
studied marinas, four of which are characterized as invasive (INV) (nine in HER, five in
PAT, three in ZEA and six in RHO). These were the macroalga Stypopodium schimperi
(INV), the sponge Paraleucilla magna (INV), the anthozoan Oculina patagonica
(CRY), the bivalve molluscs Brachidontes pharaonis (INV), Dendostrea folium (INV)
and Pinctada radiata (INV), the erect bryozoans Amathia verticillata (CRY) and
Bugula neritina (CRY) and the ascidians Ecteinascidia turbinata (CRY), Herdmania
momus, Phallusia nigra and Styela plicata. Four species were constantly present in the
study areas (D. folium, H. momus, B. neritina and A. verticillata) while another four
species were present in only one marina (P. magna, B. pharaonis, P. radiata and E.
turbinata). Additionally, the crypto-expanding crab Percnon gibbesi and the two nonindigenous echinoderms Diadema setosum and Synaptula reciprocans (INV) were
recorded in the marinas during the SCUBA surveys.
Discussion and conclusions
Visual census methods can provide useful information for mega- and macro-benthic
taxa and can also be a cost-effective and time-efficient tool for the assessment of
biodiversity in marinas (Bianchi et al., 2004; Chebaane et al., 2022). The analysis of
photoquadrats consists a non-destructive approach and is widely used for the studying
and monitoring sessile communities in both natural and artificial substrates
(Gerovasileiou & Voultsiadou, 2016; Sedano et al., 2019; Rallis et al., 2022).
2nd Mediterranean Symposium on the Non-Indigenous Species (Genoa, Italy, 22-23 September 2022)
58
sampling locations, while similarity percentages analysis (SIMPER) was used to reveal
which taxa contributed the most to the sessile community pattern of each marina.
Finally, a non-metric multidimensional scaling analysis (nMDS) was used to depict
spatial patterns in community structures for the studied marinas.
Results
In total, 60 benthic taxa were recorded in the studied marinas, 45 of which were
identified to the species level (or species complex), 12 to genus level and 13 to higher
taxonomic and/or morpho-functional categories. The taxa were classified into
Chlorophyta (4), Rhodophyta (6), Phaeophyta (3), Porifera (12), Cnidaria (4),
Polychaeta (2) Mollusca (7), Crustacea (1), Bryozoa (7) and Ascidiacea (14). The
highest species richness was recorded in HER and RHO marinas (48 and 37 taxa,
respectively) and the lowest in PAT and ZEA (25 and 26 taxa, respectively). Ascidiacea
was the most diverse group with 13 taxa in HER, but only 3 to 5 in the other studied
areas. In terms of coverage, macroalgae (in descending order: Turf-forming algae,
Rhodophyta, Chlorophyta and Ochrophyta) prevailed in all marinas (mean coverage:
60.84%), mainly on vertical substrates, while sciaphilic benthic taxa dominated below
horizontal floating platforms in HER and RHO marinas. Statistical analysis revealed
differences among the examined areas and different dominant taxa. PERMANOVA
showed that there were significant differences (p-value < 0.05) among the four sampling
locations (also in pairwise comparisons). SIMPER revealed the similarity of samples
within the marinas with 39.94% in RHO, 41.88% in HER, 45.53% in ZEA and 46.69%
in PAT. Different taxa combinations contributed to the similarity in every site with
Turf-forming algae contributing more than 25% in each area. The nMDS analysis
revealed a scattered pattern with no distinct grouping for the quadrats of different
studied areas, despite the significant differences among them (Fig. 2).
In total, four (7%) sessile CRY and eight (13%) sessile NIS were recorded in the
studied marinas, four of which are characterized as invasive (INV) (nine in HER, five in
PAT, three in ZEA and six in RHO). These were the macroalga Stypopodium schimperi
(INV), the sponge Paraleucilla magna (INV), the anthozoan Oculina patagonica
(CRY), the bivalve molluscs Brachidontes pharaonis (INV), Dendostrea folium (INV)
and Pinctada radiata (INV), the erect bryozoans Amathia verticillata (CRY) and
Bugula neritina (CRY) and the ascidians Ecteinascidia turbinata (CRY), Herdmania
momus, Phallusia nigra and Styela plicata. Four species were constantly present in the
study areas (D. folium, H. momus, B. neritina and A. verticillata) while another four
species were present in only one marina (P. magna, B. pharaonis, P. radiata and E.
turbinata). Additionally, the crypto-expanding crab Percnon gibbesi and the two nonindigenous echinoderms Diadema setosum and Synaptula reciprocans (INV) were
recorded in the marinas during the SCUBA surveys.
Discussion and conclusions
Visual census methods can provide useful information for mega- and macro-benthic
taxa and can also be a cost-effective and time-efficient tool for the assessment of
biodiversity in marinas (Bianchi et al., 2004; Chebaane et al., 2022). The analysis of
photoquadrats consists a non-destructive approach and is widely used for the studying
and monitoring sessile communities in both natural and artificial substrates
(Gerovasileiou & Voultsiadou, 2016; Sedano et al., 2019; Rallis et al., 2022).
2nd Mediterranean Symposium on the Non-Indigenous Species (Genoa, Italy, 22-23 September 2022)
58