J. Mar. Biol. Ass. U.K. (2004), 84, 669^670 Printed in the United Kingdom
Fish assemblages associated with coastal defence structures in south-western Italy (Mediterranean Sea) P. Guidetti Laboratory of Zoology and Marine Biology, DiSTeBA, University of Lecce, Via Provle Monteroni, 73100 Lecce, Italy. E-mail:
[email protected]
Fish assemblages associated with wave exposed and sheltered sides of breakwaters, and with adjacent sandy habitats were studied in western Calabria (Mediterranean Sea, south-western Italy). Overall, 26 ¢sh taxa were recorded (21 associated with exposed breakwater sides, 21 with sheltered sides, and four with sand). Fish assemblages signi¢cantly di¡ered between breakwaters (both sides) and sand, and, to a lesser extent, between exposed and sheltered sides of breakwaters in terms of whole assemblage structure, densities of species, and juvenile stages. Human-made defence structures (e.g. breakwaters) are becoming more and more common in coastal waters all around the world (Bacchiocchi & Airoldi, 2003). Defence structures are aimed at protecting coastal maritime, industrial and urban developments and such arti¢cial structures generally add novel habitats into coastal waters, especially in those regions where the coast is mostly sandy. Several studies have been published about intertidal and subtidal epibiotic assemblages associated with defence structures (Bacchiocchi & Airoldi, 2003, and references therein), whereas very little is known about ¢sh assemblages. The aim of this note is to assess putative di¡erences among ¢sh assemblages associated with wave exposed, and sheltered sides of breakwaters, and adjacent sandy habitats. The present study was done in May 2001 in western Calabria (Tyrrhenian Sea, south-western Italy; 398220 N 168010E), where breakwaters (made of transplanted boulders with their longer axes of 1^2 m) were constructed as a protection measure against coastal erosion. Fish density was estimated by visual census along 255 m transects. Juvenile stages of ¢sh (i.e. recruits) were also noted. Three sites, each including one breakwater and the adjacent sandy area, were randomly selected. Visual censuses were done at shallow depth (1^4 m), at each site, in three ‘habitats’: seaward (exposed: hereafter ‘Ex’) and landward (sheltered: ‘Sh’) sides of breakwaters, and adjacent sandy habitat (‘Sa’). Nonparametric multivariate analysis of variance (NPMANOVA) was used to test for di¡erences in ¢sh assemblages ‘among habitats’ (¢xed factor) and ‘among sites’ (random factor, orthogonal to ‘habitat’). The analyses were based on Bray ^ Curtis dissimilarities (log-transformed data), and made by NPMANOVA.exe program (courtesy of M.J. Anderson). The Bray ^ Curtis similarity matrix was used to generate the 2-dimensional non-metric multidimensional scaling (nMDS) plot. The similarity percentage procedure (SIMPER) was used to identify the ¢sh taxa mostly contributing to the di¡erences between exposed and sheltered sides of breakwaters (PRIMER package). Twenty-six ¢sh taxa were identi¢ed: 21 taxa were recorded at Ex, 21 at Sh, and 4 at Sa (Table 1). Signi¢cant di¡erences were found among ¢sh assemblages associated with the three ‘habitats’ investigated. Di¡erences ‘among sites’, and the interaction between the factors ‘habitat’ and ‘site’, conversely, were not significant (Table 2). The nMDS ordination showed that ¢sh assemblages at Ex and Sh group separately, and that both Ex and Sh dramatically separate out from Sa (Figure 1). The ¢sh species Journal of the Marine Biological Association of the United Kingdom (2004)
mostly contributing to dissimilarities between Ex and Sh are reported in Table 3. Adults of Chromis chromis, Oblada melanura, Boops boops, Diplodus sargus, Coris julis and Thalassoma pavo were mostly associated with Ex, together with Atherinidae and Table 1. List of ¢sh taxa recorded (+, present; 7, absent) at exposed (Ex) and sheltered (Sh) sides of breakwaters, and sandy habitat (Sa). Families/species
Ex
Sh
Sa
Atherinidae (unidenti¢ed) Blenniidae Parablennius gattorugine Parablennius rouxi Parablennius sanguinolentus Centracanthidae Spicara maena Gobiidae Gobius bucchichii Ammodytidae Gymnammodytes cicerellus Labridae Coris julis Symphodus cinereus Symphodus tinca Thalassoma pavo Moronidae Dicentrarchus labrax Mugilidae (unidenti¢ed) Mullidae Mullus surmuletus Pomacentridae Chromis chromis Serranidae Serranus cabrilla Serranus scriba Sparidae Boops boops Diplodus annularis Diplodus sargus Diplodus vulgaris Lithognathus mormyrus Oblada melanura Sarpa salpa Trypterigiidae Trypterigion delaisi Trypterigion tripteronotus
+
+
7
7 + 7
+ 7 +
7 7 7
+
^
7
+
+
7
7
+
7
+ + + +
+ ^ + +
7 7 7 7
7 +
+ +
+ +
+
+
7
+
+
7
+ +
^ +
7 7
+ + + + + +
+ ^ + + + + +
7 7 7 + + 7 7
+ +
+ +
7 7
670
P. Guidetti
Fish assemblages associated with coastal defence structures in south-western Italy
Table 2. Two-way crossed NPMANOVA testing for di¡erences in ¢sh assemblages ‘among habitats’ (Ex and Sh, exposed and sheltered sides of breakwaters; Sa, sand), and ‘among sites’. Source of variation
df
MS
F-value
P
Habitat=H Site=S HS Res Pairwise tests Ex vs Sa Sh vs Ex Sh vs Sa
2 2 4 9
17487.19 256.78 625.87 719.94
27.94 0.36 0.87
0.002** 0.860 n.s. 0.523 n.s.
t-value 2.226 5.573 7.470
0.003** 0.003** 0.004**
Probability levels: n.s., not signi¢cant; *, P50.05; **, P50.001.
Figure 1. nMDS plots of ¢sh assemblages associated with exposed sides of breakwaters (Ex), sheltered sides (Sh), and sand (Sa).
Table 3. SIMPER: ¢sh species contributing most (%) to the dissimilarity between Ex and Sh (exposed and sheltered sides of breakwaters), and mean density (no. individuals 125 m2). Mean density Species Chromis chromis Diplodus vulgaris Sarpa salpa Atherinidae Oblada melanura Mugilidae Boops boops Diplodus sargus Coris julis
%
Ex
Sh
14.22 9.23 8.71 8.08 7.82 7.73 7.66 4.62 4.51
121.8 20.2 72.5 3.3 18.7 10.5 24.7 22.2 25.2
14.5 176.0 34.7 29.2 2.0 17.5 1.3 6.8 10.2
di¡erent periods of the year, breakwaters should be sampled through time to get more exhaustive data. Adult ¢sh at defence structures can migrate from natural substrata to breakwaters (separated by bare sands) and/or derive from larvae settled long before at the breakwaters. Juveniles (that have lower swimming ability, and run greater predation risk than adults in bare sands), conversely, probably settle at breakwaters (where they ¢nd shelter and food) as they approach coastal waters for settlement. Both attraction and productivity enhancement (Bohnsack, 1989), therefore, may potentially explain the patterns reported here. Juveniles of Diplodus vulgaris and adults of D. sargus (both are species of commercial importance) were found at breakwaters which suggests the potential use of similar arti¢cial structures for enhancing local ¢sheries (Guidetti et al., unpublished data).
REFERENCES Mugilidae (about 50% of specimens of these two latter taxa were juveniles). Sarpa salpa was found at breakwaters, with adults only associated with Ex. Almost all Diplodus vulgaris were juveniles, and were associated with breakwaters, with densities approximately tenfold higher at Sh than at Ex. Juveniles of Lithognathus mormyrus were mostly associated with Sa. This study shows that breakwaters, adding novel rocky habitat in sandy bottoms, may host ¢sh assemblages di¡erent (and much more speciose) from those found in natural sandy habitats. Di¡erences were also observed between assemblages at exposed and sheltered sides of breakwaters, especially for juvenile ¢sh. Stephens et al. (1994) and Rilov & Benayahu (2000), from this perspective, stressed the importance of breakwaters as exceptional ¢sh habitats, both for many adult ¢sh, and their juvenile stages. Since juvenile ¢sh in coastal waters settle/recruit in
Journal of the Marine Biological Association of the United Kingdom (2004)
Bacchiocchi, F. & Airoldi, L., 2003. Distribution and dynamics of epibiota on hard structures for coastal protection. Estuarine, Coastal and Shelf Science, 56, 1157^1166. Bohnsack, J.A., 1989. Are high densities of ¢shes at arti¢cal reefs the result of habitat limitation or behavioural preferences? Bulletin of Marine Science, 44, 631^645. Rilov, G. & Benayahu, Y., 2000. Fish assemblage on natural versus vertical arti¢cial reefs: the rehabilitation perspective. Marine Biology, 136, 931^942. Stephens Jr, J.S., Morris, P.A., Pondella, D.J., Koonce, T.A. & Jordan, G.A., 1994. Overview of the dynamics of an urban arti¢cial reef ¢sh assemblage at King Harbor, California, USA, 1974^1991: a recruitment driven system. Bulletin of Marine Science, 55, 1224^1239. Submitted 5 January 2004. Accepted 26 March 2004.
