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Posidonia oceanica epiphytes of Sicily Pardi, Piazzi, Balata, Papi, Cinelli & Benedetti-Cecchi

Table 1. Most frequent species and/or genus included in the mor- and particularly among the meadows, plots and leaves.
phological groups. This descriptive study does not provide for a clear identi-
fication of the causes of the variability in ESL; thus only
Encrusting red algae conjectures are possible.
Hydroliton farinosum (J. V. Lamouroux) Penrose et Y. Chamberlain
Hydroliton boreale (Foslie) Y. Chamberlain Large-scale processes that could account for geograph-
Pneophyllum fragile Ku¨ tzing ical pattern in the Mediterranean Sea include differences
Pneophyllum coronatum (Rosanoff) Penrose in temperature, in oceanographic conditions like latitudi-
nal gradients in the influence of Atlantic waters and his-
Encrusting brown algae torical processes.
Myrionema orbiculare J. Agardh
Differences among meadows can be also related to local
Filamentous algae differences in environmental characteristics of sampled
Antithamnion spp. locations. The significance at the meadow level in each geo-
Ceramium spp. graphical area, both in island and mainland habitat, shows
Womersleyella setacea (Hollenberg) R.E. Norris that variability among meadows is independent of distan-
Sphacelaria cirrosa (Roth) C. Agardh ces; thus the different distances among meadows in the geo-
Giraudia sphacelarioides De´ rbe` s & Solier graphical areas considered did not confound our results.
Cladophora spp.
Patterns of small-scale variability similar to those docu-
Encrusting bryozoans mented in the present study have been detected by Piazzi
Electra posidoniae Gautier et al. (2004a) on the epiphytes of P. oceanica leaves and
Fenestrulina joannae (Calvet) in other species of seagrasses (Vanderklift & Lavery 2000),
Lichenopora radiata (Audouin) suggesting that this is a pervasive feature in these kinds of
Disporella hispida (Fleming) systems. Variability in ESL at the scale of metres may be
mostly influenced by differences in shoot density and in
Erect bryozoans the characteristics of the canopy, which affect light inten-
Aetea sp. sity and water movement (Gambi et al. 1989). Other fac-
Valkeria sp. tors may be relevant though, like local hydrodynamic
flows that affect dispersal, settlement and recruitment of
Hydroids propagules (Trautman & Borowitzka 1999; Vanderklift &
Sertularia perpusilla (Stechow) Lavery 2000). Moreover, the role of biotic interaction
Aglaophenia sp. such as grazing pressure and influence of established
Plumularia sp. assemblages on potential recruitment cannot be ignored
(Mazzella & Russo 1989). Experimental studies are neces-
Foraminifera sary to elucidate the causes of the spatial patterns of leaf
Elphidium crispum (Linnaeus) epiphytes of Mediterranean meadows.
Planorbulina sp.
The present study, although limited to the analysis of
Variance components indicated that most of the vari- morphological groups and not to species, may give several
ability occurred at the scale of leaf, with the exception of suggestions in order to use seagrass epiphytes as bioindi-
the encrusting red algae that displayed larger variation at cators in the studies of impact. In fact, the lack of signifi-
the scale of meadow. Variability at this scale was also cant differences between the small islands and locations
important for encrusting brown algae, encrusting bryo- on the mainland suggests that the former habitat may be
zoans, erect bryozoans and Foraminifera, while variability used as a reference condition for long-term experimental
at the scale of plot was important for filamentous and monitoring of ESL. On the contrary, our results clearly
encrusting red algae; variability at the intermediate scale indicate the necessity of stratifying studies by geographic
of site was negligible in most cases (Table 3). area. This aspect may be of higher importance in case
that species composition will also be included, as indi-
Separate ANOVA for each habitat and region showed cated in Esposito et al. (2003). Finally, the future analyses
the same patterns of ANOVA including all the factors; of ESL should consider sampling designs that allocate a
significance at the meadow level was detected independ- large number of replicates at the scales of shoots and
ently from the relative distance among the meadows. plots, while a minimum of two sites would be sufficient
to represent an entire meadow in relation to the low val-
Discussion ues of variance components at this scale.

Results show that epiphytes of Posidonia oceanica leaves Understanding how patterns in abundance, distribution
do not vary significantly between the small islands and and diversity of species change in relation to the spatial
mainland, while significant differences were detected
among the geographical regions. High spatial variability is
present at the largest and the smallest scales investigated

400 Marine Ecology 27 (2006) 397–403 ª 2006 The Authors. Journal compilation ª 2006 Blackwell Publishing Ltd