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Chemistry and Ecology
Downloaded By: [Furnari, G.] At: 10:31 24 May 2010 6. Growth performance
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consistent with Calvo et al. [41], who recorded the maximum mean shoot surface of Sicilian
coasts in the same sector.
A comparison between our data and those available from the Mediterranean basin at comparable
depth and period indicates that the average values of Sicilian sectors (except for leaf number) are
generally greater than in the rest of the basin. Consequently, the confidence intervals are different
and no overlapping boundaries are present (Table 3).
Studies focusing on P. oceanica plasticity provide evidence that leaf biometry variations are
affected by different factors (excluding depth and period) operating on different spatial scales, from
several kilometres to a few metres [71]. It is likely that the large-scale P. oceanica heterogeneity
observed in this study reflects the variability in climatic conditions [72], because there is very
high latitudinal and longitudinal variation between the two macro areas considered (Sicily vs.
Mediterranean coasts).
Recent studies of multivariate analysis performed on several P. oceanica descriptors indicate
that shoot surface is one of the best candidates to asses meadow status [70,73,74]. The data
compilation in this study provides evidence of the good condition of Sicilian meadows.
During the last decade more attention has been given to the use of reconstructive ageing tech-
niques, because there is growing evidence that these methods provide reliable estimates of
seagrass growth performance, on large temporal and spatial scales [51,82]. In Sicily, most dat-
ing measurements were made on a local scale to assess the influences of site-specific conditions
(hydrodynamism, urban and fish farm pressure) and endogenous factors (ageing and sexual repro-
duction) on P. oceanica growth performance [18,19,23,83,84]. On a regional scale, information
on P. oceanica growth is limited to the analysis of the effect of depth on spatial synchrony [85].
In this study, the history of P. oceanica growth performance of >10,500 shoots, sampled
in 238 stations spread around all the Sicilian coasts from 1 to 32 m depth was reconstructed by
lepidochronology [86] (Table 4). These new records were obtained from ∼67,000 annual rhizome
segments belonging to temporal series ranging from 1 to 48 years per shoot. The temporal range
explored varies across different sectors from the 1951–2005 window to the 1986–2005 window.
Mean vertical rhizome elongation ranges from 7.6 ± 3.3 to 10.9 ± 5.2 mm·shoot−1·yr−1 and
the confidence interval of the grand mean for Sicilian coasts was estimated at 99% between 9.6
and 9.9 mm·shoot−1·yr−1. The mean number of leaves produced per year ranged from 7.2 ± 0.8
to 7.8 ± 0.9 (99% CI of grand mean 7.47–7.52).
A previous study of growth performance data from a series of Mediterranean localities estimated
that 6.8–8.3 leaves were produced annually and that 5.9–8.9 mm·yr−1 of vertical rhizome growth
can be considered ‘normal’ for this species [53]. The new, more extensive estimates presented
Table 4. Mean values (SD) of the examined growth performance variables of Posidonia oceanica in different sectors
of Sicilian coasts (see Table 2). The confidence interval (bold) at 99% of the grand mean for each variable was estimated.
Sector Temporal No. No. No. rhizome Rhizome Leaf
range stations shoots segments elongation production
(mm·shoot−1·yr−1) (n·shoot−1·yr−1)
1 1951–2005 84 4744 34,067 10.9 (5.2) 7.4 (0.9)
2 1986–2005 13 421 2167 7.6 (3.3) 7.2 (0.8)
3 1974–2005 28 8461 10.2 (4.4) 7.4 (0.7)
4 1973–2005 62 1203 6729 9 (4.1) 7.6 (0.8)
5 1970–2005 51 1166 10 (5.1) 7.8 (0.9)
Grand mean 1951–2005 238 3025 15,641 9.6–9.9 7.47–7.52
10,559 67,065