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Chemistry and Ecology 253

Downloaded By: [Furnari, G.] At: 10:31 24 May 2010 Analysis of 319 ROV profiles showed that the progressive limit typology [39,52] is the most
frequent along Sicilian coasts (60.8%), whereas sharp and erosive limits are, respectively, 31.4
and 7.8%. The mean lower limit depth varies with typology, ranging from 23.0 m (sharp limit)
to 31.4 m (progressive limit) (Figure 3). In particular, the progressive depth limit of P. oceanica
meadows was from 11.1 m (Brucoli, Catania) to 44.0 m (Panarea, Aeolie archipelagos), and is
more frequent along the coasts of Sicily than in the small islands, where the sharp limit is the
most frequent (47.2%) [52]. Moreover, owing to the high water transparency, the lower limits
of P. oceanica meadows observed along the small islands are deeper than those found along the
Sicily coasts.

Depth records of progressive limit were classified by K mean cluster analysis in four classes
[52] (Table 1) and converted into seawater transparency levels according to Pergent et al. [53].
The class ‘very transparent waters’ is the most frequent in the north-western area of Sicily, while
the class ‘very little transparent waters’ is detected only near the urban centre of Palermo and
the petrochemical industry of Augusta, where P. oceanica does not colonise bottoms deeper than
14 m. Along the southern coasts of Sicily morphology and composition of the bottom and swell
exposure frequently limit water transparency; consequently the meadow depth limit rises.

Figure 3. Mean different lower depth limit typology (±SE) along the coasts of Sicily and small islands (n = number
of observations).

Table 1. Water transparency classification of meadows along the coasts of Sicily and small islands, based on
mean values of progressive depth limit of Posidonia oceanica meadows.

Class No. Minimum Maximum Mean Evaluation quality
observations depth (m) depth (m) depth (m)

1 50 33.1 40.0 35.6 Very transparent waters
2 39 26.0 33.0 30.4 Transparent waters
3 19 18.5 25.3 21.0 Few transparent waters
4 5 11.1 15.8 13.6 Very few transparent waters