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in this study provide evidence that one of the two growth performance parameters estimated for
Sicilian coasts, the mean rhizome elongation, is above the normal Mediterranean range: indeed on
the basis of the standardised scale the rhizome elongation in Sicily can be considered as ‘superior–
sub-normal’ [53]. Several factors may explain this strong difference, such as the relatively low
anthropic pressure present along the Sicily coasts and the different sedimentation rate [77] and
different temperature and photoperiod linked to longitudinal and latitudinal variations [86,87].
In the last case, further studies will be necessary to implement an evaluation scale that take into
account natural variations induced by geographical gradient.

7. Flowering

Fragmentation and vegetative stolonisation seem to represent the dominant reproductive mode
in the Mediterranean population of Halophila stipulacea [6]; male flowers show low frequency
and female ones were never recorded in the studies by Cancemi et al. [29] and Procaccini et al.
[22], probably because they do not find in west Mediterranean favourable conditions to ripen [6].
Although in Sicily, Famà et al. [30] also observed only male flowers, it is worth noting here that,
in September 1988, Villari [26] recorded specimens bearing immature fruits and 10 years later
near Syracuse (Ionian Sea) Di Martino et al. [58] found many flowers, both male and female,
suggesting that, although rare, female flowers are present in the west Mediterranean meadows of
H. stipulacea.

Native Mediterranean seagrass species flower between late spring (C. nodosa and N. noltii)
and summer (Zostera marina), except for P. oceanica, which flowers in autumn (September–
November).

Flowerings of Z. marina and N. noltii have never been observed along the Sicilian coasts,
probably because of their very limited distribution and the lack of continuous monitoring, while
C. nodosa flowering has been observed rarely (Stagnone di Marsala; Calvo, pers. obs.).

However, flowering of P. oceanica in Sicily [88] is more frequent than previously thought, as
indicated by both increased field observations [89] and the use of reconstructive methods that
allow detection and dating of past flowering episodes [82,90]. Thanks to that, flowering has been
detected almost every year from 1978 to 2005 along the entire Sicilian coast, as documented by
direct and retrospective observations from the last three decades.

The number of flowering shoots varies greatly depending on year, depth and location, from 1
to 200 per m2 [91]. The percentage of flowering shoots estimated by direct observation reached
a maximum of 30% in 1995 in the Egadi islands [41], followed by 10.1% recorded in 1997 by
backdating methods in the south-eastern coast of Sicily [18] and confirmed by the unusually
massive fruiting in the area in the same year [92].

The fraction of meadows flowering in any one year shows that on the western coast of Sicily [23]
flowering was more prevalent in the years 1987 (50%), 1991 (67%), 1996 (56%) and 2003 (50%).
The massive flowering recorded in 2003 along the coast of western Sicily, in particular, coincided
with the most widespread flowering event ever recorded in the Mediterranean, when >80% of
the investigated meadows flowered [67]. This outstanding flowering followed the warmest year
in past centuries across Mediterranean regions, suggesting that positive thermal anomalies may
play an important role in driving synchronous P. oceanica flowering on a large scale [67,93].

Recently, a new set of flowering performance indices [67] applied to the meadows of western
Sicily [23] showed that: the probability of finding a flowering annual rhizome segment in the
total number of annual segments analysed (Pf) was 0.0072 inflorescences per shoot per year, the
fraction of years that a given meadow has flowered (FF) was 0.196 and the fraction of shoots
presenting stalks within a particular year (FI) was on average 0.026 ± 0.007 inflorescences per
shoot. The most important dataset of flowering occurrences reported for the western Mediterranean