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Mediterranean Bioconstructions Along the Italian Coast 89

over a period of 15 years (Gadaleta et al., 2015). However, no historical data are
available on the age of the S. spinulosa reef off Apulian coast, only recently dis-
covered to be an actual “reef” (Gravina et al., 2018).
M. oculata and L. pertusa are able to build huge bioconstructions that can
exceed 1m in height and width per colony (e.g. Angeletti et al., 2014;
Taviani et al., 2017), which remain after the death of the coral, providing
an exploitable hard substrate for many associated species (Mastrototaro
et al., 2010; Vertino et al., 2010). On a geological timescale, such highly
structured bioconstructions can produce true carbonate mounds that some-
times endure for many hundred thousand to millions of years of discontin-
uous coral succession (Taviani et al., 2011).
Biostalactite building is mainly due to serpulid tubes that do not lie on
the substrate but which elevate the worm crowns by several centimetres. This
living stage, however, is still far from the final aspect of the biostalactite, as
worm tubes become embedded in a thick calcareous coat of bacterial origin.
Guido et al. (2014) described a commensal symbiotic link between worms
and bacteria: these use organic matter coming from the worms that, in their
turn, build their tubes with mineral pelites of bacterial origin. The tubes are
made of biotic carbonate, and those in the Otranto biostalactites have ages
14
that have been dated by the C method (Belmonte et al., 2009, 2016).
The elongation/growth of three 50cm biostalactites required thousands of
years, starting during the last postglacial period when the sea level rose
to the present level and submerged the cave (about 6000 years ago). The
measured slow growth (50cm in 6000 years) however, when compared
with the growth of each serpulid tube (some centimetres in few years), still
awaits an explanation.

3.2 Connectivity
Connectivity affects marine population dynamics (Moritz et al., 2013) and
community responses to pressures (Wasserman et al., 2012) and is important
for conservation decisions in both reserve network design (Boero etal.,2016;
Cerdeira et al., 2010) and restoration actions (Raeymaekers et al., 2008).
Knowledge on the connectivity of different bioconstructions is limited,
though a variety of techniques have been developed to fill this gap such as
genetic analyses, dispersal simulation models and β-diversity studies.

3.2.1 Genetic Connectivity
Bioconstructors have a low dispersal capability compared to actively motile
organisms, such as fish and marine mammals and reptiles, so might be expected
to have a lower population connectivity. In fact, dispersal in bioconstructors