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Mediterranean Bioconstructions Along the Italian Coast 85

3. PROCESSES
3.1 Building/Bioeroding Processes and the Age
of Bioconstructions
The growth of these bioconstructions depends on a positive balance between
building and bioeroding processes (e.g. Garrabou and Ballesteros, 2000). Cor-
alline macroalgae of the genera Mesophyllum, Lithophyllum and Neogonio-
lithon provide the greatest contribution to coralligenous bioconstructions
(Ballesteros, 2006). Several species of the genus Peyssonnelia,mostly
Peyssonnelia heteromorpha (Zanardini) Athanasiadis and Peyssonnelia rosa-marina
Boudouresque & Denizot, also participate in the building process as do as
many calcified nonphotosynthetic organisms, such as the foraminiferan
M. miniacea, cnidarians and bryozoans. Molluscs and serpulid polychaetes
can play a minor constructive role.
Cyanobacteria (e.g. Hyella caespitosa Bornet & Flahault, 1888; Mastigocoleus
testarum Lagerheim ex Bornet & Flahault, 1886; Leptolyngbya terebrans
(Bornet & Flahault ex Gomont) Anagnostidis & Koma ´rek, 1988), perforating
sponges (e.g. Cliona celata Grant, 1826 and Cliona viridis (Schmidt, 1862)), bor-
ing molluscs (e.g. Hiatella arctica (Linnaeus, 1767), Rocellaria dubia (Pennant,
1777) and Lithophaga (Linnaeus, 1758)), sipunculids (e.g. Aspidosiphon muelleri
Diesing, 1851) and grazing sea urchins (e.g. Sphaerechinus granularis (Lamarck,
1816)) often erode or dissolve coralligenous bioconstructions (Ballesteros,
2006; Sartoretto, 1998; Sartoretto and Francour, 1997).
The bioconstruction process in CWC reefs is mainly due to the branched
stony corals M. oculata and L. pertusa. When solitary corals such as D. dianthus
settle on these colonies, they can contribute also. Moreover, a symbiotic inter-
action with the polychaete Eunice norvegica (Linnaeus, 1767) seems to signifi-
cantly help the bioconstruction process (Mueller et al., 2013). This species
forms parchment-like tubes within living coral branches that are later calcified
by the coral (Buhl-Mortensen, 2001). In particular, E. norvegica is mainly
involved in strengthening the reef structure by thickening and connecting coral
branches (Roberts, 2005; Tursietal.,2004). In addition, massive sponges such
as Pachastrella monilifera Schmidt, 1868 and Poecillastra compressa (Bowerbank,
1866) can form mixed grounds with CWCs, as it happens in Santa Maria di
Leuca and in the Bari Canyon (Bo et al., 2012b; Longo et al., 2005).
A suite of endolithic assemblages of microborers (i.e. bacteria, fungi and
foraminiferans) and macroborers (i.e. sponges) bioerode CWC bio-
constructions. The main macroboring sponges belong to the genera Cliona
and Spiroxya (Longo et al., 2005). The bioerosion process seems to be