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88 Gianmarco Ingrosso et al.

Fig. 8 Hypothetical evolutionary scenario of the coralligenous accretions of Bogliasco.
(A) In a first phase the algal growth results in pillar-like bioherm. (B) Bottom sediments
increase during periods of heavy floods, partially or totally burying the pillars and killing
the algal cover. (C) During the burying or after the removal of the sediments, part of the
structure becomes prone to erosive processes, giving rise to mushroom-like structures.
(D) In following phases, the coralline algae grow again in sciaphilous microhabitats,
determining the irregular temporal layering of the structure (the numbers 1–4 indicate
different sheets of deposition from the oldest to the youngest). In this situation, in a core
sample (dotted rectangle), younger sheets can overlap with older ones.

(Gruet, 1971–1972). Tube growth rates range from 4.4 to 6mmday 1
(Hendrick and Foster-Smith, 2006) and the complete cycle requires from
several months to more than 10 years (Gruet, 1986). The S. spinulosa reef
recorded along the Apulian coasts showed cyclical fluctuations over a period
of 1 year (Gravina et al., 2018). Little is known about the duration of fluc-
tuations taken by older biogenic structures in palaeontological timescales
(Sch€afer, 1972). More recently, historical data from the North Sea have
documented the persistence of Sabellaria reefs over a period of approximately
1century(Firth etal.,2015). A documented age of 60 years was revealed
for some Italian S. alveolata reefs. Indeed, previous studies dating back to
the 1950s (Giordani Soika, 1956; Molinier and Picard, 1953; Taramelli-
Rivosecchi, 1961) report extensive bioconstructions from the Latium and
Sicily coasts, with detailed descriptions consistent with the present observations
from thesamesites (M.F.Gravina, personal observations; Schimmenti et al.,
2016). Along the Adriatic coasts, at Torre del Cerrano, structural changes of
S. spinulosa bioconstructions showed a Sabellaria–Mytilus succession spreading