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Vermetid reefs are bioconstructions commonly found in the southern Mediterranean Sea. They
have proved to be excellent natural archives to reconstruct both the paleosea level and sea-surface
temperature fluctuations. Moreover, up- or down-lifted fossil reefs may provide information on
the vertical displacement of coastal areas at the local scale (see Antonioli et al. [4] and Pirazzoli
et al. [5] for a complete list of references).

Vermetids precipitate an aragonite shell that is considered to be in isotopic equilibrium with the
ambient seawater. Although it has not yet been established whether vermetids have an important
effect on the isotopic composition of their shells, or whether seasonality affects this isotopic
composition, a preliminary study [6] showed that coeval and living vermetid shells, sampled in
different portions of Sicilian reefs, have the same isotopic signature (<0.01‰ variation in δ18O). A
later, more exhaustive article [7] established that the vermetid isotopic signature is in equilibrium
with the environment. Oxygen isotopes obtained from analysis of fossil remains can be converted
into temperature records by using the biogenic aragonite vs. temperature fractionation equation [8]
and AMS 14C dating for the age model.

Here, we provide a short review of the main results obtained to date on vermetid reefs as
potential archives for paleoclimatic reconstructions in the Mediterranean region.

2. Description of a vermetid reef

A typical vermetid reef is the outcome of complex synergistic building activity by the vermetid
mollusc Dendropoma (Novastoa) petraeum (Monterosato, 1892) and the encrusting red alga
Neogoniolithon brassica-florida (Harvey) Setchell & Mason (1943) [9]. Other species, namely
the vermetid Vermetus (V .) triquetrus A. Bivona, 1832, and red algae Lithophyllum byssoides
(Lamarck) Foslie (1900), Lithophyllum incrustans Philippi (1837) and Neogoniolithon mamillo-
sum (Hauck) Setchell & Mason (1943) may also support D. petraeum and N. brassica-florida in
the process of bioconstruction.

In a recent article, Calvo et al. [10] genetically characterised D. petraeum throughout its entire
distribution range in the Mediterranean Sea. Data from different sites indicate the existence of a
cryptic species complex within D. petraeum, comprising at least four species. According to the
authors, such diversification processes were mainly the result of a series of vicariant partitions by
the ancestor of the D. petraeum complex. The history of the distribution of Dendropoma popula-
tions includes fragmentation processes resulting from past isolation of water masses followed by
restricted gene flow among sub-basins.

Using literature data, a general model of a vermetid reef can be described (Figure 1(a),(b)),
following a hypothetical transect from shore to open sea [9]. (1) A small encrustation, a few
centimetres thick, built by the two encrusting red algae N. brassica-florida and L. byssoides.
This formation is widely distributed along the Mediterranean basin, where it often substitutes the
vermetid reef under sciaphilic conditions or in the absence of Dendropoma. (2) An inner margin,
formed by D. petraeum, a few centimetres thick and ∼5–50 cm wide, depending on local exposure.
(3) One or more small pools, called cuvettes, ∼10–200 cm (or more) in size and generally <50 cm
deep. Cuvettes can be compared to small retrorecifal lagoons. (4) An outer margin, consisting
of a very thick formation by Dendropoma, occasionally over 40 cm wide and 50 cm thick. This
portion, which is typically quite complex and rich in crevices, is the active part of the vermetid
platform, growing outwards and upwards. (5) An upper infralittoral belt made by the brown alga
Cystoseira amentacea var. stricta and developed below the outer margin of the platform. Given
the peculiar environmental conditions, groups of small structures (called islands or atolls) can
occur externally to the reef, due to the different erosion rate between the coast and the reef itself.

Vermetid reefs develop in the lower mesolittoral and upper infralittoral, on rocky coasts only.
Their size depends on the type of substrate, decreasing with the series: sandstone, limestone,