Metazoan/microbial biostalactites from present‐day submarine caves in the Mediterranean Sea

Abstract

Biostalactites formed by metazoan-microbialite associations from three submerged marine caves in the Plemmirio Peninsula (south of Syracuse, Ionian Sea) are randomly distributed and show different sizes and morphologies, as well as variations in surface roughness/smoothness. The biostalactites consist of crusts a few centimeters thick of small serpulids and other metazoans, associated with fine-grained carbonate; the larger ones often include a nucleus of serpulid tubes (Protula). The metazoans include mainly serpuloideans, sponges, bryozoans and foraminifers but microbial carbonates are also significant components. The composition of both the living communities and thanatocoenoses on the outer surfaces, as well as the composition and fabric of the internal framework, were analysed and used to reconstruct the history of the caves. All of the identified sessile faunas mainly consist of cryptic and sciaphilic dwellers that reflect cave conditions and their variations through time. The distribution pattern, composition and abundance of the present-day dwellers largely depend on the degree of roughness of the biostalactite surfaces and their positions within the caves. It has been suggested that the Protula specimens in the nuclei represent pioneer populations that formed aggregates during the early cave colonization phase, in response to relatively high food supply from seawater inflow and intruding continental waters. By contrast, the outer metazoanmicrobialite carbonates reflect more confined conditions in the caves caused by Holocene sea-level rises. Hypotheses are proposed for biostalactite growth, taking into account information about the growth rates of some constituents, and evidence of dissolution effects. Similarities and differences between these biostalactites and other Holocene deposits previously described from submarine caves in the Mediterranean Sea and in tropical reefs are discussed.

Macro- and megafauna recorded in the submarine Bari Canyon (southern Adriatic, Mediterranean Sea) using different tools

“…The first three species, together with E. deflexa, G. gregaria, P. (C.) radiata, S. ophidiana, S. linearis, E. vulgaris and T. coronopus, have also been reported as epibionts on live and/or dead Madrepora and Lophelia colonies collected within canyons along the Catalonia slope, off Blanes and Banyuls-sur-Mer in the entire 180-350 m sampled depth range, or in parts of it (Zabala et al, 1993). Almost all of these species are also typically widespread on shelf environments with the possible exception of H. hyndmanni, S. crystallina and P. (G.) pedunculata, seemingly restricted to the very outer shelf and the upper slope (Berning et al, 2008;Mastrototaro et al, 2010); only the latter is able to live at shallow depths, in submarine caves (Harmelin, 1970;Rosso et al, 2013;Sanfilippo et al, 2014). A further species, S. arrogata, has been recorded only once as encrusting on dead Madrepora skeletons in waters 105-110 m deep, in the Sicily Strait (Gautier, 1962).…”

Biological response to geochemical and hydrological processes in a shallow submarine cave

“…This absence could be attributed to the freshwater influence in the upper layers of the water column inside the cave. Comparable observations have been made in submarine caves from SE Sicily (Guido et al, 2013;Sanfilippo et al, 2014). Although freshwater discharge was noted from the fissure at the entrance of the cave at 6 m depth (February 2006) there are no notable signs of freshwater impact on the anthozoan populations of GSO that inhabit the ceiling and overhangs in the entrance part (Fig.…”

“…In a coastal cave, this is marked by a thin freshwater lens overlying the seawater wedge that intrudes into the aquifer under the freshwater (Terzić et al, 2010). Such submarine groundwater discharge (SGD) usually has significant biogeochemical importance through the provision to nutrients to specialized coastal habitats Burnett et al, 2003;Sanfilippo et al, 2014), as in the case of the Y-Cave.…”

Preliminary assessment of methanogenic microbial communities in marine caves of Zakynthos Island (Ionian Sea, Greece)

“…Regarding their microbiology, only few submarine caves on the Ionian coast of Sicily and Cyprus have been morphologically investigated. The submerged marine caves of Sicily are dominated by unique bioconstructions, named biostalactites, which are constituted of small serpulids and other metazoans associated with carbonate micrites (Guido et al, 2012(Guido et al, , 2013(Guido et al, , 2014(Guido et al, , 2016Sanfilippo et al, 2015). In these serpulid bioconstructions, micrite precipitates are probably induced by the presence of sulphate reducing bacteria (Guido et al, 2012).…”

“…However, insights into their microbiology are limited. Specifically, only 6 marine caves have been investigated regarding their microbial communities, namely, Grotta Azzurra and Grotta Sulfurea on the Tyrrhenian coasts of Italy (Mattison et al, 1998;Canganella et al, 2002;Maugeri et al, 2010); Gymnasium, Granchi and Mazzere caves on the Ionian coast of Sicily (Guido et al, 2012(Guido et al, , 2013(Guido et al, , 2014(Guido et al, , 2016Sanfilippo et al, 2015); and Kakoskali cave in Cyprus . However, only the former two have been investigated for their microbiota, using molecular techniques, while studies on the other three caves involved the morphological identification of microbial structures.…”