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5 Effects of Physical Parameters on the Biological
Components

In the following paragraphs four main case studies are discussed in order to give examples
about the effects of topography and hydrodynamics processes on the biological component
of the Sicily Channel and Tunisia plateau. Of course these examples are not exhaustive;
nevertheless other case studies about benthic and pelagic communities (i.e. some
commercial target species) are outside the objectives of the contract for this review.

5.1 Deep sea coral habitats

In the central area of the Sicily channel, from the Pantelleria Island to the Malta Escarpment,
NW-SE trending steep walled troughs and seamounts dominate the seabed landscape
affecting both the incoming flows at the surface layers (MAW) from the west and at the
deeper counter flow from the east (LIW). Turbidites from Lower Pliocene and Pleisticene fill
these troughs, which are bounded by subvertical faults.

On the southeastern side of the Linosa trough impressive escarpment forms a near-vertical
wall measuring 150–200 m in height. On the northeastern side of the trough the escarpment
flanks a large pelagic mud covered plateau, at the depth of about 400–500-m, which
separates the Malta trough from the Linosa trough. These bottom structures form a major
topographic obstacle for the westward-flowing LIW.

The bottom current flows seem strongly influenced by the morphological features of the
seafloor and this interaction affect the spatial distribution of sediment drifts and thus the
biogenic build-ups. In this case the flow of the LIW and the transitional Eastern
Mediterranean Deep Water directly impinging onto the area of active coral growth centred at
ca. 450-600 m. Healthy and well developed deep-sea coral mound (mainly Lophelia pertusa
and Madrepora oculata) community may take advantage of the current-advected food supply
(Freiwald et al. , 2009; Martorelli et al., 2011).

The main sites, where healthy deepwater coral banks have been recently recorded, are
shown in Fig. 9 (Bussoletti et al., 2010; Freiwald et al., 2009; Martorelli et al., 2011; Scembri
et al., 2007; Taviani et al., 2011; Zibrowius and Taviani, 2005).

South of Malta, in a depth range of 390-617 m, samples revealed thick fossil coral
frameworks with overgrowing coral assemblages mainly consisting of M. oculata and L.
pertusa associated with Corallium rubrum (here in the Sicily Channel at the known deepest
range), also Dendrophyllia cornigera was detected in some samples, and gorgonians (Vella
and Vella, 2012). The symbiotic polychaete Eunice norvegica was found to inhabit the colony
bases.

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