Preprint volume - SIBM

Pre-print Volume - Oral presentations
Topic 2: MARINE ORGANISMS AND ECOSYSTEMS AS MODEL SYSTEMS
unusual densities. Other observed suspension feeding organisms, such as the colonial
ascidian Diazona violacea and the polychaete Sabella pavonina, were extremely
abundant on the northern flank while they were significatively less recorded on the
southern one.The detritic bottom around the peak, between 140-150 m depth, was
densely populated by the crinoid Leptometra phalangium with densities of up to 43
specimens m -2 (Fig. 1). A part from this dense facies, crinoids were absent for the entire
length of the slope (about 1 mile), where only some rare Cidaris sp. were recorded. On
the edge of the detritic bottom (around 180-200 m depth) a wide belt of dead
Dendrophyllia cornigera (yellow scleractinian coral) was recorded, with sparse living
colonies (Fig. 1). The dead calyxes of this species were frequently covered by the blue
sponge Phorbas tenacior. From 200 to 500 m depth the rocks, emerging from the
coarse sand, were covered by a thick black crust of iron-manganese oxide (Zhuleva,
1988). On this substratum the biocoenosis is particularly poor, composed by tubes of
serpulids and rare encrusting specimens of the sponge Phorbas tenacior.
Fig. 1 - Zonation of the megabenthic assemblages of the Vercelli Seamount (60-200 m).
Zonazione delle comunità megabentoniche del Seamount Vercelli (60-200 m).
Conclusions - The coralligenous assemblage recorded on the summit of the Vercelli
Seamount is similar to those recorded on other seamounts along the Spanish coast
(Aguilar et al., 2009) and to that of the Gorringe Bank (Atlantic Ocean) characterised
by a dense assemblage of Paramuricea clavata and, on its upper portion, by a dense
meadow of Laminaria ochroleuca (OCEANA, 2005). The composition of the benthic
assemblages on the two sides of the seamount is in agreement with the hydrodynamic
conditions of the area (Artale et al., 1994). In the northern area the upwelling
conditions likely produce re-suspension of organic particles, but also can increase the
phytoplankton biomass development in the euphotic layer, with a subsequent sinking
41 st S.I.B.M. CONGRESS Rapallo (GE), 7-11 June 2010
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