Preprint volume - SIBM
Preprint volume - SIBM Preprint volume - SIBM
Pre-print Volume - Oral presentations Topic 2: MARINE ORGANISMS AND ECOSYSTEMS AS MODEL SYSTEMS mountains and photosynthetic communities may develop on their tops. The megabenthic assemblages zonation along the Vercelli Seamount may represent a study model to describe, through ROV imaging, seamount ecosystems in the Mediterranean Sea. Materials and methods - Vercelli Seamount, rising from the flat muddy bottom of the Tyrrhenian Sea around 2000 m depth, is located at about 50 miles off Olbia, along the Sardinian coast (41°06.114’N - 10°53.979’E). The survey was conducted with an observer class Remotely Operated Vehicle, ROV Pluto (Gaymarine, Switzerland). The ROV was equipped with an underwater acoustic tracking position system (HDR made by Gaymarine ultrashort baseline operating with a 30kHz responder), providing records of its track along the seabed. Additionally it had a depth sensor, a compass, and two parallel laser beams providing a 10 cm scale for measuring the areas of the frames (approximately 1-2 m 2 ). The ROV, moving at about 1 m height from the seabed (about 2 m of visual field), was equipped with a digital camera and a high definition video camera. To confirm the taxonomic determination of the specimens observed in the frames, we examined samples collected by dredging on the seamount (60-120 m depth) during an oceanographic campaign on board of the R/V Urania in May 2009. Results - The geomorphological characteristics of the Vercelli Seamount were previously studied by underwater photoprofiling (Zhuleva, 1988). The topography of the structure is characterised by steep rocky or detritic walls rising from the sea bottom and turning into flat coarse detritic planes gently sloping from 200-250 to 100 m depth where a rocky peak rises reaching its maximal elevation around 60 m depth (Fig. 1). The ROV observations indicated that the different portions of the rocky pinnacle (summit, from 60 to 70 m depth, SW flank and NE flank, from 70 to 100 m depth) hosted different coralligenous biocoenoses (Fig. 1). The top of the seamount showed a dense population of the kelp Laminaria rodriguezii covering almost 80% of the substratum. The substratum free from the algae was colonised by encrusting sponges. Many specimens of the crinoid Antedon mediterranea (on average 50 individuals m -2 ) occurred on the algal thalli. The two flanks of the peak were characterised by significantly different assemblages (Fig. 1). The southern side of the ridge was dominated by gorgonians which sometimes reached very high densities. On the rocky boundary close to the detritic bottom (90-100 m) the only large coral present was the gorgonian Eunicella cavolinii, and the more rare Paramuricea clavata. Specimens of Callogorgia verticillata, Corallium rubrum and the scleractinian Dendrophyllia cornigera were occasionally observed in the deepest part (90-100 m) of the pinnacle. Several specimens of Axinella verrucosa and Axinella damicornis were observed. Between 70 and 90 m the density of P. clavata progressively increased while that of E. cavolinii decreased. One colony of the arborescent antipatharian Antipathella subpinnata was observed at about 90 m depth. The northern side of the peak was characterised by the dominance of suspension feeding organisms. From the bottom to 80 m depth we recorded a very large number of colonies of the blue soft coral Paralcyonium spinulosum, while Alcyonium palmatum was only occasionally observed. P. clavata and E. cavolinii were also present on the northern side but with lower densities. Specimens of Axinella spp. were observed at all depths while the dominant sponge species from 70 to 80 m depth was Tethya citrina here showing 41 st S.I.B.M. CONGRESS Rapallo (GE), 7-11 June 2010 101
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 102
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Pre-print Volume - Oral presentations<br />
Topic 2: MARINE ORGANISMS AND ECOSYSTEMS AS MODEL SYSTEMS<br />
unusual densities. Other observed suspension feeding organisms, such as the colonial<br />
ascidian Diazona violacea and the polychaete Sabella pavonina, were extremely<br />
abundant on the northern flank while they were significatively less recorded on the<br />
southern one.The detritic bottom around the peak, between 140-150 m depth, was<br />
densely populated by the crinoid Leptometra phalangium with densities of up to 43<br />
specimens m -2 (Fig. 1). A part from this dense facies, crinoids were absent for the entire<br />
length of the slope (about 1 mile), where only some rare Cidaris sp. were recorded. On<br />
the edge of the detritic bottom (around 180-200 m depth) a wide belt of dead<br />
Dendrophyllia cornigera (yellow scleractinian coral) was recorded, with sparse living<br />
colonies (Fig. 1). The dead calyxes of this species were frequently covered by the blue<br />
sponge Phorbas tenacior. From 200 to 500 m depth the rocks, emerging from the<br />
coarse sand, were covered by a thick black crust of iron-manganese oxide (Zhuleva,<br />
1988). On this substratum the biocoenosis is particularly poor, composed by tubes of<br />
serpulids and rare encrusting specimens of the sponge Phorbas tenacior.<br />
Fig. 1 - Zonation of the megabenthic assemblages of the Vercelli Seamount (60-200 m).<br />
Zonazione delle comunità megabentoniche del Seamount Vercelli (60-200 m).<br />
Conclusions - The coralligenous assemblage recorded on the summit of the Vercelli<br />
Seamount is similar to those recorded on other seamounts along the Spanish coast<br />
(Aguilar et al., 2009) and to that of the Gorringe Bank (Atlantic Ocean) characterised<br />
by a dense assemblage of Paramuricea clavata and, on its upper portion, by a dense<br />
meadow of Laminaria ochroleuca (OCEANA, 2005). The composition of the benthic<br />
assemblages on the two sides of the seamount is in agreement with the hydrodynamic<br />
conditions of the area (Artale et al., 1994). In the northern area the upwelling<br />
conditions likely produce re-suspension of organic particles, but also can increase the<br />
phytoplankton biomass development in the euphotic layer, with a subsequent sinking<br />
41 st S.I.B.M. CONGRESS Rapallo (GE), 7-11 June 2010<br />
102