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M. Angiolillo et al. / Marine Pollution Bulletin xxx (2015) xxx–xxx
Fig. 1. Distribution of the study areas along the three explored Tyrrhenian regions (solid black borders) off southern Italy: (A) Campania, (B) Sardinia and (C) Sicily. The black
dots denoted the dive sampling areas and the codes (ID) correspond to the list provided in Table 1.
Mascle et al., 2001). The Sardinia channel is a wide opening
between Tunisia and Sardinia with a sill at about 1900 m that
allows exchanges of deep waters between the western Mediterra-
nean and the Tyrrhenian Sea. The surface layer is occupied by Mod-
ified Atlantic Water (MAW) directly coming from Gibraltar. On the
opposite side, a significant flow of Levantine Intermediate Water
(LIW) coming from Tyrrhenian Sea and extending from Sardinia
slope to the centre of the channel leaves this region to the west
(Send et al., 1999). Along south Sardinian coast, the westward
Algerian current is reported to be dominant: this current merges
with the southward currents forming the quasi-permanent South
Eastern Sardinian gyre (Sorgente et al., 2011). South Sardinia hosts
a wide range of ports, from small touristic (mostly located in the
east/south eastern coast) and industrialized areas as Cagliari
(southern coast) and Porto Scuso (south western coast). Moreover,
the south-western coast is also renewed for intense tuna fishing
activities (Addis et al., 2013).
The eight studied areas in Sicily were located in the NW por-
tion of the island and around the Egadi Archipelago (Fig. 1C),
positioned between the strait of Sicily and the Tyrrhenian Sea.
This zone represents the shallowest part of a wide submarine
canyon that connects the Sicilian continental shelf to the Tyr-
rhenian Sea abyssal plane (Colantoni et al., 1993). The Sicilian
continental shelf is very broad in front of Trapani coastlines
and narrower between Levanzo and Marettimo Islands
(Brugnano et al., 2008). The strait of Sicily can be considerate
a small intermediate basin that subdivides the Mediterranean
into western and eastern sub-basins and it is a topographically
complex region. The surface circulation is mainly characterized
by the flow of Atlantic Water (AW) flowing eastward from the
Sardinia Channel into the Tyrrhenian Sea (Astraldi et al., 1999)
and a deeper Levantine Intermediate Water (LIW), coming from
the eastern Mediterranean to west, forming a two-layer system
with a 100 m thick transitional layer. The topographic constrains
Please cite this article in press as: Angiolillo, M., et al. Distribution and assessment of marine debris in the deep Tyrrhenian Sea (NW Mediterranean Sea,
Italy). Mar. Pollut. Bull. (2015), http://dx.doi.org/10.1016/j.marpolbul.2014.12.044
3
lead the LIW flows to turn eastwards and enter the Tyrrhenian
Sea across a section offshore the Egadi Islands (Brugnano et al.,
2008). The strait plays an important role in hydrodynamic and
biological exchanges between the two principal sub-basins, act-
ing as a transitional basin and as reservoir for deep water
(Millot, 2005). This Sicilian zone hosts several touristic and com-
mercial ports and the professional fishery represents one of the
most important activities. Moreover, a rising number of recrea-
tional boats increase the fishing pressure on these areas.
2.2. Data acquisition
Surveys were conducted first mapping the seabed of the study
areas using Multibeam echo sounders (RESON 8125 and Kongsberg
Em 3002), and then carrying out exploratory video transect along
the seafloor by means of a ROV ‘Pollux’ (Global Electric Italiana).
The ROV was equipped with a digital camera (Nikon D80, 10 mega-
pixels), an underwater strobe (Nikon SB 400), and 3 jaw grabbers
(SeaBotix) to take samples. In addition, three laser beams, at a dis-
tance of 10 cm each other, provided a scale of the photos.
The ROV had a depth sensor, a compass and an underwater
acoustic tracking position system (Tracklink 1500 MA, LinkQuest),
providing detailed records of the tracks along the seabed. Geo-
graphical positions and depth were registered from the beginning
to the end of each transect, every 1 s. The ROV moved $1.5 m
above the seabed, at constant speed (approximately 0.5 knots).
Along each transect, high-resolution photo-sampling units were
acquired every %30 s in order to identify and quantify the marine
benthic litter. Litter was divided into 5 categories: fishing lines;
nets; pots; plastic (bags, bottles, other objects, etc.); other items
(glass, metal, etc.). The presence of debris was evaluated both by
occurrence (frequency of debris types) and relative abundance
(debris items mÀ2), assessed by counting the number of debris
respect to the photo area.