First section Fisheries and biodiversity Photo from MiPAAF archive Chapter 2 Ecological aspects Italian seas and the subdivision of the Mediterranean Sea in GSA Considerations on data collection for the evaluation of living resources and the monitoring of fisheries on the fleets that operate in the Mediterranean Sea determined the subdivision of the latter in a series of reference areas for both management activities and scientific surveys. Such areas represent a compromise among legislative, geographic and environmental aspects. The Mediterranean Sea was subdivided in 30 sub-areas, named GSA (Geographic Sub Areas). The term “sub” refers to the fact that the Mediterranean Sea is one of the 60 Large Marine Ecosystems on the planet. Geographical Sub-Areas in the GFCM area were established amending the Resolution GFCM/31/2007/2, on the advise of the GFCM Scientific Advisory Committee (SAC). The 30 areas largely differ in size and characteristics. The geographic division of fisheries areas in the Mediterranean Sea is still evolving and is subject to periodical improvement by SAC. 1 Northern Alboran Sea 11.2 Sardinia (east) 22 Aegean Sea 2 Alboran Island 12 Northern Tunisia 23 Crete Island 3 Southern Alboran Sea 13 Gulf of Hammamet 24 North Levant 4 Algeria 14 Gulf of Gabes 25 Cyprus Island 5 Balearic Island 15 Malta Island 26 South Levant 6 Northern Spain 16 South of Sicily 27 Levant 7 Gulf of Lions 17 Northern Adriatic 28 Marmara Sea 8 Corsica Island 18 Southern Adriatic Sea 29 Black Sea 9 Ligurian and North Tyrrhenian Sea 19 Western Ionian Sea 30 Azov Sea 10 South Tyrrhenian Sea 20 Eastern Ionian Sea 11.1 Sardinia (west) 21 Southern Ionian Sea 17 2.1 Environmental characterisation of fishing areas 2.1.1 GSA 9 - Ligurian and Northern Tyrrhenian Seas Relini G., Sartor P., Reale B., Orsi Relini L., Mannini A., De Ranieri S., Ardizzone G.D., Belluscio A., Serena F. Ecological context and geographical and environmental aspects GSA 9 (figure 2.1) covers an area of 42,410 km2 that includes the Ligurian and Northern and Central Tyrrhenian Seas and belongs to the FAO division 37.1.3 (Sardinia); the total area involves 1,245 km of coastline and includes Liguria, Tuscany and Lazio and 10 maritime departments, plus a part of the district of Gaeta. Figure 2.1 - Geographic boundaries of GSA 9. The 200 and 800 m bathymetric contours are shown, together with the port authority headquarters of the various maritime departments. 18 First section - Chapter 2 - Ecological aspects It is a heterogeneous area in terms of morphological and ecological features, containing a variety of habitats, environmental conditions and biological communities. The coastline of Liguria extends for approximately 330 km; the continental shelf in the Western Riviera, from Cape Mortola to Cape Arenzano, is very narrow, although it becomes wider towards the east, near Punta Bianca. One of the most relevant feature of the seabeds, which also has an effect on fish resources, is the number of canyons that furrow the continental slope and the high depths close to the western and central shores. The coast of Tuscany stretches for over 600 km, including around 400 km of mainland and 200 km of insular coastline in the Tuscan Archipelago. There are present areas with low, sandy coasts and with high rocky coasts, particularly along the isles of the archipelago. The continental shelf between the Gulf of La Spezia and the Island of Elba is wide and slightly sloping, particularly between Livorno and Elba, and extends 35-40 km from the coast, reaching a depth of about 150 m. Between the islands of Capraia and Gorgona the continental shelf is interrupted by the Elba canyon, which descends in depth towards north-west. The seabed between Elba and the Argentario Peninsula comprises a single basin, bounded to the west by the Elba Ridge, to the east by the Tuscany coast and to the north by the Piombino channel and the Elba Island. The continental shelf in Lazio, with a longitudinal extension of 290 km, has a narrower central section, between Cape Linaro and Cape Circeo (with an extension of 20 km), and is wider (30-40 km) towards the north (between the Argentario Peninsula and Cape Linaro) and south (between Cape Circeo and Gaeta). It has an average decreasing slope of about 0.5°; the shelf break ranges from 120 to 150 m. The central area of the Lazio shelf is characterised by the submerged alluvial fan of the Tiber river delta. The river supplies condition the physical, chemical and trophic characteristics of much of the coastal area of the central Lazio. The Pontine Archipelago is off the southern coast of Lazio and includes the islands of Ponza, Palmarola and Zannone to the west and Ventotene and Santo Stefano to the east, which are mainly composed of volcanic deposits. The Pontine Islands are characterised by steeply sloping seabeds and the presence of numerous canyons. The water circulation features a series of vortexes caused by the wind. These contain cold water and undergo significant changes from season to season. The current flow increases in the frontal region of the vortexes in winter and the associated upwelling moves towards the west and increases in intensity. This is the season in which the flow between Tyrrhenian Sea and Ligurian Sea, through the Corsica Channel, reaches its peak. Upwelling causes the mixing of waters originating from the Atlantic Ocean (AW) with the Levantine Intermediate Water (LIW), changing the physical and chemical properties of the water mass. To the North of Capraia Island, the Eastern Corsica current merges with the colder Western Corsica current forming the Ligurian current (figure 2.2). This supports a cyclonic circulation in the whole Ligurian Sea, involving waters of Atlantic origin (AW) on the surface and Levantine waters (LIW) at a greater depth. It is one of the most important upwelling areas in the Mediterranean Sea. The flow of the Ligurian current is huge: it can reach around 1.6 million m3/sec, a value similar to the Atlantic current that flows into the Strait of Gibraltar. It is a river of water approximately 20 km wide, with a depth of around 150 m, which flows continuously throughout the year, although with variations in intensity. The Ligurian Sea is one of the most important places for the transformation of waters in winter, due to the action of cold and dry continental winds. The cooling and evaporation of the masses of superficial water in the Ligurian Sea and the adjacent Gulf of Lyons are responsible to the formation of the deep-water, which is one of the great oceanographic processes of the Mediterranean Sea. 19 Figure 2.2 - Circulation of surface and intermediate currents. AW: waters of Atlantic origin (blue arrows); LIW: waters of Levantine origin (red); LC: Ligurian current (violet); WCC: Western Corsican Current, a branch of waters of Atlantic origin; ECC: Eastern Corsica Current, of Atlantic origin. The seasonal phytoplankton dynamics in GSA 9 are typical of subtropical areas, with a maximum in the cold season, from October to April, and a minimum in the summer. A positive correlation has been confirmed between the concentration of chlorophyll in spring and the remixing of the waters in the previous months (autumn-winter), under the effect of the wind. The narrow extension of the Ligurian continental shelf influences all the biotic communities of sands and detritic bottoms, as well as those of the coastal terrigenous muds. The hard bottoms often are distributed following a vertical direction (Portofino cliffs, Mesco cliffs, etc.). Some of the most interesting Gorgonian coral (Paramuricaea clavata) and red coral (Corallium rubrum) facies of the Italian coast are also in Liguria. Posidonia oceanica meadows can be found more or less 20 First section - Chapter 2 - Ecological aspects everywhere along the coast, although their extension is limited due to the steepness of the seabeds. The benthic communities of the islands of the Tuscan Archipelago also display a high level of heterogeneity. The offshore mobile bottoms host biocoenoses mainly originating from the series of detritic bottoms, which are replaced by muddy communities at greater depths. The sediments between 80 and 150 m depth in the western and southern sectors of the island of Elba host biocoenoses of detritic bottoms, characterised by the dominance of the crinoid Leptometra phalangium. These feature a highly diversified and productive community and host nurseries of commercial species, such as the European hake. The hard coastal bottoms display the typical biotic communities of vertical walls. Marine phanerogam meadows thrive particularly along the island coasts of the Tuscan Archipelago, particularly in Pianosa. As concerns Lazio, the soft bottoms closer to shore display communities typical of fine sand and well-calibrated fine sediments. Due mainly to the Tiber supplies, these communities are replaced offshore by mixed sandy-muddy bottoms, which form an area of transition to the coastal terrigenous muds (VTC) distributed along the deep portion of the continental shelf. Detritic seabeds (DC) are found at the edges of rocky shallows, around the Pontine islands and beyond the lower limit of the Posidonia meadows. The edge of the continental shelf is characterised by the presence of detritic bottoms (DL), with high concentrations of the crinoid L. phalangium. To the South of the Tiber estuary, the mobile seabeds are interrupted by the Tor Paterno bank. P. oceanica is found along practically all of the Lazio coastal areas, with the exception of the Tiber area. All the GSA 9 is characterised by a wide biodiversity, taking into account that only 14 of the 162 benthic communities (habitats) listed in the Barcelona Convention are not found here.