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Adriatic Sea (North Central) - Ecology

The area is characterized by high diversity of environmental conditions that is translated into high biodiversity (Ott 1992). Numerous studies describe the distribution and abundance of marine fauna and flora of the Adriatic Sea (e.g. Riedl 1986, Zupanovic and Jardas 1989, Jukic-Peladic et al. 2001). The Adriatic has a high rate of endemism.

On the continental shelf from 10-50 m depth, the dominant fish species in terms of biomass are red mullet (M. barbatus), poor cod (Trisopterus minutus), various species of triglids, sole (Solea solea), various species of flatfishes, gobies and pandoras (Pagellus spp.). From 50 to 100 m deep, anglerfish (Lophius spp.), European hake (Merluccius merluccius), greater forkbeard (Phycis blennoides) and red bandfish (Cepola rubescens) are also abundant, as well as blue whiting (Micromesistius poutassou) at 100 to 200 m deep. In the pelagic domain, main fish species are sardine (Sardina pilchardus), anchovy (Engraulis encrasicolus), horse mackerel (Trachurus spp.) and mackerel (Scomber spp.). In the northern area, sprat (Sprattus sprattus) is found, although it was more abundant during the 1960s and 1970s than nowadays.

The continental shelf of the Adriatic Sea is also rich in invertebrate fauna, where some of the most abundant species are cuttlefish (Sepia officinalis and S. elegans), octopuses (Eledone moschata and Octopus vulgaris), squids (Loligo vulgaris and Alloteuthis media), mantis shrimps (Squilla mantis), shrimps (Solenocera membranacea and Parapenaeus longirostris) and scallops (Pecten jacobaeus and Chlamys opercularis).

Moreover, the north-central Adriatic Sea is a strategic area for marine vertebrate conservation, sheltering important seabird populations (Zotier et al. 1998, Baccetti et al. 2002) especially around the Po River Delta. The area also supports important populations of endangered marine mammals and turtles, such as bottlenose dolphins (Tursiops truncatus), common dolphins (Dephinus delphis) and loggerhead turtles (Caretta caretta) (Delaugerre 1987, Groombridge 1990, Manoukian et al. 2001, Bearzi et al. 2004). The eastern Adriatic Sea shelters one of the smallest remaining populations of Mediterranean monk seals (Monachus monachus) and sightings of basking sharks (Cetorhinus maximus) and other pelagic sharks are still recorded in the area (Reijnders et al. 1997, Soldo and Jardas 2002).

Several studies have highlighted the important relationship between environmental factors and primary and secondary production dynamics in the Mediterranean Sea and, especially in the north-central Adriatic Sea (e.g. Agostini and Bakun 2002, Santojanni et al. 2006), such as wind mixing, river runoff, eutrophication and increase in water temperature. The wind mixing index has been positively related with recruitment of various demersal species most likely due to enhancement of fertilization and local planktonic production (Lloret et al. 2001). River runoffs from Rhône and Ebro were positively related with recruitment of demersal species (Lloret et al. 2001), as well as with anchovy (Engraulis encrasicolus) landings during its spawning season (April–August) in the South Catalan Sea (Lloret et al. 2004) and in the Adriatic Sea with the Po River runoffs (Santojanni et al. 2006). It has been suggested that the Mediterranean Sea, with special emphasis on the northern Adriatic Sea, has been subjected to increased nutrient loading and eutrophication (Caddy and Bakun 1994, DeLeiva et al. 2000). Some proliferation of jellyfish species in the Adriatic since the 1980s has been related to climatic events and eutrophication (Rottini-Sandrini and Stravini 1981, Zavodnik 1991, Arai 2001, Mills 2001). In recent times there have been described a decrease of primary production in the basin, with consequence to the whole food-web (Steenbeek et al. 2013).


In addition, the progressive increase in water temperature in the Mediterranean Sea (Bethoux and Gentilli 1990, Salat and Pascual 2002) has been positively related with an increase of sardinella (Sardinella aurita) landings and the expansion of sardinella to northern NW Mediterranean areas (Sabatés et al. 2006). This could also be related to the reduction of the sprat distribution to the northern areas of its former distribution in the Adriatic Sea (Azzali et al. 2002). Environmental factors have been related with biomass fluctuations of anchovy and sardine as well (Azzali et al. 2002, Santojanni et al. 2003, 2005, 2006). These two species are abundant in the area, however a notable decrease in anchovy was described during the late 1980s, with a subsequent recovery, and a decline in sardine biomass has been described from the early 1990s, still without a clear recovery.

Mass-balance ecosystem models developed to represent the north-central Adriatic Sea during the mid-late 1990s enabled the structure and functioning of the ecosystem to be characterized, integrating a notable amount of the ecological and biological information available (Coll et al. 2007). The models highlighted important coupling between pelagic-benthic production of plankton, benthic invertebrates and detritus. Organisms located at low and medium trophic levels, i.e. benthic invertebrates, zooplankton and small pelagic fish, as well as dolphins, were identified as keystone groups of the ecosystem. Jellyfish were found to be an important element in terms of consumption and production of trophic flows within the ecosystem modelled. A model fitted to data and comparison of models from 1975 and 1990s highlighted important changes in main marine resources of the region and food-web structure and functioning (Coll et al. 2008, 2009). Ecological models have also been used to explore alternative scenarios of fishing management (Fouzai et al. 2012).