Structure and functioning of the Northern Adriatic coastal ecosystem, within the context of the Marine Strategy Framework implementation

Abstract

The Northern Adriatic Sea summarizes all different critical elements of a ‘typical’ coastal area, such: important trawling activity in the inshore area, presence of aquaculture activities (mussels farms), widely distributed along the coast, presence of small scale fisheries activities, seaside touristic pressures, extended seaport activities. Among these pressures the project aims to investigate acquaculture and small scale fisheries activities within three miles from the coast. This would provide a better understanding of major impact sources and an identification of the processes that need to be preserved/enhanced to maintain or also increase the resilience of the system. Within this context, the main objectives of the project are: (1) to assess the role played by mussel culture farms, both in terms of negative impacts and positive feedbacks; (2) to focalize the attention on one of the main key factors presently affecting, but also structuring, the ecosystem in the NAS coastal area, in order to better understand the majors drivers also in terms of opportunities to be managed; (3) to define long term management objectives, indentifying the self-sustaining processes to be maintained or restored, in order to increase the system resilience and stimulate an adaptive management. To achieve these objectives, five issues were considered: benthic fauna; biogeochemical cycles; potential role as fish aggregating area; emergy analysis; artisanal fishery. The results of the present study show how a mussel farm located in a transitional environment near coast is a man made structure characterised by a sustainable use, with no direct impacts on bottom, acting as a fishing aggregating area also for some commercial species. Assimilating to an “extensive” acquaculture system, mussel farm is a structure characterised by the predominance of renewable inputs that, probably due to environmental factors such as currents and winds, doesn’t interfere both with benthic community and biogeochemical cycles of the area. Moreover the normal aggregating effects due to the confluence of great quantities of available food is increased by the presence, at the bottom, of some hard substrates, able to attract fishes species beyond for feeding, also for reproductive purpose. Nowadays, in a spatial planning management contest, the creation of further mussel farms even if may be encouraged by these results, at regional scale, it is not a firm economical sustainable, due to the low mussel selling price. Moving from this, modernize the production system by coupling mussel cultivations also with other incoming sources, may represent the right choice to maintain this type of sustainable acquacolture. Manage recreational fishing inside mussel farm may be among the feasible solutions. In the end, as underlined by the investigation on potential role as fish aggregating area, the farm, being off-limits to commercial fishing, may act one-sidedly also as a fish maker, for the nearby areas, where artisanal fishery is allowed. By the present, this activity is a sustainable practice, but, due to the species dependence and to the catch composition in terms of thermal affinity groups show a high potential vulnerability. Small modifications both in fleet structures and in environmental conditions could drive the situation towards unsustainability. An increase in available fishes biomass may act as buffer effect towards vulnerability causes, by supporting possible new fishermen, fronting the problem of small modification in fleet structures. Moreover some of the fish species enhanced by mussel farm are temperate or warm species. Given the dependence of local artisanal fishery from cold or temperate species, a shift of catches toward temperate and warm ones’, without affecting incomings, might, at least partially, release this type of activity from the variations of the thermal regime as forecast by IPCC.