Competition between native Ostrea edulis and invasive Crassostrea gigas oysters in the Adriatic Sea

2017-2019 –  Unity trough knowledge fund (UKF)

In the Adriatic Sea non-native invasive oyster Crassostrea gigas started to spread and presents a threat to the native European flat oyster Ostrea edulis. Pacific oyster C. gigas was introduced by aquaculture to Mediterranean Sea in the 1960s as a response to the decrease of O. edulis production caused by high mortalities due to parasitic diseases. Introduction of C. gigas was limited to the aquaculture sites, but as environmental conditions in those areas were favourable this species started to reproduce and spread outside aquaculture sites. Although C. gigas is used for aquaculture all along the Europe, in the eastern Adriatic Sea it is not the case, and it is considered an invasive species..

Invasive species spread may have negative effect on the ecosystem, and poses threat to the ecosystem stability and function. Spreading of invasive oyster may also have negative effects on the fisheries and aquaculture if invasive species effects commercially important species. In a case of the two oyster species this could be expressed through competition for space, food and larviphagy caused by invasive oyster. Although, C. gigas presence in the eastern Adriatic is detected, there is no information about its biology and ecology in Adriatic Sea, its effect on the native oyster populations, and effects that could have on fisheries and aquaculture sector. Furthermore, there are no monitoring or management plans and strategies. This situation requires immediate reaction in terms of research and proposal of measures for management of invasive oyster species.

The main objective of this project is an assessment of impact of the invasive oyster species C. gigas on the ecosystem, fisheries and aquaculture, with focus on the native commercially important oyster species O. edulis. This will be achieved through:(i) determination of the current state and population dynamics of the invasive oyster populations along the eastern Adriatic Sea, and its impact on distribution of native oyster;

(ii) exploring food competition between the invasive and native oyster;

(iii) determination of vectors of spread of the invasive oyster along the eastern Adriatic Sea

(vi) making recommendations for the future research and management of the invasive species.

This projct is significant as it will provide first measurable insight into population dynamics of C. gigas in the eastern Adriatic. Thus, this research will present scientific basis for establishment of management strategies for C. gigas in the Adriatic Sea.

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