Distribution patterns of two co-existing oyster species in the northern Adriatic Sea: The native European flat oyster Ostrea edulis and the non-native Pacific oyster Magallana gigas

• Published in: Ecological Indicators
• Main Authors: Stagličić, Nika, Šegvić-Bubić, Tanja, Ezgeta-Balić, Daria, Bojanić Varezić, Dubravka, Grubišić, Leon, Žuvić, Luka, Lin, Yaping, Briski, Elizabeta
• Format: Article in Journal/Newspaper
• Language: English
• Published: Elsevier 2020
• Subjects: Pacific; Pacific oyster
• Online Access: https://oceanrep.geomar.de/id/eprint/49534/; https://oceanrep.geomar.de/id/eprint/49534/1/Distribution%20patterns%20of%20two%20co-existing%20oyster%20species%20in%20the%20northern%20Adriatic%20Sea.pdf; https://doi.org/10.1016/j.ecolind.2020.106233

The Pacific oyster Magallana gigas, globally one of the most translocated marine species, has never been commercially farmed in any part of the Croatian eastern Adriatic Sea, where the native flat oyster Ostrea edulis is the only cultured oyster species. The Pacific oyster has, however, established populations on the west coast of the Istria peninsula, in the northeast Adriatic Sea. Current distribution, abundance and size structure of the flat and Pacific oysters were studied there along spatial and depth gradients in natural and artificial habitats to assess their potential for coexistence. This is the first quantitative assessment of native and non-native oyster populations on a Mediterranean-wide scale providing a baseline for determining future changes in their distribution. Both species were omnipresent, with the Pacific oyster displaying a more pronounced variability in abundance and size in relation to survey regions and depths. The population density of flat oysters was low, generally less than 1 individual/m(2), with no difference among regions. The density of the Pacific oyster was significantly higher, being on average 5 individuals/m(2). Dense, reef-forming aggregations of Pacific oysters were contained in Lim Bay, a nationally-important shellfish aquaculture area, where its mean density was 107 individuals/m(2). Along the open coastline its densities were considerably lower and followed a latitudinal gradient. The observed abundance and size distribution patterns of the Pacific oyster suggest that Lim Bay was the introduction point, with feral settlement likely originating from short-lived experimental aquaculture trials and subsequently dispersing by prevailing local currents. The flat oysters were larger in size and settled at different depths compared to the Pacific oysters. The vertical range of Pacific oysters was mostly contained in the tidal zone, while flat oysters were present in the subtidal exclusively. Such spatial partitioning likely resulted from introduced oysters occupying a vacant ...