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

Reproductive cycle of a non-native oyster, Crassostrea gigas, in the Adriatic Sea

“…Interestingly, in the 1970s, wild populations of the Pacific oyster had been reported in the intertidal zone of the rocky shore in Lim Bay, in the northern Adriatic Sea, Croatia (Filić & Krajnović-Ozretić, 1978;Hrs-Brenko, 1982). Official data about C. gigas introduction is lacking, but according to several studies (Filić & Krajnović-Ozretić, 1978;Hrs-Brenko, 1982;Stagličić et al 2020), it has been assumed that current presence and high abundance of the Pacific oyster is a consequence of short-term experimental aquaculture trials conducted in early 1970s. It seems that conditions in the Lim Bay area were favourable and the Pacific oyster started to spread.…”

“…It seems that conditions in the Lim Bay area were favourable and the Pacific oyster started to spread. For several decades, the presence of the Pacific oyster in Croatian waters was neglected; however, the species has recently become a focus of several studies in the eastern Adriatic Sea concerning its presence, distribution and abundance (Šegvić-Bubić et al, 2016;Ezgeta-Balić et al, 2019;Stagličić et al, 2020). Yet, there is a lack of knowledge on C. gigas biology and ecology in this region, including its reproductive cycle in environmental conditions of Lim Bay.…”

“…Ruiz et al, 1992;Massapina, 1999;Steele & Mulcahy, 1999;Lango-Reynoso et al, 2000, 2006Dutertre et al, 2009;Enríquez-Díaz et al, 2009;Thomas et al, 2016;Antonio & Camacho, 2019), but in the Mediterranean region, data are generally scarce (Shpigel, 1989;Dridi et al, 2007Dridi et al, , 2014Ubertini et al, 2017), and completely lacking in the Adriatic Sea. The presence of larva and small specimens (~20 mm) in Lim Bay (Ezgeta-Balić et al, 2019;Stagličić et al, 2020) might indicate favourable environmental conditions for successful reproduction of C. gigas; however, to confirm this hypothesis, detailed research on its reproductive biology is needed.…”

Translocation and Aquaculture Impact on Genetic Diversity and Composition of Wild Self-Sustainable Ostrea edulis Populations in the Adriatic Sea

“…In addition, increased fertilization success has been recently linked with high population densities, where oysters with a nearest neighbor ≤1.5 m were found to brood significantly more larvae than individuals with nearest neighbors ≥1.5 m (Guy et al, 2019). Since the concentrated chemical release of adult conspecifics is the driver for dense gregarious localized settlements (Tamburri et al, 2008), it can be argued that during spawning season, oyster farms with a high density of mature oysters per square meter, produce and attract O. edulis larvae more successfully than the adjacent wild populations that are scattered at low densities along the bays (<1 oyster/m 2 , Stagličić et al, 2019). Such an attraction bias was further confirmed by the slightly greater pairwise relatedness observed between farmed and wild populations compared to the farmed and impacted populations (2.7% vs. 2.6%).…”

Quantifying current and future risks of invasiveness of non‐native aquatic species in highly urbanised estuarine ecosystems—A case study of the River Neretva Estuary (Eastern Adriatic Sea: Croatia and Bosnia–Herzegovina)

“…Amongst the extant species: three freshwater fishes [northern pike Esox lucius L., largemouth bass Micropterus salmoides (Lacepède), European catfish Silurus glanis L.], two brackish invertebrates [blue crab Callinectes sapidus Rathbun, Australian tubeworm Ficopomatus enigmaticus (Fauvel)] and one marine invertebrate [Asian date mussel Arcuatula senhousia (Benson)] were sampled as part of a survey of the RA area carried out in 2019; the tunicate warty comb jelly Mnemiopsis leidyi A. Agassiz was sampled in a previous survey in 2018; whereas, the freshwater fish featherfin squeaker Synodontis eupterus Boulenger and the marine fishes white grouper Epinephelus aeneus (Geoffroy Saint‐Hilaire) and white trevally Pseudocaranx dentex (Bloch & Schneider) have been previously recorded in the RA area (Dulčić et al., 2017, 2018; Glamuzina, Bartulović, et al., 2017). The two horizon species included the marine invertebrates Pacific oyster Crassostrea gigas (Thunberg) and Manila clam Ruditapes philippinarum (Adams & Reeve), both of which have not yet been reported from the middle Eastern Adriatic Sea coast (Stagličić et al., 2020), but are present in major port areas of the Northern Adriatic Sea, hence in proximity to the RA area (Savini et al., 2010). Note, pilot fish Naucrates ductor (L.), albeit recorded in the RA area (Glamuzina, Bartulović, et al., 2017), was not included as part of this screening study as it is a typical offshore pelagic species.…”