Non-native Pacific oyster Magallana gigas (Thunberg, 1793) was introduced to the Mediter-ranean Sea for aquaculture purposes in the 1960s. Although this species was not introduced for aquaculture to the Croatian part of the Adriatic Sea, in the 1970s, it was reported in the Lim Bay, in the North-eastern Adriatic. Until recently, there has been no research on the species in the Croatian part of the Adriatic. The aim of this research was to summarize existing and novel data on the distribution of M. gigas in coastal areas of the Eastern Adriatic and to provide a baseline for the future monitoring and assessment programmes of the species. Distribution of M. gigas was determined by three different methods: (i) a visual census of the presence of M. gigas specimens in the medio-littoral zone; (ii) DNA identification of M. gigas larvae in the water column; and (iii) the presence of M. gigas in the subtidal zone at depth between 25 and 40 m. Magallana gigas has a well-established population in the medio-littoral zone of natural and anthropogenic habitats along the coast of the North-eastern Adriatic Sea (west coast of Istria peninsula), but it is not present in the deeper layers . In the Central-eastern and South-eastern Adriatic Sea, the species was either absent or sporadically recorded with no evidence of fully established populations. Considering the great invasion success of M. gigas worldwide and effects that this species could have on the invaded ecosystem (e.g. competition for food and space with native species), detailed future monitoring is needed for the Eastern Adriatic Sea.

The Mediterranean monk seal ( Monachus monachus ) is sporadically reappearing in the eastern Adriatic, but the capacity of this region to support transient individuals or future recolonisation remains poorly understood from a prey-resource perspective. We assessed the status and multi-year trends of key prey taxa known to constitute important components of monk seal diets by integrating three complementary indicators: fishery-independent biomass indices from the MEDITS trawl survey (2002-2025), fishery-dependent landings per unit effort from small-scale coastal fisheries (SSF LPUE) monitored under the EU DCF (2012-2025), and official national landing statistics (2012-2024). Species-specific trend signals were standardised and combined using a reliability-weighted traffic-light framework to classify relative prey availability as improving (Green), stable and/or inconsistent (Yellow) or declining (Red). Among 12 evaluated prey species, 6 were classified as stable or inconsistent, 4 as improving and 2 as declining. Improving classifications were driven mainly by positive MEDITS trends for Pagellus erythrinus , Pagellus bogaraveo and Mullus barbatus , and by concordant positive signals for Scorpaena scrofa . Declining classifications indicated consistent negative trends for Conger conger , and mixed but overall negative evidence for Sepia officinalis , driven primarily by fishery-independent and landings trends. Overall, the eastern Adriatic prey base appears heterogeneous rather than uniformly depleted, with improving signals restricted to a few demersal fishes and declining signals concentrated in selected high-value prey. These findings suggest that prey availability is unlikely to represent a basin-wide barrier to monk seal recolonisation, but may impose local constraints where declining prey resources overlap with intense coastal fisheries. The proposed framework identifies priority taxa and nearshore data gaps for targeted monitoring and provides a basis for more spatially explicit assessments of monk seal habitat suitability in the Adriatic.