Bivalve larval collectors in Brijuni National Park as a means of noble pen shell (Pinna nobilis) juvenile collection

Sakupljači ličinki školjkaša, prvenstveno namijenjeni za hvatanje mlađi kritično ugrožene plemenite periske, postavljeni su 2020. na dvije lokacije unutar Nacionalnog parka Brijuni, u uvali Javorike i u uvali Pisak. Postavljeno po 3 replikata na 2, 4, 6, 8 i 10 metara dubine (Javorike) te na 2 i 4 m dubine (Pisak). Ciljevi rada bili su utvrditi brojnost i veličinu juvenilnih periski, utvrditi kvalitativni i kvantitativni sastav obraštajne zajednice na sakupljačima te rezultate usporediti sa sličnim istraživanjem provedenim 2019. godine. U uvali Javorike zabilježeno je 40, a u uvali Pisak 11 jedinki juvenilne periske. Prosječno po sakupljaču zabilježeno je 2,86 (Javorike), odnosno 2,75 (Pisak) juvenilnih periski, veličine od 0,4 do 2,5 cm (Javorike), odnosno od 0,8 do 3,4 cm (Pisak). Smanjenje broja juvenilnih periski te smanjenje njihove maksimalne veličine u usporedbi s rezultatima 2019. može se povezati s manje odraslih jedinki koje se razmnožavaju u okolini te sa sporijim rastom juvenilnih jedinki na sakupljačima. U obraštajnoj zajednici u Javorikama zabilježene su 42 svojte (12.667 jedinki) među kojima su najbrojniji školjkaši (90% udjela), zatim rakovi (8%). U uvali Pisak zabilježeno je 38 svojti (5.098 jedinke), također su najbrojniji školjkaši (88% udjela), puževi (6%) te rakovi (5%). Na obje lokacije najbrojnija je invazivni školjkaš Anadara transversa (8.988 odnosno 4.093 jedinke) koja time utječe na prihvat juvenilnih periski kao i na indekse raznolikosti zajednice.Bivalve larval collectors, primarily aimed for noble pen shell juvenile collection, were set in 2020 in two locations within the National Park Brijuni, in Javorike Cove and in Pisak Cove. Three replicates were set at 2, 4, 6, 8 and 10 m depth (Javorike) and at 2 and 4 m depth (Pisak). Aims of the research were to determine number and size of juvenile pen shells, to determine qualitative and quantitative composition of fouling community and to compare results with similar research made in 2019. In Javorike Cove 40 and in Pisak Cove 11 individuals of juvenile noble pen shells were noted. Average of 2.86 (Javorike), and 2.75 (Pisak) juvenile pen shells per collector were noted, sizes 0.4 to 2.5 cm (Javorike), and 0.8 to 3.4 cm (Pisak). Reduction in the number of juvenile pen shells and the reduction of their maximal size in comparison with the results of 2019 survey could be connected with smaller number of spawning adults in the surrounding and with the slower growth of juveniles in collectors. In the fouling community in Javorike 42 taxa (12.667 individuals) were determined among which the bivalves were the most numerous (90% share), then crustaceans (8%). In Pisak Cove 38 taxa (5.098 individuals) were determined, among which bivalves also were the most numerous (88% share), then gastropods (6%) and crustaceans (5%). On both locations the most numerous was invasive bivalve Anadara transversa (8.988 and 4.093 individuals respectively), which in that way affect the attachment of juvenile pen shells as well as community diversity indices