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Marine underwater habitats dominated by seagrass Posidonia oceanica play an essential role in fish community assembly, affecting taxonomic and functional diversity, abundance and fish behavior. The value of seagrasses as habitat depends on the spatial arrangement of the seascape elements and the availability of alternative habitats. Little is known about the effect of the seascape context of P. oceanica meadows on fish assemblages in the Mediterranean Sea. To identify P. oceanica meadows' relative importance as a habitat for fishes, fish communities in the Croatian Adriatic Sea were investigated, using SCUBA lure-assisted visual census. The results show a significant effect of different arrangements of P. oceanica meadows' seascape elements and surrounding habitats on fish community structure. Fragmented mosaic meadows with P. oceanica growing directly on and between rocky-algal reefs/boulders had significantly higher fish abundances compared to both types of continuous meadows (bordering rock and bordering sand). Continuous meadows bordering sand harbored the highest number of unique species. Evidence that alternative structured habitats within proximity to seagrass beds may affect the community structure of associated fish assemblages is provided, highlighting the need to consider P. oceanica meadows' seascape context in conservation management and experimental design for fish community structure., Naselja morske cvjetnice Posidonia oceanica igraju važnu ulogu u strukturiranju zajednica riba te utječu na taksonomsku i funkcionalnu raznolikost, brojnost i ponašanje riba. Relativna vrijednost naselja morskih cvjetnica ovisi o prostornoj organizaciji elementa podmorskog okoliša te dostupnosti alternativnih staništa. Međutim, nedovoljno je poznato koji sve čimbenici utječu na strukturu zajednice riba povezanih s ovom morskom cvjetnicom. S ciljem utvrđivanja utjecaja različite prostorne organizacije elementa podmorskog okoliša na zajednice riba, proveden je vizualni cenzus uz pomoć mamca u naseljima cvjetnice P. oceanica u hrvatskom dijelu Jadranskog mora. Utvrđen je značajan utjecaj različite prostorne organizacije elementa podmorskog okoliša na strukturu zajednice riba – u rascjepkanim mozaičnim naseljima u kojima se P. oceanica isprepliće s kamenom podlogom obraslom makro-algama zabilježena je značajno veća brojnost riba u odnosu na kontinuirana cjelovita naselja (uz sediment ili uz kamenitu obalu). U radu su predstavljeni dokazi da dostupnost alternativnih strukturiranih staništa u neposrednoj blizini naselja morske cvjetnice P. oceanica utječe na strukturu zajednice riba koje u njoj žive. Neophodno je uzeti u obzir kontekst prostornog rasporeda elemenata podmorskog okoliša kojima dominira morska cvjetnica P. oceanica prilikom planiranja znanstvenih istraživanja, ali i kod upravljanja priobalnim područjima.

Fish communities within two Croatian MPAs were surveyed using both diver-operated underwater video (DOV) via SCUBA and lure-assisted visual census (Lure-UVC) via snorkling. Both methods were applied at similar depths within replicate MPA locations, Kornati NP (4) and Brijuni NP (2). We predicted that the methods detect similar fish communities, habitat mosaics, and fish habitat preferences. To avoid inter-observer variability- errors, fish and habitat identification in all surveys was done by the CK. Habitat types were defined by a common protocol. Higher species richness (35 > 30) was detected by lure-UVC in Kornati. In Brijuni, DOV detected more species (31 > 25). The MPA-specific communities observed by the two methods were 72% similar within Kornati NP and 92% similar within Brijuni NP (Sørensen Index). Both methods recognized the same six habitats in Brijuni NP and five common habitats in Kornati NP, with one unique observed by DOV. In Kornati NP, Lure-UVC detected significant habitat preferences for 10 (28%) species of which nine preferred transitional habitats, the edges between R and U (RU) and R and P (RP) ; DOV detected significant habitat preferences for 15 (50%) species of which 12 preferred either R or RP transitions. In Brijuni NP lure-VC detected four (13 %) and DOV seven (28 %) species with significant habitat preference, and all eleven species were significantly attracted to transitions from rocky reefs to sedimentary bottoms (RU) and all significantly avoided bare sand (U). We conclude that the two methods are comparable in their ability to sample fish communities, habitats and habitat preferences. Decisions about which method to use should focus on availability of resources and target depths. Lure-UVC is more cost and time efficient because it does not need SCUBA and video-processing but requires the presence of a fish/habitat expert in the field, preferably the same individual. DOV requires costly SCUBA operation and lengthy post- video analysis in the lab but allows for multiple experts relying on permanent records. Sample sizes per unit field-time is high for DOV and depends on the number of divers operating DOV. DOV can be applied at wider depth range than surface-based UVC.

Predator - prey relationships are complex and chemical communication plays an important role. The role of chemical communication between Scorpaena porcus and Pomatoschistus spp. was assessed including the added effects of a herbicide. Tank trials featured living free - roaming and confined S. porcus as well as a maquets. This allowed for manipulations of cues perceived by the prey. Trials were performed in chemically polluted and unpolluted seawater. Pomatoschistus spp. assessed predation threats using multiple sources of information. Kairomones of S. porcus were detected by the prey, yet simultaneous visual and olfactory cues resulted in stronger anti - predator responses. Glyphosate disrupted predator - prey interactions.This work was supported by the Croatian Science Foundation under the project COREBIO (3107).

Demersal fish and benthic macroinvertebrates were censused in spring 2009 in six embayments and one open Adriatic shallow water location. Relative faunal abundance and species richness, diversity, and evenness were calculated and compared across bays and across natural and developed coastline within bays. We found that the faunal communities of the most enclosed bays, Novigrad Sea and Karin Sea, (1) exhibit significantly higher fish richness and faunal diversities than any of the other bays, (2) were more dissimilar from the open Adriatic community, (3) experienced significant reductions in biodiversity at developed compared to natural coastlines and (4) harbor two threatened fish and highest densities of juvenile fish. Their diversity, uniqueness, und sensitivity to development make Novigrad and Karin seas candidates for legal protection.