Vransko jezero jedno je od najvećih slatkovodnih jezera na relativno malom i zatvorenom krškom otoku. Prema fizikalnim i kemijskim pokazateljima, to jezero je oligotrofno, monomiktičnog karaktera sa zimskom cirkulacijom i ljetnom termalnom stratifikacijom. Istraživanje mikrofitobentosa provedeno je u studenome 1995., te u veljači, svibnju, lipnju, kolovozu i studenome godine 1996. i 1997. Uzorci mikrofitobentosa sabirani su grabilom na pet lokaliteta (Slika 1): V1 (oko 13 m), V2 (oko 22 m), V3 (oko 33 m), V4 (oko 51 m) i V5 (oko 73 m). U kvalitativnom sastavu mikrofitobentosa, utvrđeno je 138 vrsta mikrofita koji su pripadali sistematskim skupinama: Cyanobacteria, Bacillariophyceae i Chlorophyceae (Tablice 1 i 2). Najbrojnija skupina bila je Bacillariophyceae (99 vrsta ili 71,7%) s relativnim učestalostima vrsta od 1 do 6.
Najzastupljeniji u strukturi mikrofitobentosa bili su planktonski oblici Campylodiscus noricus i Cyclotella radiosa. Relativno malim brojem vrsta bile su zastupljene skupine Chlorophyceae (26 vrsta ili 18,8%) i Cyanobacteria (13 vrsta ili 9,5 %). Nazočnost pojedinih vrsta Chlorophyceae u strukturi mikrofitobentosa bila je pojedinačna s niskom relativnom učestalošću, uglavnom 1, osim vrste Mougeotia sp. koja je imala relativnu učestalost 3 na lokalitetima V1 i V2. Od Cyanobacteria prevladavale su nitaste alge roda Lyngbya i Phormidium s relativnom frekvencijom od 1 do 5. Od ukupnoga broja utvrđenih vrsta u mikrofitobentosu, 94 vrste ili 68% bile su indikatori saprobnosti. Najviše je bilo oligosaprobnih do betamesosaprobnih indikatora.
Na osnovi indikatorskih vrijednosti nađenih vrsta u mikrofitobentosu tijekom istraživanja, P–B indeks saprobnosti kretao se od 1,3 do 1,7 (Tablica 3), što upućuje na dobru kakvoću jezerske vode.Lake Vrana represents one of the largest freshwater lakes on a relatively small and entirely karstified island. According to its physical and chemical factors, this lake is ologotrophic, monomictic, with winter circulation and thermal stratification in summer. Microphytobenthic investigations of the Lake were performed in November 1995, and in February, May, June, August and November of 1996 and 1997, respectively. During the investigations microphytobenthic samples have been collected at five locations (Figure 1): V1 (around 13 m depth), V2 (around 22 m depth), V3 (around 33 m depth), V4 (around 51 m depth) and V5 (around 73 m depth). Qualitative microphytobenthic composition consisted of 138 microphytic species belonging to: Cyanobacteria, Bacillariophyceae and Chlorophyceae (Tables 1, 2). Bacillariophyceae were the most numerous (99 species or 71.7 %), with relative frequency from 1 to 6.
Planktonic forms Campylodiscus noricus and Cyclotella radiosa were the most represented species in microphytobenthic structure. The groups Chlorophyceae and Cyanobacteria were represented with relatively small number of species, the former with 26 species or 18.8% and the latter with 13 species or 9.5%.
Particular species of Chlorophyceae were represented individually in microphytobenthic structure with low relative frequency, mostly 1, except in the case of Mougeotia sp. which had relative frequency 3 at the locations V1 and V2. The filamentous algae of the genera Lyngbya and Phormidium were dominant among Cyanobacteria, with relative freguency from 1 to 5. From the total number of microphytobenthic species determined, 94 species or 68% belonged to saprobic indicators. Most of them were oligosaprobic to betamesosaprobic indicators. Based on indicator values for the determined microphytobenthic species, P–B saprobity index was ranging between 1.3 and 1.7 (Table 3), which suggests good quality of lake waters
