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Blue-green algae or cyanobacteria are photosynthetic microorganisms that can be found in most habitats and have ability to multiply quickly (forming “blooms”) under specific conditions. Nitrogen and phosphorus enriched water in combination with higher temperature, lower water level and anthropogenic pressure enhances effects of algal blooms. Surveys in different parts of the world have found that approximately 45% to 90% of cyanobacterial blooms produce toxins (cyanotoxins). Reservoirs and slow moving rivers can provide suitable conditions for cyanobacterial bloom development, which may decrease water quality and affect various biological communities. Investigation of cyanobacterial diversity and composition was conducted along the karstic river Cetina and artificial reservoir Peruča which is used for recreational purposes, in the sub mountain Croatia. Samples were collected in August 2012 along the river (~ 32, 5 river kilometers) on 23 study sites including spring and main flow of the river Cetina (upstream and downstream from the reservoir Peruča). A total of 22 taxa were found of which Anabaena sp., Chroococcus sp., Gleocapsa sp., Merismopedia sp., Nostoc sp., Oscillatoria sp. and Pseudanabaena sp. were dominant. Moreover, five taxa with toxic properties: Anabaena sp., Lyngbya sp., Microcystis sp., Nostoc sp. and Oscillatoria sp. have been recorded. Generated taxonomical list of cyanobacteria provided insight information on biodiversity of the river Cetina and reservoir Peruča. Obtained data showed diversity in algological flora as a result of dynamics in environmental conditions. Physical parameters which were recorded along the research sites showed that the pH of the river and the reservoir were similar and ranged from 5, 6 to 6, 3 units what corresponded to the ecological status of the observed water system due to external factors, physical parameters and a large amount of degraded organic matter with dominance of cyanobacterial taxa in the water column. Furthermore, research on the river Cetina indicates how this type of aquatic habitat operates and it can point out how some similar ecosystems can function. Long-term climate change predictions suggest that changes in temperature and weather patterns may increase the scale of hazard presented by cyanobacterial blooms. This in turn may increase the scale of risk to human health by cyanotoxins. Planning and preparedness with respect to cyanobacterial investigations will therefore remain important for the foreseeable future.

On the jabuka cliffs, the marine flora and fauna are very diversified. About 300 taxa have been identified so far, more than 150 being noted for the first time in the area. The foraminiferan Discoramulina bollii, and the bryozoans Apousina filum and Buffonnellaria divergens had not been previously noted in the Adriatic Sea. Five benthic communities were identified along the rocky walls from the supralittoral zone to about 60 m depth, some of them exhibiting a belt-like distribution. A noticeable feature of these assemblages is the microhabitat co-occurrence of species typical from particular depth zones and/or habitat niches. Considering the considerable biotic interest of the Jabuka islet, a protection status should be given to its terrestrial and marine parts.