The influence of time of exposure to the marine environment on the change in the ratio of Escherichia coli bacteria and intestinal enterococci in the sea for swimming

U ovom je radu istraživan je utjecaja vremena izloženosti morskom okolišu na promjenu omjera broja bakterija Escherichia coli i crijevnih enterokoka u moru za kupanje. Terenska istraživanja provedena su na plaži Gojača u Kaštel Sućurcu tijekom sezone kupanja 2022., dok su in situ eksperimenti provedeni u neposrednoj blizini Instituta za oceanografiju i ribarstvo. Rezultati terenskih istraživanja pokazali su da je omjer broja bakterija E. coli i crijevnih enterokoka manji na točki udaljenijoj od izvora onečišćenja, što je rezultat značajnijeg smanjenja broja E. coli nego crijevnih enterokoka tijekom izloženosti okolišnim čimbenicima na putu od izvora onečišćenja do kontrolne točke. Rezultati in situ eksperimenata pokazali su smanjenje omjera s vremenom izloženosti indikatorskih mikroorganizama utjecaju okolišnih čimbenika, što je također rezultat bržeg ugibanja E. coli u odnosu na crijevne enterokoke. Brže ugibanje obaju indikatorskih bakterija u površinskom sloju u odnosu na dublji sloj mora ukazuje na važnost Sunčevog zračenja za reduciranje indikatorskih bakterija u morskoj vodi.In this thesis, the influence of the exposure time in the marine environment on the change in the ratio of the number of Escherichia coli and intestinal enterococci in bathing seawater was investigated. The field research was conducted on Gojača beach in Kaštel Sućurac during the 2022 bathing season, while the in situ experiments took place in the immediate vicinity of the Institute of Oceanography and Fisheries. The results of the field investigations showed that the ratio of the number of Escherichia coli and intestinal enterococci is lower at a point further away from the pollution source, which is because the number of E. coli decreases more than that of intestinal enterococci during exposure to environmental factors on the way from the pollution source to the control point. The results of the in situ experiments showed a decrease in the ratio with the time the indicator microorganisms were exposed to the influence of environmental factors, which is also the result of a faster reduction of E. coli compared to the intestinal enterococci. The faster reduction of both indicator bacteria in the surface layer compared to the deeper layer of seawater indicates the importance of solar radiation for the reduction of indicator bacteria in seawater. (2