engleski

DECREASING OF ZOOXANTHELLAE DENSITY IN CORAL Cladocora caespitosa (L., 1767) IN LABORATORY CONDITIONS

Cladocora caespitosa is a common colonial scleractinian coral in the Adriatic Sea. It occurs naturally with numerous endosymbiotic and photosynthetic zooxanthellae from genus Symbiodinium. In extreme conditions corals can expel zooxanthellae or may even digest them. This study investigates number of zooxanthellae in polyps of C. Caespitosa in colonies under different experimental conditions. Two colonies were held in separate glass aquaria in filtered sea water at temperature of 15 – 20 °C. One colony was fed with freshly hatched brine shrimp (Artemia salina Linnaeus, 1758) at intervals of 2-3 days and the other colony was starving. Both aquaria were kept in dark conditions during experiment. Every three days zooxanthellae from polyps were enumerated using haemocytometer. Ten replicates were counted from each sample and the mean and standard deviation were calculated. In the first month of the experiment the zooxanthellae density ranged from 7.17 x 106 to 7.09 x 106 cells per polyp (mean = 7.12 x 106 ; SD = 8.76 x 105 ; n = 122) in colony that was not fed and from 6.93 x 106 to 6.86 x 106 cells per polyp (mean = 6.9 x 106 ; SD = 7.58 x 105 ; n = 138) in colony that was fed. The first significant decrease in zooxanthellae density was noted on 28th day of the experiment in both colonies. The zooxanthellae were not detectable in polyps at 61st day experiment in colony that was not fed and at 85th day in fed colony. A small number of zooxanthelae was also found in sea water during the experiment in both aquaria.

zooxanthellae; Cladocora caespitosa; Adriatic Sea

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