We sampled ctenophore species Mnemiopsis leidyi in the slovenian part of Gulf of Trieste between August and October 2021. We wanted to find out how the changing environmental conditions affect the biometrics, chemical composition and fecundity of said ctenophore. This species occurs in very high numbers in this part of the year, and because it is an invasive species, it can disturb the local ecosystem. The ctenophore can be a predator or a competitor with local species, and because of its seasonal occurence, it also dies off in high numbers in a relatively short period of time, which can cause disturbance in microbial degradation, resulting in a disturbed carbon cycle in the system. In our study, we concluded that the sesonal environmental changes do not have a big effect on chemical composition of individuals, but we did observe a connection with a higher carbon content with higher chlorophyll a concentrations in seawater. The temperature effect is notable when examining the speed of egg hatching, which is slower in lower temperatures. The number of eggs produced varied highly, but we noticed that the individuals with a bigger mass produced more eggs. The average number of eggs produced was lower than in the similar studies in these areas, which might be correlated with an ever higher oligotrophy in the Gulf of Trieste, or it might be due to smaller dimensions of individuals selected for the study.
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