Inter-specific competition between the diatom Chaetoceros tenuissimus and harmful algae Karenia mikimotoi and Chattonella marina

This study investigated the inter-specific competition between the diatom Chaetoceros tenuissimus and the harmful algae Karenia mikimotoi and Chattonella marina under varying initial cell densities. Experiments were conducted using both monoculture and co-culture methods in a controlled laboratory environment. The results indicated that the growth of C. tenuissimus, K. mikimotoi, and C. marina in monoculture was not influenced by the initial cell densities (1000 or 10 000 cells ml−1). However, an increase in initial inoculation density accelerated the time to reach maximum cell density and the onset of the stationary growth phase. The initial cell density significantly impacted the inter-specific competition between C. tenuissimus and K. mikimotoi, with the species at higher concentrations prevailing in the competition. In the competition experiments with four different initial concentration combinations of C. tenuissimus and C. marina, neither species were eliminated by the other. Simulation of the co-culture experiments using the Lotka–Volterra inter-specific competition model revealed that C. marina could only outcompete C. tenuissimus when its initial cell concentration was significantly higher. In the experiment in which each filtrate was exposed to the other species, no clear inhibitory effect was observed in any of the combinations. This study contributed to a better understanding of the inter-specific relationships between harmful algae and diatoms.