How diatom Cylindrotheca closterium vanquish invasive copepod Oithona davisae

Abstract

Some diatoms are rich food for herbivorous copepods, while others are toxic for their recruitment. No negative effect of diatom Cylindrotheca closterium was ever observed for copepods, and some estuarine copepods preferred it as a food. Data on grazing diatoms by abundant now in the Black Sea coastal waters invasive copepod Oithona davisae are still contradictory. Interaction of O. davisae and C. closterium, both having high colonizing potential and both typical for coastal waters, was studied in experimental culture. Two weeks after inoculation of C. closterium the cultured O. davisae was drastically fouled by globulous conglomerates of diatom cells. Diatom cells in "colonies" on copepod exoskeleton were interconnected by means of adhesive substances at one of their flexible ends at the point-wise areas at various parts of copepods exoskeleton, and the opposite flexible ends performed various circular roll-over fan-shaped movements around the axis passing through the point of their attachment. "Colonies" behaved as integrated aggressive organisms against any approaching flagellate and prevented normal locomotion of copepods. Herein we present the first report on epizoic behavior of C. closterium: quick disastrous colonization of alive copepods O. davisae by diatom "colonies" led to total extinction of cyclopoid experimental population while alive diatoms formed dense network on copepods degenerative tissues.