The air–water interface: A microhabitat for hypotrichous settlers (Protista, Ciliata)

The spatial distribution of Oxytri cha bifaria (a hypotrich ciliate) was studied in the laboratory to gain information about a poorly known habitat—the air‐water interface. The results show that this species settles on the interface whenever a bacterial film grows. The ciliate’s locomotory behavior is restricted on newly colonized interfaces but returns to normal patterns on solid substrata when a complete bacterial film develops on the interface. When the bacterial film is broken, ciliate motion is restricted to the micro‐“floes” of bacteria, thus inducing a patchy distribution on the ciliates. Field observations confirm laboratory results. Behavior‐induced patterns in microhabitat distribution may have effects on the reproductive biology of these protozoa.