The Spatial Distribution and Ecology of Zoochlorellae‐Bearing Ciliates in a Productive Pond¹

Abstract

ABSTRACT. The spatial distributions of five zoochlorellae‐bearing ciliate species ( Euplotes daidaleos, Frontonia vernalis, Acaryophrya sp., Disematostoma bütschlii , and Stokesia vernalis ) were investigated in a productive freshwater pond. The vertical profiles of all species were compared to the levels of O 2 , CO 2 , light, temperature, dissolved inorganic nitrogen, and the availability of particulate food sources. In the stratified water column, Stokesia remained close to the water surface: all other species reached peak abundance close to the oxic‐anoxic boundary. The latter behavior probably accommodated the ciliates’requirements for aerobic respiration and particulate food and their dependance on the essential resources of light and dissolved nutrients, which came from opposite directions. With the collapse of stratification, Euplotes and Frontonia returned to the sediment where they reverted to a heterotrophic nutrition although they retained some zoochlorellae. Acaryophrya and Disematostoma also became heterotrophic, but they remained evenly distributed in the water column and they lost their zoochlorellae. Stokesia disappeared, presumably because it encysted. There was some evidence for vertical spatial separation of the five species in the water column.