Ciliate plankton dynamics and survey of ciliate diversity in the Salton Sea, California, 1997–1999

Abstract

Planktonic ciliates and other protozoa were monitored at mid-lake stations in the saline, polymictic Salton Sea during the period 1997–1999, at approximately two-week intervals. Additionally, in 1999, a survey of ciliate diversity in a variety of microhabitats was undertaken. Ciliates generally comprised < 20 percent of the total zooplankton biovolume, with copepods, rotifers and larvae of a barnacle and polychaete worm making up the rest. However, in early 1999 tintinnids constituted ~40 percent of total zooplankton biovolume, and in September 1998 when metazooplankters were very scarce, ciliates represented nearly 100 percent. An anaerobic ciliate, Sonderia sp., invaded the mid-water column during periods of anoxia and high sulfide levels in 1998 and 1999. Large ciliates, such as Condylostoma spp. and Favella sp. increased in abundance over the three-year period while the smaller forms, mostly scuticociliates, did not. This pattern may be due to a decrease during our study in abundance of the filter-feeding hybrid tilapia (Oreochromis mossambicus x O. urolepis honorum), which may have selectively grazed upon the larger forms. An inverse relationship between copepod abundance and large ciliate abundance suggests copepods also prey on the larger forms. A total of 143 ciliate taxa were found as well as protozoans in other groups such as heliozoans and choanoflagellates.