Theses and Dissertations

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Defense Date

9-2003

Document Type

Thesis - NSU Access Only

Degree Name

M.S. Marine Biology

Department

Oceanographic Center

First Advisor

Andrew Rogerson

Second Advisor

Charles G. Messing

Third Advisor

Patricia Blackwelder

Abstract

The current study examines salinity tolerance in naked amoebae. A biodiversity study was conducted in the Salton Sea, an inland lake in southern California, with an average salinity of 44 ‰. Amoebae were also collected from hypersaline ponds around the perimeter of the Sea where salinities averaged 160 ‰. A total of 45 species of amoebae were isolated, about one third of which were new to science. One Salton Sea species, Platyamoeba pseudovannellida n.sp. was found to survived over the range 0 - 150 ‰. A first estimate of abundances of amoebae in the Sea showed that densities could reach 237,120 cells L-1. Many of the isolates were observed to consume cyanobacteria and algae suggesting that amoebae are important regulators of blooms in the Sea, although this was not tested experimentally. Samples from the intertidal zone of a beach, a habitat also subject to salinity fluctuations, provided the first abundances of naked amoebae in sand. Densities ranged between 181 and 8473 amoebae cm-3, again suggesting that amoebae are important micrograzers in this challenging environment. From the aforementioned studies, 6 clones of amoebae were isolated for salinity tolerance experiments (2 marine beach isolates, 2 Salton Sea isolates, and 2 hypersaline pond isolates). A seventh clone, Acanthamoeba polyphaga, a common freshwater/soil amoeba was obtained from the Culture Collection of Algae and Protozoa (CCAP). The experiments compared the effects of gradual versus no acclimatization and used growth rate and culture yield as indices of effect. Generally, amoebae were tolerant over a wide range of salinity conditions and were not markedly influenced by pre-conditioning to salinity regimes. Acanthamoeba grew in 0 -12 ‰, marine clones 2 and 3 in 0 - 110 ‰, Salton Sea clones 4 and 5 in 0 - 150 ‰, and the hypersaline clones 6 and 7 in 0 - 270 ‰ salt. The results suggest that most amoebae are essentially unaffected in terms of growth and yield by moderate and severe salinity changes. The survival and activity of large populations of amoebae in sites subject to salinity challenges suggest that they should be considered in future studies designed to understand their as yet undefined ecological role.

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