Theses and Dissertations

Defense Date

2007

Document Type

Thesis

Degree Name

M.S. Marine Biology

Department

Oceanographic Center

First Advisor

Andrew Rogerson

Second Advisor

Curtis M. Burney

Third Advisor

Anthony Moss

Abstract

Previous work by Moss et al. (2001) reported surface associated protists on the ctenophore Mnemiopsis sp. They frequently observed the ciliate Trichodina ctenophorii and a Flabellula-like amoeba attached to the comb plate surface. They noted that the ciliate and the amoeba were found on the subsagittal, subtentacular, and the auricular comb plates. The amoeba had a maximum width of about 15 μm and cells were crescent shaped. Ultrastructural evidence suggested that these protists were parasites although the exact nature of the association remained to be determined. This was the background for the present study.

The present investigation documented the frequency of occurrence of gymnamoebae on ctenophores around Florida to assess the universality of this association. In addition, the study estimated the number of Flabellula-like comb plate amoebae per comb surface. The study also set out to isolate all surface associated amoebae, including the Flabellula-like amoeba ‘symbiont’, using a variety of media formulations. The goal was to provide material to facilitate the identification and characterization of this amoeba.

Over the 2 year duration of the project, 140 Mnemiopsis sp. were collected from 16 locations around Florida and surface tissue was processed for attached gymnamoebae. Eleven morphotypes of amoebae were isolated from 52 of the 140 Mnemiopsis sp. The Flabellula-like gymnamoeba was present on 85% of the specimens, and the greatest concentration on Florida ctenophores was 946 amoebae mm-2 of comb plate surface. One isolated amoeba closely resembled the Flabellula-like amoeba described by Moss et al. (2001). It is interesting to note that although most ctenophores harbored the ‘symbiont’ it was only isolated into culture 2% of the time. No geographic factors appeared to favor the presence of amoebae on ctenophores. The shortest generation time (ie. fastest growth) calculated for the flabellulid amoeba was 20.9 hours at a salinity of 10 ppt and a temperature of 23°C. The amoeba grew best in seawater supplemented with malt/yeast extract to stimulate the growth of attendant prey bacteria. The results suggest that this amoeba, which was numerous on the surface, was predisposed to life on the ctenophore surface and could only be switched to laboratory conditions with difficulty. The amoeba had an unusual stage in the life cycle forming large fused, multinucleate cells in old cultures. This, together with its unique appearance (not resembling any published species) and the problems in amplifying its DNA by PCR (encountered by collaborators at Wood’s Hole Oceanographic Center) suggest that it an interesting amoeba new to science.

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