TitlePrey density-dependant protozoan bacterivory
NameTuorto, Steven John (author), Tagon, Gary (chair), Kerkhof, Lee (internal member), Vetriani, Costantino (internal member), Morin, Peter (outside member), Rutgers University, Graduate School - New Brunswick,
DescriptionThe initial ingestion rates of the marine, bacterivorous ciliates E. vannus, E. plicatum, and Cyclidium sp. were measured as a function of prey concentration. A method was developed using bacteria engineered to express green fluorescent protein (GFP-bacteria) as a naturally cultured tracer to directly measure ingestion rates at bacterial concentrations ranging from 5&#00215;104 to 1010 bacteria ml-1. Ingestion rates increased with prey density ranging from 103-105 bacteria ciliate-1 h-1, and maximum ingestion rates were observed at a prey density of 109 bacteria ml-1. Ingestion rate data for all three grazers was best modeled by a Type III functional response equation. In lieu of these results combined with a re-analysis of previous reports of ciliate ingestion, it was concluded that in nature, a traditional Type II response is probably rare and unstable.
Next, using GFP-bacteria as prey, ingestion rates, food vacuole formation rates, and the maximum number of food vacuoles were measured over time for the same ciliate species at a low (106-107 bacteria ml-1) and a high (109 bacteria ml-1) prey concentration. The time required to reach steady state maximum food vacuole capacity and digestion rate were subsequently estimated. Food vacuole content and ingestion rates increased with prey concentration. Digestion rate decreased with increasing food vacuole content, refuting the idea that digestion is a rate constant. Estimates of ingestion rate and digestion efficiency suggested that ciliates are capable of exerting substantial top-down control on bacteria at typical water column concentrations.
The ingestion rates of each ciliate were next measured as a function of benthic bacterial concentration, by culturing GFP-bacteria directly in sediment microcosms to densities ranging 108-1010 bacteria per milliliter of pore water (ml-1 PW). Ingestion rates increased continually with sediment bacterial concentration, ranging from 102-105 bacteria ciliate-1 h-1. A decrease in ingestion rates below 2&#00215;108 bacteria ml-1 PW suggests a possible lower prey concentration threshold for benthic bacterivory. Benthic ingestion rates measured at a typical sediment bacterial concentration (109 bacteria ml-1 PW) were two times higher for both species of Euplotes, and 27 times higher for Cyclidium sp., than those measured for these species when grazing on suspended prey.
NoteIncludes bibliographical references (p. 85-92).
CollectionGraduate School - New Brunswick Electronic Theses and Dissertations
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