Date Awarded


Document Type


Degree Name

Master of Science (M.Sc.)


Virginia Institute of Marine Science


Epibiosis is a common phenomenon in aquatic environments. The chitinous exoskeletons of crustaceans provide stable surfaces for attachment and growth of epibiotic microorganisms. Epibiont ciliate colonization on copepods is commonly recorded but has rarely been studied in Chesapeake Bay; also, little is known about the life cycles of epibiont ciliates in the bay.

The present work focuses on the life cycle of Zoothamnium intermedium in Chesapeake Bay. A peritrich ciliate belonging to the genus Zoothamnium was found as an epibiont on the calanoid copepods Acartia tonsa and Pseudodiaptomus pelagicus during the summer in the York River, a tributary of the lower Chesapeake Bay. By using primers conservative for the genus Zoothamnium, two almost identical (99.8% similarity) 2171-bp ribosomal DNA (rDNA) sequences containing the complete small subunit (SSU) and partial internal transcribed spacer (ITS) rDNA regions were obtained from epibiont ciliates on the two hosts, indicating that they were the same ciliate species. Based on phylogenetic analysis and morphological characteristics, the epibiont was presumptively identified as Z. intermedium. In winter, Z. intermedium was only found on P. pelagicus, never on A. tonsa or A. clausi. The continuous presence of Z. intermedium on P. pelagicus during the winter suggests that it used P. pelagicus as its primary host for overwintering. PCR assays specific to Z. intermedium were designed to detect this ciliate in the environment. Positive PCR results were obtained from some sediment samples, potentially implicating the existence of a benthic cyst stage as another possible overwintering strategy. In the laboratory, formation of cyst-like cells from detached zooids was observed at 5°C. In detachment-recolonization trials, colonization of telotrochs to the same host species was higher than across host species, indicating a certain seasonal host specificity.



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