Non-occurrence of free-living Paramoeba invadens in water and sediments of Halifax Harbour, Nova Scotia, Canada

Abstract

Seawater and sediment samples from various sites in or near Halifax Harbour were cultured for Paramoeba, as were tissues of the natural sea urchin host Strongylocentrotus droebachiensis sampled from Hahfax Harbour. An solate of Paramoeba from a Halifax Harbour water sample was not virulent on injection into healthy sea urchins. However, some sea urchins in cages near the outfall pipe of Dalhousie University's seawater system were infected during the annual peak of the seawater temperature cycle. Results indicate that (1) there is no evidence of a free-living endemic population of Paramoeba invadens in or near Halifax Harbour, (2) S. droebachiensis, the natural host for P. invadens, do not harbour a reservoir population of this orgamsm at temperatures sub-optimal for paramoebiasis, and (3) Paramoeba which are morphologically ~ndistinct from laboratory stocks of P. ~n v a d e n s were recovered near the outfall pipe. These organisms may have been released via the outfall pipe into Halifax Harbour and subsequently lost virulence.