Occurrence of the Parasitic Dinoflagellate Amoebophrya ceratii in Chesapeake Bay Populations of Gymnodinium sanguineum

Abstract

ABSTRACT. Chesapeake Bay populations of the red-tide dinoflagellate Gymnodinium sanguineum were regularly infected by the parasitic dinoflagellate Amoebophrya ceratii during the summers of 1988-1991. Infections developed inside the nucleus of G. sanguineum and were always lethal to the host. Parasite generation time was ~ 40 h at 23° C, with the intracellular, trophont phase lasting 39.5 ± 0.3 h, and the extracellular, vermiform stage persisting for ~ 20 min. Near surface accumulations of G. sanguineum sometimes exceeded 1,000 cells/ml; however, host abundance was relatively low when integrated over the surface mixed layer of each station (mean = 12.2 cells/ml ± 2.96 SE; n = 60). Parasitized hosts were encountered in 75% of the samples where host abundance was > 1 per ml, and epidemic outbreaks (20-40% hosts infected) were observed on several occasions. Epidemic infections were generally located several meters below surface accumulations of G. sanguineum and were always restricted to a narrow region near the pycnocline. Consequently, integrated station values for parasite prevalence were low, with an average 2.7% (± 0.31 SE; n = 60). Parasite induced mortality removed up to 8% of G. sanguineum populations per day, but averaged < 2% of host biomass throughout the Bay. Thus, parasitism by A. ceratii does not appear to be a major factor regulating G. sanguineum bloom in the main stem of Chesapeake Bay.

Effects of two strains of the parasitic dinoflagellate Amoebophrya on growth, photosynthesis, light absorption, and quantum yield of bloom-forming dinoflagellates

“…ex Gymnodinum instriatum (previously Gyrodinium instriatum). The former is the same parasite referred to as A. ceratii (Coats & Bockstahler 1994), A. ceratii ex Gymnodinium sanguineum (Coats et al 1996), and Amoebophrya sp. ex Gymnodinium sanguineum (Gunderson et al 1999, Yih & Coats 2000, while the latter is a new strain isolated from the Rhode River subestuary of Chesapeake Bay.…”

“…Interestingly, Amoebophrya sp. ex A. sanguinea always invades the host's nucleus (Coats & Bockstahler 1994), while Amoebophrya sp. ex G. instriatum grows within the host's cytoplasm.…”

“…Species of Amoebophrya are particularly noteworthy, as they are widely distributed in coastal environments and have been reported from numerous host species (Cachon 1964, Taylor 1968, Elbrächter 1973, Nishitani et al 1985, Cachon & Cachon 1987, Fritz & Nass 1992, Coats & Bockstahler 1994, Coats et al 1996. Amoebophrya spp.…”

“…Amoebophrya spp. prevent reproduction of their hosts (Elbrächter 1973), have relatively short generation times (Coats & Bockstahler 1994), and have a simple life cycle that culminates in death of the host (Cachon 1964), all of which make these parasites likely candidates for controlling host populations. The life cycle of Amoebophrya spp.…”

“…appear well adapted to exploit host populations in enriched coastal settings (Yih & Coats 2000); however, infection levels are highly variable, ranging from <1 to 80% (Taylor 1968, Elbrächter 1973, Fritz & Nass 1992, Coats & Bockstahler 1994, Coats et al 1996. Furthermore, estimates of host mortality resulting from Amoebophrya infections range from a maximum of 8% daily in the mainstem of Chesapeake Bay (Coats & Bockstahler 1994) to 54% daily in a shallow subestuary of the bay (Coats et al 1996). Parasitism may also alter host physiology in ways that influence rates of primary production or release of dissolved organic compounds, but those processes have not been addressed previously.…”