Encystment in a Dynamic Environment: Deposition of Dinoflagellate Cysts by a Frontal Convergence

Abstract

The dinoflagellate Gyrod~n~urn uncatenum forms massive summer red tides in Chesapeake Bay (USA) and tributary estuaries These blooms are delimited in the downstream direction by estuanne fronts which may serve to concentrate and recirculate the population Toward the end of the bloom cycle, G uncatenum sexual stages accumulate in the frontal convergence and are transported downward along the frontal interface These stages are retained below the pycnocline in net upstream flowing bottom waters and settle out into the sediments along the subsurface transport pathway Examination of s e d~m e n t s indicates that major deposits of cysts of G uncatenurn are bounded in an upstream direction by a b e n t h~c front (where the pycnocllne intersects the bottom) Above this area, motile cells and sexual stages are absent from the water column and cysts are absent from the sediment Streamflow-induced variations in the location of the estuarine front in 1979 and in 1980 result in deposition of cysts in different regions predictable from examination of the location of the convergence Thus it IS proposed that the convergence zone of the estuarine front and the associated pycnocline serve to transfer encysting dinoflagellate forms from surface waters to their ultimate seedbed locations

Dinoflagellate resting cysts isolated from sediments in Marlborough Sounds, New Zealand

“…The deposition of cysts at estuarine fronts has been recorded by Tyler et al (1982) who suggested that the convergence zone of the estuarine front and associated pycnocline serve to transfer the encysting dinoflagellates from surface waters to their ultimate seedbed locations. A similar enhanced vertical transport may tie occuring in Kenepuru Sound at its confluence with Pelorus Sound (Bradford et al 1987) and this could be a contributing factor to the higher cyst concentrations in and around Kenepuru Sound Since both the total cyst numbers and the total number of cyst species present are greater in the inner Marlborough Sounds, possibly toxic species of dinoflagellate resting cyst are likely to appear in these areas in the future.…”

Analysis of the hydrographic conditions and cyst beds in the San Jorge Gulf, Argentina, that favor dinoflagellate population development including toxigenic species and their toxins

“…Dinocysts are comparable in size to medium-coarse silt particles and their hydrodynamic behavior is similar to that of other small sedimentary particles and thus become selectively concentrated in fine-grained sediments (Tyson, 1995). Previous work has demonstrated that the frontal regions encompass the location of peak cyst concentration and the examination of sediments underlying bloom areas indicated that the cysts seeding the bloom are not exactly within the bloom area (Tyler et al, 1982). At the Patagonian Shelf, Carreto et al (1998b) described an important concentration of A. tamarense cysts in the tidal front localized at Valdés Peninsula.…”

Dinoflagellate resting cysts as factors in phytoplankton ecology of the North Sea

“…In studies about the vertical distribution of cysts, the bulk was found to occur in the uppermost two to three centimetre sediment layer (Anderson et al, 1982;Tyler et al, 1982;White & Lewis. 1982;Nehring, 1994b, in press).…”

“…Temperature (Anderson, 1980;Anderson et al, 1985a), fight and oxygen are important factors that determine whether a newly-formed cyst will eventually germinate. When buried in deeper sediment layers by sedimentation or bioturbation (Anderson et al, 1982), cysts may contribute little to bloom initiation, due to anoxia and other inhibitory microenvironmental factors .…”

“…Each core was processed using a modified biological technique of Anderson et al (1982) and Matsuoka et al (1989) without any chemicals. The upper 2 or 3 cm of a sediment core was partitioned into 0.5 cm up to 1 cm depth, the rest in 1 cm horizontal intervals and mixed with filtered seawater.…”