termination of a bloom, dinoflagellates (especially Alexandrium species) undergo
sexual reproduction and the swimming zygotes form dormant cysts that can remain
viable in the sediment for years. Recurrent toxic blooms in the Gulf of Maine have
been a problem for a century or more. The main cyst seedbed is in the north-east part
of the gulf near the mouth of the Bay of Fundy. One long-standing dilemma about
these blooms is that the circulation patterns in the gulf are mainly to the west and
south (Fig. 3.20) and should create, in effect, a one-way transport system with limited
opportunity for cells to circulate back to the northeast. Anderson et al. (2005) and
McGillicuddy et al. (2005) hypothesized a resolution based on models of the
circulation patterns: cells accumulate in a retentive eddy near the mouth of the Bay of
Fundy, allowing cysts to be deposited in that area to reseed future blooms. Cells that
escape that retention zone into the eastern segment of the Maine Coastal Current
bloom farther downstream and form a second seedbed offshore of the Androscoggin
and Kennebec Rivers (Fig. 3.20). Germination of cysts in this second seedbed
propagates the species farther along the Maine coast.
Fig. 3.20 Conceptual model of A. fundyense cysts and motile cell dynamics in the
Gulf of Maine. Areas enclosed with dashed lines denote cyst seedbeds that provide
inoculum cells. Major current systems are shown with shaded arrows. The shaded
areas represent growth and transport of motile cells.
(^) (After Anderson et al. 2005.)