Meeting Abstract

24.6  Monday, Jan. 4  Cell motility, life stage transitions and cyst distribution of the harmful alga, Heterosigma akashiwo TOBIN, E.D.*; GRUNBAUM, D; CATTOLICO, R.A.; School of Oceanography, Univ. of Washington; School of Oceanography, Univ. of Washington; Depart. of Biology. Univ. of Washington etobin@u.washington.edu

In many harmful algal blooming (HAB) species, transitions between a vegetative, motile phase in the water column and a dormant, non-motile cyst phase in the sediments regulate the timing and location of bloom events. Many HAB species use motility during vegetative growth to control depth and locate favorable parts of their environment. We hypothesized that HAB species have distinct swimming behaviors during pelagic-benthic transitions, and that these behaviors facilitate deposition of cysts in shallow locations where survival and re-emergence are likely. We used video-based tracking to quantify cell swimming behaviors of H. akashiwo, a harmful marine flagellate, during the transition into resting cells. Cells were induced into the resting stage by subjecting them to low temperature (10°C) and darkness for 14 days. Our tracking methods provide detailed characteristics of individual cell swimming behaviors, including directionality, total speed, mean vertical and horizontal velocities, and oscillatory speed, which we used to assess physiological state and changes in motility during pelagic-benthic transition. Cells exhibited distinct swimming characteristics during transition, which can be used to determine timing and location of cyst formation. We did not observe downward swimming or active habitat selection. A simple 2D estuary model suggests that swimming during pelagic-benthic transition does not alter contact rates with shallow sediments compared to passive sinking, and that passive transport by turbulent mixing may be the primary determinant of accumulation in sediments, and consequently, potential for future HABs.