SUBMARINE POLLINATION IN THE MARINE ANGIOSPERM ZOSTERA-MARINA (ZOSTERACEAE) .2. POLLEN TRANSPORT IN FLOW-FIELDS AND CAPTURE BY STIGMAS

Flow chamber observations of the filamentous pollen of Zostera marina L. (Potamogetonales) revealed that pollen rotated and moved toward inf lorescences where they were captured by stigmas. The mechanics of this abiotic pollination process were examined and found to be related to the flow environment around emergent flowers. The translational moveme nt of pollen was imparted by the advection of the fluid (e.g., pollen kinetic energy, K, ranged from 0.8 x 10(-14) to 2.4 x 10(-14) J, and t he average K of the fluid was approximate to 0.7 x 10(-14) J), while t he rotational motion was imparted by the fluid shear stress (tau) with in the velocity gradient (e.g., pollen shear stress, sigma(t) = omega mu where omega is the rotational velocity and mu is the dynamic viscos ity, ranged from 3.4 x 10(-4) to 26 x 10(-4) Pa, and the average fluid shear stress was tau approximate to 10 x 10(-4) Pa; Ackerman, 1997, A merican Journal of Botany 84: 1099-1109). These results indicate that there is a greater potential for pollination by filamentous pollen rel ative to spherical pollen. Functionally, while spherical pollen needs to be directly upstream from stigmas to be captured, filamentous polle n need only be in the vicinity of inflorescences and flowers to be cap tured by stigmas. Thus, in addition to direct interception on stigmas, filamentous pollen can be captured while they rotate past flowers or when they are redirected through the velocity gradient towards flowers . Filamentous pollen is an adaptation to submarine pollination in seag rasses.