SUBMARINE POLLINATION IN THE MARINE ANGIOSPERM ZOSTERA-MARINA (ZOSTERACEAE) .1. THE INFLUENCE OF FLORAL MORPHOLOGY ON FLUID-FLOW

An understanding of the process of submarine pollination should provid e insight into the evolutionary and reproductive ecology of the marine angiosperms (seagrasses). The flow around the reproductive organs of the seagrass Zostera marina L. (Potamogetonales) was, therefore, exami ned in a flow chamber. The phenological emergence of flowers during (1 ) pollen capture and (2) pollen release, and by fruit during (3) seed release, led to a reduction in flow rate toward the inflorescence. Thi s change in Row due to floral emergence was associated with a 50% incr ease in the fluid shear stress [tau = (2.2 +/- 0.3) x 10(-3) Pa for an immature flower vs. tau = (3.1 +/- 0.5) x 10(-3) Pa for a receptive f lower]. The Reynolds number (Re) and fluid shear stress around inflore scences and infructescences were comparable, indicating a dynamic simi larity in the processes of pollen capture and fruit dehiscence [Re = 4 7 +/- 5, tau = (1.6 +/- 0.3) x 10(-3) Pa for inflorescences; Re = 38 /- 5, tau = (1.3 +/- 0.1) x 10(-3) Pa for infructescences]. These resu lts indicate that the emergence of reproductive organs leads to change s in fluid shear stress, which will affect the release, transport, and capture of particles including pollen. Theoretical considerations of these observations using aerosol-filtration theory suggest that pollen capture in Z. marina occurs through direct interception of pollen by stigmas.