HYDRODYNAMICALLY INDUCED SYNCHRONOUS WAVING OF SEAGRASSES - MONAMI AND ITS POSSIBLE EFFECTS ON LARVAL MUSSEL SETTLEMENT

Underwater observations of eelgrass (Zostera marina L.) beds at the mo uth of the Jordan River, Maine, USA, indicated that the eelgrass blade s gently undulated with low-amplitude movements under low current spee ds. When the above-canopy speeds exceeded 10 cm s(-1), dramatic large- amplitude waving of many blades in synchrony occurred. The eelgrass wa ving caused wide variability in horizontal water current speeds measur ed above the canopy. During three summers (1986, 1989, 1990), the blad e tips (distal 30 cm) had an average of about 3 x more recently settle d (plantigrade) blue mussels (Mytilas edulis) compared to regions lowe r (30-90 cm) on the blade. Because waving of seagrass blades results i n the blade tips moving through much more of the water column than low er regions of the blade and in enhanced turbulent mixing above the pla nt canopy, we hypothesize that such movements increase the likelihood of blade encounter with mussel larvae, and explain enhanced mussel abu ndances on blade tips. We further hypothesize that the enhanced mixing may direct larvae into seagrass beds generally. Large-amplitude, sync hronous waving of terrestrial grasses has been termed 'honami,' (Japan ese: ho = cereal; nami = wave) and has been shown to dramatically alte r aerodynamical conditions within and above the grass canopy. We sugge st that 'monami' (mo = aquatic plant) is important in coastal hydrodyn amics and has major implications for larval settlement and recruitment .