2010 Volume 4 Pages 25-31
Submerged plant communities in Lake Izunuma-Uchinuma have declined drastically in the past 30 years and only isolated populations are now observed. We investigated the present status of submerged plant populations in Lake Izunuma-uchinuma and surrounding environments for 2008 and 2009. We found five species of submerged plants (Myriophyllum spicatum L., Ceratophyllum demersum L., Najas oguraensis Miki, Potamogeton octandrus Poir., and Hydrilla verticillata (L.f.) Royle). Ceratophyllum demersum and Myriophyllum spicatum were dominant in 2008 and 2009, respectively. Hydrilla verticillata, a dominant submerged plant in the past, was only found sporadically, and growth density of the species has declined greatly. Two stable populations of submerged plants were found in Izunuma, but no submerged plants were found in Uchinuma in 2009. There were no obvious pattern in underwater visibility of points with submerged plants, except these points have sandy floors. Based on the comparisons with previous investigations, submerged plant communities in Lake Izunuma-Uchinuma experienced both decline and changes of species composition, and further investigations about the causes should be considered.
