Question

what helps vallisneria survive under water

Answer 1

Underwater grasses or submerged aquatic vegetation (SAV), they improve water quality by reducing erosion, trapping loose sediment and absorbing nutrient pollution. During photosynthesis, they add the dissolved oxygen to the water underwater critters need to survive.
Vallisneria (named in honor of Antonio Vallisneri) is a genus of freshwater aquatic plant, commonly called eelgrass, tape grass or vallis. The genus is widely distributed in tropical and subtropical regions of Asia, Africa, Europe, and North America.
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