Regeneration of submerged macrophyte populations in a disturbed Lake Ontario coastal marsh

Previous studies in disturbed Great Lakes coastal marshes have determined that seed banks for submerged macrophytes tend to be depauperate if not absent. This was thought to be a major factor that would prevent the regeneration of macrophyte populations under improved conditions, so the transfer of seed or adult plants from healthy wetlands within the same region has been recommended as a restoration strategy. Cootes Paradise is a large, disturbed coastal marsh with a poor seed bank for submerged plants. In this report a large increase in submerged macrophyte population densities following the reduction of carp (Cyprinus carpio) densities from approximately 700 kg/ha in 1996 to 50 kg/ha in 1997 is documented. Much of this regeneration occurred in areas devoid of aquatic vegetation in 1996. It was determined that these plants developed from vegetative structures buried in the sediment. It is recommended that detailed surveys of both seed and vegetative propagule banks be undertaken before assessing the likelihood of the recovery of submerged macrophyte communities in disturbed coastal marshes.