Removal of Sea Lettuce, Ulva spp., in Estuaries to Improve the Environments for Invertebrates, Fish, Wading Birds, and Eelgrass, Zostera marina

摘要

Mats (biomasses) of macroalgae, i.e. Ulva spp., Enteromorpha spp., Graciolaria spp., andCl&dophoraspp., have increased markedly over the past 50 years, and they cover much larger areas than they once did in many estuaries of the world. The increases are due to large inputs of pollutants, mainly nitrates. During the warm months, the mats lie loosely on shallow sand and mudflats mostly along shorelines. Ulva lactuca overwinters as buds attached to shells and stones, and in the spring it grows as thalli(leaffronds). Mats eventually form that are several thalli thick. Few macroin-vertebrates grow on the upper surfaces of their thalli due to toxins they produce, and few can survive beneath them. The fish, crabs, and wading birds that once used the flatsto feed on the macroinvertebrates are denied these feeding grounds. The mats also grow over and kill mollusks and eel-grass, Zostera marina. An experiment was undertaken which showed that two removals of U. lactuca in a summer from a shallow flat in anestuarine cove maintained the bottom almost free of it.