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Ulva spp., Kornmania sp., and Ulvaria sp. (Sea lettuce)
Copyright © 2006 Jan Holmes
Species of sea lettuce form light yellowish green to dark green sheets and are common to our area and most shorelines around the world. They inhabit the mid to subtidal forming individual sheets up to one meter long in some species. Sea Lettuces can be found attached to a hard substrate or free floating in quiet bays. Mature species are either one or two cell layers thick.
A microscope is required for positive identification, but morphological features of some species can help narrow the possibilities: Kornmannia is just one cell thick. It lives epiphytically on seagrasses and other seaweeds. Ulva spp. are two cell layers thick. Numerous species of Ulva are found in our area but one speces, Ulva fenestrata, is perforated with small holes and easy to identify. Ulvaria spp. begins growth as a collapsed hollow sac two cell layers thick, which later splits open to form sheets one cell thick. Ulvaria has a chemical in its tissues that turns dark green when dried; a feature which may help you pick it out during sunny days of low tide exploration. Lively debate among phycologists continues over where species in these genera belong taxonomically, so don’t be discouraged if you can't pin down a positive identification.
Sea lettuces are opportunistic species that can form massive blooms when conditions are right. As the bloom spreads and begins to die, it can deplete an area (and all of the bottom dwelling plants and animals that live there) of oxygen, and cause massive die-offs of fish and invertebrates. Non-point source pollution including nutrient runoff from agricultural lands and over-fertilized urban and rural sites are thought to be a contributing factor in sea lettuce blooms.
This
page was created by Jan Holmes on 8/19/06.
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