Abstract

Although Cladophora is associated with objectionable odors when it decomposes, submerged filaments are recognized to provide substrate for growth of epiphytic organisms (Stevenson Stoermer 1982). By analyzing for fucoxanthin, an indicator pigment for diatoms, we found that that specimens of Cladophora from Lake Ontario contained 38 mg fucoxanthin, or approximately 36 million diatoms, per g ww Cladophora: an abundant growth of the pennate diatom Cocconeis pediculus was confirmed by scanning electron microscopy. Similarly, epiphytic gastropods on the Cladophora were found to contain 29 mg/g fucoxanthin, and SEM images of tissue digests confirmed grazing on C. pediculus. Using Wezernak and Lyzenga’s data (1975) for the standing crop of Cladophora, and additional data for the abundance of planktonic diatoms in Lake Ontario, we estimate that epiphytic diatoms on Cladophora are approximately 4 percent of the planktonic diatom population. Similar calculations for Lake Erie suggest that epiphytic diatoms on Cladophora could be as much as 25 percent of the summertime planktonic diatom population. While these estimates contain uncertainties, they illustrate the value of improved measurements for submersed aquatic vegetation and epiphytic populations, to quantify their contribution to the food web.