| The green algal genus Cladophora Kutz. forms conspicuous nearshore populations in marine and freshwaters worldwide, commonly dominating periphyton communities. Cladophora has previously been characterized as an autogenic ecological engineer because its complex structure fosters functional and taxonomic diversity of benthic microfauna. In Chapter 1, we assemble evidence that Cladophora's structure likewise supports functional and taxonomic diversity of epiphytic microorganisms, and show that this alga exerts previously under-appreciated allogenic impacts on littoral biogeochemistry by influencing phosphorus and carbon cycling. Cladophora produces substantial amounts of sequesterable carbon in the form of highly crystalline, degradation-resistant cellulose (Chapter 2) We determined percent dry weight of cellulose from replicate collections of Cladophora glomerata-dominated periphyton made weekly from Lake Mendota, Dane Co., WI, from early July though mid-October of 2011, finding that that community cellulose content can exceed 40%, the mean for the entire sampling season was 26.2%, and that all but the final sample exceeded 15% cellulose. We used these data to conservatively estimate the amount of periphytic cellulose produced annually in Lake Mendota as between 97.8 X 10 6 and 36.7 X 106 kg. Additional carbon cycle impacts include vast quantities of sequesterable hydrocarbon generated by enormous populations of epiphytic diatoms (Chapter 3) that characteristically occupy Cladophora's huge surface area. We estimated the amount of 16:1 fatty acids produced in Lake Mendota annually by Cladophora-associated periphytic diatoms to be 3,000-80,000 kg in 2009 (survey period from early June through early December) and 700-7300 kg in 2010 (survey period one month shorter, from early June through late October). Finally, in a pyrosequencing study of Cladophora-associated bacteria, we identified more than 110 bacterial genera at the 80% confidence level without finding evidence for the presence of E. coli or related pathogens. We demonstrated that replicate community samples were similar and that community composition changes during the growth season. |
