The response of Lake Michigan benthic algae to an in situ nutrient manipulation

TitleThe response of Lake Michigan benthic algae to an in situ nutrient manipulation
Publication TypeThesis
Year of Publication1985
AuthorsJr. HJCarrick
DegreeMaster of Science
Number of Pages86 pp.
UniversityBowling Green State University
CityBowling Green, OH

The idea that Lake Michigan phytoplankton become secondarily growth-limited by silicon, following enrichment with phosphorus, has been well established. Conversely, the possibility that Lake Michigan epilimnetic, benthic algae are growth-limited by silicon is virtually unstudied, and was explored in the present experiment using nutrient-releasing artificial substrates (NRS). Treatments consisted of Si, N+P, Si+N+P, and controls (CONT). Forty-eight NRS were placed in Little Traverse Bay, Lake Michigan, at a depth of 10 m using SCUBA. Four replicate NRS of each treatment were sampled after 7, 14, and 31 days of exposure. Algal biomass as estimated by chlorophyll-a, particulate silica, and total biovolume increased through time (P < 0.0001, for each). Chlorophyll-a was greatest on Si+N+P and N+P substrates compared to Si and CONT substrates (P<0.0001). Particulate silica was greatest on Si+N+P followed by N+P and was lowest on Si and CONT substrates (P<0.0001). Estimates for total biovolume were different among all four treatments, with the means ordered from highest to lowest as Si+N+P, N+P, Si, CONT (P<0.0001). Communities on CONT and Si substrates were composed primarily of diatoms (98%) and changed little, in terms of biomass, throughout the study. The algal biovolume on N+P and Si+N+P substrates increased nearly 9-fold over the controls and consisted primarily of the green alga Stigeoclonium tenue and the blue-green alga Schizotrhrix calcicola. In addition, diatom biovolume was highest on Si+N+P substrates throughout the experiment (P<0.0001), and increased 2-fold on Si+N+P substrates by day 31, consisting chiefly of Achnanthes minutissima (38.9%) and Cocconeis placentula (29.1%). The lack of response to enrichment with Si alone and highest accumulation of chlorophyll-a, particulate silica, total biovolume, and diatom biovolume on Si+N+P substrates suggests that Si may become an important factor to benthic algal growth following enrichment with N+P. Furthermore, a similar shift from a diatom to a green and blue-green dominated algal community has been observed for upper Great Lakes phytoplankton following N+P enrichment, demonstrating the possibility that both communities are structured by comparable nutrient processes. Lastly, the response of algal communities to nutrient addition may be characterized by the reaction of a very few species or guilds of species.