Kayla Peirick, “Measuring Diatom Growth at Multiple Light Intensities”
Mentor: Carmen Aguilar-Diaz, Freshwater Sciences, Freshwater Sciences (School of)
Poster #152
Diatoms are a type of phytoplankton that grow well in the Milwaukee Harbor. They have an ornate external silicate (glass) frustule, and use triglyceride fats (oils) as ballast to counteract the weight of their glass house. The combination of containing oil and having high protein content makes diatoms nutritionally valuable primary producers and thus an important food source to support zooplankton communities and larval fish. Understanding how much growth diatoms are capable of in different conditions can be used to study the productivity of the Milwaukee Harbor and Lake Michigan fisheries. This experiment compared the growth of diatoms at different intensities of light to understand productivity of diatoms at different places in the water column. This experiment used Fragilaria, a species of diatom that forms long strands, which were isolated by MS Student Mary Larson from samples from the Milwaukee Harbor. Diatoms were added to 250ml polycarbonate bottles filled with a nutritious growth medium including added dissolved silicate. Growth at five levels of light were compared: Level 1 (L1) at 642 µEinsteins/m2/sec, L2 at 254 µEinsteins/m2/sec, L3 at 76.5 µEinsteins/m2/sec, L4 at 25.7 µEinsteins/m2/sec, L5 at 10.7 µEinsteins/m2/sec, and a dark group (DK). The lowest, L5, is similar to a brightly lit office, and full sun is about 2500 µEinsteins/m2/sec. Algal growth is being measured by analyzing progressive change of dissolved silicate in the growth medium, and by using chlorophyll as a proxy for biomass increase. This information is useful in understanding diatom growth as day length and light intensity change throughout the year. Field sampling of the harbor and lake includes taking light intensity measurements throughout the water column at different stations in the Milwaukee Harbor. The lab experiments are useful for interpreting observed light intensities and diatom density in the Milwaukee Harbor.