The Effects of Phosphorus Deficiency on Digestive Resistance and the Quality of Oocystis as a Food Source for Daphnia pulex x pulicaria
Abstract
Phosphorus limitation and predation are two factors that strongly influence algae. Some genera of green algae, such as Oocystis, have developed thickened cell walls and/or gelatinous sheaths that resist digestion. In certain strains of algae, phosphorus deficiency enhances digestion resistance, but results vary and sometimes contradict. This study utilized Daphnia juvenile growth assays to determine the relationship between phosphorus limitation and digestion resistance in Oocystis and to observe variation in digestion resistance among strains collected from different lakes in northeast Indiana. In Daphnia juvenile growth assays, Daphnia were fed algae grown in one of three treatments: phosphorus plentiful MBL medium or P+ (0.54 mg K2PO4), phosphorus deficient MBL medium or P- (no K2PO4 added), and phosphorus deficient MBL medium with a phosphorus supplement or P- w/ P (2 µ/L stock P) added immediately added before feeding. Only two strains of algae, Oocystis Shriner and Oocystis Simonton, show significant differences between treatments. The P+ treatment was significantly higher than the other treatments. All the strains, except Oocystis Crooked, had significantly longer mean length in the phosphorus plentiful treatment than the other two treatments. The phosphorus supplement did not increase mean growth or length indicating that the nutrient deficiency is due to digestion resistance. Two-way ANOVAs comparing between strains and treatments indicated that there was variation between strains in mean Daphnia growth and variation between strains and treatments in mean length. The lipid index did not indicate any differences between treatments. This study shows that phosphorus deficiency can enhance digestion resistance in Oocystis but the effects vary between strains.
Degree
M.S.
Advisors
Gillespie, Purdue University.
Subject Area
Biology|Ecology|Aquatic sciences
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