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Terry was Dr. Peard’s first graduate student to work on C. sowerbii. The following abstract is from Terry’s thesis, Variable Polyp Feeding and Dispersal of Frustule Larvae of the Freshwater Hydrozoan, Craspedacusta sowerbii.
Asexual proliferation is believed to be the primary mode of reproduction contributing to the distribution and abundance of polyp colonies within populations of Craspedacusta sowerbii. However, little is known about the settlement behavior of C. sowerbii larvae and the factors that affect dispersal.
C. sowerbii polyp colonies incorporate energy reserve material from feeding into asexual larvae (frustules). A study was conducted that examined the distance over which C. sowerbii asexual larvae disperse in relation to colony feeding. Feeding rates were manipulated to test the hypothesis that increased polyp feeding results in frustule larvae that travel farther distances. Increased polyp feeding is thought to increase energy reserves allocated to frustules.
Colonies were fed within four schedules that ranged from high to low feeding. The resulting frustules were observed and their positions were recorded at 1 hr intervals from the time of liberation from the colony to the time of settlement. True distance traveled over the course of dispersal (total distance), shortest linear distance from the origination point to settlement point (actual distance), and path linearity were calculated from the dispersal paths.
Frustules released from heavily fed colonies traveled greater total distances than frustules from the least fed colonies (p.05). Mean total distance traveled for heavy feeding was 71 +/- 12.35 mm (mean +/- 1 s.d.) while mean total distance traveled for low feeding was 45.1 +/- 16.49 mm. Actual distance traveled did not differ among the feeding regimes. Total distance traveled and actual linear distance were positively correlated (r = 0.445, p = 0.056).
The results suggest that frustule larvae produced from heavily fed polyp colonies have the potential to disperse greater distances from parent colonies. However, the settlement distances recorded did not reflect this potential. Several factors contributed to the observed results including the low linearity of dispersal paths, the possible presence of chemical settlement inducers, and the lack of distinction between feeding schedules due to short larval production time.
The picture above shows Joy doing on-site water chemistry anaylsis for her thesis. The following abstract is from Joy’s thesis, Habitat Characterization of the Freshwater Medusa, Craspedacusta sowerbii.
The freshwater medusa, Craspedacusta sowerbii, is not a rare species in Pennsylvania’s watersheds. At least 95 bodies of water in Pennsylvania have at one time been inhabited by this species. Although C. sowerbiiis not a rare species in Pennsylvania, its appearance in these bodies of water is often very sporadic. This sporadic appearance may be due to chemical or physical properties of these bodies of waters. The purpose of this study is to determine the chemical and physical parameters accompanying the presence of C. sowerbii medusae.
Select chemical and physical parameters from bodies of water which have been inhabited with C. sowerbii were compared to the same parameters from sites which have not been known to be inhabited by C. sowerbii. Discriminant function analysis (DFA) showed that medusa sites could be predicted using the parameters measured with 97.37% accuracy. This indicates that medusae populations may be distributed according to select chemical and physical characteristics of bodies of water. According to multivariate stepwise DFA, chloride is the most important component in distinguishing medusa from non-medusa sites. Medusa sites in this study have significantly lower chloride levels (t = -3.73, p = 0.000) than non-medusa sites.
These results do not directly support the hypothesis that C. sowerbii is a “hard water species”. No significant difference was found between the mean values of total hardness at medusa and non-medusa sites (t = -0.44, p = 0.659). However, both mean values of total hardness do indicate that the medusa and non-medusa sites contain moderately hard water, (81.57 ppm and 92.06 ppm respectively). Therefore, this study can not accept nor reject the hypothesis that C. sowerbii requires hard water to complete its life cycle.
The results of this study do not indicate that an increase in temperature stimulates the production of medusa in the sites studied. No significant difference was found between the water temperature during the first analysis compared to the water temperature of the second analysis (t = -1.95, p = 0.061) at the medusa sites. In addition, no significant difference was found between the total number of plankton/m3 during the first analysis compared to the total number of plankton/m3 during the second analysis at the medusa sites. This indicates that an increase in the total plankton does not stimulate the production of medusa in the site studied.
Michael was Dr. Peard’s fourth graduate student. The following abstract is from Michael’s thesis, The Effects of Calcium and Water Hardness on the growth and bud production of the freshwater hydrozoan, Craspedacusta sowerbii.
This study reports on the effects of different calcium concentrations and associated water hardness levels on the growth and bud production of the freshwater hydrozoan, Craspedacusta sowerbii. Four calcium treatments (low, moderate, high, and very high) contained increasing concentrations of CaSO4.2H2O; a treatment containing no calcium sulfate served as a control. Two additional controls included a sulfate control and a calcium chloride control. The calcium hardness, total hardness, and alkalinity, as well as the sulfate and chloride concentrations of each treatment and control were measured after the solutions were prepared and the pH adjusted.
Each replicate, 12 per treatment, consisted of a 60×15 mm Petri dish containing one C. sowerbii colony and 20 mL of the appropriate treatment water. Colony growth and bud production data were collected for 12 weeks and analyzed using a Between-Within Two-Factor Mixed Design Repeated Measures ANOVA; colony survival was analyzed using a Two-Way Chi-Square.
Results suggest that the polyps of C. sowerbii require calcium in their culture water for nematocyst discharge. However, the effects of higher calcium concentrations (and water hardness) on the hydroid of C. sowerbii were not statistically significant. The growth of colonies, as measured by the number of polyps per colony per week, and frustule production were not affected by calcium concentration. These results suggest that the distribution and asexual reproduction of the hydroid stage of C. sowerbii are not affected by calcium levels and water hardness. Greater colony survival and frustule production were achieved when the calcium source was calcium sulfate dihydrate rather than calcium chloride. Although medusa production was not significantly different among the calcium treatments, two treatments with the greatest calcium concentration did produce the most medusae.
Jason conducted extensive field collections of Craspedacusta, diligently built a comprehensive literature file related to Craspedacusta, and established our first jellyfish web site. Jason’s laboratory research focused on the molecular variations among separate populations of the freshwater jellyfish Craspedacusta throughout the United States and from several foreign countries and between Craspedacusta sowerbi and Limnocnida sp.