Our Students and Their Research

The occurrence of bacterial clumping in marine systems was investigated as related to the presence of flagellate predators. The factors of movement, bacterial concentration, and flagellate species were included in this investigation. The flagellate Bodo parvulis was found to cause clumping in a strain of bacteria isolated from Canary Creek in Lewes, Delaware. The role of Bodo was explored in the clumping process with specific regard to exopolymer secretions and the trophic dynamics possibly affected by them.

An investigation of ingestion rates of the estuarine and calanoid copepod A. tonsa in mesocosms of differing scales was completed. The gut florescence method was used to determine levels of gut fullness and this value was used in the empirical formula of Dam and Peterson (1988) to determine ingestion rates. Results suggest that scale does not affect rates of ingestion in A. tonsa, however, the effect of scale may be apparent in lower trophic levels, which is reflected in the trophic behavior of A. tonsa.

Estimates of maximum consumption of fish are important because they provide a necessary component to mass balance bioenergetics models which define the growth of fish as the difference between energy input (consumption) and energy loss (egestion, excretion, and metabolism). In this study, I conducted laboratory experiments to examine the maximum consumption rate of white perch (Morone americana) as a function of fish size and water temperature. The experiments were performed at four different temperatures (27.5, 25.1, 18.5, and 15.4°C at eight size groups (mean weights 0.92, 1.36, 1.78, 15, 25, 43, 80, and 152 g) of fishes. The results indicate that maximum consumption rate per unit weight for white perch decreases as fish weight increases, and increases as temperature increases. The highest maximum consumption rate (0.42 g/g/day) was fir the young of year fish at 25.1°C, and the lowest peak rate (0.04 g/g/day) was for the adult white perch at 18.5°C.

A new method was developed for studying the effects of nitrate and acetate addition in stimulating denitrification in brackish pond sediment. This was done using an air tight flow through core system and measuring N₂ gas evolution using a membrane inlet mass spectrometer. The experimental design allowed for direct measurement of denitrification without the use of inhibitors nor significant altering on dissolved gases. It was determined that nitrate concentration had a direct effect on dissolved gases. It was determined that nitrate concentration has a direct effect on the denitrification process as shown by the immediate increase in N₂ production. It also was found that there was no coupling between oxygen consumption and nitrogen evolution. The comparison to published values indicated that this direct, immediate measurement method gave similar denitrification results with better replicability. These experiments showed that the method had high precision, reliability, and rapid analysis. It also could be done with a small volume of sample.

The impact on microoganisms (<1.6 microns) of alachlor in varying concentrations was investigated during the summer in closed system batch incubations.  Micrroorganisms in water filtered from the Patuxent River at the Chesapeake Biological Laboratory were exposed to alachlor at concentrations ranging from 0.002 to 20.0 mg/L along with controls in replicate BOD bottles and incubated for five days during each of three experiments.  Microorganism concentrations and dissolved oxygen remaining were measured at the end of the incubations.  Gas chromatograph analysis was performed to determine the final concentration of alachlor in one of the samples.  Alachlor had a significant effect on both factors at the 20.0 mg/L concentration in the second experiment and at the 2.0 mg/L concentration in the third one, however each effect was the opposite of that in the second experiment.  A negative relationship between microorganism concentration and total community respiration was noted in two experiments. The explanation for the observed results is elusive due to possibly varying effects on genera of microorganisms within the examined assemblages.  An almost total loss of initial the initial amount alachlor was noted in the sample quantified at the end of the incubations.

Since the discovery and subsequent acceptance of the microbial loop. Scientists have been working to understand its role in the movement of carbon within the marine ecosystem. The following study is a further attempt to define the relationships of the microbial loop by testing for the ingestion of fluorescently labeled bacteria (FLB's) by the mixotrophic dinoflagellate Gymodineum sanguineum. Feeding experiments were run to test for grazing rates; the G. sanguineum did not ingest the FLB's. Next, feeding experiments were done using the ciliate Uronema marinum, the flagellate Paraphysomonas sp., and natural samples. The FLB's were ingested by the ciliate. In summary, FLB's were not ingested by Gymnodineum sanguineum, however, they were edible as proven by their ingestion by the ciliates.

Larval Gobiosoma bosc were stocked at densities of 4/l in 1, 2, 10, 50, 100 and 150 l tanks and reared for 20 d to determine effects of tank size on their survival, growth, and production. Survival, growth and production were dramatically affected by tank size. Tank size effects were most pronounced when comparing larvae reared in ≤ 10 and ≥ 50 l tanks. The instantaneous mortality coefficient was 10 times lower in the 50 l tank than in the 10 l tank. The instantaneous growth coefficient was 1.5 times greater in the 50 l tank than in the 10 l tank. Gross production was more than 7.5 times higher and net production was more than 11 times higher in the 50 l tank than in the 10 l tank. Tank size had no apparent effect on production of dynamics of larval Gobiosoma bosc in tank sizes <50 l. Scaling relationships were developed to predict survival, growth, and production as a function of tank size and to project probable results in larger tanks or ecosystems. Tank size effects on larvae reared in tank sizes between 10 and 50 l and > 150 l still must be determined, and this research needs to be replicated to evaluate the accuracy of the models developed.

During the summer months from May to October, a shift in the size classes of Chrysaora quinquecirrha is observed. The gelatinous zooplankton in the early to mid summer consist of three classes, a small, medium and a large size class. By the end of August, a more moderate sized plankter has replaced these extremes of size previously seen. The question that this study hopes to address is: are there two distinct populations of C. quinquecirrha in the Bay at the beginning and end of the summer or only one population which undergoes degrowth during the summer. The hypothesis is that the larger sized sea nettles are undergoing a period of starvation. When the jellyfish starve, the medusa diameter is reduced. This catabolism could account for the lack of large size classes late in the summer. The delta 15N values should confirm that starvation is occurring; an increase in the delta 15N values should be observed. The definition of the C. quinquecirrha population as one distinct population rather than two calls for reevaluation of the food web of the Chesapeake Bay and a closer examination of nutrient cycling within the Bay.

The effect of cadmium, Iead, and mercury on calcium influx were measured in estuarine amphipods of the genus Gammarus (spp). Influx experiments involved 2 minute exposure to metal solutions of increasing concentration (0.5 - 100 mmol L^-1) that were made up in a ⁴⁵Ca labeled 0.07 mmol Ca L^-1 solution in 16 ppt seawater. Since trace metal effects on divalent regulatory mechanisms are greater in fresher water, it would be helpful to understand at what salinity these effects become important. Cadmium had no effect on the level of calcium influx. At the Iowest concentration of lead there was no effect on influx, but at increasing concentrations, the influx level experienced a downward trend. Mercury seemed to affect influx only at the highest concentrations, where influx seemed to increase.