Theses and Dissertations

Defense Date

1998

Document Type

Dissertation

Degree Name

Ph.D. Oceanography/Marine Biology

Department

Oceanographic Center

First Advisor

Gary S. Kleppel

Second Advisor

Richard E. Dodge

Third Advisor

Mahmood Shivji

Fourth Advisor

Nancy Marcus

Fifth Advisor

George McManus

Abstract

The objectives of this study were (1) to survey the percent hatching success of eggs produced by calanoid copepod species from a variety of ecosystems (i.e., polar, temperate, and sub-tropical), (2) to describe the relationship between egg production, hatching success of Acartia tonsa and the physical and food environments of Florida Bay, and (3) to describe the relationships between hatching success and maternal diet. In order to fulfill the first objective, an incubation system was designed to allow the monitoring of eggs at sea for extended periods of time. The second objective was addressed with a series of egg production experiments with the copepod Acartia tansa from Florida Bay. Egg production and hatching success were compared to seasonal changes in the food environment. The third objective was addressed by experiments conducted with cultured Acartia tonsa offered microencapsulated artificial diets, which differed in nutrient concentration and composition (protein:carbohydrate:lipid).

Experiments in the field were conducted between December 1993 and June 1996 and included eight species from six locations (Weddell Sea: Calanoides acutus, Calanus propinquus, Metridea gerlachie; Irish Sea: Acartia clausi, Temora longicornis; Gulf of Mexico: Temora stylifera, Undinula vulgaris; Port Everglades, Florida: Acartia tonsa; Florida Bay: A. tansa). No pattern was evident in hatching success between species from the various locations, because percentages were often highly variable (ranges as wide as 0% to 100% for one experiment) among individuals of the same species. A. tonsa was the exception, in that individual variability was usually low 90% in the summer and fall. The hatching success of eggs produced by A. tonsa from Florida Bay, however, did not vary seasonally. Hatching success was generally >80% throughout the year. Egg production rates in Florida Bay, like hatching success, did not vary seasonally. Mean egg production varied among sampling sites; however, differences among the hatching success means determined at the four sites were not significant.

Egg production rates for A. tonsa in Florida Bay were low compared to other locations. A temperature dependent growth model overestimated egg production rates in Florida Bay. Principal components analysis revealed possible relationships between egg production, hatching success, and microzooplankton biomass. Microflagellate, dinoflagellate, and microzooplankton biomass, in combination with temperature or salinity were the best predictors of egg production and hatching success at the individual sites. The lack of consistency among sites may have been due to differences in environmental conditions at the sites, which in turn, could have affected the biochemical composition of the algae and their grazers.

Artificial diets, microencapsulated in a Ca-alginate matrix, were developed to determine the relationships between maternal diet and hatching success. Artificial diets are less variable than natural diets. Cultured animals were used to reduce age and genotype variability. An experimental microencapsulated diet ("Basic" diet) was designed to support egg production with hatching success similar to that of eggs produced on a mixed algal diet. Attempts to produce the experimental diet were only partially successful. Egg production rates were low < 10 eggs female-1 d-1), but hatching success was high (>80%). The "Basic" diet was subsequently modified to determine the effects of nutrient concentration and composition on egg production and hatching success. The mean hatching success of eggs produced by copepods offered the "Reduced Basic" diet (overall nutrient reduction) was lower than that of eggs produced on the "Basic" experimental diet while there was an increase in the variability. Neither egg production nor hatching success increased significantly when the particle concentration of the "Reduced Basic" diet was doubled to approximate the nutrient concentrations provided by the "Basic" experimental diet. The percent hatching success of eggs produced on the "Reduced Lipid" diet was significantly lower than that on the "Basic" diet. The mean hatching success of eggs produced on the "Reduced Protein" diet was lower than the hatching success of eggs produced on the "Basic" diet, but the difference was not significant.

The lowering of hatching success resulting from the reduction of dietary lipids may be associated with the order in which nutrients are used for energy (i.e., crustaceans will use carbohydrates and then lipids as an energy source, resorting to proteins when there are insufficient quantities of the other nutrients) in combination with lipids required for egg production. The variable hatching success measured in the field may be the result of the combined effects of the unknown age of the animals used in the experiments, time elapsed from the last mating, the nutrient composition of the diet and the degree to which a species utilizes it body stores (which are affected by past feeding history) for egg production.

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