Biology Theses and Dissertations
Permanent URI for this collectionhttp://hdl.handle.net/1903/2749
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Item Effects of Salinity on Settlement and Metamorphosis of the Eastern Oyster (Crassostrea virginica)(2016) Priester, Anna Priester; Meritt, Donald W; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The eastern oyster (Crassostrea virginica) is a euryhaline species known for its historic populations, valuable fishery, and ecological importance. One of the most critical periods in the oyster’s life cycle is its transition from a free-swimming pelagic larva into its sessile benthic form. Despite the importance of this transition, which includes attachment to a substrate (settlement) and metamorphosis into the juvenile, our understanding of salinity tolerance during these processes is limited. This study was designed to quantify the effects of salinity on settlement and metamorphosis and to determine if those effects were influenced by the salinity in which the larvae were reared. Multiple cohorts of pediveliger larvae from hatcheries grown in Low (10), Medium (15-16.5) and High (22-27.5) salinities were allowed four days to settle in twelve salinity treatments ranging from 5 to 35. A set of additional experiments was extended to 14 days to investigate if the settlers were also able to complete metamorphosis and demonstrate juvenile growth within the same range of salinities. Settlement consistently occurred all tested salinities (5-35), indicating that pediveliger larvae can adapt to a broader salinity range than described in previous research. Highest settlement rates were achieved in treatment salinities between 11 and 30 for all three larval groups. Settlement performance outside that optimal range was highest for the larvae group reared in salinities closest to those extremes. Settlers from the 14-day experiments demonstrated metamorphosis and high post-settlement survivorship in all salinity treatments, but juvenile growth rates were reduced in salinities less than 9 and above 30. This highly repeated study reveals the impressive capacity for pediveliger larvae to tolerate a wide range of salinities and has direct implications for oyster aquaculture and our understanding of natural recruitment.Item RELATIONSHIPS BETWEEN LARVAL MORPHOMETRICS AND SETTING EFFICIENCY IN THE EASTERN OYSTER, CRASSOSTREA VIRGINICA(2009) Vlahovich, Emily Ann; Meritt, Donald W; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)In oyster hatcheries, the decision to move larvae from rearing tanks to setting tanks is based on physical and behavioral characteristics. These criteria can suggest conflicting action and a more reliable method may result in higher spat production. I observed hatchery reared Crassostrea virginica larvae, beginning with larvae retained on a 200 µm sieve. Aliquots of larvae were measured or placed in a setting vessel, and the remaining were returned to the culture cone daily. Each day had an associated setting efficiency, loss, and set of larval morphometrics, including shell height and length and eyespot diameter. Day was most strongly correlated with setting efficiency. Eyespot diameter was moderately correlated with setting efficiency, and shell morphometrics were weakly correlated with setting efficiency. I estimated daily spat production, which peaked on day 2. These results suggest spat production may be increased by altering current hatchery methods to consider eyespot diameter or days past retention on a 200 µm sieve when deciding to place larvae in setting tanks.Item CHEMICAL INDUCTION OF SETTLEMENT IN LARVAE OF THE EASTERN OYSTER CRASSOSTREA VIRGINICA (GMELIN)(2009) Grant, Melissa; Meritt, Donald W.; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Although numerous studies have been conducted to examine the effects of neuroactive compounds on bivalve larvae, few have identified chemicals capable of inducing settlement behavior in the eastern oyster Crassostrea virginica. In this study, I treated competent C. virginica larvae with select chemicals to identify those which are capable of inducing settlement behavior at an average salinity of 9.6 (±0.1). The compounds γ-aminobutyric acid and acetylcholine chloride, both at 10-4M, did not significantly increase the percentage of larvae exhibiting settlement behavior. As compared with the control, a significant increase in settlement behavior was induced by treatment with 3-isobutyl-1-methylxanthine, 5-hydroxytryptamine, and L-3, 4-dihydroxyphenylalanine all at 10-4M, as well as ammonia as a solution of 7.9mM NH4Cl (pH=8.0). These findings differ somewhat from the results of similar studies involving other species in the Crassostrea genus and may be of value to hatchery personnel or researchers interested in the chemical induction of settlement behavior in the eastern oyster.