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search.filters.applied.f.advisor: Yen, Jeannette × search.filters.applied.f.resourcesubtype: Dissertation ×

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Crustacean Behavior and Morphology in Low and Intermediate Reynolds Number Environments

2022-05-02 , Ruszczyk, Melissa

An organism’s physical environment can dramatically affect an organisms’ behavior and morphological design. The Reynolds number represents the ratio between inertial and viscous forces in a fluid environment. This study is concerned with the challenges crustaceous plankton face resulting from living in a low- and intermediate-Reynolds number aquatic environment. In the first part of this study, the freshwater copepod Hesperodiaptomus shoshone is exposed to a Burgers vortex- a flow feature meant to mimic turbulent eddies found in an organism’s environment. Male and female copepods were exposed to four vortex intensity levels plus a negative control in either a horizontal or vertical orientation of the vortex axis. Trajectory analysis of H. shoshone swimming behavior shows that this copepod changes its swimming behavior in response to vortex orientation and not vortex level- a notable difference from marine copepods exposed to the same flow feature. These results may be linked to ecological and geographic differences between freshwater and marine copepods. In the second part of this study, the pleopod synchrony in the mysid shrimp Americamysis bahia is quantified. Shrimp and krill beat their pleopods in an adlocomotory sequence, creating a metachronal wave. Usually, pleopod pairs on the same abdominal segment beat in tandem with each other, resulting in one 5-paddle stroke. Americamysis bahia’s pleopods on the same abdominal segment beat independently from each other, resulting in two 5-paddle metachronal cycles that run ipsilaterally along the body, 180° out of phase with each other. High-speed recordings of A. bahia stroke kinematics reveal how this mysid changes its stroke amplitude, beat frequency, and inter-appendage phase lag to achieve high speeds. Trends with Strouhal number and advance ratio suggest that the stroke kinematics of metachrony in A. bahia are tuned to achieve large normalized swimming speeds. In the third part of this study, stroke kinematics in Pacific krill, Euphausia pacifica, are quantified for the first time. Euphaisia pacifica (1-3cm body length) achieve similar swimming modes as the larger E. superba (4-6cm body length) through a different set of stroke kinematics. To better understand the relationship between stroke kinematics, resulting swimming mode, and length scale, these data are used in tandem with previously published stroke kinematics of other 5-paddle metachronal swimmers, including mysid shrimp and stomatopods, to identify broad trends across species and length scale in metachrony. Principle component analysis (PCA) reveals trends in stroke kinematics, Reynolds number, and swimming mode as well as variation among taxonomic order. Additionally, uniform phase lag, i.e. when the timing between power strokes of all adjacent pleopods is equal, in 5-paddles systems is achieved at different Reynolds numbers for each swimming mode, which highlights the importance of taking into consideration stroke kinematics, length scale, and resulting swimming mode in bio-inspired design applications.

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Risk and resources in the plankton: effects on copepod population growth and zooplankton community dynamics

2012-07-03 , Lasley, Rachel Skye

The focus of my thesis research is on the interplay between individual behavior, population dynamics and community-level processes within zooplankton communities in coastal Maine. The target organisms of my thesis work are marine copepods. Copepods are small (1-10 mm) crustaceans that perform the essential ecosystem function of consuming and assimilating primary production (phytoplankton) making it available to higher trophic levels such as commercially important fishes. Therefore, copepod population growth is of critical importance to marine food webs. Fertilization limitation has been suggested as a constraint on copepod population growth but field surveys describing the prevalence of fertilization limitation are lacking. During my doctoral research, I explored the in situ fertilization success of two marine copepod species, Temora longicornis and Eurytemora herdmani in coastal Maine. I collected monthly zooplankton samples and analyzed clutches from field-caught females using an egg-staining technique. My results indicate that both species exhibit fertilization limitation in nature and the factors correlated with their fertilization span population, community and ecosystem level factors. To determine a causal relationship between predator density and copepod mating success, I conducted laboratory experiments to assess the effects of a common mysid shrimp predator, Neomysis americana on Eurytemora herdmani mating success. I subjected males and females to predators or predator cues. I found that the presence of a mysid predator, or only a predator cue, reduced copulation frequency and spermatophore transfer leading to a 38-61% decrease in E. herdmani nauplii production. These results suggest that mysid predators can constrain copepod population growth through non-consumptive processes. To determine the effects that resources can impose on copepod behavior, I explored the behavioral and fitness consequences of Temora longicornis ingesting Alexandrium fundyense, a phytoplankton species that forms harmful algal blooms in coastal Maine. My results suggest that ingesting A. fundyense causes copepods to swim faster and with more directional persistence compared to control algae. Temora longicornis increased their average swimming velocity by 24%, which leads to a 24-54% increase in their theoretical encounter rate with predators. Therefore, these findings suggest behaviorally mediated copepod-algal interactions may have significant impacts on harmful algal bloom dynamics and the fate of toxins in marine food webs.

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