Aspects of sensory cues and propulsion in marine zooplankton hydrodynamic disturbances

The hydrodynamic disturbances generated by two types of free-swimming, marine zooplankton were quantified experimentally in the laboratory with a novel, infrared Particle Image Velocimetry (PIV) system. The study consisted of three main parts: (1) the flow fields of free-swimming and tethered Euchaeta antarctica were compared to determine the effects of tethering, (2) three species of copepods (Euchaeta rimana, Euchaeta elongata, and Euchaeta antarctica) that live in seawater in a range of temperatures (23 ºC - 0 ºC) and a corresponding range of fluid viscosity (0.97 - 1.88 mm2 s-1) were analyzed experimentally and with a computational fluid dynamics model (FLUENT) to assess the effect of size and fluid viscosity on the flow fields, (3) the flow fields were collected for individuals of two species of euphausiids (Euphausia pacifica and Euphausia superba) to compare the effect of size and Reynolds number on propulsion and the spatial extent of the flow disturbance. In addition to the measured flow fields around solitary krill, flow fields were collected around small, coordinated groups of E. superba to examine group sensory cues through hydrodynamics. In the first part of this investigation, it was determined that tethering zooplankton during data collection resulted in flow fields with increased asymmetry and larger spatial extent due to the unbalanced force applied to the fluid by the tether. In response to these findings, only flow fields collected for free-swimming organisms were used in the subsequent studies. In the second part of the study, the increase in viscosity between subtropical and temperate fluid environments in conjunction with increased size and species-specific swimming speeds resulted in similar Reynolds numbers among E. elongata and E. rimana (in both cruising and escaping modes). During cruising (Re ~10), the spatial extent of the copepod hydrodynamic disturbances and propulsion costs were similar between species. In the case of fluid distrubances of escape (Re ~ 100), the spatial extent and energetic cost were larger for the larger species ( E. elongata). In the third part of the study, the hydrodynamic disturbance produced by E. superba (larger krill species) was found to be longer in horizontal spatial extent and at scales more appropriate for communication within schools than the hydrodynamic disturbance produced by E. pacifica. However, the sensory cue in coordinated groups of krill was complicated by the interaction of multiple flow disturbance fields, which suggests that hydrodynamic cues between krill in groups are restricted to small distances. The energetic cost of propulsion was ten times greater for the larger species of krill, and energetic expenditure did not appear to decrease for krill swimming in coordinated groups.Ph.D.Committee Chair: Dr. Donald Webster; Committee Co-Chair: Dr. Jeannette Yen; Committee Member: Dr. Philip Roberts; Committee Member: Dr. Terry Sturm; Committee Member: Dr. Thorsten Stoesse

Geographical Assessment of Microalgae Biofuels Potential Incorporating Resource Availability

Previous assessments of the economic feasibility and large-scale productivity of microalgae biofuels have not considered the impacts of land and carbon dioxide (CO2) availability on the scalability of microalgae-based biofuels production. To accurately assess the near-term productivity potential of large-scale microalgae biofuel in the US, a geographically realized growth model was used to simulate microalgae lipid yields based on meteorological data. The resulting lipid productivity potential of Nannochloropsis under large-scale cultivation is combined with land and CO2 resource availability illustrating current geographically feasible production sites and corresponding productivity in the US. Baseline results show that CO2 transport constraints will limit US microalgae based bio-oil production to 4% of the 2030 Department of Energy (DOE) alternative fuel goal. The discussion focuses on synthesis of this large-scale productivity potential results including a sensitivity analysis to land and CO2 resource assumptions, an evaluation of previous modeling efforts and their assumptions regarding the transportation of CO2, the feasibility of microalgae to meet DOE 2030 alternative fuel goals, and a comparison of the productivity potential in several key regions of the US

An active learning environment to improve first-year mechanical engineering retention rates and software skills

This work proposes a foundational change from traditional lecture to an active learning environment in the Colorado State University First-Year Introduction to Mechanical Engineering course of 145 students. The goal of this approach is to improve computational capabilities in Mechanical Engineering and long-term retention rates with a single broad emphasis. Major and minor changes were implemented in the course, from specific day to day in-class activities to the addition of laboratory sessions to replace traditional classroom lecture. These laboratories of no more than fifteen students were delivered by Learning Assistants, which were upper-level undergraduate peer educators. To evaluate proficiency, a MATLAB post-test was delivered to students who were instructed through lecture only ( Lecture ) and those who were instructed with the above changes ( Active ). A survey was also provided upon completion of the course to the Active group for student reflection on their perceived software capability and the usefulness of approaches. Post-test results suggest that the Active group was more proficient in MATLAB than the Lecture group. Survey results suggest that the Active group recognize they had not achieved expert use of the software but that they were likely to use it throughout their careers and that all approaches were useful, in particular the use of Learning Assistants. Future longterm retention statistics will shed light on the possible effectiveness of this approach, which are currently unavailable

Pheromone Trail Following in Three Dimensions by the Freshwater Copepod \u3cem\u3eHesperodiaptomus shoshone\u3c/em\u3e

Finding mates can pose a particular problem for obligately sexual planktonic organisms, resulting in a variety of adaptations to ensure sufficient mating. Several types of mate-finding behavior have been observed in marine copepods, but the one most effective at low population density, following a pheromone trail, has not been observed in freshwater copepods. Using three-dimensional (3D) videography, we show that males of the large-bodied alpine species Hesperodiaptomus shoshone follow pheromones in the female\u27s trail. Using a trail mimic comprised of female-conditioned water, we found that males followed female scent without the presence of the female. This behavior was reduced when the female scent was diluted, suggesting that the male\u27s behavior can be modified by the intensity of the chemical signal. Analyses of the 3D trajectories of copepods that formed mating pairs indicate that the male does not make a direct approach to the female, as might be expected if he relied purely on hydrodynamic or visual cues. Instead, males that are \u3e0.5 cm from females react to crossing female trails by making an abrupt turn and spending more than 2 s following the female\u27s trail. Furthermore, flow field analysis showed that at this distance it was unlikely that copepods could distinguish the hydrodynamic signal from the background flow. This is the first demonstration of chemical trail following in a freshwater copepod and has important implications for encounter rates and viable population densities in similar species