DISPERSAL, MOVEMENT PATTERNS, AND ANTENNA HYDRODYNAMICS OF ARTEMIA (ANOSTRACA) DURING DEVELOPMENT

Movement plays a significant role in organisms’ overall fitness as it is important for dispersal, escaping predators, feeding, and finding mates. Developmental changes add extra complexity regarding how an organism has evolved to move since changes in morphology and size may require different mechanisms of movement. Due to the physiological, morphological, and behavioral changes occurring during development, movement capacity, navigational capacity, and movement goals are dynamic. In other words, the parameters defining the movement are different at each life stage. Artemia, also known as brine shrimp, are planktonic crustaceans. Brine shrimp larvae pass through several life stages by adding new body segments and appendages in each molt as they grow to adulthood. The body size increases 20-fold, the swimming speed increases 5-fold, and the locomotory mode changes from antennae beating to metachronal paddling. In addition to morphological and locomotory changes, behavioral changes also occur in Artemia, especially after larvae start to feed and reach sexual maturity. All of these changes impact different aspects of movement, such as the hydrodynamics of the swimming appendages, their swimming patterns (i.e., the sequence of spatial positions of the organism in time), and their dispersal. In this thesis, I investigated the effects of developmental changes on the dispersal, movement patterns, and antenna hydrodynamics of Artemia.Chapter one provides an introduction to the developmental changes in Artemia and their potential impacts on Artemia’s movement. It gives an overview of the natural habitat of Artemia spp. before explaining the development challenges due to the morphological, physiological, and behavioral changes. Finally, it summarizes the background and goals for chapters two, three, and four.Chapter two examined the antenna hydrodynamics of Artemia larvae from early developmental stages. At the lower end of the intermediate Re regime (1 < Re < 20), organisms typically employ rowing propulsion using paired appendages or an array of appendages. To date, no study has investigated the antenna kinematics of Artemia over a range of parameters to assess how various kinematic parameters affect the resulting swimming hydrodynamics. In this chapter, we recorded the swimming motion of an Artemia nauplius under a light microscope and measured the kinematics of one of the antennae. We explored a range of parameters describing the antenna kinematics and Re and quantified the resulting flow fields using the 2D immersed boundary method. We found that the Artemia larva employs a sweep angle of around 3π/4 radians and a recovery angle of approximately π/2 radians. In addition, the antenna bends around the middle to reduce drag during the recovery stroke. These parameters do not necessarily maximize the spatially and temporally- averaged flux resulting from the motion of the antenna. However, the specific parameters fall in the parameter landscape such that increases in each parameter yield diminishing returns in terms of flux. Furthermore, flux increases and plateaus with Re. This coincides with the change of locomotory mode during the post-metanaupliar stage, where the larva starts to beat the thoracic legs together with the antenna.In chapter three, we investigated the movement patterns of plankton larvae during early develop- ment. Organisms perform various tasks while moving, such as searching for food and mates, avoiding predators, etc. In this chapter, we investigated the swimming behavior of Artemia at two different early developmental stages: nauplii, the non-feeding life stage, and metanauplii, the first feeding life stage. We analyzed their movement patterns by recording the swimming of Artemia larvae in 3D and identified a statistical distribution that describes their movement patterns. We found that both nauplii and metanauplii do a superdiffusive composite Correlated Random Walk (CCRW) with a diffusion coefficient changing from 1.62 to 1.70. according to the displacement analysis and ensemble variance of displacement curves. We proposed two non-mutually exclusive hypotheses to explain the unexpected movement patterns of nauplii: i) Nauplii perform a superdiffusive CCRW because it benefits subsequent life stages even though it does not affect the nauplii’s fitness, and/or ii) a superdiffusive CCRW pattern contributes to the overall fitness of nauplii by increasing the chance of finding a suitable ecological niche in their local environment, hence, increasing the survival chance.Chapter four provides an overview of our study to quantify and predict the dispersal of Artemia in complex flow environments. We used Artemia spp. larvae to experimentally quantify how the height and density of simplified beds of macrophytes alter the distributions of Artemia in flow. The results clearly show that both the average time to arrive in zone positions downstream of the macrophyte beds and the variance depend strongly on the density of the macrophytes. Macrophyte height has a weaker effect on arrival times, likely because the brine shrimp are injected near the bottom of the tank where differences in flow speeds are negligible. Finally, the downstream arrival times are a non-monotonic function of the effective diffusivity of the agents. This study highlighted the strong effect of macrophytes, natural and artificial reefs, and other structures on plankton retention time. Furthermore, dense, tall structures may create slow-flow regions downstream that could also shelter plankton.Chapter five is the concluding chapter, where the thesis research findings are summarized and put into the context of the biology of Artemia and other organisms. The results are evaluated in separate sections for each chapter. The limitations and future work for each chapter are also outlined.