Spatial Variation in Oyster Macroparasites Across the Georgia Coast

Sofia Markiewicz, a student at Scripps College, worked in the lab of Dr. Jeb Byers

Abstract Oysters are a key coastal foundation species that have declined drastically across the US coasts due to the combined effects of overharvesting, pollution, and disease. With climate change, there The eastern oyster (Crassostrea virginica) is a keystone species and ecosystem engineer that stabilizes sediments, cycles nutrients, improves water quality, and provides habitat for fish and crustaceans. Oysters are prone to several macroparasites, including pea crabs (Zaops ostreum), mud blister worms (Polydora websteri), and boring sponge (Cliona spp.), all of which can damage their gill tissue and shells. Although oyster populations have been widely studied in other areas of the eastern United States, the geographic and environmental factors that influence macroparasite infection in Georgia’s oyster population are still largely unknown. In this study, we sampled oysters from 24 reefs across eight distinct sites along the Georgia coastline and examined them for macroparasite infection. The relationships between macroparasite prevalence and geographic location and environmental conditions (specifically reef complexity, reef shell density, dissolved oxygen, water temperature, and salinity) were examined. We found no correlation between location and macroparasite prevalence for any of the macroparasites examined. However, increased prevalence of blister worms was correlated with low salinity and low reef complexity. Prior research has also shown that shellfish infected with blister worms exhibit decreased shell strength, and are therefore more vulnerable to damage and predation. Understanding what conditions affect blister worm prevalence and how they may be altered by by climate change (e.g. changing salinity) is important for evaluating locations where oyster reefs are likely to have low macroparasite infection and be less prone to damage, in order to better maintain high-quality reef habitat. This is especially crucial in a relatively understudied environment such as Georgia, where the effects of these conditions are less well known. 


Assessing the impacts of Hyalophysa lynni infection on oxygen consumption of commercial shrimp

Roland Berg, from Lewis & Smith College, worked with Megan Tomamichel and others in the lab of Dr. Jeb Byers.

Abstract Shrimp black gill disease (sBG), caused by the parasite Hyalophysa lynni, may be contributing to the recent declines in commercial shrimp populations off the Southeastern US coast. H. lynni attaches to shrimp gill tissue, triggering an immune response that causes gill melanization characteristic of sBG. While effective at killing the parasite, this immune response also deteriorates surrounding gill tissue; thus, sBG is speculated to alter host respiration. To address the impact of H. lynni infection on host oxygen uptake, we isolated individual shrimp in containers filled with artificial seawater and monitored the changing dissolved oxygen (DO) concentrations of their water over the course of five days. Afterwards, we diagnosed shrimp with sBG by pulling their gill tissue and performing a DNA extraction and PCR assay to identify the presence of H. lynni DNA. Although our results suggested that H. lynni infection did not impact host oxygen consumption, several other factors were significant predictors of a system’s DO concentration (most significantly time, shrimp length, water temperature, and shrimp gill color). Further research is needed to determine shrimp black gill’s effects on other gill functions, such as acid-base balance and ammonia excretion, as well as H. lynni’s impact on host respiration outside of restful experimental conditions.


Microparasite challenge and subsequent energy trade-offs in an invasive crab species

Zain Aryanpour, a student at the University of Alabama, worked with Dr. Jeb Byers and Carrie Keogh to examine the cost of infection on immune response of an invasive crab species.

Abstract: Invasive species often show phenotypic distinctions in relation to their native-range species. A topic of current interest in populations of invasive species is their immune systems and functions, and whether costs of immune function are altered given the differences in selective pressures they experience in the invasive range. In our study, an invasive Asian shore crab species, Hemigrapsus sanguineus, was utilized as the model system for investigating the short-term energy demand in response to microparasite challenge, the potential relationship between supposed immune stimulation and bacterial killing ability, and the potential relationship between bacterial killing ability and respiration rate. For experimental variables, we utilized LPS injections as the microparasite challenge, optimized a bacterial killing assay to measure immune strength, and used a Qubit Respirometer to measure oxygen consumption for pre- and post-injection crabs. We then ran ANCOVA analyses on bacterial killing and oxygen consumption data and analyzed the relationships between data. The data suggests that microparasite challenge had no effect on energy expenditure in LPS crabs but PBS-injected control crabs showed significantly higher oxygen consumption than LPS crabs after injection. The challenge had little to no effect on bacterial killing ability on either experimental or control crabs. And finally, there is no significant relationship between bacterial killing ability and respiration rate. The results could either be explained by experimental errors in LPS injections (insufficient concentration of LPS, although 0.25 mg/mL was sufficient in previous studies) or the potential explanation that microparasite challenges are not costly on these crabs. A further comprehensive study with a combination of micro- and macroparasite challenges plus additional replicates would most likely give a clearer overview of the immune response and function in this wild population. Further experiments comparing native and invasive parasite response would also improve this study.

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