Hall Emily R.

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Hall
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Emily R.
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  • Article
    Effects of ocean acidification on the performance and interaction of fleshy macroalgae and a grazing sea urchin
    (Elsevier, 2021-11-24) Burnham, Katherine A. ; Nowicki, Robert J. ; Hall, Emily R. ; Pi, Joshua ; Page, Heather N.
    When predicting the response of marine ecosystems to climate change, it is increasingly recognized that understanding the indirect effects of ocean acidification on trophic interactions is as important as studying direct effects on organism physiology. Furthermore, comprehensive studies that examine these effects simultaneously are needed to identify and link the underlying mechanisms driving changes in species interactions. Using an onshore ocean acidification simulator system, we investigated the direct and indirect effects of elevated seawater pCO2 on the physiology and trophic interaction of fleshy macroalgae and the grazing sea urchin Lytechinus variegatus. Macroalgal (Dictyota spp.) biomass increased despite decreased photosynthetic rates after two-week exposure to elevated pCO2. Algal tissue carbon content remained constant, suggesting the use of alternative carbon acquisition pathways beneficial to growth under acidification. Higher C:N ratios driven by a slight reduction in N content in algae exposed to elevated pCO2 suggest a decrease in nutritional content under acidification. Urchin (L. variegatus) respiration, biomass, and righting time did not change significantly after six-week exposure to elevated pCO2, indicating that physiological stress and changes in metabolism are not mechanisms through which the trophic interaction was impacted. Correspondingly, urchin consumption rates of untreated macroalgae (Caulerpa racemosa) were not significantly affected by pCO2. In contrast, exposure of urchins to elevated pCO2 significantly reduced the number of correct foraging choices for ambient macroalgae (Dictyota spp.), indicating impairment of urchin chemical sensing under acidification. However, exposure of algae to elevated pCO2 returned the number of correct foraging choices in similarly exposed urchins to ambient levels, suggesting alongside higher C:N ratios that algal nutritional content was altered in a way detectable by the urchins under acidification. These results highlight the importance of studying the indirect effects of acidification on trophic interactions simultaneously with direct effects on physiology. Together, these results suggest that changes to urchin chemical sensing and algal nutritional quality are the driving mechanisms behind surprisingly unaltered urchin foraging behavior for fleshy macroalgae under joint exposure to ocean acidification. Consistent foraging behavior and consumption rates suggest that the trophic interaction between L. variegatus and fleshy macroalgae may be sustained under future acidification. However, increases in fleshy macroalgal biomass driven by opportunistic carbon acquisition strategies have the potential to cause ecological change, depending on how grazer populations respond. Additional field research is needed to determine the outcome of these results over time and under a wider range of environmental conditions.
  • Article
    Exposure of blue crab (Callinectes sapidus) to modified clay treatment of Karenia brevis as a bloom control strategy
    (Elsevier, 2023-08-21) Devillier, Victoria M. ; Hall, Emily R. ; Anderson, Donald M. ; Lewis, Kristy A.
    Harmful algal blooms (HABs) of the toxic marine dinoflagellate Karenia brevis, commonly called red tides, are an ongoing threat to human health and marine ecosystems in Florida. Clay flocculation is a standard control strategy for marine HABs in China and Korea and is currently being assessed for use in the United States. We evaluated the effects of a PAC-modified clay called Modified Clay II on mortality, eyestalk reflexes, and righting reflexes of 48 adult blue crabs (Callinectes sapidus). Crabs were exposed to clay alone (0.5 g L − 1), untreated K. brevis (1 × 106 cells L − 1), or a combination of K. brevis and clay for eight days. Clay treatment reduced cell concentrations in the water column by 95% after 24 h. We detected no significant differences in mortality, righting reflexes, or eyestalk reflexes between treatments. Our results indicate that the clay alone is not harmful to adult crabs at typical treatment concentrations within the measured time frame, and that treatment of K. brevis with this clay appears to have a negligible impact on crab mortality and the reflex variables we measured. These results suggest that Modified Clay II may be a viable option to treat K. brevis blooms without impacting adult blue crab populations. Additional controlled experiments and field tests are needed to further evaluate the impact of clay on natural benthic communities.
  • Article
    Mesocosm study of PAC-modified clay effects on Karenia brevis cells and toxins, chemical dynamics, and benthic invertebrate physiology
    (Elsevier, 2024-02-28) Devillier, Victoria M. ; Hall, Emily R. ; Lovko, Vincent J. ; Pierce, Richard H. ; Anderson, Donald M. ; Lewis, Kristy A.
    Modified clay compounds are used globally as a method of controlling harmful algal blooms, and their use is currently under consideration to control Karenia brevis blooms in Florida, USA. In 1400 L mesocosm tanks, chemical dynamics and lethal and sublethal impacts of MC II, a polyaluminum chloride (PAC)-modified kaolinite clay, were evaluated over 72 h on a benthic community representative of Sarasota Bay, which included blue crab (Callinectes sapidus), sea urchin (Lytechinus variegatus), and hard clam (Mercenaria campechiensis). In this experiment, MC II was dosed at 0.2 g L - 1 to treat bloom-level densities of K. brevis at 1 × 106 cells L - 1. Cell removal in MC II-treated tanks was 57% after 8 h and 95% after 48 h. In the water column, brevetoxin analogs BTx-1 and BTx-2 were found to be significantly higher in untreated tanks at 24 and 48 h, while in MC II-treated tanks, BTx-3 was found to be higher at 48 h and BTx-B5 was found to be higher at 24 and 48 h. In MC II floc, we found no significant differences in BTx-1 or BTx-2 between treatments for any time point, while BTx-3 was found to be significantly higher in the MC II-treated tanks at 48 and 72 h, and BTx-B5 was higher in MC II-treated tanks at 24 and 72 h. Among various chemical dynamics observed, it was notable that dissolved phosphorus was consistently significantly lower in MC II tanks after 2 h, and that turbidity in MC II tanks returned to control levels 48 h after treatment. Dissolved inorganic carbon and total seawater alkalinity were significantly reduced in MC II tanks, and partial pressure of CO2 (pCO2) was significantly higher in the MC II-only treatment after 2 h. In MC II floc, particulate phosphorus was found to be significantly higher in MC II tanks after 24 h. In animals, lethal and sublethal responses to MC II-treated K. brevis did not differ from untreated K. brevis for either of our three species at any time point, suggesting MC II treatment at this dosage has negligible impacts to these species within 72 h of exposure. These results appear promising in terms of the environmental safety of MC II as a potential bloom control option, and we recommend scaling up MC II experiments to field trials in order to gain deeper understanding of MC II performance and dynamics in natural waters.