Harmful Algal Blooms - Amy Grogan

Abstract Members of the raphidophyte genus Chattonella, including Chatonella subsalsa, have been responsible for harmful algal blooms (HABs) and fish kills worldwide. The exact ichthyotoxic pathways are currently unclear, however, past research suggested two broad mechanisms: physical irritation from algal cells causing respiratory distress or the synthesis of a bioactive compound or toxin. Cellular extracts have been shown to cause fish mortality, but it is unclear whether damage caused by C. subsalsa is necessitated by physical contact with algae cells in nature. In this study, larvae of the killifish Fundulus heteroclitus were exposed both directly and indirectly (separated by 1 μm mesh) to C. subsalsa isolates during various culture growth stages in order to determine if their physical contact is necessary to elicit gill damage and subsequent mortality as well as identify if culture growth phase influences lethality. Results showed significant mortalities of indirectly exposed F. heteroclitus larvae (Kruskal Wallis rank sum test, p = 0.007) suggest that C. subsalsa does produce a water borne bioactive compound(s), and cells were most potent during exponential growth. This implies that C. subsalsa blooms may have far reaching impacts and severe environmental consequences such as reduction of fish recruitment and population loss as well as sublethal damages inflicted by toxins and trophic transfer.

Methods Algal cultures of C. subsalsa were obtained from Dr. Dianne Greenfield's lab in Charleston, SC. Cultures were raised in f/2 medium in an incubator at 25 C under a 12:12 light:dark regime. Regular counts were conducted with a Sedgewick-Rafter chamber in order to develop a growth curve. Algal growth regularly progresses through four broad growth phases, lag, exponential, stationary, and decline. Exponential growth or maximum growth is thought to be associated with increased lethality of HABs. The exponential growth phase of C. subsalsa cultures was further categorized as early exponential, mid exponential, and late exponential. Exposure experiments were performed at the aforementioned exponential phases as well as the lag phase (a time of low cell densities and little or no growth) and the stationary phase (a time when growth slows but cell density is high) in order to determine if growth phase played a role in C. subsalsa's lethality.

Adult F. heteroclitus were captured using killie traps. Only sexually mature fish, lengths of 40 mm or greater, were retained and brought back to laboratory facilities at Coastal Carolina University. Breeding groups were kept in ten gallon aquarium with temperate and lighting parameters set to mimic summer conditions. Eggs were collected using a Janiak style egg collector (Janiak & McIntosh 2014). Fish eggs were air incubated in the method of Coulon et al. 2012 for fourteen days then submerged in 25 ppt artificial seawater to induce hatching. Larvae were maintained on a diet of live Artemia nauplii for a minimum of seven days post hatch prior to use in experimental trials.

Experiment A total of five experiments were conducted targeting each of the previously mentioned growth phases. The exposure treatments to C. subsalsa included a direct contact, in which larvae were added to live culture and an indirect contact (mesh exposure), in which larvae were separated from live culture by a 1 μm mesh. Experiments ran for 48 hours and were checked at four hour intervals at which time dead larvae were removed and preserved in a 10% formalin buffer.

Analysis/Conclusion Both the percent mortality of exposed larvae as well as the degree of gill damage incurred during exposures were used to determine the lethality of C. subsalsa at various growth phases. The mid exponential and late exponential growth phases were found to be the most lethal and significant mortalities occurred in the mesh exposure treatment suggesting C. subsalsa produces a waterborne bioactive compound. The results of this study have been submitted to the Journal of Experimental Marine Biology and Ecology for publication.

With HABs continuing to be a growing problem South Carolina Algal Ecology Lab is actively working to monitor blooms in order to gain a fuller understanding of their origins and repercussions. As human activities have a great influence on this issue, it is important to educate the public about practices to prevent harmful algal blooms. It is crucial to educate young minds about science and the role of society in preserving our natural resources. Working as a GK-12 fellow I hope to have inspired students to care about our local ecosystems and learn the many ways they can help keep South Carolina healthy and beautiful. Understanding environmental health and the impacts of human activity will be needed a key skill for promoting a bright future!

Want to Learn More?!? Check out these links! NOAA Harmful Algal Blooms 10 Things You Can Do to Save the Ocean! Ocean Conservancy Be an Ocean Guardian

 
shell hab/home.txt · Last modified: May 22, 2017 by agrogan