Biological mechanisms of coral immunity

Palmer, Caroline V. (2010) Biological mechanisms of coral immunity. PhD thesis, James Cook University.

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Hard corals underpin the existence and biodiversity of tropical reefs, however they are declining globally at an alarming rate, largely because of increases in disease prevalence and thermal bleaching events. Despite extensive documentation of coral reef demise, no substantive investigations into the coral host's biological mechanisms for disease resistance, bleaching mitigation or wound healing have been conducted. Coral immunology may therefore provide important insights into understanding the capacity of corals to resist global coral declines. The principal objectives of this thesis were therefore, firstly, to investigate the presence of well-characterised invertebrate innate immunity effector responses, including the melanin-synthesis pathway, the coagulation pathway, immune cell activation and antioxidants, within a number of species from the anthozoan orders Scleractinia, Alcyonacea and Zoantharia. The second objective was to establish the extent to which coral immunity effector responses are activated following physical injury and infection. Finally, the potential influence of warmer seawater temperatures on coral immunity levels and activation were investigated. These objectives were addressed using anthozoans from the Great Barrier Reef Australia, the Caribbean and Hawai'i, using both colourimetric enzyme assays and histological techniques.

Principal findings include establishing the presence of each of the four invertebrate immunity effector responses investigated within corals. A coagulation enzyme, three types of enzymes involved in melanin synthesis and several immune cells were identified for the first time, indicating that anthozoan immune systems are as complex as phylogenetically higher invertebrates. Furthermore, an antioxidant property of coral fluorescent proteins (FP) was established and, in combination with the presence of FPs in coral tissues with increased immune activity, these findings suggest a further potential function of these colourful proteins. Comparative baseline levels of a suite of coral immunity components were found to explain among-family variation in both coral bleaching and disease susceptibility, suggesting immunity as a physiological link between, and mitigator of, these two threats. Furthermore, the ability of hard corals to activate an immune response was demonstrated by a discernable increase in all measured effector responses, both enzymatic and cellular, with both injury and infection. Similarly, the cells and phases of wound healing were characterised within a hard coral for the first time, demonstrating conservation of mechanisms from the phylogenetically basal corals to humans. Additionally, within one coral species, elevated seawater temperature increased baseline levels of immunity but suppressed responses to injury, explaining links between warming sea surface temperatures and increasing disease prevalence that have been found for several coral diseases, but also suggesting the potential for corals to acclimatise to ocean warming.

Overall, this thesis presents novel findings in a number of areas of coral innate immunity, thereby laying the foundations for this new field of research for scleractinian corals. Coral immunology is an emerging field that is highly relevant to understanding the capacity of corals and coral reefs to persist in a warming world. Preliminary tools developed here will significantly advance the capacity to quantify coral health and, therefore, to better predict the future state of the world’s coral reefs.

Item ID: 32217
Item Type: Thesis (PhD)
Keywords: coral immunity; coral immunology; immunity mechanisms; melanin; amedobocyte; wound-healing; disease resistance; coral bleaching; scleractinian corals; Hawaii; Great Barrier Reef; GBR; Caribbean
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Publications arising from this thesis are available from the Related URLs field. The publications are:

Palmer, Caroline V., Bythell, John C., and Willis, Bette L. (2010) Levels of immunity parameters underpin bleaching and disease susceptibility of reef corals. FASEB Journal, 24 (6). pp. 1935-1946.

Palmer, Caroline V., Modi, Chintan K., and Mydlarz, Laura D. (2009) Coral fluorescent proteins as antioxidants. PLoS ONE, 4 (10). p. 7298.

Palmer, Caroline V., Roth, Melissa S., and Gates, Ruth D. (2009) Red fluorescent protein responsible for pigmentation in Trematode-infected Porites compressa tissues. Biological Bulletin, 216 (1). pp. 68-74.

Palmer, Caroline V., Mydlarz, Laura D., and Willis, Bette L. (2008) Evidence of an inflammatory-like response in non-normally pigmented tissues of two scleractinian corals. Proceedings of the Royal Society of London Series B, Biological Sciences, 275 (1652). pp. 2687-2693.

Date Deposited: 30 Apr 2014 06:33
FoR Codes: 06 BIOLOGICAL SCIENCES > 0608 Zoology > 060804 Animal Immunology @ 50%
06 BIOLOGICAL SCIENCES > 0601 Biochemistry and Cell Biology > 060199 Biochemistry and Cell Biology not elsewhere classified @ 50%
SEO Codes: 97 EXPANDING KNOWLEDGE > 970106 Expanding Knowledge in the Biological Sciences @ 100%
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