Coral disease: Difference between revisions
Edited lead and stress factors section from sandbox: User:Otterreef/coral disease https://en.wikipedia.org/w/index.php?title=User%3AOtterreef%2FCoral_disease&wvprov=sticky-header |
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| ⚫ | '''Coral diseases''' are transmissible [[Pathogen|pathogens]] that cause the degradation of coral colonies. Coral cover in reef ecosystems has decreased significantly for a diverse set of reasons, ranging from variable environmental conditions to mechanical breakdowns from storms.<ref name=": |
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=== Lead === |
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| ⚫ | '''Coral diseases''' are transmissible [[Pathogen|pathogens]] that cause the degradation of coral colonies. Coral cover in reef ecosystems has decreased significantly for a diverse set of reasons, ranging from variable environmental conditions to mechanical breakdowns from storms.<ref name=":13">{{Cite journal |last=Harvell |first=Drew |last2=Jordán-Dahlgren |first2=Eric |last3=Merkel |first3=Susan |last4=Rosenberg |first4=Eugene |last5=Raymundo |first5=Laurie |last6=Smith |first6=Garriet |last7=Weil |first7=Ernesto |last8=Willis |first8=Bette |date=2007 |title=Coral disease, environmental drivers, and the balance between coral and microbial associates |url=http://www.tos.org/oceanography/issues/issue_archive/issue_pdfs/20_1/20.1_breaking_waves.pdf |journal=Oceanography |language=en |volume=20 |pages=172–195 |issn=1042-8275}}</ref><ref name=":43">{{Cite book |title=Diseases of coral |date=2016 |publisher=Wiley Blackwell |isbn=978-0-8138-2411-6 |editor-last=Woodley |editor-first=Cheryl M. |location=Hoboken, New Jersey |editor-last2=Downs |editor-first2=Craig A. |editor-last3=Bruckner |editor-first3=Andrew W. |editor-last4=Porter |editor-first4=James W. |editor-last5=Galloway |editor-first5=Sylvia B.}}</ref> In recent years, diseases that infect and kill coral have shown to be a threat to the health of coral reefs. Since the first coral disease was reported in 1965, many different kinds of diseases have popped up in mostly [[Caribbean|Caribbean waters]].<ref name=":02">{{Cite journal |last=Sokolow |first=S |date=2009-11-16 |title=Effects of a changing climate on the dynamics of coral infectious disease: a review of the evidence |url=http://www.int-res.com/abstracts/dao/v87/n1-2/p5-18/ |journal=Diseases of Aquatic Organisms |language=en |volume=87 |pages=5–18 |doi=10.3354/dao02099 |issn=0177-5103}}</ref> These diseases are diverse, including pathogens of [[bacteria]], [[Fungus|fungi]], [[Virus|viruses]], and [[Protozoa|protozoans]].<ref name=":13" /> Coral diseases have widespread implications, impacting entire [[Ecosystem|ecosystems]] and [[Community (ecology)|communities]] of organisms. Researchers are working to understand these diseases, and how potential treatments could stop these pathogens from causing the widespread death of corals in a way that permanently impacts the community structure of reefs.<ref name=":52">{{Cite journal |last=Sweet |first=Michael |last2=Jones |first2=Rachel |last3=Bythell |first3=John |date=2012-06 |title=Coral diseases in aquaria and in nature |url=https://www.cambridge.org/core/product/identifier/S0025315411001688/type/journal_article |journal=Journal of the Marine Biological Association of the United Kingdom |language=en |volume=92 |issue=4 |pages=791–801 |doi=10.1017/S0025315411001688 |issn=0025-3154}}</ref><ref name=":62">{{Cite journal |last=Pollock |first=F. Joseph |last2=Morris |first2=Pamela J. |last3=Willis |first3=Bette L. |last4=Bourne |first4=David G. |date=2011-10-20 |title=The Urgent Need for Robust Coral Disease Diagnostics |url=https://journals.plos.org/plospathogens/article?id=10.1371/journal.ppat.1002183 |journal=PLOS Pathogens |language=en |volume=7 |issue=10 |pages=e1002183 |doi=10.1371/journal.ppat.1002183 |issn=1553-7374 |pmc=PMC3197597 |pmid=22028646}}</ref> |
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| ⚫ | Like other organisms, [[Scleractinia|stony corals]] and [[Alcyonacea|soft corals]] are subject to disease. This may not have been obvious in the past, but is becoming increasingly apparent in the twenty-first century. The rising ill health of corals is partially the result of the corals being subjected to increasing amounts of stress as the physical environment around them becomes less suited to their needs.<ref name=": |
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== Stress Factors == |
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| ⚫ | Like other organisms, [[Scleractinia|stony corals]] and [[Alcyonacea|soft corals]] are subject to disease. This may not have been obvious in the past, but is becoming increasingly apparent in the twenty-first century. The rising ill health of corals is partially the result of the corals being subjected to increasing amounts of stress as the physical environment around them becomes less suited to their needs.<ref name=":13" /><ref name=":43" /> Corals live within a precise range of abiotic environmental conditions including water temperature, salinity and water quality. Variations outside the normal range of these parameters may make the corals less able to grow and reproduce successfully, and may make them more susceptible to diseases.<ref name=":13" /> One of the major consequences that can occur with stress is the coral expelling its [[zooxanthellae]], which are [[Mutualism (biology)|mutualistic]] [[algae]] that live inside coral. Corals without their symbionts become [[Coral bleaching|bleached]], which effectively kills them since they are unable to gain the correct nutrients without their symbionts. Corals being sensitive to stress factors makes it difficult to study diseases, because the pathogen could impact any part of the coral-symbiont [[Mutualism (biology)|mutualism]] in the same ways that environmental factors do.<ref name=":72">{{Cite journal |last=Bourne |first=David G. |last2=Garren |first2=Melissa |last3=Work |first3=Thierry M. |last4=Rosenberg |first4=Eugene |last5=Smith |first5=Garriet W. |last6=Harvell |first6=C. Drew |date=2009-12 |title=Microbial disease and the coral holobiont |url=https://linkinghub.elsevier.com/retrieve/pii/S0966842X09002078 |journal=Trends in Microbiology |language=en |volume=17 |issue=12 |pages=554–562 |doi=10.1016/j.tim.2009.09.004}}</ref> |
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==Pathogens== |
==Pathogens== |
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[[File: |
[[File:Healthy_and_diseased_corals.jpg|thumb|Healthy (left) and diseased [[staghorn coral]]]] |
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Transmissible diseases are illnesses brought on by biological pathogens that are acquired through [[Contagious disease|contagion]].<ref name=":02" /> Biological agents used to transmit these diseases include viruses, bacteria, [[cyanobacteria]], fungus, protozoa, algae, [[Parasitism|parasites]], and more.<ref name=":02" /><ref name=":13" /> Since corals have algal symbionts, they are considered animals and plants. This means they are impacted by both animal viruses and plant viruses.<ref name=":2">{{Cite journal |last=Marhaver |first=Kristen L. |last2=Edwards |first2=Robert A. |last3=Rohwer |first3=Forest |date=2008-09 |title=Viral communities associated with healthy and bleaching corals |url=https://onlinelibrary.wiley.com/doi/10.1111/j.1462-2920.2008.01652.x |journal=Environmental Microbiology |language=en |volume=10 |issue=9 |pages=2277–2286 |doi=10.1111/j.1462-2920.2008.01652.x}}</ref><ref name=":3">{{Cite journal |last=Soffer |first=Nitzan |last2=Brandt |first2=Marilyn E |last3=Correa |first3=Adrienne MS |last4=Smith |first4=Tyler B |last5=Thurber |first5=Rebecca Vega |date=2014-02 |title=Potential role of viruses in white plague coral disease |url=https://www.nature.com/articles/ismej2013137 |journal=The ISME Journal |language=en |volume=8 |issue=2 |pages=271–283 |doi=10.1038/ismej.2013.137 |issn=1751-7362 |pmc=PMC3906806 |pmid=23949663}}</ref> These plant and animal pathogens can come from marine environments, or crossover from terrestrial diseases.<ref name=":02" /> |
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Coral diseases mostly take the form of a narrow band of diseased tissue separating the living tissue from the exposed skeleton. The band moves across the surface of the colony at the rate of a few millimetres a day, leaving behind bare skeletal material that is rapidly [[biofouling|colonized]] by algae.<ref name=Spalding>{{cite book|author1=Spalding, Mark|author2=Ravilious, Corinna|author3=Green, Edmund Peter|title=World Atlas of Coral Reefs|url=https://books.google.com/books?id=cFawvYZlKHoC&pg=PA132 |year=2001 |publisher=University of California Press |isbn=978-0-520-23255-6 |pages=132–133}}</ref> |
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Little is still known about how these diseases transmit, and scientists are still researching how to control diseases and protect corals.<ref name=":62" /> Studies do show that there is no [[vertical transmission]] in coral pathogens. This means corals do not pass diseases to their offspring through [[Gamete|gametes]], and that coral pathogens are transmitted through contagion from host-to-host.<ref name=":02" /> |
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Many of the diseases that affect corals are known by their most obvious symptoms such as [[black band disease]], [[White band disease|white pox]] and [[yellow-band disease]].<ref name=Sheppard/> However, in many instances it has not been possible to identify the [[pathogen]]s responsible for the disease and culture them in the laboratory; that the coral is sick and the tissue is necrotic is apparent, but whether the fungi or bacteria present caused the disease or merely fed on the already dying tissue is not clear. There is also a minute crab a millimetre or so wide which is often associated with diseased corals, but whether it introduces the disease or just moves in to consume the necrotic tissue is uncertain.<ref name=Sheppard>{{cite book|author=Sheppard, Charles |title=Coral Reefs: A Very Short Introduction |url=https://books.google.com/books?id=bc2kAwAAQBAJ&pg=PT106 |year=2014|publisher=Oxford University Press |isbn=978-0-19-150523-2 |pages=106–108}}</ref> Some of the bacteria found on diseased corals are terrestrial species that are not normally considered pathogenic. Further research has shown that [[virus]]es may be involved in [[White plague (coral disease)|white plague]] infections, the coral small circular single-stranded [[DNA]] (ssDNA) viruses being present in association with diseased tissue. Viruses in this group are known to cause disease in some plants and animals.<ref name=Soffer>{{cite journal |author1=Soffer, Nitzan |author2=Brandt, Marilyn E. |author3=Correa, Adrienne M.S. |author4=Smith, Tyler B. |author5=Thurber, Rebecca Vega |year=2014 |title=Potential role of viruses in white plague coral disease |journal=ISME Journal |volume=8 |issue=2 |pages=271–283 |doi=10.1038/ismej.2013.137|pmc=3906806 |pmid=23949663}}</ref> |
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In many instances it has not been possible to identify the pathogens responsible for the disease by [[Bacteria culture|culturing]] them in the laboratory. This is because some diseases have many different kinds of bacteria associated with them. For example, 50 different bacteria varieties have been found on sites of [[black band disease]].<ref name=":02" /> Also, it is not always clear if fungi or bacteria present on dead [[Necrosis|necrotic tissues]] are caused by the disease, or if the bacteria is simply feeding on the dead tissues.<ref name=":3" /> The way that pathogens impact corals also varies depending on the type of pathogen and species of coral. For example, cyanobacteria pathogens are able to affect the coral’s ability to do work, including blocking [[Nitrogen fixation|nitrogen fixing]]. This means that when coral symbionts try to change nitrogen into a usable form for the coral, pathogens will block this ability to do work.<ref name=":2" /> Another example is a small circular single-stranded [[DNA]] (ssDNA) virus being present in association with diseased tissue on white plague disease.<ref name=":3" /> |
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== Identification == |
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There are some visible signs that a coral has a disease. This includes, but is not limited to, tissue loss, abnormal coloration, and mistakes in skeleton structure.<ref name=":62" /> These symptoms show that corals have diseases, but they can also be caused by environmental factors. Without an understanding of what cellular interactions are occurring, diseases can be difficult to diagnose.<ref name=":72" /> |
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The most common way to tell if a coral is healthy is by looking at its coloration. A dead or unhealthy coral will be bleached, which means they have 40%-50% or more of their pigmentation missing.<ref name=":2" /> Some coral diseases take the form of a narrow band of diseased tissue separating the living tissue from the exposed skeleton. The band can move across the surface of the colony at the rate of a few millimeters a day, leaving behind bleached skeletal material.<ref name=":8">{{Cite book |last=Spalding |first=Mark Douglas |title=World atlas of coral reefs |last2=Ravilious |first2=Corinna |last3=Green |first3=Edmund Peter |date=2001 |publisher=university of California press |isbn=978-0-520-23255-6 |location=Berkeley (Calif.)}}</ref> |
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The physical coloration of coral is an easy way of identifying some pathogens, since many diseases are identified by their most obvious symptoms such as [[black band disease]], [[White band disease|white pox]] and [[yellow-band disease]].<ref name=":9">{{Cite book |last=Sheppard |first=Charles |url=http://dx.doi.org/10.1093/actrade/9780199682775.001.0001 |title=Coral Reefs: A Very Short Introduction |date=2014-06-26 |publisher=Oxford University PressOxford |isbn=0-19-968277-1}}</ref> Sometimes diseases look identical on a macroscopic level, and need to be identified in other ways.<ref name=":02" /><ref name=":52" /><ref name=":62" /> For example, multiple diseases cause a break in pigmentation, which gives the coral a white band. Since a white band is a similar symptom in different diseases, identification of those diseases can be difficult.<ref name=":02" /> In these cases the diseases are labeled through the rate at which they affect the coral.<ref name=":52" /><ref name=":62" /> For white band diseases, their rates of tissue loss range from 0.1(cm/day) in white plague disease to 9(cm/d) in white band disease 2. White plague and white band disease 2 both have the same outward symptoms, but the rate at which they infect corals are drastically different, distinguishing them as different diseases.<ref name=":52" /> |
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== Resistance == |
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Although not a lot is known about how corals and their symbionts resist pathogens, corals do have an [[Innate immune system|innate immune system.]] This means that corals do have some resistance to diseases. When corals are exposed to pathogens they will produce [[antibiotic]] compounds to help protect them.<ref name=":62" /> This includes the secretion of [[mucus]], which can harbor antibacterial properties.<ref name=":2" /> In addition to antibiotics, corals have other natural defenses against illnesses. [[Phagocytosis]] is a cellular defense that corals use in order to target pathogens. It involves healthy cells migrating to the location of the pathogen to get rid of it through the process of phagocytosis.<ref name=":62" /> |
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==Distribution== |
==Distribution== |
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Although coral diseases are problematic on any reef environment, [[Caribbean]] reefs are the biggest hotspot for diseases, especially compared to [[Indo-Pacific]] reefs.<ref name=":13" /><ref name=":9" /><ref name=":10">{{Citation |last=Willis |first=Bette L. |title=Coral Disease on the Great Barrier Reef |date=2004 |url=https://doi.org/10.1007/978-3-662-06414-6_3 |work=Coral Health and Disease |pages=69–104 |editor-last=Rosenberg |editor-first=Eugene |access-date=2023-10-13 |place=Berlin, Heidelberg |publisher=Springer |language=en |doi=10.1007/978-3-662-06414-6_3 |isbn=978-3-662-06414-6 |last2=Page |first2=Cathie A. |last3=Dinsdale |first3=Elizabeth A. |editor2-last=Loya |editor2-first=Yossi}}</ref> Over 70% of disease reports come from Caribbean areas, affecting 75% of hard coral species found in those areas.<ref name=":13" /> |
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Corals growing in the [[Caribbean Sea]] are particularly affected by disease, perhaps because of the limited water circulation and the density of the human population on the surrounding land masses. Disease is also present in the tropical [[Indo-Pacific]], but it is not so widespread, perhaps because of the more dispersed locations of the reefs.<ref name=Sheppard/> |
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Coral diseases that are distributed throughout an area can have a big impact on other parts of reef communities. Not only do coral diseases impact the overall accretion and surface area of the coral, it also affects coral reproduction, the diversity and prosperity of reef species, [[topography]] of structures, and community dynamics.<ref name=":13" /> Disease outbreaks can also shift community dynamics in reefs, where species with previously small populations could outgrow more dominant species because of disease outbreaks. Specifically, White Pox disease in the Florida Keys have impacted the prevalence of ''A. Palmata'' corals by reducing their numbers by 70%.<ref name=":72" /> This shows that coral diseases not only impact individuals, but also have a ripple effect to entire reef communities. |
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Coral diseases also impact [[aquarists]] and coral laboratory settings. These diseases, however, are seemingly different from the diseases in the wild. Studies have found that some diseases impact aquarium corals, but are not an issue in the wild, and vise-versa.<ref name=":13" /><ref name=":52" /> For example, red bug parasites are unique to aquariums, with no wild counterparts having been documented yet. There are also some parasitic flatworm species that infest aquarist's tanks, but are not seen in the wild. These differences in diseases in the wild and aquariums is thought to be because of the varying conditions in the two environments, including water quality and captive coral breeding.<ref name=":52" /> |
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== Climate Change == |
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Corals and their symbionts are sensitive to environmental abiotic changes, and these environmental factors could make the corals more vulnerable to catching pathogens. Environment factors include, but are not limited to, changing ocean water temperatures, increased rainfall, more frequent storms, [[ocean acidification]], and rising sea level. These changes in environmental factors are byproducts of [[climate change]], which means that climate change has the potential to impact the prevalence of coral diseases.<ref name=":02" /> |
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Some coral diseases show variations depending on which season it is. Patterns show that diseases are more pervasive in warmer months during the summer. Because of this, rising ocean temperatures related to climate change could be making coral diseases more prevalent, although evidence is not conclusive because of other complex factors that connect to seasonality.<ref name=":02" /> Furthermore, the rise in sea temperature from climate change is expected to increase the frequency and severity of tropical storms. These storms do mechanical damage to reefs, through increased wave action, and stirring up and re-deposition of sediment.<ref name=":43" /> If coral reefs are damaged, they are less likely to be able to ward off diseases due to higher levels of stress.<ref name=":02" /> |
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Other stress factors related to climate change include an increase in [[pollution]] for pathogens to feed on with more rain and runoff, increased [[ultraviolet]] radiation, and a reduction in the [[aragonite]] saturation of surface seawater that is connected with [[ocean acidification]].<ref name=":13" /><ref name=":02" /><ref name=":11">{{Cite journal |last=Meissner |first=K. J. |last2=Lippmann |first2=T. |last3=Sen Gupta |first3=A. |date=2012-06 |title=Large-scale stress factors affecting coral reefs: open ocean sea surface temperature and surface seawater aragonite saturation over the next 400 years |url=http://link.springer.com/10.1007/s00338-011-0866-8 |journal=Coral Reefs |language=en |volume=31 |issue=2 |pages=309–319 |doi=10.1007/s00338-011-0866-8 |issn=0722-4028}}</ref> |
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== Conservation == |
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Coral diseases have the possibility to change the structures of reefs in a negative way, because one-third of corals are at risk of going extinct because of coral bleaching.<ref name=":62" /><ref name=":72" /> This bleaching, partially caused by diseases, is linked to a decrease in coral cover and loss of [[biodiversity]] in reefs.<ref name=":62" /> This rapid loss of a healthy environment has pushed [[Conservation biology|conservation]] biologists to begin focusing more on how to help conserve coral reefs for the future. |
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Coral diseases are also shown to impact other parts of reef communities. They not only impact the overall accretion and surface area of the coral, they also affect coral reproduction, the diversity and prosperity of reef species, topography of structures, and community dynamics.<ref name=":13" /> This means that coral diseases are not only an issue for individual coral colonies, but are also a danger to coral reef ecosystems as a whole. |
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There has been a recent push in conservation to research pathogen load on corals. If people are able to know how many pathogens a coral or environment has, then researchers will be able to better understand the health of ecosystems or individuals, and possibly predict and prevent pathogens outbreaks in the future.<ref name=":62" /> Conservation biologists and researchers are still learning how corals interact with their environment and diseases, which are quintessential understandings needed for the conservation of corals in relation to diseases.<ref name=":72" /> |
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The future conservation for coral reef diseases relies heavily on being able to quickly diagnose and implement conservation efforts towards specific coral diseases. To help with this, the Global Coral Reef Monitoring Network (GCRMN) is working to create a standardized method for identifying and labeling coral diseases. This will improve the ease of researching and publishing information on specific diseases, which would allow conservation biologists to implement conservation tactics targeting certain corals or diseases.<ref name=":72" /> |
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Since researchers are still studying how diseases impact corals, it is difficult to find a “cure” that works against coral pathogens. Work has been done for treatments that work in a lab or aquarium setting, but these treatments cannot be used in the wild due to the widespread nature of corals, the cost of treatments, and considerations of how it could impact the environment.<ref name=":52" /> |
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==Bacterial communities== |
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The bacterial communities in coral reefs are similar overall, but for each individual coral the bacterial community can differ greatly. Coral is thought to follow the "Anna Karenina Hypothesis". This means that healthy coral will have similar bacterial communities, but diseased corals that are infected with the same disease will have different bacterial communities.<ref name="Bucher">{{cite web |last1=Bucher |first1=Maite |title=Health and Disease Signatures of the Coral Microbiome • iBiology |url=https://www.ibiology.org/microbiology/coral-microbiome/ |website=iBiology |publisher=iBiology |accessdate=14 May 2020}}</ref> |
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* [[White pox disease]] is caused by [[Serratia marcescens|''Serratia marcescens'']] bacteria, and can be identified by white spots on the coral.<ref name=":13" /> |
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* Black Necrosing Syndrome is a fungal disease that leads to the death of clumps of tissues on gorgonian corals.<ref name=":10" /> |
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* [[White pox disease]], caused by ''[[Serratia marcescens]]''. |
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* [[Black band disease]] impacts a variety of coral species, and is caused by [[cyanobacteria]] that degenerates the tissues of the coral skeleton.<ref name=":52" /><ref name=":72" /><ref name=":10" /> |
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* [[Black necrosing syndrome]], or Dark spots disease, probably [[fungal]].{{citation needed|date=November 2017}} |
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* Brown band disease is brought about by infections caused by [[protozoa]]. It can be identified through a brown band that separates healthy portions of coral skeleton from unhealthy sections of the skeleton.<ref name=":52" /><ref name=":43" /> |
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* [[Black band disease]], probably caused by an assortment of photosynthetic and non-photosynthetic bacteria. |
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* Brown band disease is brought about by infections caused by [[protozoa]]. It can be identified through a brown band that separates healthy portions of coral skeleton from unhealthy sections of the skeleton.<ref name="Woodley">{{cite book |author1=Woodley, Cheryl M. |url=https://books.google.com/books?id=U8gbCQAAQBAJ |title=Diseases of Coral |author2=Downs, Craig A. |author3=Bruckner, Andrew W. |author4=Porter, James W. |author5=Galloway, Sylvia B. |date=2016 |publisher=John Wiley & Sons |isbn=978-0-8138-2411-6 |pages=1–2 |author4-link=James W. Porter (ecologist)}}</ref> |
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* [[White band disease]] is a collective term for diseases that have similar white appearances that cannot be easily differentiated from one another. White syndrome diseases include [[White band disease|White Band Disease]] 1 and 2 and [[White plague (coral disease)|White Plague]] 1, 2, and 3.<ref name=":10" /> |
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* [[Skeletal eroding band]] (SEB) erodes away parts of the coral skeleton while building up its own loricae, which has a black appearance. It is caused by the [[protozoan]] [[Halofolliculina corallasia|''Halofolliculina corallasia'']].<ref name=":52" /><ref name=":10" /> |
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* [[White band disease]], the cause of this disease remains unknown. |
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* [[ |
* [[Yellow-band disease]] is caused by a bacterial pathogen.<ref name=":52" /> |
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* Bacterial Bleaching is bleaching caused by the bacterial pathogen ''[[Vibrio|Vibrio shiloi.]]''<ref name=":72" /><ref name=":52" /> |
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* Ulcerative white spot disease is caused by [[vibrio]] bacteria.<ref name=":52" /><ref name=":10" /> |
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* [[Yellow-band disease]], possibly caused by an unidentified species of ''[[Vibrio]]''. |
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* Growth anomalies, like enlarged polyps, are caused by microorganisms.<ref name=":52" /> An example of this is a [[Trematoda|trematode]] infecting a finger coral (''Porites compressa).''<ref name=":10" /> |
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* Brown jelly disease is caused by [[ciliate]] protozoans.<ref name=":52" /> |
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* Red slime algae is a kind of cyanobacteria that can infect corals.<ref name=":52" /> |
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* Red bug disease are parasitic organisms that infest corals. This disease only occurs in aquariums.<ref name=":52" /> |
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==References== |
==References== |
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Revision as of 18:18, 1 November 2023
Lead
Coral diseases are transmissible pathogens that cause the degradation of coral colonies. Coral cover in reef ecosystems has decreased significantly for a diverse set of reasons, ranging from variable environmental conditions to mechanical breakdowns from storms.[1][2] In recent years, diseases that infect and kill coral have shown to be a threat to the health of coral reefs. Since the first coral disease was reported in 1965, many different kinds of diseases have popped up in mostly Caribbean waters.[3] These diseases are diverse, including pathogens of bacteria, fungi, viruses, and protozoans.[1] Coral diseases have widespread implications, impacting entire ecosystems and communities of organisms. Researchers are working to understand these diseases, and how potential treatments could stop these pathogens from causing the widespread death of corals in a way that permanently impacts the community structure of reefs.[4][5]
Stress Factors
Like other organisms, stony corals and soft corals are subject to disease. This may not have been obvious in the past, but is becoming increasingly apparent in the twenty-first century. The rising ill health of corals is partially the result of the corals being subjected to increasing amounts of stress as the physical environment around them becomes less suited to their needs.[1][2] Corals live within a precise range of abiotic environmental conditions including water temperature, salinity and water quality. Variations outside the normal range of these parameters may make the corals less able to grow and reproduce successfully, and may make them more susceptible to diseases.[1] One of the major consequences that can occur with stress is the coral expelling its zooxanthellae, which are mutualistic algae that live inside coral. Corals without their symbionts become bleached, which effectively kills them since they are unable to gain the correct nutrients without their symbionts. Corals being sensitive to stress factors makes it difficult to study diseases, because the pathogen could impact any part of the coral-symbiont mutualism in the same ways that environmental factors do.[6]
Pathogens
Transmissible diseases are illnesses brought on by biological pathogens that are acquired through contagion.[3] Biological agents used to transmit these diseases include viruses, bacteria, cyanobacteria, fungus, protozoa, algae, parasites, and more.[3][1] Since corals have algal symbionts, they are considered animals and plants. This means they are impacted by both animal viruses and plant viruses.[7][8] These plant and animal pathogens can come from marine environments, or crossover from terrestrial diseases.[3]
Little is still known about how these diseases transmit, and scientists are still researching how to control diseases and protect corals.[5] Studies do show that there is no vertical transmission in coral pathogens. This means corals do not pass diseases to their offspring through gametes, and that coral pathogens are transmitted through contagion from host-to-host.[3]
In many instances it has not been possible to identify the pathogens responsible for the disease by culturing them in the laboratory. This is because some diseases have many different kinds of bacteria associated with them. For example, 50 different bacteria varieties have been found on sites of black band disease.[3] Also, it is not always clear if fungi or bacteria present on dead necrotic tissues are caused by the disease, or if the bacteria is simply feeding on the dead tissues.[8] The way that pathogens impact corals also varies depending on the type of pathogen and species of coral. For example, cyanobacteria pathogens are able to affect the coral’s ability to do work, including blocking nitrogen fixing. This means that when coral symbionts try to change nitrogen into a usable form for the coral, pathogens will block this ability to do work.[7] Another example is a small circular single-stranded DNA (ssDNA) virus being present in association with diseased tissue on white plague disease.[8]
Identification
There are some visible signs that a coral has a disease. This includes, but is not limited to, tissue loss, abnormal coloration, and mistakes in skeleton structure.[5] These symptoms show that corals have diseases, but they can also be caused by environmental factors. Without an understanding of what cellular interactions are occurring, diseases can be difficult to diagnose.[6]
The most common way to tell if a coral is healthy is by looking at its coloration. A dead or unhealthy coral will be bleached, which means they have 40%-50% or more of their pigmentation missing.[7] Some coral diseases take the form of a narrow band of diseased tissue separating the living tissue from the exposed skeleton. The band can move across the surface of the colony at the rate of a few millimeters a day, leaving behind bleached skeletal material.[9]
The physical coloration of coral is an easy way of identifying some pathogens, since many diseases are identified by their most obvious symptoms such as black band disease, white pox and yellow-band disease.[10] Sometimes diseases look identical on a macroscopic level, and need to be identified in other ways.[3][4][5] For example, multiple diseases cause a break in pigmentation, which gives the coral a white band. Since a white band is a similar symptom in different diseases, identification of those diseases can be difficult.[3] In these cases the diseases are labeled through the rate at which they affect the coral.[4][5] For white band diseases, their rates of tissue loss range from 0.1(cm/day) in white plague disease to 9(cm/d) in white band disease 2. White plague and white band disease 2 both have the same outward symptoms, but the rate at which they infect corals are drastically different, distinguishing them as different diseases.[4]
Resistance
Although not a lot is known about how corals and their symbionts resist pathogens, corals do have an innate immune system. This means that corals do have some resistance to diseases. When corals are exposed to pathogens they will produce antibiotic compounds to help protect them.[5] This includes the secretion of mucus, which can harbor antibacterial properties.[7] In addition to antibiotics, corals have other natural defenses against illnesses. Phagocytosis is a cellular defense that corals use in order to target pathogens. It involves healthy cells migrating to the location of the pathogen to get rid of it through the process of phagocytosis.[5]
Distribution
Although coral diseases are problematic on any reef environment, Caribbean reefs are the biggest hotspot for diseases, especially compared to Indo-Pacific reefs.[1][10][11] Over 70% of disease reports come from Caribbean areas, affecting 75% of hard coral species found in those areas.[1]
Coral diseases that are distributed throughout an area can have a big impact on other parts of reef communities. Not only do coral diseases impact the overall accretion and surface area of the coral, it also affects coral reproduction, the diversity and prosperity of reef species, topography of structures, and community dynamics.[1] Disease outbreaks can also shift community dynamics in reefs, where species with previously small populations could outgrow more dominant species because of disease outbreaks. Specifically, White Pox disease in the Florida Keys have impacted the prevalence of A. Palmata corals by reducing their numbers by 70%.[6] This shows that coral diseases not only impact individuals, but also have a ripple effect to entire reef communities.
Coral diseases also impact aquarists and coral laboratory settings. These diseases, however, are seemingly different from the diseases in the wild. Studies have found that some diseases impact aquarium corals, but are not an issue in the wild, and vise-versa.[1][4] For example, red bug parasites are unique to aquariums, with no wild counterparts having been documented yet. There are also some parasitic flatworm species that infest aquarist's tanks, but are not seen in the wild. These differences in diseases in the wild and aquariums is thought to be because of the varying conditions in the two environments, including water quality and captive coral breeding.[4]
Climate Change
Corals and their symbionts are sensitive to environmental abiotic changes, and these environmental factors could make the corals more vulnerable to catching pathogens. Environment factors include, but are not limited to, changing ocean water temperatures, increased rainfall, more frequent storms, ocean acidification, and rising sea level. These changes in environmental factors are byproducts of climate change, which means that climate change has the potential to impact the prevalence of coral diseases.[3]
Some coral diseases show variations depending on which season it is. Patterns show that diseases are more pervasive in warmer months during the summer. Because of this, rising ocean temperatures related to climate change could be making coral diseases more prevalent, although evidence is not conclusive because of other complex factors that connect to seasonality.[3] Furthermore, the rise in sea temperature from climate change is expected to increase the frequency and severity of tropical storms. These storms do mechanical damage to reefs, through increased wave action, and stirring up and re-deposition of sediment.[2] If coral reefs are damaged, they are less likely to be able to ward off diseases due to higher levels of stress.[3]
Other stress factors related to climate change include an increase in pollution for pathogens to feed on with more rain and runoff, increased ultraviolet radiation, and a reduction in the aragonite saturation of surface seawater that is connected with ocean acidification.[1][3][12]
Conservation
Coral diseases have the possibility to change the structures of reefs in a negative way, because one-third of corals are at risk of going extinct because of coral bleaching.[5][6] This bleaching, partially caused by diseases, is linked to a decrease in coral cover and loss of biodiversity in reefs.[5] This rapid loss of a healthy environment has pushed conservation biologists to begin focusing more on how to help conserve coral reefs for the future.
Coral diseases are also shown to impact other parts of reef communities. They not only impact the overall accretion and surface area of the coral, they also affect coral reproduction, the diversity and prosperity of reef species, topography of structures, and community dynamics.[1] This means that coral diseases are not only an issue for individual coral colonies, but are also a danger to coral reef ecosystems as a whole.
There has been a recent push in conservation to research pathogen load on corals. If people are able to know how many pathogens a coral or environment has, then researchers will be able to better understand the health of ecosystems or individuals, and possibly predict and prevent pathogens outbreaks in the future.[5] Conservation biologists and researchers are still learning how corals interact with their environment and diseases, which are quintessential understandings needed for the conservation of corals in relation to diseases.[6]
The future conservation for coral reef diseases relies heavily on being able to quickly diagnose and implement conservation efforts towards specific coral diseases. To help with this, the Global Coral Reef Monitoring Network (GCRMN) is working to create a standardized method for identifying and labeling coral diseases. This will improve the ease of researching and publishing information on specific diseases, which would allow conservation biologists to implement conservation tactics targeting certain corals or diseases.[6]
Since researchers are still studying how diseases impact corals, it is difficult to find a “cure” that works against coral pathogens. Work has been done for treatments that work in a lab or aquarium setting, but these treatments cannot be used in the wild due to the widespread nature of corals, the cost of treatments, and considerations of how it could impact the environment.[4]
Coral Diseases
- Aspergillosis, caused by the fungus Aspergillus sydowii, affects Gorgonian soft corals commonly known as sea fans.[6][11]
- White pox disease is caused by Serratia marcescens bacteria, and can be identified by white spots on the coral.[1]
- Black Necrosing Syndrome is a fungal disease that leads to the death of clumps of tissues on gorgonian corals.[11]
- Black band disease impacts a variety of coral species, and is caused by cyanobacteria that degenerates the tissues of the coral skeleton.[4][6][11]
- Brown band disease is brought about by infections caused by protozoa. It can be identified through a brown band that separates healthy portions of coral skeleton from unhealthy sections of the skeleton.[4][2]
- Rapid Wasting disease is caused by fungus growing on areas damaged by the feeding of parrotfish.[4]
- White band disease is a collective term for diseases that have similar white appearances that cannot be easily differentiated from one another. White syndrome diseases include White Band Disease 1 and 2 and White Plague 1, 2, and 3.[11]
- Skeletal eroding band (SEB) erodes away parts of the coral skeleton while building up its own loricae, which has a black appearance. It is caused by the protozoan Halofolliculina corallasia.[4][11]
- Yellow-band disease is caused by a bacterial pathogen.[4]
- Bacterial Bleaching is bleaching caused by the bacterial pathogen Vibrio shiloi.[6][4]
- Ulcerative white spot disease is caused by vibrio bacteria.[4][11]
- Growth anomalies, like enlarged polyps, are caused by microorganisms.[4] An example of this is a trematode infecting a finger coral (Porites compressa).[11]
- Brown jelly disease is caused by ciliate protozoans.[4]
- Red slime algae is a kind of cyanobacteria that can infect corals.[4]
- Red bug disease are parasitic organisms that infest corals. This disease only occurs in aquariums.[4]
References
- ^ a b c d e f g h i j k l Harvell, Drew; Jordán-Dahlgren, Eric; Merkel, Susan; Rosenberg, Eugene; Raymundo, Laurie; Smith, Garriet; Weil, Ernesto; Willis, Bette (2007). "Coral disease, environmental drivers, and the balance between coral and microbial associates" (PDF). Oceanography. 20: 172–195. ISSN 1042-8275.
- ^ a b c d Woodley, Cheryl M.; Downs, Craig A.; Bruckner, Andrew W.; Porter, James W.; Galloway, Sylvia B., eds. (2016). Diseases of coral. Hoboken, New Jersey: Wiley Blackwell. ISBN 978-0-8138-2411-6.
- ^ a b c d e f g h i j k l Sokolow, S (2009-11-16). "Effects of a changing climate on the dynamics of coral infectious disease: a review of the evidence". Diseases of Aquatic Organisms. 87: 5–18. doi:10.3354/dao02099. ISSN 0177-5103.
- ^ a b c d e f g h i j k l m n o p q r Sweet, Michael; Jones, Rachel; Bythell, John (2012-06). "Coral diseases in aquaria and in nature". Journal of the Marine Biological Association of the United Kingdom. 92 (4): 791–801. doi:10.1017/S0025315411001688. ISSN 0025-3154.
{{cite journal}}: Check date values in:|date=(help) - ^ a b c d e f g h i j Pollock, F. Joseph; Morris, Pamela J.; Willis, Bette L.; Bourne, David G. (2011-10-20). "The Urgent Need for Robust Coral Disease Diagnostics". PLOS Pathogens. 7 (10): e1002183. doi:10.1371/journal.ppat.1002183. ISSN 1553-7374. PMC 3197597. PMID 22028646.
{{cite journal}}: CS1 maint: PMC format (link) CS1 maint: unflagged free DOI (link) - ^ a b c d e f g h i Bourne, David G.; Garren, Melissa; Work, Thierry M.; Rosenberg, Eugene; Smith, Garriet W.; Harvell, C. Drew (2009-12). "Microbial disease and the coral holobiont". Trends in Microbiology. 17 (12): 554–562. doi:10.1016/j.tim.2009.09.004.
{{cite journal}}: Check date values in:|date=(help) - ^ a b c d Marhaver, Kristen L.; Edwards, Robert A.; Rohwer, Forest (2008-09). "Viral communities associated with healthy and bleaching corals". Environmental Microbiology. 10 (9): 2277–2286. doi:10.1111/j.1462-2920.2008.01652.x.
{{cite journal}}: Check date values in:|date=(help) - ^ a b c Soffer, Nitzan; Brandt, Marilyn E; Correa, Adrienne MS; Smith, Tyler B; Thurber, Rebecca Vega (2014-02). "Potential role of viruses in white plague coral disease". The ISME Journal. 8 (2): 271–283. doi:10.1038/ismej.2013.137. ISSN 1751-7362. PMC 3906806. PMID 23949663.
{{cite journal}}: Check date values in:|date=(help)CS1 maint: PMC format (link) - ^ Spalding, Mark Douglas; Ravilious, Corinna; Green, Edmund Peter (2001). World atlas of coral reefs. Berkeley (Calif.): university of California press. ISBN 978-0-520-23255-6.
- ^ a b Sheppard, Charles (2014-06-26). Coral Reefs: A Very Short Introduction. Oxford University PressOxford. ISBN 0-19-968277-1.
- ^ a b c d e f g h Willis, Bette L.; Page, Cathie A.; Dinsdale, Elizabeth A. (2004), Rosenberg, Eugene; Loya, Yossi (eds.), "Coral Disease on the Great Barrier Reef", Coral Health and Disease, Berlin, Heidelberg: Springer, pp. 69–104, doi:10.1007/978-3-662-06414-6_3, ISBN 978-3-662-06414-6, retrieved 2023-10-13
- ^ Meissner, K. J.; Lippmann, T.; Sen Gupta, A. (2012-06). "Large-scale stress factors affecting coral reefs: open ocean sea surface temperature and surface seawater aragonite saturation over the next 400 years". Coral Reefs. 31 (2): 309–319. doi:10.1007/s00338-011-0866-8. ISSN 0722-4028.
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