Host Parasite Interactions,Coral Disorders andScientific UnknownsM

y previous article contained adetailed description of theextensively researched and

characterised coral diseases. I explainedthat scientifically, to qualify for theclassification of disease the disease-causing agent must satisfy Koch’sPostulates. This article features somecoral aliments that have been discoveredin recent years, the majority of which haveno known cause.

The coral maladies featured belowhave all, at one time, been describedusing the all embracing term “coraldisease” and in the most part, in theabsence of scientific analysis. Numeroussightings have been made of “coraldiseases” in the wild. The discovery of adenuded coral skeleton often prompts thediver to take a closer look. This sighting isinvariably logged as the discovery of yetanother coral disease. Such a conclusionwas made when observing parrotfishpredation (Fig 1). The condition wasgiven the name Rapid Wasting Disease.Scientific investigations were made intothe phenomena that appeared to becaused by a fungus that the parrotfishwere distributing1. Scientific analysis hassince proven that there is no microbialagent involved. The “disease” was simplythe result of parrotfish browsing and the

fungus was utilising available space onthe reef5.

Monitoring coral disease in the wild isa difficult task because divers are limitedby the time they can spend submerged.Therefore in some ways the hobbyist hasa superior vantage point. However theobservation of a “coral disease” does nottell us anything about the cause, just thesymptoms. Any determination of diseasecausation must be performed underexperimental conditions.

Experimental conditions aredesigned to eliminate all factors that mayinfluence the results of the experiment,save what in theory should occur. Theexperimenter must first postulate ahypothesis. The experiment is thendesigned to prove or disprove thishypothesis. The logistics of designing anexperiment to determine what is causinga coral disease is a very complex task.Experiments in closed systems such asaquaria are not ideal because no matterhow the specimen is housed, it isimpossible to determine if theseconditions are what the specimen isaccustomed to in nature. Any deviationfrom wild conditions could weaken thecoral and thus bias any experimental dataacquired.

Ideally the experiment must housespecimens under the conditions theyhave evolved to suit. This includes naturalseawater, wave action, depth ofplacement and nutrition. For hermatypiccorals that contain zooxanthellae,nutrition is customarily in the form of light.All factors that could influence theexperimental data must be eliminated.Even for a scientist with a research grant,the eradication of all the potentialinfluencing factors is near to impossible,so please don’t try this at home!

Genuine coral diseases have beenobserved in aquaria but their occurrenceis relatively rare. It is more conventionalfor a coral to die because it is kept in anenvironment that is unsuitable for thatspecies. For the reasons stated above,

10 • MARINE WORLD – JUNE/JULY 2005

Coral disease Chris Aslett, BSc (Hons) MRes

Fig 1. Parrotfish predation – photography by Andy Bruckner, 1998

Fig 2. Hyperplastic growth of Diploria strigosa– photograph by Andy Bruckner, 1996

filaments are oftenmore dispersed.RBD II affects D.strigosa, C. natans,Montastreaannularis, M.cavernosa, Poritesasteroides andSiderastrea radians.During the day RBDII can bedistinguished fromRBD I because ithas a diffuse netlike form, which atnight compacts intoa tight mass7. RBDhas been observedin the Caribbean,and on the GreatBarrier Reef (Fig4).14.

Yellow Blotch Syndrome(YBS)

also known as Yellow Band Disease, iscommon in M. annularis and C. natansthroughout the Caribbean. Syndromeprogression is slow and destroys the coraltissue at a rate of approximately 0.6 cmper month. Ancient colonies appear to bemore susceptible to the condition thatstarts as a foci or band of translucentyellow tissue and radiates concentricallyoutward14 cit., 2 (Fig 5). An unknowncrystalline material has been discoveredin the gastric cavity of the affected corals16

cit., 2. From 1997 to 1998 90% ofCaribbean M. annularis had acquired thesyndrome that inactivates up to 96% of

the coral’s zooxanthellae. The symbioticdinoflagellates are not expelled butdevelop large void spaces within them,and lack the customary cellular machineryfound in healthy zooxanthellae. Scientistshave proposed that the syndrome has aprimary effect on the zooxanthellae and asecondary effect on the ¥cnidarian host15.

Algal Galls have been described in Pseudoplexaurasea fans in the Florida Keys and theCaribbean (Fig 6). The galls are producedas a consequence of a skeletal infectionby the microalgae Entocladia endozoica.The sea fans try to defend themselves by“walling off” the infected area withcalcareous sclerites and scleroproteins.Sclerite recruitment encapsulates themicroalgae in galls and prevents themfrom deriving nutrition from the coraltissue. However, the galls have adeleterious effect on the elasticity andtensile strength of host’s skeleton.Invariably the skeleton breaks, exposingthe microalgae to the high light intensitiesfound on shallow reefs.

The increase in illuminationstimulates the microalgae to produce_zoospores that are released into thewater column. Eventually the fractureheals and seals the microalgae beneaththe coral tissue, enabling the wholeprocess to start again. Scientists believethat the amino acids tyrosine and cytosineextracted by the microalgae from the coraltissue play a key role in regulating thereproductive cycle of the microalgae 3.

until scientific research has determined acause for many of the coral maladiesdescribed below, it is not possible toconclude if the observations made byscientists and hobbyist alike, are thesymptoms of authentic coral diseases.

Skeletal abnormalities have been observed in hard corals andlead to a distortion of the typical coralstructure. These abnormalities arise fromregions of accelerated growth that resultin tumours. There are 2 known types,hyperplasia and neoplasia. Hyperplasmscontain zooxanthellae and are made fromnumerous cell types6. Scientific researchhas revealed that coral hyperplastic cellsstore fewer fats than normal cells18 (Fig2).

Coral neoplasms are made from onlyone type of cell, calicoblastic epithelialcells. These cells lack zooxanthellae and

deposit the calcareous material usuallyfound between corallites (Fig 3). As thetumour grows it protrudes upwards andcovers the normal tissue, killing it in theprocess6.

Red Band Disease (RBD) shares some similarities with Black BandDisease (BBD), described in my previousarticle. Like BBD, RBD is a cyanobacterialmat colonised by other microorganismsthat act in unison to destroy the coraltissue1. There are 2 types RBD I, andRBD II. RBD I has been described inAgaricia, Colpophyllia, Mycetophyllia,Stephanocoenia, and Gorgonia ventalina.The colouration of RBD is more maroonthan BBD and the cyanobacterial

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Fig 3. Neoplastic growth of Acropoa palmata – photography by Andy Bruckner, 1999

Fig 4. G. ventalina with RBD I – Photography by Andy Bruckner, 1997

¥Cnidarian – “any of the various invertebrateanimals of the phylum Cnidaria, characterized bya radially symmetrical body with a saclikeinternal cavity, including the jellyfishes, hydras,sea anemones, and corals”. www.dictionary.com

Dark Spot Syndrome (DSS) has been reported throughout theCaribbean. Brown or purple fociaccompanied by a lack of polyp extension

are symptomaticof the condition(Fig 7)8. Tissueloss is onlyexperienced atthe focus ofinfection4. DSSis commonest inS. sidereal,Stephanocoeniaintersepta, S.

michelinii and M.annularis8. Tissue

necrosis occurs at a rate of 4.0 cm permonth. Like YBS, the zooxanthellae arereduced in number and unable to divide15.

Brown Jelly was thought to be a condition only foundin aquaria until it was observed in 2003on the Great Barrier Reef 9. Brown Jellycan affect all zooxanthellates. Brown Jellylooks exactly how the name suggests. It isa brown jelly-like mass that hovers overand envelopes the coral and uponoccasion, releases strings of “jelly” intothe water column (Fig 8). Microscopy hasrevealed that the “jelly” is a mixedpopulation of microorganisms consistingof protozoa, bacteria and fungi.Microscopy has revealed that theprotozoan Helicostoma nonatum ingeststhe zooxanthellae of affected corals. Ithas yet to be determined if the organismsare just performing housekeeping dutiesby consuming a degrading specimen, or ifthe microbes are involved in an infectiveprocess10. Outbreaks appear to besporadic and affect both established andrecently introduced specimens.

Rapid Tissue Necrosis(RTN)

or Shut Down Reaction is commonest inSPS corals and denudes the coralskeleton at a rate of approximately 1” perhour. Tissue loss is experienced at such arate as to allow the observer to watch asthe flesh vanishes from the skeleton. Theailment is associated with housing coralsin poor conditions. Healthy tissue andbare skeleton share a discreteboundary11. The cause of disease isunknown but the bacterium Vibriovulnificus has been isolated from RTNlesions13.

Skeletal Eroding Band(SEB)

is the result of an infection by the ciliate

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Coral disease

Fig. 5. M. favolata with Yellow Blotch Syndrome – photography by AndyBruckner, 1998.

Fig. 6. A Pseudoplexaura sea fan exibiting Algal Galls – photography by Laurie Richardson

_Zoospores- “Amotile flagellated asexual spore, as of certain algae and fungi. Also called swarm spore”.www.dictionary.com

Fig. 7. Dark spot syndrome affecting M. annularis – photography by AndryBruckner, 1998

Halofolliculina corallasia. The ciliateinfects and grows within the coral,secreting its microscopic shells (loricae)that disrupt the tissue. SEB has beenfound on the Great Barrier Reef and inthe Indo-Pacific region. The familiesPocilloporidae, Acroporidae, Faviidae,Pritidae, Fungiidae and Merulinidae are allsusceptible9.

Black Necrosis Syndrome affects Gorgonia on the northern GreatBarrier Reef. Black patches of tissueslough away from the skeleton. Thecondition is caused by an unidentifiedfungus9.

Pink Spot has been observed on the Great BarrierReef. The lifecycle of the parasiticflatworm Podocotyloides stenometra iscomprised of 2 larval stages ofdevelopment, prior to adulthood. Duringthe larval stages the flatworm uses amollusc for its first host and the coral P.compressa for its second. Maturity is onlyachieved within butterflyfish. An infectedcoral polyp becomes pink and swollenand therefore more vulnerable topredation by butterflyfishes. When thebutterflyfish eats the polyp it then

becomes host to the flatworm. After theinfected polyps have been consumednormal polyps can regenerate 9.

ConclusionExcluding the above, there have beenmany more reports of coral ailments thatrequire scientific investigation. Themajority of the conditions detailed here

are likely to be a consequence of shifts inthe ecological balance of the reefenvironment, caused by §anthropogenicactivity. If you have witnessed any “coraldiseases” in your aquaria and wish toshare your experiences, please feel freeto contact me through my web site(http://www.reefranch.co.uk). My nextarticle will inform the hobbyist of themeasures that can be taken to preventcoral diseases in their aquarium, andwhat is the best way to deal with anoutbreak when it occurs.

References1.http://ourworld.compuserve.com/homepages/mccarty_and_peters/coral/rwd.htm [last accessed07.03.05]2.http://www.coris.noaa.gov/about/diseases/diseases.html#yellow%20blotch [last accessed07.03.05]3.http://www.coral.noaa.gov/coral_disease/algal_galls.shtml [Last accessed 07.03.05]4.http://www.coral.noaa.gov/coral_disease/dark_spots.shtml [last accessed 07.03.05]5.http://www.unep-wcmc.org/marine/coraldis/cd/parrotfish.htm#poop [last accessed 07.03.05]6.http://www.unep-wcmc.org/marine/coraldis/cd/neoplasia.htm [lastaccessed 07.03.05]7.http://www.unep-wcmc.org/marine/coraldis/cd/rbd.htm [lastaccessed 07.03.05]8.http://www.unep-wcmc.org/marine/coraldis/cd/dsd.htm [lastaccessed 07.03.05]9.http://www.reef.crc.org.au/discover/coralreefs/Coraldisease.htm[last accessed 07.03.05]10.http://www.reefkeeping.com/issues/2004-06/eb/ [last accessed 07.03.05]11.http://reefshow.com/html/modules.php?name=News&file=article&sid=126#RTN [last accessed07.03.05]12.http://www.reefs.org/library/talklog/c_bingman_040697.html [last accessed 07.03.05]13.http://reefshow.com/html/modules.php?name=News&file=article&sid=126#RTN [last accessed07.03.05]14.http://www.reefball.org/coraldiseaseoffline/RBDPAGE.HTM [last accessed 14.03.05]15. Bruckner, A.W. 2001. Coral health andmortalit: Recognizing signs of coral diseases andpredators. In: Humann and Deloach (eds.), ReefCoral Identification. Jacksonville, FL: FloridaCaribbean Bahamas New World Publications,Inc. pp. 240-271.16. Cervino, J., Goreau, T. J., Nagelkerken, G.W., Smith, G. W. & Hayes, R. (2001) Yellowband and dark spot syndromes in Caribbeancorals: distribution, rate of spread, cytology, andeffects on abundance and division rate ofzooxanthellae. Hydrobiologia 460, 53-63.17. Santavy, D.L. and E.C. Peters. 1997.Microbial pests: Coral disease research in thewestern Atlantic. Proc. 8th Int. Coral Reef Symp.1:607-612.18. Yamashiro, H., Oku, H., Onaga, K., Iwasaki,H. & Takara, K. (2001) Coral tumours storereduced level of lipids. Journal of ExperimentalMarine Biology and Ecology. 265, 171-179.

Fig 8. Euphyllia cristata affected by Brown Jelly – photograph by Chris Aslett ,2005

§Anthropogenic- “of, relating to, or resultingfrom the influence of human beings on nature”.www.dictionary.com

Chris is a Master ofResearch in AppliedFish Biology graduatewith over 20 yearsexperience of keepingmarines. He has recentlyopened a marineaquarium store in Leeds– The Reef Ranch.

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