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Coral Reefs Sea Change

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Lecture on coral reefs for The Evergreen State College program, Sea Change

Lecture on coral reefs for The Evergreen State College program, Sea Change

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  • Coral reefs are piles of limestone and calcareous sediments built by a thin veneer of living organisms. Australia’s Great Barrier Reef is the only living thing that can be seen from space without magnification. However, modern reefs are young (~10,000 years), growing on the skeletons of older reefs (100,000 years ago) drowned by a Holocene rise in sea level.
  • But the virtual backbone of coral reefs is formed from hermatypic corals.
  • Distinct symbiont species which are found in different corals look nearly identical. LaJeunesse et al looked at Symbiodinium that previously had been grouped together as subsets of the same species. They examined specific DNA markers -- identifiers -- from the organisms cell nuclei, mitochondria and chloroplasts. Even though the symbionts appeared very much the same, except for their size, genetic evidence confirmed that the two are different species altogether. hundreds of other coral symbionts already identified with preliminarily genetic data are also distinct species with unique ecological distributions.
  • Hydrological, Meterological, Geomorphological, Climatological factors
  • Various other classifications also exist...
  • (e.g., Oahu = 300 m of Coral Rock). Red Sea fringing reef: No FW floods or terrigenous inputs.
  • Especially in the Caribbean and off continental areas that drop off steeply into deeper water, corals form fringing reefs.
  • The 300 km barrier reef off Belize is second in length to the 2,000 km of the Great Barrier Reef.
  • Great Barrier Reef in Australia is 2000 km long and 5-75 km wide Actually many reefs of various sizes and shapes Very long and complex geographic history
  • The Oxford English Dictionary says the word is  "an adoption of the native name "atholhu" applied to the Maldives, which are typical examples of this structure".
  • Atolls are often horse-shoe shaped, with sandy strips of land (cays) surrounding a large central lagoon. Channels through the reef may facilitate exchange of water with the lagoon, or the lagoon could be isolated from direct exchange.
  • In 1842, Charles Darwin proposed the Subsidence Theory to explain the structure of atolls.
  • In 1842, Charles Darwin proposed the Subsidence Theory to explain the structure of atolls.
  • In 1842, Charles Darwin proposed the Subsidence Theory to explain the structure of atolls.
  • What other system have we studied that is determined by an 20 degree barier?
  • Coral reefs are found where there is a) warm, b) well-lit, c) clear, d) full salinity, e) subtidal waters, with e) high energy and f) low [nutrient] that allow calcareous organisms to secrete skeletons faster than these skeletons are eroded. ~1% of total Ocean surface area Most in Indo-Pacific North to Hawai’i and Southern Japan Caribbean Brazil south of Amazon’s Mouth
  • Coral reefs are the most species-rich environment in the ocean. A single reef may contain 500 fish species. The Great Barrier Reef system contains ~350 spp. of hermatypic corals, >4000 spp. of molluscs, 1500 spp. of fish, and 240 spp. of seabirds. Much of the biodiversity still remains to be described.
  • As has been recorded many times on land, clines in species richness have been recorded for marine organisms as well, including: For all taxa, species richness peaks in the Indonesian-Philippine region in the Pacific and in the Caribbean in the Atlantic.
  • The symbionts ( Symbiodinium spp .) of hermatypic corals require light for photosynthesis.
  • While reef-forming corals exist as deep as 70 m, most coral growth occurs shallower than 25 m.
  • Shallow water corals synthesize UV absorbing compounds to reduce damage from high light levels.
  • Areas with high levels of sedimentation and turbidity harm both autotrophic and heterotrophic sources of coral nutrition. What is the differene between turbidity and sedimentation?
  • Suspended particles absorb/scatter sunlight, leading to less light for photosynthesis by symbionts.
  • As sediment settles out of the water, it can smother/kill small corals or at least inhibit feeding. And corals can’t settle out on soft sediments.
  • ,but this solution costs energy
  • What does it mean to be stenohaline? Most are intolerant of salinities <32-35 psu. Some Red Sea and Persian Gulf species can survive salinities as high as 42 psu.
  • Coral colonies can begin to die after only an hour or two of exposure. What kinds of things do you think kills them off? UV Light, Heat, Dessication…
  • Because corals are efficient in acquiring, conserving, and recycling nutrients, especially in the absence of effective grazing) algae and outcompete corals for light.
  • Corals grow best in locations exposed to at least moderate amounts of wave energy/flow. Why would this be?
  • On the plus side, waves and longshore currents bring nutrients and phytoplankton to coral colonies.
  • On the negative side, episodic storms, like cyclones and hurricanes, can destroy coral calcium carbonate skeletons. Evolved many different forms to maximize survival in high energysystems. Different strategies.
  • Branching corals typically have fast growth rates, but are vulnerable to storm damage.
  • Massive (brain) corals grow more slowly, but are very stable.
  • The morphology of plate-like corals enhance light collection in deeper water.
  • Encrusting corals are found in areas with high wave energy.
  • Over time, loose calcareous sediments from algae and corals (45%) and coral and algal rubble (41%) collect in gaps within the 3D framework.
  • A variety of algae play important roles on coral reefs. Some species, like Halimeda and Porolithon , have 95% or more of their body mass as calcium carbonate. The heavy skeleton deters herbivores and enables some species to live in the most wave-exposed reef habitats.
  • The inner lagoon/reef flat has small coral colonies (patch reefs) mixed among sand flats and seagrasses.
  • The inner lagoon/reef flat has small coral colonies (patch reefs) mixed among sand flats and seagrasses.
  • On one Caribbean reef, 75% of new coral colonies developed from coral fragments, 25% from settlement of planulae.
  • Not surprisingly, planulae from brooding corals settle close to their parents.
  • There is little open space and many species with common needs, like space and light. Upright branching corals grow more rapidly than encrusting or massive corals.
  • Faster growers may extend over and shade slower-growing forms. Shaded portion of coral often dies.
  • Many slower-growing corals produce mesenterial filaments from their gastrovascular cavities. Filaments contact living tissue of adjacent colony and digest it. Filaments may be several cm long. Other species battle with long sweaper tentacles, loaded with nematocysts.
  • The relative importance of photosynthesis ranges from >95% to ~50%.
  • Tourism in the Caribbean is worth over $10 billion, much of the attraction derived from healthy reefs and beaches.
  • Between just south of the equator and 8 degrees north, about 675 km south-west of Sri Lanka. he total area including land and sea is about 90,000 square km.
  • "The Maldives are being threatened by the rise in sea level due to global warming and increasingly violent weather.” Concrete retainer walls
  • Worse (not worst) Case Scenario: Corals extinct in 50 years.
  • In the Caribbean, grazing by D. antillarum kept abundance of foliose algae low, in spite of overfishing of herbivorous fishes at many sites. Potential predators were also removed by overfishing.
  • In just a few days, the bottom was littered with Diadema tests. Even faster, dead urchins appeared in Texas in August 1983 and from there to Bermuda, 4000 km from Panama in September.
  • No other organisms demonstrated any direct effects of the pathogen.
  • Other urchins have not increased in abundance to full this gap, in general. Hypotheses included 1) Allee effect on fertilization, 2) lack of adult cues for settlement, and 3) inadequate recruitment to overcome high larval/early juvenile mortality. Densities dropped 100-fold at sites in Jamaica. Two fishes that consumed lots of Diadema before the epidemic (both toadfishes) switched to other prey.
  • Adult corals were smothered by algae and larval recruitment of new corals failed. The only exception was at San Blas Is., Panama where herbivorous fishes kept algal populations/density/biomass close to pre-epidemic levels.
  • The massive die-off of Diadema highlighted the critical role of this herbivore in mediating competition between corals and fleshy algae.
  • Some areas are still dominated by long-lived, algae (like Sargassum ) These are chemically-protected from the few herbivorous fishes remaining.
  • Under food stress, they will switch to more massive corals, the reef-builders. When hard corals are depleted, they will eat hydrozoans, other anthozoans, sea anemones, sponges, molluscs, and algae
  • Young A. planci (<6mo.) are cryptic and feeds on coralline algae. At 6 months, they switch to corals and can grow from 1 cm to 25 cm in two years. Individuals are capable of consuming 5-6 m 2 of coral/yr. At these densities, they may increase species diversity by consuming the competitive dominant corals.
  • Outbreaks (population densities of Acanthaster which eat corals faster than they can regrow) have been noted since the 1960’s across the whole range of the species. At the GBR, outbreaks move from north to south over ~15 years. This may be driven by the East Australian Current.
  • Research at GBR has shown that reefs which receive large numbers of coral larvae from distant reefs recovery to normal levels of coral cover within 10 years. Even after coral cover is back to normal, the distribution of species may take much longer to reach pre-outbreak conditions as succession proceeds. If the frequency of outbreaks is faster than the pace of reef recovery, reefs will be dominated by weedy corals and some slower-recruiting species may go extinct.
  • However, storms are unlikely to cause significant damage to deep dwelling corals (even if A. planci is found there). With each female producing a billion eggs in a lifetime, a minor change in larval success can produce a dramatic increase in adult populations in just three years. Natural fluctuations in temperature, salinity, or planktonic productivity could improve larval survival and therefore trigger outbreaks.
  • It can swallow juveniles whole and spit out the spines.
  • In the Indo-Pacific, the humphead wrasse Cheilinus undulatus ) is an active predator on Acanthaster (and other toxic prey like sea hares and boxfish
  • Nutrient levels feeding into the GBR lagoon has increased several-fold since European settlement of Australia, with recent increases in fertilizer application. Many recent outbreaks have occurred near urbanized areas. It is very possible that outbreaks are a natural phenomenon, enhanced in space and frequency by current anthropogenic activities.
  • It does not appear that A. planci experiences disease outbreaks at high densities and they have few natural predators. Because A. planci can move at rates of 4 m/hr, control is an ongoing effort. Speaking of tourism, is promoting tourism a good way to save coral reefs?
  • `

Coral Reefs Sea Change Coral Reefs Sea Change Presentation Transcript

  • Coral reefs• What is a Reef?• Types of Reefs• Reef Formation• Reef Distribution• Coral Biology• Coral Reef Ecology• Reef ConservationML2007S. Norton
  • What is a reef?"...a rigid structure composed of calcareousskeletons of various organisms, interlockedor cemented together by growth, and ofdetrital material derived from the break upof such skeletons, and the structuremaintains its upper surface at or near thelevel of the sea." (MacNiel, 1954)
  • Coral reefsLimestone and calcareous sediments built byliving organisms.Coral colonies are short-lived (years to decades).They are the largest biogenic structures on theface of the earth.www.abc.net.au/science/news/enviro/EnviroRepublish_1003558.htmCoral reefs have been around for millions of years.
  • Reef Forming Organisms• Worms (Polychaeta, etc.)• Calcareous Algae• Sponges (Porifera)• Bivalves (and other membersof Mollusca)• Other minor phyla (Bryozoa,Brachiopoda, etc.)• Corals (Cnidaria)
  • Hermatypic Corals
  • Corals• Cnidaria– Anthozoa• Colonial polyps• Photosynthetic zooxanthellae– Symbiodinium spp.• Hermatypic (Scleractinia) corals form reefs
  • Symbiodinium spp.Virtual look-alikes;distinct species.
  • Reef Formation“Evolutionary Sequence”Fringing > Barrier > Atoll
  • Three major types of coral reefs• Fringing• Barrier• Atoll• Proposed by Darwin (1842)“On the Structure andDistribution of Coral Reefs”
  • Three major types of coral reefs• Fringing• Barrier• Atoll• ...cuspate,mesh,patch,platform...• Proposed by Darwin (1842)“On the Structure andDistribution of Coral Reefs”• Morphology based on “size,shape and nearby land ifany”
  • Fringing ReefNearshore, well-lighted marine watersNarrow zone if submarine slope is steepWide zone if submarine slope is gentleYoung volcanic islands in tropics ideal:•Lots of oxygen and nutrients•Very low FW input, so high S‰ & low silt
  • Fringing ReefsCoral Rock of Fringing Reefs is relatively“thin” (usually 25-50 m), except wherelandmass is subsidingLongest reef in world is Red Sea = 4000 km ifstraightened out.
  • Fringe ReefsCastro & Huber Fig. 13.14Reef regions include the flat, crest, and slope.Mangroves, seagrass or sandy beaches may line the shore;fringing reefs typically lack a lagoon.
  • Fringing Reefs grade into Barrier ReefsCastro & Huber Fig. 13.17www.tropichorizon.com/belize.htmlBarrier reefs typically have a deeper water lagoonor channel separating the reef crest from the shore.
  • Barrier ReefsLinear structures separated by a lagoon (up to 100 km)100-200 m thickness of coral rockAnnular around islandReefs rise from terrace or platform
  • Great Barrier Reef• 2000 km long• 5-75 km wide• Long, complex geographichistory
  • AtollsName originally from Darwin (1842).Maldives
  • AtollsCastro & Huber Fig. 13.22Found primarily in the Pacific, atolls develop on the tops of seamounts.
  • Formation of AtollsRaven et al. 6.21Subsidence Theory:Atolls begin as fringingreefs around volcanicislands that have emergedabove sea level.
  • Formation of AtollsRaven et al. 6.21Subsidence Theory:As magma sources drop, theseamount subsides and thereef becomes a barrier reef.
  • Formation of AtollsRaven et al. 6.21Subsidence Theory:As the seamount continuesits subsidence below thesurface, corals grow on topof the seamount, keepingcorals in the photic zone.
  • Atoll ExamplesDeep sea atolls from sea floor (e.g.,Palau).Shelf atolls from continentalshelf (e.g., Belize).Eniwetok Atoll is 1.25 km ofshallow-water coral limestones ontop of a 3.25 km high volcano
  • A Map of Earths Coral Reefs• The pink regions represent the primary reef areas.• The dark gray lines are major ocean currents.• The lighter gray lines represent the 20 degree isotherm latitude. It is above orbelow this location that the water is too cold to sustain coral polyps.
  • Global distribution of coral reefsPurves et al. Fig. 54.28Reefs are absent where coastal waters are too cold or rivers bring inlow-salinity water and high sediment loads.
  • Global diversity of coralsAt the species level (??), there are over 700 species of corals in theIndo-Pacific versus approximately 60 in the Atlantic.Purves et al. Fig. 54.28The center of biodiversity of corals is the Indo-Pacific: Australia,Micronesia, Indonesia, Philippines, etc.Genera of corals
  • Biodiversity of coral reefsCoral reefs harbor more examples of evolutionary diversity (phyla,classes, etc.) than any place on Earth.The Great Barrier Reef~350 spp. of hermatypic corals>4000 spp. of molluscs1500 spp. of fish240 spp. of seabirds.Nybakken & Bertness Table 9.2
  • Clines in diversityClines in species richness have been recorded for marine organismsas well, including:fishcoralssnailslobstersRoberts et al. 2002. Science 295:1280-1284
  • General Conditions for Coral Reefs• 20-30°C• 32‰ S or above• Adequate Surface Substrate• High Light Levels• 25 m or shallower (light)• Low Turbidity (feeding, light, substrate)
  • Necessary conditions for coral reefs: LightThe symbionts require light forphotosynthesis.Karleskint Fig. 15.10
  • Necessary conditions for coral reefs: LightMost coral growth occurs shallowerthan 25 m.Karleskint Fig. 15.10
  • Necessary conditions for coral reefs: LightThe compensation point is 1-2% ofsurface intensity.Karleskint Fig. 15.10
  • Necessary conditions for coral reefs: LightShallow corals synthesize UVabsorbing compounds.Karleskint Fig. 15.10
  • Necessary conditions for coral reefs:Low turbidity and sedimentationSedimentation and turbidity harmcoral nutrition.www.gbrmpa.gov.au/corp_site/info_services/publications/sotr/overview/part_02.html
  • Suspended particles absorb/scattersunlight.www.gbrmpa.gov.au/corp_site/info_services/publications/sotr/overview/part_02.htmlNecessary conditions for coral reefs:Low turbidity and sedimentation
  • Sediments smother small coralsand/or inhibit feeding.www.gbrmpa.gov.au/corp_site/info_services/publications/sotr/overview/part_02.htmlNecessary conditions for coral reefs:Low turbidity and sedimentation
  • Some corals produce largequantities of mucus to trap andremove sediment.www.gbrmpa.gov.au/corp_site/info_services/publications/sotr/overview/part_02.htmlNecessary conditions for coral reefs:Low turbidity and sedimentation
  • Necessary conditions for coral reefs: Full salinity watersCorals are stenohalinephotography.nationalgeographic.com
  • Necessary conditions for coral reefs: Subtidal watersThe upper limit of coralcolonies is the lowerpart of the intertidal.Castro&HuberFig.13.16
  • Necessary conditions for coral reefs: Low [Nutrients]Grow well under low[nutrient].Under higher[nutrient], fleshyalgae flourish.knowledge.allianz.com
  • Necessary conditions for coral reefs: High wave energyAt least moderate amounts of wave or current
  • Necessary conditions for coral reefs: High wave energyWaves and longshore currentsbring nutrients andphytoplankton.dnr.louisiana.gov
  • Necessary conditions for coral reefs: High wave energyStorms destroy coral calciumcarbonate skeletons.
  • Castro & Huber 13.7Branching corals:fast growth ratesvulnerable to storm damageMorphological diversity among corals
  • Castro & Huber 13.7Massive corals:grow more slowlybut are very stableMorphological diversity among corals
  • Castro & Huber 13.7Plate-like corals:enhance light collectionMorphological diversity among corals
  • Castro & Huber 13.7Encrusting corals:high wave energy.Morphological diversity among corals
  • Castro & Huber 13.7Free-living corals:single polypnot cemented to the surfaceMorphological diversity among corals
  • Mechanisms for reef growthCastro & Huber Fig. 13.8Corals provide a large framework forreef development.Encrusting coralline algae, sponges, andbryozoans bind the CaCO3 sedimentstogether.They build a 3-D framework.Calcareous sediments from algae andalgal rubble collect in gaps.Further geological processes turn thiscomplex into limestone.
  • Importance of calcareous algaeOn the Great Barrier Reef, 17-40% of surface sediment are derivedfrom calcareous red algae and 10-30% from Halimeda.coexploration.org/bbsr/coral/assets/images/halimeda.jpgHalimeda and Porolithon, have 95% or moreof their body mass as calcium carbonate.www.coralreefnetwork.com/marlife/stepath/rhodophyta2.html
  • Distribution of corals along a reefNybakken & Bertness Fig. 9.23The inner lagoon/reef flat.
  • Distribution of corals along a reefNybakken & Bertness Fig. 9.23At the reef crest:-Pacific: crustose coraline algae, heavybranching corals-Atlantic: just branching corals.
  • Distribution of corals along a reefMassive corals dominate themiddle depths of the reefslope.
  • Patterns of coral recruitmentBoth sexual reproduction (brooding and broadcast) and asexualreproduction (fragmentation) contribute to the recruitment of new corals.
  • Patterns of coral recruitmentLevinton 2001 Fig. 5.12Planulae settle close to theirparents.Both sexual reproduction (brooding and broadcast) and asexualreproduction (fragmentation) contribute to the recruitment of new corals.
  • Interspecific interactions on coral reefsAmong primary space occupiers,competition is a critically importantphenomenon.
  • Interspecific interactions on coral reefsExploitative CompetitionHeron Island, Joe Connell in Nybakken & Bertness Fig. 9.2719631965Faster growers may extend overand shade slower-growing forms.
  • Interference Competition-Mesenterial filamentsInterspecific interactions on coral reefs
  • Importance of Invertebrate-Alga SymbiosisCoral ReefsHigh productivity in low [nutrient] water (over 2000g C m-2y-1)Some octocorals have no nematocysts, reduceddigestive tracts and show no behavioural changes inthe presence of µzooplankton preySome die without light, but can live and grow in FSWInsufficient zooplankton populations to sustain reefgrowth (~10%)
  • Autotrophy vs. heterotrophy in coralsIn general, shallow water corals rely moreon their symbionts for nutrition.Nybakken & Bertness Fig. 9.8Deeper water corals are more predaceous.Nybakken & Bertness Fig. 9.26This pattern can even be seenintraspecifically in these skeletonsof Montastrea cavernosa fromshallow water (left) vs. deep water(right) in the Caribbean Sea .
  • Importance of ReefsWhile they comprise only 0.2% of the ocean’s surface, coral reefs arehome to a third of the ocean’s fish species.
  • Importance of ReefsCoral reefs provide food for up toone billion people in Asia alone.wwf.org
  • Importance of ReefsTourism in the Caribbean is worth over $10 billion.noaa.gov
  • Threats• Coral bleaching• Climate Change• Sea Level Rise• Ocean Acidification• Temperature Increases• Crown of Thorns Starfish• Diadema antillarum losses• Harvesting for coral and foraquarium trade• Tourism
  • a-sul.blogspot.comImportance of ReefsTourism in the Caribbean is worth over $10 billion.
  • Coral BleachingExposed reef flat in Hawai’i with white patches of coralthat have expulsed their algal symbionts.
  • • Archipelago is 823 km long and 130 km wide at its greatest width.• ~90,000 square km.• 26 natural Atolls• About 200 islands are inhabited.Sea level rise and the Maldives
  • • Maldives islands are on average1.5 meters above sea level• Flooding will be a problem• Sea level may rise so quickly thatit will erode the coral islands.Sea level rise and the Maldives
  • Ocean AcidificationIncreased Atmospheric[CO2] results indecrease in pH of theoceans.Corals and otherorganisms with calciumcarbonate skeletonscan’t lay down CaCO3and skeletons dissolve.
  • Tales of two echinodermsDiadema antillarum -long-spined urchinWhile not described as such, both species play major roles in thehealth of coral reefs - keystone species??Acanthaster planci -Crown of thorns starfish
  • Diadema’s storysv.wikipedia.org/wiki/TagghudingarBefore 1983, D. antillarum was alarge, abundant herbivore found onCaribbean coral reefs, eelgrass beds,mangrove roots, and sand flats.Noctural foraging by D. antillarumin seagrass beds brought nutrientsinto the patch reefs that it used forshelter.Levinton 2001, CD
  • Lessios 1988. Fig. 1In January 1983, sick D. antillarum appeared at Punta Galeta,Panama.Spatial and temporal patterns of Diadema mortalityWithin a year, thedisease spread2000 km east.At a wide range of sites, D. antillarum populations plummeted bymore than 93% from pre-outbreak levels, up to 98% reductions.
  • What was responsible?The fast spread of the disease andspread of disease to lab animalsliving in running seawater indicateda water-borne agent.www.health.qld.gov.au/EndoscopeReprocessing/images/page_images/137_clostridium.jpgTwo species of Clostridium bacteria,collected from infected animals,were lethal when injected intohealthy animals.
  • The delayed recoveryRecruitment of D. antillarum failed across the Caribbean within 5-7 months after theepidemic.Over a decade later, recruitment of D. antillarum was still sparse.Hughes (1994. Science 265:1547-1551)documented changes in Diademapopulations and community impacts inJamaica.
  • In Jamaica, coral% cover declinedfrom an average of52% in 1980 to3% in the 1990’s.Hughes 1984. Fig. 5Within months of the mass mortality of Diadema, populations of fleshy andfilamentous algae exploded across the Caribbean.Consequences of Diadema’s absence
  • The bottom lineIn Jamaica, overfishing of herbivorous fishes increased thevulnerability of the coral reef to algal competition, but the fleshy algaewere kept in check by Diadema.Hughes 1984. Fig. 6Reefs dominated by coralsin the 1970’s weredominated by algae in the1990’s.
  • The NEW bottom lineIdjadi1, Haring, Precht, 2011 MEPS
  • The story of Acanthaster planciAcanthaster planci ranges from theIndian Ocean, through the Indo-Pacificto the Pacific Coast of central America.In general, this species prefersfeeding on hermatypic corals,especially the dominant coral inthe Indo-Pacific, Acropora spp.
  • The story of A. planciAcanthaster planci feeds on corals byeverting its stomach over the coralsurface.www.reef.crc.org.au/discover/plantsanimals/cots/On the Great Barrier Reef (GBR), a healthy coral reef (40-50% coralcover) can support 20-30 individuals per hectare.
  • The story of AcanthasterOutbreaks have been noted sincethe 1960’s.
  • Recovery after Acanthaster outbreaksEven on heavilydamaged reefs, somecorals remain aliveand begin recovery.Reefs with poorer larval supply may not recover after 15 years or more.Levinton 2001. CD
  • What causes outbreaks?2) They are the result of natural fluctuations caused by variation in the number ofnew recruits.1) Under conditions of food stress (e.g, after a storm), adult Acanthaster living indeep water will use chemical cues to form aggregations in shallow water.
  • Milne 1995. Fig. 15.8Examining rubble onreefs does reveal periodswith high concentrationsof Acanthaster spines asfar back as 3,355 yearsago.What causesoutbreaks?
  • www.culture-bx1.u-bordeaux.fr/Ateliers/Internet/Etudiants/recifs/stress.htmlThe giant triton, Charonia tritonus, cutsopen an adult Acanthaster with its radulaand scapes up gonads and viscera.What causes outbreaks?3) Overharvesting of predators leads to highersurvival of Acanthaster juveniles and adults.This species has been collected for its shell and numbers areseverely reduced.Its effectiveness, even before its overharvest, is questioned becauseeach triton typically eats only one adult starfish per week.
  • What causes outbreaks?If predation is important, why would one see sudden, simultaneousoutbreaks in multiple places in the same years?In the Red Sea, pufferfishes and triggerfishes kill up to 4,000individuals/ha/yr, leading to low abundance of A. planci there.www.bio.davidson.edu/people/midorcas/animalphysiology/websites/1999/Rice/Aaron.htmIn the Indo-Pacific, the humpheadwrasse Cheilinus undulatus) is an activepredator on Acanthaster.While adults are large (up to 200 kg),they are not known to occur at highdensities.
  • What causes outbreaks?4) Anthopogenic changes in water quality, especially after high rainfallon land, have been proposed (Birkeland 1982) to drive outbreaks.A) Low salinities and high temperatures from terrestrial runoff mayimprove larval survival.B) Increases in nutrients in runoff stimulates phytoplanktonproduction and this improves larval survival.
  • Strategies for Acanthaster controlAcanthaster outbreaks at economically-valuable sites (e.g.,tourist sites) may be controlled by injecting sodiumbisulfate into each starfish.Efforts of control the latest outbreak at just a few sites costthe Australian government $1 million/yr.
  • Acknowledgements (Incomplete)• Reef map courtesy of Jeremy Staford-Deitsch from his book entitled Reef.• University of Hawaii, http://www.hawaii.edu/HIMB• http://earthobservatory.nasa.gov• Chuck Fisher• Steve Norton