Corals & Coral. Taxonomy Non-Scleractinian Corals Coral Biology Polyp Structure Corallite Structure Colony Form Corallite Arrangements

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1 Lecture 2: Corals & Coral Reefs Kristin McCully 11 Jan 2010 Announcements LSS Tutoring Sign up starting Jan 13 at: Opportunities: Midway research in Potts Lab contact Kristin or Anne UC Davis Bodega Bay Research Experience for Undergraduates on marine & coastal science apply by Feb 12 at: 2 Taxonomy Outline: Corals Non-Scleractinian Corals Coral Biology Polyp Structure Corallite Structure Colony Form Corallite Arrangements 3 Corals Stony Corals = anemone-likeanthozoansor hydrozoans which secrete a skeleton One of several dominant reef-builders and spaceoccupiers on corals reefs Along with soft corals, sponges, algae Defined taxonomically Kingdom Animalia Phylum Class Cnidaria Anthozoa Hydrozoa > 2700 species, >210 genera About 1000 associated with reefs About 800 are reef builders 4 1

2 Great variety in colony form corallite arrangement Coral Classification The broad, polyphyletic term corals includes organisms in several Orders and 2 of the 4 Classes of Cnidarians: Anthozoa and Hydrozoa Ph Anthozoa Cl SCl hydrocorals Or 5 6 Coral Taxonomy Phylum Cnidaria Class Hydrozoa C: Hydrozoa Or: Milleporina Fire coral sc: Alcyonacea Or: Gorgonacea sc: Hexacorallia Or: Antipatharia Class Scyphozoa (jellyfishes) Class Cubozoa(box jellies, sea wasp) Class Anthozoa 7 C: Hydrozoa Or: Stylasterina Lace coral sc: Alcyonacea 8 2

3 Class Hydrozoa: Fire corals Millepora ~50 described species Contain zooxanthellae Major contributors to reefs in some places Yellow to tan color Many growth forms Not eaten by crown-ofthorns (Acanthaster planci) Very vulnerable to coral bleaching Above: Millepora platyphylla Below: Millepora alcicornis, Florida 9 Millepora sp. Very powerful nematocysts that can cause burning sensation in humans 2 kinds of polyps Gastrozooids short feeding polyps with mouths Dactylozooids longer thin polyps with nematocyst batteries but no mouths 10 Class Hydrozoa: Lace Corals Stylaster & Distichopora Stylaster elegans Distichopora violacea Temperate & tropical Shallow to abyssal depth Shallow: Stylaster thin lacy branches Distichopora thicker, smoother branches Caves & overhangs No zooxanthellae Only minor contributors to reefs 11 Sub-Class Alcyonaria/Octocorallia Anthozoanswith exactly 8 tentacles Soft corals & sea fans in Order Alcyonacea Do not secrete rigid skeleton and have soft body Most do secrete scleritesmade of calcite in varying parts of colony Many have zooxanthellae, but less than scleractinian corals 12 Above: sea fan (gorgonian) most common in Caribbean Below: fleshy and lobed most common in Indo-Pacific 3

4 Blue coral Heliopora coerulea Blue color of skeleton due to iron salts deposited in aragonite Greatest geological longevity of any coral (to Cretaceous!) Indo-Pacific (Red Sea to Samoa) Colonies are large with vertical branches light blue to brown 13 Organ Pipe Coral Tubipora musica Dark red skeleton composed of vertical tubes joined by thin horizontal layers Polyp at upper end of tube Indo-Pacific 14 Order Antipatharia (Black Corals) Black skeleton Important long-lived, habitat-forming, sessile benthic suspension feeders Usually found on deep, shaded reef slope Harvested for jewelry Protected by CITES Above: Antipathes grandis -endemic to Hawaii, 1 of 2 species used for jewelry & now rare at scuba depth Below: Wire coral Cirrhipathes anguina Photos from ography.com Hermatypic (Reef-Building) Corals Heavily calcified CaCO 3 skeletons Deposit aragonite (1 of 3 crystalline forms of CaCO 3 ) Live in shallow warm water Have zooxanthellae (endosymbiotic dinoflagellate) Contain chlorophyll Major source of energy to corals Greatly increase rate of calcification 16 4

5 Coral Nutrition: Filter-FeedingFeeding Tentacles capture prey & push into coelenteron Intracellular digestion Extracellular digestion Use nematocysts Usually feed at night More zooplankton prey at night Avoid predation by corallivores 17 Coral Nutrition: Photosynthesis Dinoflagellateendosymbionts called zooxanthellae Zoox belong to genus Symbiodinium Categorized into clades based on gene sequences Corals & zoox are generalists or specialists Also in numerous other invertebrate taxa 18 Zooxanthellae Acquiring zoox Vertical transmission = zoox in egg Horizontal transmission = from seawater Density & identity may fluctuate over time in response to seasonal Zoox clade diagram LaJeunesse 2005 variables such as irradiance and temperature Prevalence of type at particular location is related to environmental regime physiological suitability to regime 19 Coral-Zooxanthellae Symbiosis Benefits for coral: Photosynthate (carbohydrates or lipids) Enhanced calcification N recycling Benefits for zooxanthellae: Supply of N (from coral s heterotrophy) Fixed position in water column and favorable light regime for zoox Bleached coral Protection of zooxfrom planktonic grazers Supplementary CO 2 for photosynthesis arising from 20 coral respiration 5

6 Coral-Zooxanthellae Symbiosis Davies Coral Reproduction Asexually Asexual larvae Fragmentation Sexual Baird et al Sexual system 63% Gonochoric Hermaphroditic Reproductive mode Brooding Broadcast spawning 22 Internal fertilization Brooding Release only sperm Female polyps keep eggs in coelenteron Can brood larvae for weeks Larvae can settle immediately Most are ahermatypic Pocillopora damicornis can brood sexual & asexual larvae at the same time and can also broadcast spawn (Yuoh& Dai 2009) Do not contain zoox Most zooxanthellate scleractinians have vertical transmission of zoox 23 Broadcast Spawning External fertilization May release eggs & sperm at same time or different time Sperm can detect & find egg in water column Wide dispersal potential 24 6

7 Mass Spawning = Synchronous release of gametes by many species of corals, in one evening between dusk and midnight Synchronous using signals: SST & Δdaylight stage of lunar cycle sunset Ancient gene for sensing moonlight in Acropora millepora on GBR (Levy et al Science) Why? Timing optimizes offspring survival Satiating predators Coral Life Cycle 26 Polyp & Corallite Structure 27 Polyp Structure Polyp = living individual (unit) Coelenteron = sac-like body cavity Stomach & gonads Mesenteries = large surface area for Digestion Photosynthesis Respiration Reproduction Secrete septa & calcareous skeleton Tentacles for feeding & defense 28 7

8 Veron 2000 Polyp Structure Nerve net Slow Nondirectional Bipolar neurons 2 tissue layers Ectodermis Endodermis + Mesoglea Non-cellular b/t 2 layers Contains interstitial cells (like stem cells) 29 Nematocysts = stinging cells on tentacles for defense & feeding mons/b/b0/nematocyst_discharge.png 30 Corallite Structure coenosteum Corallite = individual unit of skeleton Costae = radial elements of corallite outside wall Septa = radial elements of corallite inside wall Columella = center of corallite Coenosteum = porous matrix between corallites Paliformlobe = pillar-like projections on inner margin of septa that may form paliform crown 31 Growth = Budding Budding = formation of new polyps in a colony Intratentacular Extratentacular Parent polyp divides itself into two Daughter polyps form on the or more daughter polyps side of the parent polyp

9 Growth = Budding Which type of budding is this? Extratentacularbudding Intratentacular budding 33 Orbicella annularis Dana. In: "Report on the Florida Reefs", 1880, by Louis Agassiz 34 Corallite Arrangements Coral Colony Form Branching Massive Laminar Solitary/Free-living Foliaceous 36 9

10 BIOE 163/OCEA 157: L02: Corals & Coral Reefs 1/10/2010 Coral Colony Form Outline: Coral Reefs Definition of reef & coral reef Ancient reefs Stromatolites Types of Reef Fringing Barrier Atoll Patch Columnar Formation of Atolls Zonation of Reef Encrusting 37 Defining Reefs 38 Coral Reefs Reef (navigation): submerged hazard to navigation (ridge of rocks or sand at or near surface of water) Reef (geology): significant, skeletal framework that influences deposition of sediments in its vicinity and is topographically higher than surrounding sediments Bioherm or biogenic reef: produced by biological as well as geological processes Coral Reef = physical structure which has been built up, and continues to grow over decadal timescales, as a result of the accumulation of calcium carbonate laid down by hermatypic (reef-building) corals and other organisms Ex: oyster reef

11 Wood 1995 Ancient Reefs Reef builders share ability to extract CaCO 3 from water and deposit it in solid, skeletal form High diversity Now can be seen in geological structures Reefs decline greatly at mass extinctions & glaciations 41 Ancient Reef- Builders Cyanobacteria stromatolites Sponges Algae Bryozoans Tabulate & rugose corals Paleozoic Rudist bivalves Cretaceous Coccolithophorids Forams First scleractinian corals with algal symbionts - Triassic 42 Living Stromatolites - Western Australia Rudists, Egypt ges/abu-5.jpg Rugosecorals & Tabulate corals 43 Earliest reefs - 3.5Ba-600Ma Produced O 2 of early planet Cyanobacteria + metal oxides precipitating around them Still found in Western Australia & Bahamas McNamara (1992) Warm, shallow reef flats 44 11

12 Cyanobacteria - Stromatolites - W. Australia Living cells Fossil cells McNamara (1992) 45 Reef Types Fringing Reefs= coral reefs which lie close to shore Barrier Reefs= Coral reefs which have a more extensive lagoon than fringing reefs Atolls= Round, oval or horseshoeshaped carbonate structures which surround a lagoon Patch Reef = almost any size of reef which does not fit the "Classical Three Many other names: 'ridge reef' in Red Sea, crescentic, ribbon in GBR, reticulated 46 Reef Types World Atlas of Coral Reefs 47 Atoll Formation 1. When corals fringe a volcanic island, they develop a fringing reef 2. When the island slowly subsides, coral reef growth keeps up with relative sea level 3. The increasingly distant line of reefs forms a barrier reef 4. Finally when island subsidence is complete, the remaining ring of reefs enclosing a central lagoon is called an atoll. (From Sheppard Ch. 1) Fletcher et al. Geology of Hawaii reefs 48 12

13 Atoll Formation Exception: West Australia atolls developed on edge of sinking continental slope, not volcanic island Charles Darwin World Atlas of Coral Reefs 50 Proving Darwin s Theory Proving Darwin s Theory Solid black is volcanic rock (basalt) Everything above it is limestone or derivatives. Ladd et al Drilling showed that there was a very thick layer of reef and limestone over volcanic rock, which proved that atolls were formed by subsidence as Darwin hypothesized, not sea level change. Ladd et al

14 Reef Zonation Reef Flat May be 10 m wide or 1000 m wide between beach and reef crest Zones: Reef flat Reef crest Reef slope reef flat 53 Corals grow up to water line, but are limited by tidal level Extreme stresses Light Temperature Salinity Oxygen Reef Flat Reef Crest Biodiversity is low, but well-adapted to tolerate extreme stresses Life Species well-adapted to extreme stresses Species for which reef flats lies at extreme edge of their normal or preferred range Deeper reef flats may have more species Seaward edge of reef flat Most wave-exposed part of reef Very few coral species can grow here Dominant reef builder = wave-resistant coralline algae

15 Morelock/7_image/spur.jpg Reef Crest Spur & groove system Spurs dip gradually into deeper water Grooves have steep sides Width & spacing may be related to average wavelength Primary conduits for sediment export from the reef Coralline algae + sediment pushed in cracks very solid reef matrix 57 Reef Slope Seaward edge of reef flat and crest Reef plunges steeply Region of highest diversity, growth, and activity May support corals to 50 m or more Gradient (as depth ) of Wave energy Light Sedimentation Temperature (gradually or thermocline) 58 Reading Required: Corals: Sheppard 2.1 & 2.2 Corals & Soft Corals Veron 2000 Coral structure Coral Reefs: Sheppard Ch. 1 Recommended: Zooxanthellae-coral symbiosis: Sheppard Ch. 4 Coral reproduction review: Baird et al. (2009) Annual Review of Ecology, Evolution, and Systematics Reef types & zonation: Veron2000 Corals & Coral Reefs Reef-building & calcification: Hallock 1997 (Life and Death of Coral Reefs, Ch. 2) History of reef-builders: Veron2000 Geologic History 59 15