Transcript • Corals, the basics – What are corals? – Why study corals?

27 April 2009
OCN 621 – Biological Oceanography
• Corals, the basics
– What are corals?
• Taxonomy
• Anatomy
• Life Cycles
– Where did corals come from?
– Why study corals?
What are corals?
• Phylum Cnidaria
– “to sting”
– Diploblastic
• Exclusively marine
– Found in all oceans at all depths
• Zooxanthellate or Azooxanthellate
– Hermatypic or Ahermatypic
• Produce calcium carbonate
• Not all are “habitat forming”
– Easy to think corals are only in reefs!
– Many different forms
Collins et al., 2006
Taxonomy
• Class Hydrozoa
– Stylasteridea (Lace Corals)
• Class Anthozoa
– Subclass Hexacorallia
• Order Scleractinia (Stony Corals)
• Order Antipatharia (Black Corals, Wire Corals)
• Order Zoanthidea (Zooanthids)
– Subclass Octocorallia
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Order Alcyonacea (Soft Corals)
Order Stolonifera (Organ Pipe Corals)
Order Gorgonacea (Sea Fans and Sea Whips)
Order Helioporacea (Blue Coral)
Morphology
• Colonial
– Scleractinia, Stylasterids
• Reef Building/Habitat forming
– Octocorals
• Fans, whips
• Solitary
– Scleractinia, Zooanthids
– Genetically distinct individuals
(mainly)
– Can live in groups, clusters, or
all alone
NMITA
The polyp
• Polyp
– Living veneer
• Radial symmetry
– Scleractinians–
Hexa-radial
– Octocorals – Octoradial
• Only 3 tissue types
• Simple nerve net
• Polyps
interconnected
– Coenosarc
• Build Skeletons
Nematocyst
Nematocyst
Skeleton – Hard Corals
• Scleractinians &
Stylasterids
• Calcium carbonate
– Aragonite and
Calcite
• Layers, thin veneer
of live tissue
• New coral recruits
grow on old coral
skeletons
Portalès Plan
• Cross section of a calice
• Skeleton – not soft
tissue
• Taxonomic aid
– Arrangement of septa
Skeleton – Hard Corals
Skeleton – Soft Corals
• “Gorgonin” and
calcite skeletons
– Horny protein
• Sclerites
– Calcium
carbonate
Watling
Colonial Coral Life Cycle
Planulae
larvae
Settling
First polyp
Brooding
Asexual
Spawning
Zygote
Life Cycle
• Asexual
– Budding
• Intratentacular
• Extratentacular
– Fragmentation
– Parthenogenesis
– Polyp Bail Out
• Sexual
– Gonochorism
– Hermaphrodites
• Simultaneous
• Alternating
• Sequential
Life Cycle
• Fertilization
– Internal (Brooding, Spawning)
– External (Broadcast Spawning)
– Self-fertilization vs. outcrossing
– Parthenogenesis
• Larval development
– Planktonic
– Internal brooding
– External surface brooding (octocorals only)
Life Cycle
• Timing of sexual reproduction
– Seasonal high temperatures
– Lunar periodicity
– Tidal phase
– Conspecific cues
– Food availability
• Phytoplankton blooms
• Seasonal detrital food falls
– Solar insolation
Where did corals come from?
• Reef building corals evolved at the beginning
of the Mesozoic ~240 Ma
• Preceded by Tabulate and Rugose Corals
– Non-reef building, Tetra-corals, azooxanthellate
– Calcite – not aragonite
– Extinct at the end of the Paleozoic
Humans
Modern
corals
Rugose/
Tabulate
corals
Evolution
• Several major extinction events
• Permian-Triassic boundary (248 Ma)
• 57% of marine invertebrate families and up to 95% of
all species on the earth became extinct
• Triassic-Jurassic boundary (213 Ma)
• disappearance of 49 out of 67 genera of corals,
• pause in reef development of 4 - 10 million years
• Cretaceous-Tertiary (K-T) boundary (66 Ma)
• dinosaurs went extinct (and 75% of all species)
• probably caused by a meteor impact causing major,
rapid climate change
Veron, 1995
Evolution
• Large environmental changes in past 240 Ma
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Tectonic drift
Oceanic basins & circulation patterns
Climate/temperature changes
Sea level rise/fall and rates of change
Episodic natural disasters
• Geologically robust
• Not as fragile as regarded?
Why Study Corals?
• Biodiversity and complexity
– Coral reef ecosystems rival tropical rain forests
– Large array of biological and ecological processes
– Diversity of life history strategies
• Ecosystem engineers
– Corals create habitat for many organisms
– Hermatypic corals (via photosynthetic symbionts)
form the base of the food chain
• Economically Important
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Tourism
Fisheries
Subsistence for local populations
Source for natural products chemistry
Why Study Corals?
• Sedentary
• Simplifies measures of growth, mortality, recruitment,
fecundity, competition and predation
• Measure directly on same colonies
• Long-lived
• Many cohorts
• Long archives
• Skeleton
• Archive of information for retrospective analysis
• Can be easily dated
• Sensitive to environmental changes
• Canary in the mine
• Or are they?
Conclusions
• All oceans, all depths, with or without
zooxanthellae
• Vast array of morphologies
• Vast array of life histories
• Calcite corals appeared ~570ma, aragonite
corals appeared ~240ma
• May not be as fragile as we think –
geologically robust
Glossary
• Diploblastic
– Two major germ layers –
Ectoderm and Endoderm
• Zooxanthellate
– With photosynthetic alage
– Also Hermatypic
• Azooxanthellate
– Without photosynthetic algae
– Also Ahermatypic
• Sclerite
– Calcium carbonate plates in
Octocorals
• Parthenogenesis
– Growth of asexual larvae
• Calice/Corallite
– Skeleton housing the
polyp itself
• Corallum
– the entire skeletal unit
housing a corallite or
group of corallites
• Septa
– Divisions within the
corallite