MARE 194

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MARE 194

• Coral Reproduction

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Corals are quite prolific

• Colonies are often in a constant state of asexual
  reproduction
• intermixed w/ occassional sex.

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Reproduction, Defined

• Successful Reproduction ? the population of a
  species will ? in a favorable environment
• Remember, reproduction (larval recruitment
  survival to reproductive age) must at least
  mortality ( emigration)

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Two types of reproduction

• Asexual (clones)
• vs
• Sexual (new genetic combos)

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Asexual ReproductionBenefits Costs

• Permits proliferation of successful genotype
• Proliferation not impeded by conditions necessary
  for gamete union
• Requires only 1 individual
• But
• Only 1 genotype results that may suffer more from
  environmental change than population of variable
  genotypes

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Types of Asexual Reproduction in Corals

• Fission
• Transverse
• Radial
• Pedal Laceration
• Budding
• Fragmentation
• Accidental
• Planula Larvae
• Polyp Bail-Out

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Coral ReproductionAsexual Budding Fission

• Growth new skeleton new polyp
• Polyps? Fission or Budding

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Asexual Reproduction

• FISSION (Transverse) the new polyp is formed by
  the oral disc (mouth) invaginating to produce a
  new mouth w/in the original ring of parental
  tentacles
• Also called
• Intratentacular
• Reproduction
• Or
• Intentional
• Fragmentation

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Asexual Reproduction

• FISSION (Radial)
• Also called
• Intratentacular
• Reproduction
• Or
• Intentional
• Fragmentation

Fungia sp.
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Asexual Reproduction

• PEDAL LACERATION parts of the pedal disc (foot)
  detach from the rest of the animal gradually
  differentiate to form a new single-module.
• Also called
• Transverse Fission

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Pedal Laceration, or Transverse Fission
Fungia scutaria
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Asexual Reproduction

• BUDDING the new mouth is formed outside the
  original ring of parental tentacles
• Also called Extratentacular Reproduction

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Asexual Reproduction

• Phoenix Affect Although colonies may appear
  completely dead, residual tissue in skeletal
  recesses allows for a more rapid recovery of some
  coral colonies

Fungia scutaria
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Asexual Reproduction

• Fragmentation when breakage of one/several
  sections of coral form into new colonies, growing
  over the substrate upon which theyve settled
• Accidental or Intentional (Fission)

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Asexual Reproduction

• Accidental Fragmentation breakage of coral that
  reattaches to the substrate over time grow into
  full branching colonies
• New colonies have advantage of proximity to
  parent colony good conditions low competition
• Primary Causes wave or storm action
• Sea Turtles

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Asexual Reproduction

• Accidental Fragmentation? new polyps can form
  from the tiniest of fragments

Fragment of a single skeletal element forming a
complete polyp
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Asexual Reproduction

• Asexual Production of Planula Larvae formation
  of planula larvae within the coelenteron
• spit out through mouth of parent
• Already contains zooxanthellae (some of the
  highest survival rates)
• Enters plantonic life cycle

In Hawaii? common in Pocillipora damicornis
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Asexual Reproduction

• Asexual Production of Planula Larvae

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Asexual Reproduction

• Polyp Bail-out Under conditions of environmental
  stress, the polyps will
• Break their intercalical tissue connections
• Emerge from their calices float off into water
  column
• Resettle as independent polyps
• Asexually bud, reproduce new colony

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Polyp Anatomy Reminder
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Asexual Reproduction

• Polyp Bail-out

Initially only observed in Seriatopora hystrix
(Great Barrier Reef), but now recently observed
in Pocillopora damicornis in Hawaii

• Advantages
• Better to try your odds elsewhere than lose zxth
• Best suited for fast-growers

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Sexual ReproductionBenefits Costs

• Costs
• Energy costs into egg production are very high
  (compared to asexual)
• In HI Pocillopora expends 25-50 of it's biomass
  in spawned gametes on annual basis
• Must be synchronized, or reproductive process
  lost for entire year
• Simultaneous hermaphrodites may result in
  inbreeding ? genetic disorder possibilities
• Benefits
• Ensures genetic variability maintained in
  population
• If no other individual in area, selfing can occur
  ensure perpetuation
• Most evidence shows significant barriers to self
  fertilization

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Sexual Reproduction

• Most marine animals have a life cycle that can be
  divided into adult and larval stages - e.g.
  corals
• Larva stage from zygote formation until larva
  recruits to the preferred habitat and
  metamorphoses into adult

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Sexual Reproduction in Corals

• Hermaphroditism vs. gonochorism
• reproduction is at the individual level

• Hermaphroditic either simultaneous or
  sequential
• Simultaneous - self fertilization very rare
• Gametes must mature at same time in same place

• Gonochoric both sexes are separate, one
  individual produces sperm, another egg
• depend on a neighboring colony of the opposite
  sex to complete the fertilization process

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Broadcast SpawningSexual Reproduction

• The release of gametes
  (egg/sperm) into the water
  where fertilization takes place
  externally to the parents
• SYNCHRONIZATION of the utmost importance? sperm
  only swims for a few hours, dilution of the
  gametes occurs
• Massive amounts of gametes produced to ensure
  success
• Some eggs contain zxth

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Broadcast SpawningSexual Reproduction

• In Hawaii most at specific times over the
  summer
• Montipora?2 days after new moon, 9 PM
• Porites compressa Fungia scutaria? 2 days after
  full moon (Porites _at_ midnight, Fungia _at_ 6 PM)

Coral egg spawning division
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Broadcast SpawningSexual Reproduction

• Simultaneous Hermaphrodites?
  release gamete bundles which allow sperm
  to float w/ the fatty eggs. Saves energy for
  swimming to find unfertilized egg.

• Most Hawaiian corals are not hermaphroditic----the
  Montipora genus is the exception.

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Broadcast SpawningSexual Reproduction

• Gametes float to surface after release. WHY???
• Avoid all those filter feeders
• Avoid planktivorous fishes
• Why do most spawn at night???
• Predation, most obvious
• predator satiation
• Dispersal w/tidal lunar processes
• Limits UV radiation damage

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Sexual Reproduction

• Broadcast Spawning Events

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Spawning Events
Ningaloo Bay

• Killer Spawn (1989)
• NW region of Australia,
  isolated bay
• Spawning slick remained in bay due to unusual
  tides/currents
• Millions of gametes did not disperse, ? used up
  most O2 for respiration, more as they decayed
• Over few days over 1,000,000 reef fish died, as
  well as most of the bays corals
• Again! March 2008
• Corals bleached after spawn
  fish clams died
• Climate change? Less intense winds
  the norm?

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Sexual Reproduction

• Brooding process by which sperm is taken in
  through the mouth after release into the water
  column
• internal fertilization occurs
• housed in coelenteron until viable larvae emerges

• Costs
• Substantial reproductive energy cost to parent
• Benefits
• Emerging polyp nearly ready to settle, so
  survival rate high

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Planula Larvae

• After produced/released, must survive as
  plankton?quite different than sessile, benthic
• May be very widely dispersed
• When it comes time to settle, cues include
  chemicals light
• May be eaten by planktivores, including other
  corals
• Those w/long planktonic stages need protection
  against UV radiation UV-absorbing chemicals in
  tissues

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Planula Larvae
Fluorescing Montipora larvae

• FOOD! (differs from sp to sp)
• Zxth provided by parents produce energy
• Zxth taken in while plankton produce energy
• Feed on smaller forms of plankton
• Non-feeding live on reserves from egg, settle
  quickly

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Larval Dispersal
Cyphastrea ocellina 60 d larvae

• Larvae may end up in the same reef, or different
  reefs in far-away places
• Hawaiis Corals
• -most larvae short-lived
• So may use Island Stepping Stones
• Closest island it Johnson Atoll (720 km away)
• P. damicornis is one coral that could have
  survived long enough to make that trip

But maybe it's something else...
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Larval Dispersal

• Rafting polyps form on drifting/floating debris
  only to be dislodged once the item strikes land.
• Polyp settles forms colony
• Driftwood
• Pumice (lava rock
• that floats)

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Larval Settlement
Newly-settled rice coral

• Cues
• Light
• Surface temperature
• Presence of other organisms (algae-may be sign of
  1st organism to settle clear areas)
• Sites for settlement often cryptic
• Under overhangs, caves
• Colonies eventually grow outward
• Some sites untouchable
• Some soft corals excrete toxins to inhibit stony
  coral settlement

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Larval Settlement

• Successful Recruitment? when larvae have
  successfully attached and formed a polyp large
  enough to be observed
• Once attached, young polyps first begin to lay
  down the foundations of skeletal calyx

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Photo by Case 9