Recruitment to the reef

 

column spacer Recruitment
 
 

Sexual reproduction: spawning, larval development, & dispersal of larvae

 
This section deals with spawning, larval development, & dispersal of larvae in corals. The same topics for other reef organisms can be accessed via the icons. Other topics relating to recruitment, namely, SETTLEMENT & METAMORPHOSIS and SURVIVAL DURING EARLY LIFE, are found in their own sections. hot buttons for spawning/metamorphosis/dispersal section of BCCR website hot button for sponges section on spawning/metamorphosis/dispersal hot button for corals section on spawning/metamorphosis/dispersal hot button for snails section on spawning/metamorphosis/dispersal hot button for sea urchins & relatives section on spawning/metamorphosis/dispersal hot button for fishes section on spawning/metamorphosis/dispersal
 
 

Sexual reproduction: spawning, larval development, & dispersal of larvae: corals & gorgonians

  Most corals are hermaphroditic, with gonads being located on the mesenteries within the digestive cavity. Some species release their eggs; in others, the eggs are fertilised on the mesenteries and the larvae are brooded there for a few days before being released. In still other species, eggs may be released in bundles with sperm. The sperm break free at the sea surface and swim off to fertilise eggs released from other individuals. In all species the fertilised eggs develop into planulae larvae that are about 1-2mm in size. Coral planulae mostly do not feed, but swim in the plankton for a few days before settling and metamorphosing into a polyp. The polyp begins to feed on small planktonic organisms and secretes its calcareous skeleton. As the polyp grows larger it undergoes repeated asexual divisions to produce the coral colony.
   
 

diagram showing coral life cycle



  Breeding patterns of Caribbean corals are quite variable as shown by these few examples:
 
photo composite showing a variety of breeding patterns in Caribbean corals
 
  Instead of being released from the mouth as is common in most species, eggs of some coral species are released from the polyp tentacles. The tentacles are hollow and eggs move into and along them, then exit via slits that form in the tentacles. How the eggs get from the gonads in the gastrovascular cavity (“gut”) into the tentacles is not explained by the authors of this short account. The eggs, however, in the boulder coral Stephanocoenia intersepta in Curacao, Netherlands Antilles, are already fertilised when they leave the tentacles, suggesting that this happens during the few moments of exposure to seawater as they move along the tentacle in the region of the slit. Vermeij et al. 2010 Coral Reefs 29: 411; photographs courtesy the authors.
 
photograph of boulder star coral Stephanocoenia intersepta that releases fertilised eggs from slits in its tentacles
photograph of boulder star coral Stephanocoenia with fertilised eggs in its tentacles ready to be released
close view of boulder star coral Stephanocoenia intersepta ready to release 2 fertilised eggs from slits in its tentacles
Boulder star coral Stephanocoenia intersepta that releases fertilised eggs from slits in its tentacles
Boulder star coral Stephanocoenia intersepta with fertilised eggs in its tentacles
Close view of boulder star coral S. intersepta about to release 2 fertilised eggs from a slit in its tentacle
 
 
Larvae, whether from corals or other invertebrates, require solid stable substrata on which to settle. Algal growths are generally avoided. Although sea-urchin and other grazing has long been thought to favour coral colonisation be removing algae, there has been little direct evidence for it prior to a study done on the south coast of Barbados involving sea urchins Diadema antillarum on a limestone seawall. Eleven years after its installation the seaward side of the wall lacked Diadema and predictably revealed heavy algal growth and absence of cora (see photo on Left below). In contrast, the leeward side hosted numerous mature sea urchins that grazed the rock surface of algae, therefore allowing colonisation by a variety of corals (Right photo below). Macintyre et al. 2005 Coral Reefs 24: 273; photographs courtesy the authors.
photograph showing seaward side of limestone wall in Barbados and absence of sea urchins Diadema antillarum   photograph
 
 

photograph of Pocillopora damicornis on the Great Barrier ReefIn coral species in which eggs are fertilised within the digestive cavity, the planula larvae may be retained until some suitable stimulus is received. To learn more about such stimuli, let's look at an example of an Indo-Pacific species of cauliflower coral Pocillopora damicornis, which has been extensively studied.

 

 

 

Corals Pocillopora damicornis on
the Great Barrier Reef, Australia

 
 
Release of larvae by the Indo-Pacific cauliflower coral Pocillipora damicornis is synchronised to the lunar cycle, with maximum release each month occurring during the week following a full moon. Such synchronicity is also found in many Caribbean corals. Jokiel 1985 Proc 5th Intern Coral Reef Sympos 4: 307. graph showing planula releases by an Indo-Pacific coral through the year
 
The same researcher lists the factors that will DISRUPT and NOT DISRUPT larval release-times in Pocillopora in Hawaii:

DISRUPT:
1. heavy rainfall
2. extreme low tides
3. high temperatures
4. volcanic dust

5. typhoon-force winds
6. heavy cloud cover
7. el Nino effects
8. lower mean sea level
9. high waves
10. fast currents

NOT DISRUPT:
1. jet-engine noise
2. lunar eclipse
3. SCUBA-divers nearby
4. other corals spawning
 
 

photograph of mound coral Montastrea sp.

Similar factors are involved in spawning in Caribbean
species of boulder coral Montastrea:

1.temperature: neither
too high nor too low

2. moon phase: 5-8d after full moon ( autumn) 3. time of day: 2-4h after sunset 4. season: autumn is the principal time of year
 
 

photograph of male pillar coral Dendrogyra cylindrus spawningphotograph of female pillar corals Dendrogyra cylindrus spawningMany other coral species, such as pillar corals Dendrogyra cylindrus in the Caribbean, spawn at night in synchrony with the moon cycle. Sexes are separate and, as reported by a researcher in the Florida Keys, they spawn simultaneously in August two to three days after the full moon. Males spawn first, with the females following a few minutes later. Neely et al. 2013 Coral Reefs 32: 813. Photographs courtesy the authors.

 

Sperm of Dendrogyra cylindrus forms
a blanketing cloud around the males

 

 

 

 

 

 

Eggs are released by females
in buoyant mucous strands

   
 

photograph of gamete bundles being released from boulder coral Montastraea faveolataScientists off the coast of Veracruz, Mexico report a mass spawning of boulder coral Montastraea faveolata in mid-evening on 29 August, 2002, 7d after the full moon. Other boulder corals and tubeworms are noted to be also spawning at that time. Beaver et al. 2004 Coral Reefs 23: 324.

 

 

 

Gamete bundles being released from
polyps of boulder coral Montastraea
faveolata
at night in Mexico 0.3X

   
 

Caribbean brain corals Diploria labyrinthiformis normally spawn at night synchronised with phases of the moon, so it was unexpected for researchers in Bonaire to witness pre-dusk spawning by this species. The significance of the event is unclear, but the authors provide a photograph of a butterflyfish Chaetodon photograph showing s foureye butterflyfish Chaetodon capistratus eating freshly spawned gamete bundles from a brain coral Diploria labyrinthiformiscapistratus feeding on the freshly released photograph showing gamete bundles being spawned by a brain coral Diploria labyrinthiformisgamete bundles, that does suggest that daylight spawning may favour a new set of opportunistic predators. Muller & Vermeij 2011 Coral Reefs 30:1147. Photographs courtesy the authors.





Brain coral Diploria
labyrinthiformis
releases
gamete bundles...

...that are subsequently eaten
by a foureye butterflyfish
Chaetodon capistratus

 
 

While many gorgonians spawn their gametes freely into the ocean, some species including Pseudopterogorgia elisabethae, Briareum asbestinum, and Pterogorgia anceps brood their fertilised eggs on the surface of the colony (see photographs of gorgonian Pterogorgia anceps carrying brooded eggs on its surfacephotograph). According to observations in Carrie Bow Cay, Belize on Pterogorgia anceps, the eggs are held on the colony’s surface near the polyp bases until they develop into motile planula larvae, at which time they swim away. Whether the brooding strategy is in response to external factors is at this time not known. Ritson-Williams 2010 Coral Reefs 29: 437. Photographs courtesy the author.

 

Pterogorgia anceps brooding
its eggs at the polyp bases

 
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