Reproduction

Corals exhibit a variety of reproductive strategies: some species are separate sexes others are hermaphrodites , some spawn gametes into the water column others brood larvae internally (Roberts et al. 2009). Three quarters of shallow water Scleractinian corals are hermaphrodites, whereas most cold water Scleractinians are gonochoric. There are only 3 hermaphrodite Scleractinian corals found in cold water out of a toal of 15 species, one example being Carophyllia cornuformisis  (Roberts et al. 2009).

Figure 8: Mass coral spawning showing eggs being released from polyps (Image taken from Kaiser et al 2005)

 

Sychronous spawning is a spectacular event witnessed in 85% of shallow water scleractinian species. This type of mass broadcast spawning is related to phases of the moons lunar cycle (Roberts et al. 2009). Gametes are released synchronously into the water collumn from numourous colonies (Figure 12), this increases the chances of cross-fertilisation. Spawning can be effected by light levels, tempertature, tidal cycles and chemicals released from gametes (Roberts et al. 2009).
In cold-water corals synchronous spawning has never been directly witnessed but there is evidence to suggest that mass spawning does occur: Firstly, no planula larvae have been observed in historic sections of L.pertusa and other frame work species  and secondly shallow water species of the same family are also broadcast spawners (Burges and Babcock 2005), (Roberts et al. 2009).  

In tropical waters moonlight is the main factor in gamete release, but spawning in cold-water corals is thought to be conveyed in other ways. Reproductive maturity may be linked to maximum resource availability this coincides with the end of summer during phytoplankton blooms and in increase in biomass of associated trophically linked organisms (Burgess and Babcock 2005). The exact environmental cues triggering reproduction are unknown but seasonal food cycles and nutrient availabilty are thought to play a key role in the release of gamete release in late Autumn (Burgess and Babcock 2005).

Leave a Reply