Wednesday, September 20, 2017

Asexual Reproduction


Corals reproduce in a variety of ways, using both asexual and sexual means.  This article focuses on the different modes of asexual reproduction, a critical topic when trying to differentiate between some of the more confusing corals with shared or separate walls, particularly within the Faviidae.  The mode of asexual reproduction is not generally a 100% clear cut method of identification, but used in conjunction with other clues can significantly aid the process.

Before discussing the main terms and concepts, it is important to understand when looking at a coral colony that specific characteristics may not be repeated across the whole colony surface; make sure you scan the entire colony and then concentrate your efforts on the mid flanks of the coral.  Why?  Because often at the edges of the colony or on the apex, the corallites are affected by stressors such as competition from neighbouring corals, or exposure to high light levels.  These stressors can modify corallite appearance, making identification of predominant characteristics difficult.  For more in-depth information on the key steps to examining a coral colony have a read of the Coral Identification article.

(Photo of coral colony with mid flanks highlighted)

Throughout this article the term corallite is used – this is the hard skeletal part of a coral individual.  When splitting or growth of the corallite is discussed, the living tissue (the polyp) overlaying the corallite will also split or grow.



Asexual Reproduction for Fun and Profit

It has already been mentioned that relying on reproductive characteristics alone is unlikely to ensure successful coral identification.  But it is an important step in the process.  Below are two examples of how knowledge of asexual reproductive modes in corals can help with identification:

Favia vs. Montastrea

Favia and Montastrea are similar looking members of the Faviidae, possessing corallites with separate walls.

(Photos of Favia and Montastrea distance (un- named!))

Close inspection of these coral colonies shows the one on the left has corallites reproducing by intra-tentacular budding, whereas the one on the right has corallites with extra-tentacular buds.  Intra-tentacular budding is characteristic of Favia whereas extra-tentacular budding is characteristic of Montastrea.

(Photo of close up of Favia with intra-buds and Mont with extra-buds, this time named)

Favia vs. Favites

Favia predominantly forms corallites with separate walls, whereas Favites’ corallites have common walls.  However, in some instances Favia may appear to have common walls or Favites may appear to have separate walls, i.e. sometimes the difference is confusing.  In this instance, examining budding within the colonies can assist in differentiating between the genera.

(Photos of favia and favites unnamed but subcerioid, subplocoid so look similar)

Favia reproduces via intra-tentacular budding and the daughter corallites tend to be equal in size.  Favites also reproduces by intra-tentacular budding but the daughter corallites tend to be unequal in size.

(Photos of close up favia with equal sized daughters and favites with unequal daughters – this time named)

Learning Resources

Links

Suggested Reading

  • Veron, J. E. N. (2000). Corals of the World. Melbourne: Australian Institute of Marine Science.
  • Yamashiro, H., & Nishihira, M. (1998). Experimental study of growth and asexual reproduction in Diaseris distorta (Michelin, 1843), a free-living fungiid coral. Journal of Experimental Marine Biology and Ecology, 225(2), 253-267.