Shapes of Coral

Date October 7, 2019

IMG_3032.jpg

You may have heard of boulder corals and soft corals, but did you know there were “runners”, “vines” and “trees” too?



I recently had the fantastic opportunity to catch up with Hantu Blog volunteer, Gina Tan. We spoke about sinking corals, butterflyfish and coral spawning. I was absolutely fascinated by her insight and unique views of the life history of reefs and wanted to learn her opinion about how our reefs, and in particular, Singapore reefs, might have adapted over time to become what we see today!

DN: Generally, how many type of coral forms are there?

GT: There are many different types of coral forms. Jackson (1979) classified corals into six basic colony forms: runners, sheets, mounds, plates, vines and trees. However, these are not the easiest way to identify a growth form when we do reef surveys. Generally, a lot of coral scientists prefer to use “branching” and “massive” to describe coral forms, especially when they are talking about reef impacts. “Branching corals” are generally used to refer to corals that are more sensitive to impact, compared to massive corals, which are relatively more resistant to impact. 

Coral forms

Six basic coral colony forms as described in Jackson (1979) “Morphological strategies of sessile animals”.



DN: Which are the dominant coral forms in Singapore?

GT: Most of the corals in Singapore are classified as massive.

DN: Why do you think this is?

GT: Compared to other coral forms, massive corals are able to invest more on maintenance – this means that they sort of have a better immune system. In a place like Singapore, where there is a lot of disturbance and sedimentation, massive corals are able to work harder to resist the high frequency of impacts that are dealt to it.

IMG_0206-5

Branching corals in Singapore suffering from bleaching.

DN: You mentioned branching corals grow faster than massive corals, and that there are some trade offs?

GT: Yes, the trade-off is between growth and maintenance (in general). Branching corals grow fast but are able to invest less in maintenance, so they are more sensitive to impact. While massive corals compromise with slow growth in order to invest more in maintenance. This means that massive corals are more likely to survive impact, and this could be a reason of why we see more of them in Singapore – with each impact, branching corals die away, while massive corals survive. Massive growth forms are more stable and less susceptible to damage.

IMG_5370.jpg

Some coral forms are specialists and are able to thrive in environments where other corals are not able to colonise.

DN: What are the advantages of branching corals?

GT: Branching corals are focussed on growth, this means they grow faster, and can quickly dominate a reef via asexual reproduction, or what we sometimes call, fragmentation. Rather than invest energy on growth, massive forms invest on maintenance – for example, producing mucus to get rid of sedimentation. 

IMG_6151.jpg

Reefs form a complex living structure upon which other reefs organisms like fish and anemones are able to find shelter and colonise.

DN: What kind of habitat would a reef dominated by branching coral support, and what kind of habitat would a reef dominated by massive coral support?

GT: Branching corals are preferred habitat for many juvenile fishes. For example, butterflyfish and damselfish, as they have more complex structures that can provide shelter from predators. Apart from shelter, some corallivorous (coral-eating) butterflyfish also fancy branching corals as a food source! However, when branching corals are limited, some species of butterflyfish are able to switch their food preference to massive corals instead. Generally, a reef dominated by massive coral is considered less complex as there is less shelter available for juvenile fishes, and perhaps cannot support as diverse communities of fish as branching corals.

DN: You mentioned massive corals push down on a reef while branching corals grow upwards, how does this work?!

GT: Massive corals have denser skeletons compared to branching corals, so their overall mass is much heavier compared to the lighter branching corals. I guess the massive corals are like big and heavy loads pushing down on the seabed, causing the reef to “sink” compared to the lighter branching corals that are able to stack on top of each other without crushing the colony below since they are much lighter and less dense.

IMG_5232.jpg

Singapore reefs are home to over 120 species of coral that come in a vast variety of shapes, each with their unique advantage to survive and thrive in these complex environments.

DN: In your opinion, is there a “better” type of reef?

GT: A “better” reef would be one that is highly resistant to impact – but there isn’t really one. A reef that consists mainly of massive corals would likely be one that is frequently disturbed. This high frequency of impact, would result in the survival of highly resistant massive corals. The more susceptible branching corals would not be able to survive. Branching corals are found in reefs with less impact. They require lots of sunlight and nutrients so they can invest lots of energy in growth. I imagine a better reef would have a good balance of both. That being said, all reefs are unique and are a result of their unique environment. Perhaps in some areas, growing fast may be an advantage, while in another, growing slowly with a strong “immune system” is a better strategy to survive.

Leave a Reply

XHTML: You can use these tags: <a href="" title=""> <abbr title=""> <acronym title=""> <b> <blockquote cite=""> <cite> <code> <del datetime=""> <em> <i> <q cite=""> <s> <strike> <strong>