Did you know? Coral symbionts.

A photosynthesising animal?

Yesterday I went for a talk titled 'Coral-dinoflagellate symbiosis: evolution, ecology and interaction states' by Dr. Michael Stat. While the title might sound complex, here's a few facts about coral and some new ones based on what I learnt yesterday!

1. Corals represent an endosymbiotic system where an animal (the coral) has single-celled dinoflagellates of the genus Symbiodinium (a type of algae) living inside the corals' tissue. 

2. The relationship is symbiotic because the two species have a close and long-term relationship with one another. In this case, it's mutual as both partners exchange nutrients.

3. The photosynthetic ability of the algae means the coral, in essence, makes its own food. 

4. Turns out, corals have host specific (specific to that particular type of coral) and shared symbionts. The difference is based on the acquisition strategy i.e. whether the symbiont was horizontally transmitted (symbionts expelled into the ocean and picked up) or vertically transmitted (symbiont is passed on from generation to generation).

5. One of the big threats that corals face is called bleaching. Bleaching occurs when the conditions necessary for the coral to thrive change drastically. For example when the ocean temperatures increase beyond what the coral can tolerate. At this point, the symbionts are either expelled or lose their pigmentation.

6. If conditions go back to normal, tolerable levels, the coral can recover. In this case, some corals perform better than others. Scientists were curious as to why this was the case. Basically, if you are the kind of coral that tightly associates with only one type of symbiont, your recovery is likely to be less or not at all (depending on the intensity and duration of the stress).

Here is the abstract of the talk in case you are interested.

Corals form an obligate symbiosis with unicellular photosynthetic dinoflagellates. The diversity of dinoflagellates associated with a host is the result of both evolutionary and ecological influences. While mutualism is the paradigm for coral-dinoflagellate symbiosis, recent evidence shows that not all host-symbiont interactions are equally beneficial. The dynamics of host-symbiont partnerships and the exchange of nutrients that ultimately defines the interaction state of the symbiosis are important factors that contribute to the variability in response of corals to changes in the environment.