THIS ALGAE IS TOO BIG!

Graduate Student: Sammy Davis

Coral reefs are characterized by a high diversity of fish, invertebrates, algae (and even bacteria!), many of which are valued for tourism and fisheries. However, coral reefs are among the most highly threatened by natural disturbances and climate change. Major disturbances to coral communities can lead to a shift in the community - a reef dominated by coral becomes dominated by macroalgae (organisms similar to plants that produce their energy using photosynthesis). These macroalgae are known to harm coral, taking over the reef and turning it into a forest of macroalgae! Herbivory, or consumption of algae by fish and invertebrates like sea urchins, is a key process that can prevent macroalgae growing, but can herbivores reverse a shift once the macroalgae is established, helping the coral to return to dominance?

diver

Sammy hypothesized that herbivores may not be able to eat macroalgae once it reaches a certain size. The focal species, Turbinaria ornata, is known to be unpalatable (e.g. not tasty at all!) at the largest adult stage - what about the smaller recruits and juveniles? The smaller sizes have fewer defenses, such as nasty chemicals and spiny blades, so they may be better for herbivores to eat. Sammy separated Turbinaria into size classes and fed each size classes to herbivorous fish to find out how much of each size class was consumed. Sammy found that consumption by herbivores decreased as the size of the individuals increased. Once the individual algae large enough, it appears to be avoided by herbivores! This suggests that Turbinaria may be able to persist on reefs once it is large enough to avoid consumption, and that herbivores may be unable to reverse a macroalgal state once it has become established! This suggests that we need to take extra precautions to protect the important species that prevent macroalgae from taking over to protect our beautiful coral reef ecosystem.


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