When we think of coral reefs, we immediately imagine corals of different shapes and sizes with many colourful fishes swimming above and around these beautiful corals. We might even see a big fish or shark swim by that catches our attention. Then when we look closer, we start to see little cryptic animals like crabs, worms, nudibranchs, and small fish like gobies and blennies. Many of these animals can be found on top of reef bommies or burrowed within reef structures and are usually less than 6 cm (2.4 in). They are everywhere on the reef. Some of them even live exclusively in a particular habitat in the reef and never leave this habitat. When we look in staghorn corals in particular, we often see tiny adorable fish called coral gobies. They come in many different colours, from brown with redheads and five lines on their heads (like the Fiveline Coral Goby), to yellow (like the Yellow Coral Goby) or yellow-green (like the Emerald Coral Goby), or even green with red lines and dots (like the Broad-barred Coral Goby). These colourful gobies live exclusively in corals and never leave their particular coral once they settle in it.
Two tagged gobies from my project that are different species living together in a live coral: Fiveline Coral Goby (Gobiodon quinquestrigatus) on the left and Yellow Coral Goby (Gobiodon okinawae) on the right. © Catheline Froehlich
Why do gobies remain in their corals and what does the coral get out of it? It turns out that coral gobies and their corals have a mutually beneficial relationship whereby they each benefit from each other’s presence. Corals provide shelter, breeding sites, and food for gobies. In return, gobies remove harmful seaweed, reduce bleaching susceptibility, and deter predators. What’s really cool is how they actually help each other out. When algae begins to grow on a coral branch, the coral sends a chemical message to the goby to tell it to remove the algae. Then the goby picks the algae off and either spits it out or ingests it. Now what about coral predators? If a damselfish comes around and tries to eat the coral, the goby releases a toxin through its skin that deters the damselfish. There are also bigger fish that would happily munch on a goby due to their small size, and that is one of the main reasons why gobies don’t ever leave their coral. Predation risk along with easily finding sites to lay their eggs are what make living in corals such an attractive strategy. These coral-fish interactions are really cool, which is why I am studying them, plus it helps that gobies are super cute!
Pictured here is my assistant Abigail Shaughnessy as she searches for coral gobies in a staghorn coral. © Catheline Froehlich
We know that corals are important for gobies for many reasons, but we have yet to figure out what characteristics about corals are especially crucial. Even more exciting is that gobies are often social and live in groups of the same or different species in corals. These group-living tendencies depend on the species of gobies and their body size: bigger-bodied goby species only live in groups if the coral is big enough, but smaller-bodied species live in groups regardless of coral size. Clearly, coral size is not the only thing that affects group living. Accordingly, my fellowship project at Lizard Island aims at addressing these unknowns about habitat characteristics and determining how they affect behavioural decisions of gobies.
Zoltan Florian Marine Biology Fellowship Recipient
PhD Student at Wollongong University