The surprisingly dazzling world of coral reefs

by Esha Gokhale

The world of coral reefs has always fascinated me. Did you know that the Great Barrier Reef in Australia, the largest coral reef system in the world, covers more than two thousand square kilometres?! What really got me thinking is how these massive and stunning reefs are built by such tiny animals. What are the early life-history processes that are responsible for building these habitats that house about 25% of all marine life? Which factors facilitate this reef-building and which ones deter? Determined to find answers to these questions, I dove into the world of coral settlement and recruitment last field season.

Coral spawning is one of the methods used by “hard” or “reef-building” corals to reproduce, where male and female corals release eggs and sperm into the water column. These male and female “gametes” combine to form a “baby coral” called planula. This spawning process most often occurs as a synchronised event, increasing the chances of survival for the planulae. Settlement and recruitment are post-spawning processes, where coral planulae look for suitable substrates to “settle” on. This happens because of a variety of physical, biological, and chemical cues. Their chances of survival depend mainly on the kind of substrates the planulae have selected. Recruitment happens when the floating planulae successfully find a suitable substrate, attach, and establish themselves as members of the reef community.

While these planulae are extremely minuscule and invisible to the naked eye, there is a way to make their studying practical and spectacular, to say the least. Fluorescence imagery is a novel, feasible and non-invasive method that can be implemented easily. Corals contain fluorescent proteins in their tissues, which when excited under blue or UV light, glow green like those radium stars on a ceiling! After reading about this property, finding out that underwater UV torches exist and are also easily accessible, and that there was ACTUALLY a way to study coral settlement and recruitment during my fieldwork AND collect REAL data, my excitement knew no bounds!! But there was some time before I could begin. First, I had to team up with Naveen, Tanmay, and Chaitanya to come up with an experiment and a proper study design. After ticking that off the checklist, it was time to collect real data.

However, though I learnt all of this in theory, I had not put any of this into practice. There was a lot of preparation to be done, like making quadrats (a basic 1m x 1m square made of PVC pipes to estimate the abundance of certain plants or animals), readying the necessary equipment and dive gear, etc. When we finally decided to commence our fieldwork after acquiring our permits, multiple protocol discussions and dry runs, I could not believe that we were really doing this. Plus, there was the thrill of collecting data for my very own study for the first time. We took extra precautions for the UV torch, as well as for the cameras and other equipment that we were supposed to take underwater while diving. There was a LOT of trial and error, along with a general beginner’s confusion with our technique, so of course there was some anxiety.

As soon as I switched on the UV torch, I remember forgetting every single thing that was bothering me, to marvel at the beauty of these tiny, green, glowing creatures on the seafloor. It was like looking at bioluminescence but having the power to recreate it whenever I wanted! Until this very moment, I had some doubts as to whether this “novel technique” would really work, and this event turned all my doubts to dust. It was a moment to remember, not just for me, but also for all the people accompanying me for this dive.

With this successful and eventful beginning, our fieldwork progressed without major hitches. Dare I say, we had a good (but very hectic) and fulfilling field season!