By Mayuresh Gangal
On Valentine’s Day of 2015, while diving on the reefs of Kadmat Island in the Lakshadweep, two PhD students Rucha Karkarey and Anne Theo stumbled across a strange site. Millions and millions of tiny fish swimming in giant shoals. On looking closer, they identified these small fish to be surgeonfish larvae.
Surgeonfish are a group of algae-eating herbivorous fish commonly found in coral reefs. They are called surgeonfish because of their distinct scalpel-like modified scales at the base of their tail. When Rucha and Anne saw these surgeonfish in such a large number, the realisation dawned on them — they had stumbled upon a “recruitment event”.
You can view the recruitment event here:
What is a recruitment event?
Adult surgeonfish typically lay their eggs in coral reefs and once these eggs hatch the small fish larvae emerge and move away from the coral reef into the open ocean. After spending some time in the open ocean, these larvae return to the reef on a specific day in big shoals and find a patch of reef around which they can spend their adulthood. This event is called a recruitment event. It is extremely difficult to observe this event directly because people are still trying to understand what factors trigger the surgeonfish to return to the reef in such large numbers. Rucha and Anne described the whole event in their publication “Homeward bound: fish larvae use dispersal corridors when settling on coral reefs” as a natural history note in the Journal “Frontiers in Ecology and the Environment”. The study can be accessed here.
Rucha and Anne reported that surgeonfish species were choosy when selecting a specific site on the reef. For example species like the goldring bristle-tooth, Indian Ocean mimic surgeonfish, powder-blue tang, and brown tang mainly recruited and settled on reefs on eastern side of the island, where as dominant recruiters like the orange-striped bristle tooth tang, lavender tang, and Thompson’s surgeonfish recruited on reefs on both east and west side of island.
Furthermore, the larvae of three predominant species in the shoal looked alike. These larvae formed such big shoales to reduce their chances of being predated upon. In addition to being similar, it was harder for predatory fish to single them out.
Recruitment events are very drastic changes for the other inhabitants of coral reefs, particularly to damselfish, who also feed on algae. These small fish identify a patch of reef as their territory and allow only a certain kind of algae to grow there, defending it against other algae eaters like surgeonfish. The surgeonfish recruitment event suddenly brings millions of mouths which can potentially invade their “algal gardens”.
In the next section of the article, we took this idea of a sudden influx of millions of recruits flooding the reefs, and viewed it from the point of view of the other residents. These would encompass damselfish, predatory fish like groupers, and many more. If we imagine that residents of reefs also live in societies like us with administrations overseeing “reef affairs”, then this is a small glimpse of how a “breaking news” on reef television would look at the time of a surgeonfish larvae recruitment event.
Reef News:
BREAKING NEWS! Surgeonfish are recruiting in massive numbers in and around Kadmat’s reef. There is a palpable sense of anxiety among the residents. At this moment, the Head of Kadmat Reef security General Ziyad is giving an official statement in a press conference. So we will take you straight to the press conference…
Journalist 1: General Ziyad, can you please provide some details about this massive movement of surgeonfish in the reef?
General Ziyad: I would like to tell all the residents of the reef to stay calm! The sudden presence of surgeonfish is not new to the older residents.
Journalist 2: How can you say this is nothing new? We have not seen movement in such a proportion before, can you clarify?
General Ziyad: Well… as you all know, the current year is supposed to be warmer than usual, threatening the coral structure we depend on. If corals bleach and die this summer, the coral structure will crumble and thousands of us will be shelter-less. Algae will grow on broken coral rubble and it will not allow new coral seeds to settle and grow. Meaning… we won’t have our coral homes in this reef.
Journalist 2: So you think surgeon recruits will help to clear the algae?
General Ziyad: Yes. We need all the mouths we have to fight this invasion of algae. In light of this possibility, the reef administration, with the help of the Department of Security and Defence and Department of Disaster Management, has created a special “Anti-Bleaching Task Force or ABTF” composed of algae-eating surgeonfish recruits. The idea behind ABTF is to increase the number of positions of the herbivores on the reef to get rid of algal cover on corals where we live. So, we had requested all surgeonfish couples to help us, and this massive recruitment is just a response to that. I take this opportunity to thank all the surgeonfish couples for showing such enthusiastic support in the time of our need. Such a massive recruitment would not have been possible without you.
Journalist 3: But there are unhappy noises from the damselfish community who are afraid of a possible invasion by surgeonfish to their gardens. What do you have to say about that?
General Ziyad: We appreciate the importance of the gardens to our damselfish brothers, not just in terms of livelihood but also sentimental value and cultural identity associated with them. However, they must realise that this is in preparation of a possible crisis. We count on their support and cooperation.
Journalist 4: It seems like this ABTF is a kind of militarisation or “surgeonisation” of the affairs of the reef?
General Ziyad: Allegations of these sorts are completely baseless. As you can see, we have brought the best predators like groupers and Moray eels to facilitate the authorities in the selection process of these recruits. We are doing all we can in selecting only the best of these recruits who can do the job in case a disaster like bleaching comes upon the reef. I urge once again all the residents of the reef to be accommodative and to understand that although these steps look drastic, they are necessary for the reef’s future.
Journalist 1: But how is the administration going to deal with the graser hooliganism? Has the administration forgotten the herbivore riots after the 2010 bleaching event?
General Ziyad: We are aware of problems like lobbying and hooliganism might happen. That is why we have brought so many predators to keep such incidences in check. We have given strict instructions to ABTF to accept algae grown by gardeners only if they are willing to donate. Crop raiding and hooliganism won’t be tolerated. However, if such incidents happen, please report them to your nearest groupers. They have been notified to be lenient with damselfish and other gardening communities.
Journalist 3: So how long will the ABTF stay?
General Ziyad: As of now I cannot give any specific date. Although it could be a slight inconvenience now, I assure you that in the coming month you would be thankful to ABTF. I think that would be all. No further questions. Thank you all for coming.