Written by Carla Elliff
I sat down today to write about coral reefs. I’ve been studying this ecosystem for about eight years now. I have a bachelor’s degree in oceanography and a master’s and doctorate in geology. This doesn’t make me a coral reef know-it-all, but I can say I have quenched my basic curiosity about this amazing world and now I’m digging into deeper questions… What management strategies are best suited for a particular reef site? How can climate change decrease shoreline protection? How can we make better use of coral reef ecosystem services? What species are more resilient? Questions such as these will definitely take me a while to answer.
But today my burning question was: what do people want to know about corals and coral reefs?
In academia it is very easy to lose touch with the “outside world”. So, while I was musing about what I’d like to write about corals and coral reefs, I suddenly thought “should I be writing about what I want or about what the general public wants to know?”.
Which is why today I give you the first “coral reef autocomplete interview” – a parody of WIRED’s autocomplete interviews on YouTube!
WIRED is an American magazine that created this type of interview using the web’s most searched questions. They basically google keywords like “what”, “does” and “how” followed by the interviewee’s name or subject they are addressing. Their guests are usually Hollywood celebrities, but keeping within Reefbites’ scope I found an interview with Al Gore talking about climate change to use as an example: https://www.youtube.com/watch?v=TOl9WbpcBVM
So, what does the internet want to know about corals and coral reefs?
I googled “what”, “do” and “how” followed by “corals” and “coral reefs” and these were the top questions I found:
1. What corals eat
Corals actively catch tiny organisms called zooplankton to eat. Each coral polyp stretches long tentacles at night in search of prey. The tentacles sting free-swimming zooplankton and pull them into the polyp’s mouth, which are then digested in the stomach. A very concerning situation regarding this feeding strategy has emerged recently among researchers. Corals have been found to ingest microplastics in the same way they do zooplankton, with still unknown effects on coral physiology and development.
However, many corals get most of their energy using a different strategy. Corals have evolved a peculiar life strategy: living within their tissue are microalgae called zooxanthellae. Coral and zooxanthellae have what we call a symbiotic relationship, where living together is easier than living apart. Corals provide carbon dioxide and a safe home to the microalgae, where they are less vulnerable to predators. In exchange, the microalgae use this carbon dioxide and sunlight to produce sugars through photosynthesis. They produce more energy than they need, so a good portion is transferred to the polyp, supplying the coral’s main source of energy.
2. What coral reefs are dying
The answer to this question is actually harder than you would expect. Coral reefs around the world have experienced immense degradation, there is no doubt about that. However, some reefs are very difficult to get to and we have limited data about their health over the past years/decades. This means we can’t give a precise number on coral mortality and reef degradation due to a lack of data.
In general, reefs closer to populated coastal areas tend to be in poorer shape. This is because they are directly subjected to all sorts of human impacts: overfishing, pollution, unsustainable tourism… These impacts can promote coral diseases with pathogens that can wipe out entire regions of susceptible corals, excessive sedimentation that smothers polyps, water eutrophication, and so much more!
On top of these impacts there is also climate change, which causes a lot of stress (so much that corals expel their energy-giving zooxanthellae and go through the process known as coral bleaching, and can even die in this process). This means that coral reefs farther away (even in remote areas!) are not free from danger either, since the effects of climate change are global and our human impacts are reaching farther and farther!
3. Do corals have brains
Corals are cnidarians (like jellyfish and anemones), so they have a simple nervous system that does not include a brain. Cnidarians are thought to be one of the first groups of organisms to have evolved a nervous system. The nerve net in corals connect through the polyp to allow basic senses, like detecting prey or chemical substances in the water.
Funnily enough, even though corals do not have brains, there is a group of coral species called brain corals because they form a colony in the shape of this organ! Take that, Mother Nature.
4. Do coral reefs need sunlight
If we are talking about shallow-water coral reefs, in general yes. These reefs are found in shallow waters precisely because they need to be within good range of sunlight. This relates to the first question about what corals eat. Since hard corals are the main builders of coral reefs and the main source of energy of many coral species comes from the photosynthesis of their symbiotic microalgae, coral reefs generally rely on sunlight to thrive. However, there are corals that do not have this symbiotic strategy (azooxanthellate corals) and, therefore, do not rely on the sun. Over geologic time, our shorelines have experienced important rises and falls in sea level. This has led to ancient coral reefs “drowning” because they were unable to keep-up with the rising sea.
However, when considering deep-water coral reefs, then the answer is certainly no. As the name suggests, these reefs are located at depths of up to 6,000 m and have only been studied in greater detail over the past 20 years. These amazing ecosystems are very difficult (and expensive) to reach, but researchers have already found thousands of species and some specimens believed to be more than 4,000 years old!
5. How corals are formed
Corals are formed by polyps and they can live either individually or in a colony. Individual polyps form corals like the mushroom coral Fungia scutaria. However, corals that form colonies are generally more common and include brain corals and branching corals.
Corals can reproduce either asexually or sexually. In asexual reproduction, either coral polyps can separate from their parent polyps and start a new colony or a fragment of the original colony (containing many polyps) breaks off and then starts a new colony. In sexual reproduction, polyps produce eggs and sperm that, once fertilized, generate coral larvae. These tiny coral larvae are very vulnerable and, if they survive this initial phase, they can settle on a hard surface and begin to grow into polyps.
6. How coral reefs are formed
Coral reefs are formed mostly by corals (which in turn are formed as described above) and also by lots of other critters. Some organisms are considered reef-builders because they secrete calcium carbonate in thin layers, slowly forming the reef framework. These reef-builders include not just corals, but also encrusting algae, sponges and other calcifying organisms. All these organisms working together generate this complex three-dimensional carbonate structure supporting a huge amount of biodiversity!
Hope you enjoyed this autocomplete interview! What more does the internet want to know about coral reefs?