Have you ever wondered how do corals grow bigger or how their branches are getting longer? Coral reefs are mainly built by stony or hard corals, together with their endosymbiotic algae (algae living in the corals), zooxanthellae. To give you some information on how the calcification process works. The main elements needed to build the skeleton are Ca2+ (Calcium ions) and DIC (Dissolved Inorganic Carbon). Both of these elements are transported into a specific area of the coral called the “calcifying region”, which is situated under each single polyp. Here, the calcium carbonate (CaCO3) is formed throughout a chemical reaction. Finally, the calcium carbonate (or technically crystals of aragonite) is deposited to form the skeleton. The process involves the polyp’s cells and the Zooxanthellae, and by the mutualistic work of these two counterparts the skeleton is formed. However, if for any reasons (i.e. high temperature) one of the two parts is not working properly the process stops and the coral may die.
Have you ever wondered how corals are eating and defending themselves … here you will see some small extensions/tentacles protruding from each of the polyp housings. They are referred to as the defensive/offensive stinging mechanisms similar to sweeper tentacles and are often linked to their feeding and defending. Inside each of the polyps are the small animals that look similar to an upside-down jellyfish with tentacles that surround the mouth part, depending on the coral species, the amount of tentacles may vary. They will move around to collect small particles floating in the water, usually plankton. These tentacles are also used for defending themselves against predators such as the coral eating snail, Drupella sp or the invasive Crown of Thorns Starfish. They also keep smaller predators such as crabs and invertebrates away. These tentacles are seldom seen, but do come out when they are feeling threatened or during feeding.
The Dascyllus aruanus, known commonly as humbug damselfish, has found in your coral frame its home. This particular fish is known by multiple common names, such as three stripe damselfish, humbug dascyllus, or black and white damselfish. They only reach an adult size of 3-4 inches (7.6-10 cm). Sporting three broad black stripes on a white body, the humbug damselfish has a zebra like appearance. The stripes run slightly off vertical through the eyes and mouth, midbody and bisecting the caudal peduncle, making it half black and half white. There are several contestants for the title of most important reef fish family, but the Damselfish are certainly one of the front-runners. Not only are there numerous species, but also many of these species are present on Maldivian reefs in prodigious numbers. The humbug damselfish that you can see in the picture is associated with isolated coral heads in sheltered inshore habitats. Like all damselfish, they can be territorial and aggressive, especially as they get older.
What is biodiversity? Biodiversity is the variety of living species that can be found in a particular place, for instance the number of coral species on your coral frame. Coral reefs are said to have the highest biodiversity of any ecosystem on the planet—even more than a tropical rainforest. In this particular image you can see two species of the Acropora genus, one of the fastest growing species of coral. Since we collect broken fragments from the bottom and not original colonies, the biodiversity on the frames is often between 1 and 4 species of corals, depending on location of collection. You will see that these small pieces have already grown quite a bit in the one year since construction. Of course we always try to keep the diversity high between all of the frames and during maintenance we often add new pieces onto the frame. Hopefully soon we will see lots of different marine species occupying your frame, which is the goal of our Coral Conservation Project.
The fish you can see here is a striped triggerfish and these guys fiercely protect your frame from intruders, such as me the marine biologist that tries to clean your frame. It has happened more than a few times that one of these fish has bit my finger in defense of their home or tried to steal my toothbrush (which I use for scrubbing algae of your frame).
Striped Triggerfish (Balistapus undulates) are part of a moderately large family with 40 species in tropical waters worldwide, and 17 species reported in the Maldives. Trigger fish have very strong jaws with dog like teeth that are used to crush hard-shelled snails or invertebrates. Triggerfish are smart fish that can be seen manipulating their environment; you can watch them carry broken pieces of corals around the reef.
This is your 6 month frame progress update. Your frame is doing fantastic!
Looking at your frame, we can see lots of new growth, especially of the acropora corals (the branching & fast growing corals). We can see some of the corals are competing for space, which is a good problem to have, it means your frame is thriving. We can also see that your frame is contributing to the overall health of the coral ecosystem. We see lots of life such as little fish, crabs, worms and mollusks around your frame. Overall your frame has survived the warm months of March, April and May just fine, unfortunately some of the other frames in our colony weren’t so lucky.
Over the following months we will continue with maintenance to keep harmful algae and predators off your frame and to give your frame the best chance for successful growth.
Coral reefs are built and made up of thousands of tiny animals called coral “polyps” that can live individually (like many mushroom corals do) or in large colonies that comprise an entire reef structure. A polyp has a sac-like body and an opening, or mouth, encircled by stinging tentacles called nematocysts or cnidae (imagine an upside down jellyfish). The polyp extracts calcium and carbonate ions from seawater to build itself a hard, cup-shaped skeleton made of calcium carbonate (limestone). This limestone skeleton protects the soft, delicate body of the polyp. Coral polyps are usually nocturnal, meaning that they stay inside their skeletons during the day. At night, polyps extend their tentacles to feed. Most coral polyps have clear bodies whereas their skeletons are completely white, like human bones. Generally, their brilliant color comes from the zooxanthellae (tiny algae) living inside their tissues. Several million zooxanthellae live and produce pigments in just one square inch of coral. These pigments are visible through the clear body of the polyp and are what gives coral its beautiful color.
We have some unfortunate news this month as we are starting to see some evidence of bleaching around the coral frames. Coral bleaching can be ascribed to warming ocean waters for extended periods of time where the symbiotic algae (Zooxanthellae) living inside the tissue coral is expelled by their host and in turn leave behind a bleaching white skeleton. This algae shares a mutualistic relationship with the corals; the coral provides shelter to the algae and in turn the algae can provide as much as 90% of the nutrients produced by photosynthesis which is used towards their growth. Corals can survive bleaching events such as this, but if they are subject to more stress or prolonged heated waters, they will surely die. Unfortunately, your frame is also showing minor signs of bleaching of around 20%. This is a rough estimate based on the amount of bleaching fragments of the entire frame. As you can see from the images, their white skeletons are not something anyone can miss, especially in the water. The degree of bleaching on your frame varies from fragment to fragment and ranges anything between minor bleaching on the branching tips, surface bleaching (those directly exposed to the sun’s rays) and intermediate bleaching (still some symbiotic algae present but pale in color).
Unfortunately, there is not much we can do at this stage, but wait to see whether they recover or not in the next months. Should they not recover and they are completely dead, they will be removed from the frame and replaced with new live ones. This is of course a major setback for our coral conservation project, but it is also the reality we are dealing with today.
Unfortunalty we found that some of the Acropora corals on your frame show signs of Skeleton Eroding Band disease (SEB). The occurrence and distribution of the coral disease has been experienced in the Great Barrier Reef, the Red Sea, Mauritius as well as the Maldives. Skeletal eroding band disease is caused by dense aggregations of the ciliate Halofolliculina corallasia and was of the first coral diseases described from the Indo-Pacific. Little is known about its etiology or impact. Skeletal eroding band is visible as a black or light gray band that slowly advances over corals, leaving a dead coral in its wake. If you look closely you will notice that part of the coral doesn’t have live polyps anymore and the coral branch looks bleached. Corals in the family Pocilloporidae and Acroporidae are most susceptible to the disease, the former being up to five times more susceptible than other families. In order to stop the disease from spreading we do our best to remove infected corals from the frame and replace them with healthy coral fragments.
In some unfortunate cases, much like we can see in nature, there are some dead fragments on your frame such as this one pictured (see below the live branch). This is often the result when corals undergoes very high level of stress where they cannot seem to recover. This is not because your frame isn’t suitable, but since all the fragments were collected from the sand they already received lots of stress before attached onto your frame, so it happens from time to time that fragments might receive further high stress levels due to increased water temperatures and they lose the symbiotic algae Zooxanthellae that they need to survive. They will turn bleach white and if stress conditions persist they will die completely since they have no more animals for feeding or defending the corals and then they are often competing with invasive algae that grow over the polyps when this happens they will also die off. During the maintenance these pieces of dead coral is usually removed while the live part remains attached.
Just look at this amazing species growing on your coral frame! This is a soft coral that belongs to the genus Sarcophython and it’s the only one we have ever encountered on one of our frames, so it is simply amazing. There are over 36 species within this genus and they are widespread in all tropical and sub-tropical seas. Unlike the hard corals that we attached onto your frame, soft corals don’t have any skeletal support and they are mostly considered as non-reef building corals. Similar to anemones, they have a tubular shape with small crown of tentacles which can reach up to 60 cm in diameter. Notice how only a few tentacles are sticking out, when they feel annoyed or threatened (or camera shy) they will contract the tentacles and expel the water that fills them, in some cases even taking the shape of a ball.
Looking at your frame, you will see that it is doing well since the last update, although we did notice a couple of dead fragments on the top and sides of the frame. Since your frame is located in the deeper waters around 5 meters, we can see that some fragments are not doing too well and is having difficulty attaching onto the frame compared to the shallower frames, the reason for this is not yet known. We have done some recent maintenance on the frame, cleaned invasive algae and predators to allow for better progress. In the upcoming months we will show you close-ups of your frame and the coral fragments, with some interesting facts and findings about those that are on your frame. After 6 months you will see a similar post showing once again the progress of your frame.
Coral reefs are susceptible to multiple impacts from both natural and anthropogenic sources. Nowadays, we are facing an increase in direct and indirect damage on corals by human activities. An example is the overfishing, which is depleting fish stocks. In addition, a secondary effect is due to the fishing tools that get entangled in corals. Fishing lines often get stuck on corals and results in great damaged due to the continuous rubbing on the coral tissue and by the over-growing of algae which may increase the competition with corals. Unfortunately, your frame has been damaged by a ghost fishing line, but this was quickly picked up during the, giving the colonies new chance to survive. We will up to date you on the progression of the new colonies with the next updates.
