As you can see from the picture, your coral frame are colonized by some little, brown and green organisms called Ascidia. The species is called Didemnum molle (also known as the green barrel sea squirt or the green reef sea-squirt.) and is very common in the Indo-Pacific area. Ascidia is a filter-feeder, feeding on suspended plankton and detritus and its green color is given by the algae living in symbiosis with them, in this way the algae is protected by the predation and the Ascidia can receive energy from its little hosts. Luckily they don’t possess any threat to the corals when they are few in numbers, however they can colonize quite quickly on the frames through asexual budding, as such they are regularly removed to minimize competition with growing corals.
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.
Look at this little fish using your coral frame as cover from bigger predators.
The Bennett’s Sharpnose Pufferfish (Canthigaster bennetti) is also known as Bennett’s Toby. As with many other puffers, they have a symbiotic relationship with types of bacteria such as Pseudoalteromonas tetraodonis. This bacteria produces tetradotoxin which is a powerful neurotoxin. These tetradoxin’s are found in their skin and internal organs. Tetradoxin is approximately 100 times more toxic than cyanide. This provides the fish with protection against predators.
The body background color is usually a light white grey on the lower body while the upper body is an olive green color. The entire body has small blue-green dots spread across it and there are light brown squiggles on the upper body.
As with all pufferfish or blow fish as they are sometimes known, they have the ability to take water into their stomach to swell themselves up, making it harder for a predator to fit them in its mouth.
Bennett’s Sharpnose Pufferfish are usually seen on sandy bottoms with isolated rubble. During the day they are normally seen in pairs. If a diver nears them they will usually swim off at a slight angle allowing one of their eyes to point backwards to watch you as can be seen above.
Bennett’s Sharpnose Pufferfish have four teeth which are fused into a sharp edged beak and the teeth continue growing throughout their life. For their size they have a powerful bite. They feed on a variety of species of algae.
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 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 10%. This is a rough estimate based on the amount of bleaching fragments of the entire frame. The degree of bleaching on your frame range from the branching tips that shows some signs of stress with a few tips left white and some intermediate bleaching (branches left pale due to limited algae)
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.
In some unfortunate cases, much like we can see in nature, there are some dead fragments on your frame such as this one pictured. 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.
Here we would like to give some information about this nice looking Pocillopora meandrina colony that is located on your coral frame. They are also known as the cauliflower coral and are quite common around the Maldives. Pocillopora meandrina occurs on shallow reefs and amongst coral communities on rocky reefs, at depth from 3-27 m and their radiating branches can reach up to 40 cm in diameter. In this species many or most of the branches are flattened on the ends and some may be curved and their colors may vary from cream, green or pink. Pocilloporid corals, not excluding P. meandrina, are generally amongst the strongest coral competitors with relatively high rates of calcification. However, coral species exhibiting high rates of calcification usually have relatively high mortality rates
Naturally, like all living things in the ocean, they have some natural enemies. Corals are no different, they also have to fight against predators such as coral crabs or snails that feed on the living tissue of corals and often leave vulnerable scars such as this one pictured. Since we did not notice the predator on the coral we assume that it was possibly Drupella cornus or more commonly known as the horn drupe. They are a species of sea snail that can grow up to about 40 mm and their shells consist of tiny horned bumps and often have a whitish or blackish shell and predominantly feed on hard corals such as this Acropora species. Their mouth consist of three to four tiny teeth and they will glue themselves onto the coral and start feeding, leaving a white mark behind. Since they eat the entire polyp, it is seldom that these parts of the corals survive and many times they end up covered in algae and die. When we see bigger sections with this king of damage, the pieces are removed to avoid algae build up
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.
Depth is an important factor for most of the corals, since most of them have photosynthetic unicellular algae in their tissue. Thus, they need to expose their tissue to light in order to trigger the photosynthesis process. For this reason, shallow water (1 – 2 m) would be ideal. In fact, the first few meters are usually crowded by corals. However being exposed to light increases the risk of damage to the coral tissue. In a similar way to the human skin that are exposed to excessive sunlight. Corals in the shallow are more susceptible to damage by the light than deeper corals. Although, simply putting them too deep would be also tricky. To positioning corals between 2 and 5 meters seems to be the best range for most of the corals. Your frame shows healthy colonies growing up at around 5 m.
