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.
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.
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.
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 tiger cowrie (Cypraea tigris) is one of the larger species of cowrie. They are marine snails in the family Cypraeidae. They are an extremely attractive sight as they move across the reef. They are nocturnal and are only seen on the move at night. During the day they can be seen on the reef holed up in their shells, sometimes in the open. Roughly egg-shaped, the shell is glossy on the exterior and measures up to 15 cm in length. Most are however in the 10 cm range. The exterior of the shell is a pale whitish color covered with a large number of dark brown or blackish spots. On the lower section of the shell it is a whitish color and the opening is lined with tooth-like serrations.
The tiger cowrie is found across the Indo-Pacific region, from the east coast of Africa including Madagascar to Micronesia and Polynesia, the Coral Sea and the Philippines. They are found in depths of 1 meter to 40 meters. They are usually found on reefs but have also been seen on sandy bottoms and in grass beds
Here you will see the partial shape of the cable tie that we used to stabilize this particular fragment to the iron frame. In one month we can already see that this Acropora have started to overgrow this plastic tie and will soon be part of the skeleton forever. Plastic cable ties are a good compromise for attaching corals to the structure, since the material is cheap, resistant and the results are great, however we are looking into using different materials to improve our techniques of reducing plastics in the ocean. When this colony have reached the minimum size for spawning it will release its gametes in the water that ultimately leads to the formation of new colonies elsewhere on the reef
Have you ever wondered why some corals are more colorful than others… That is because some corals increase the production of colourful protein pigments (such as these purple tips) when they are exposed to more intense sunlight and this colony, of a branching Acropora, is simply amazing. Scientist have found that these pink, blue and/or purple proteins act as sunscreens for the corals by removing substantial light components that might otherwise become harmful to the algae hosted in their tissue. Corals rely on these light-dependent miniature plants, the so-called zooxanthellae, since they provide a substantial amount of food. Furthermore, these tips consist of a particular polyp called an “apical polyp”. It is responsible of the growth of the particular branch. For instance, it will reproduce asexually by cloning itself, potentially an infinite number of times throughout its lifetime. Here and there, one of the “radial polyps” will differentiate becoming a new apical polyp with its distinguished purple color, driving the growth of a new branch.
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.
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 moderate signs of bleaching of around 40%. 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), intermediate bleaching (still some symbiotic algae present but pale in color) and those completely bleached.
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.
Acropora corals are among the most common genera of corals in tropical reefs with up to 150 species already described. Corals are composed of tiny individual polyps each that resemble an upside-down jellyfish with the mouth in the middle, surrounded by the tentacles. Here you can appreciate the tiny polyps in this picture. Furthermore, Acropora corals are called hexacorallia since each polyp has six, or multiples of six, tentacles. Such structures are used for hunting prey, microorganisms, but also used for defense. These tentacles are armed with unicellular weapon needle-like composed with a strong mix of toxins. Humans are not harmed by these toxins but it may cause inflammation along with some itching if touched.
Just look at this amazing coral attachment. 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 into 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 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.
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.
A fresh scar from a broken branch, the white indicate the calcium skeleton underneath that is produced by the tiny polys above year after year. Since collected fragments are picked up rather than broken down from existing colonies they often have dead sections covered with overgrowing algae and dead or damaged polyps, as such these sections are removed for faster recovery. You can already see the new polyps starting to grow along the bottom of the scar, soon the branch will regrow into its former state.
We would like to give some information about this colony of Acropora digitifera that lives on your coral frame. This species forms digitate colonies; the branches may be 1 cm in diameter and up to 10 cm long. This species strongly prefers shallow water. It is usually cream or light brown in color with blue branch tips, but can also be brown with purple tips. It is common near reef crests’ as it prefers strong water movement and it is very common in the Maldives. The most important known threat is the reduction of coral reef habitat due to bleaching, disease and predation. However, it seems to be strong enough to resist to habitat loss more than other species of corals. However, since the current situation with multiple stresses (mainly rising temperature of the ocean) acting simultaneously the species is considered Near Threatened by the International Union for Conservation of Nature (IUCN).