Thank you for signing up to keep in touch with the Coral Conservation Project. Pictured above, you will find your coral frame as it was few days after construction. Your personal page will allow you to see more regular updates and amazing facts about the corals and animals living on your frame. By now having all the updates on one page, seeing the progress of your frame will be much easier and convenient. If you want to satisfy your curiosity even more, you can take a look at our Marine Blog Life and videos from the Marine Lab Diary or connect with us for more information.
Here is the start of a healthy coral reef relationship!
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.
Humans get a sun tan – corals become more colourful.
Looking at your frame, you will see that it is doing amazing and the corals are really growing well since the last update even after the heated months and some stormy weather. We have done some recent maintenance on all the frames which include cleaning them, removing the invasive algae and coral predators to maximize growth. In the upcoming post 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.
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.
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.
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.
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).
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.
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 30%. 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) and/or 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.
It is unfortunate to see that some coral frames are exposed to greater mortality compared to others mainly due to environmental factors, such as predation, high water temperature or diseases. Often times we see that broken fragments used for frame construction are not recovering due to prolonged stress from lying in the sediment and then exposed to the sun and human contact and as a result they slowly die and become covered with competing algae. In other cases, the fragments may also be heavily exposed to predation from a mollusk called Drupella spp. It is a corallivore species which feeds mainly on adult corals of Acropora genus. During our maintenance we remove the predators from the frames, although the result of their feeding is quite severe in some cases, in which case, the fragment is unlikely to survive. When we see a high number of dead fragments, we remove them completely and replace them with new ones.
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 coral 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.
Looking at your frame, we can often see these “algae mats” forming on the frame or on the corals, in this case, the steel bar to the left. This is commonly known as red slime algae, also frequently found in aquariums. This in fact is not algae, but rather an oxy-photosynthetic bacterium which have dominated marine environments for more than three million years, commonly known as cyanobacteria. Usually corals can prevent algal settlement on the live tissue, however newly settled recruits or broken fragments and juveniles seem to be the most vulnerable due to their small size and vulnerability to physio-logical challenges. Tissue death can often follow due to the exposure of hypoxic, sulfide-rich microenvironments that is associated with this bacterium. During frame maintenance we remove these with a toothbrush to minimize any association with the fragments.
Corals have many “enemies” in nature, one of them is a mollusk and its name is Drupella cornus. This is a species of snail with small shells (no more than 5 cm) covered by tiny bumps. The shells can sometimes be brown or pinkish; depending on the algae that are growing on it. This species is usually common in living corals of the Indo-Pacific, where is frequently found hiding from predators in the crevices during the day. Drupella is considered a threat for corals since it eat live coral tissue by stripping the soft body from the coral skeleton. This species prefer to feed on fast-growing coral species such as Acropora or Pocillopora, but it can feed on massive coral species, such as Porites in absence of their favorite preys.
When corals are stressed by changes in water conditions such as temperature, light intensity, or nutrients, they expel the symbiotic algae living inside their tissues, causing them to turn completely white, this is also known as coral bleaching. When a coral bleaches, it is not dead, but may soon starve if conditions persist. If their stress levels are not severe, corals may recover. If the algae loss is prolonged and the stress continues, coral eventually dies. Here in the Maldives, the peak of temperature is around March – June. This year (2018), we have seen some of the corals turn white but luckily only a small percentage. Hopefully, their algae will return soon and as a result their once beautiful colors.
