Look at this amazing visitor to your frame! These are just a few of the species that would often visit the coral frames and are extremely helpful at times when cleaning the frames. This species is called the Moon Wrasse (Thalassoma lunare) a very typical and brightly colored species of fish found in the Maldives. It belongs to the wrasse family which consists of over 600 described species that range on average around 20 cm although the Humphead and Napoleon wrasse can grow up to 2 meters! They are carnivores by nature, feeding on a wide range of small invertebrates such as crabs or snails. Many smaller wrasses follow the feeding trails of larger fish, picking up invertebrates disturbed by their passing.
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.
You coral frame is starting to be colonized by different fish communities. In this photo you can see a convict surgeonfish (Acanthurus triostegus) in the background. This species of surgeonfish have a pale color with distinct vertical black stripes, including one going through each eye. Convict surgeonfish are often found in schools but also individually. This is an herbivorous species that actively grazes on algae found on rocks and corals. This continuous grazing on the algae helps to maintain the algae population
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.
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.
Have you ever wondered how corals are eating and defending themself… 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 animal that look similar to an upside-down jellyfish with tentacles that surrounds the mouth part, depending on the coral species, the amount of tentacles may vary. They will move around to collect anything that passes around in the water, usually small plankton where after they will maneuver it towards their mouth where the food will digested and passed down. 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 the smaller predators such as crabs or invertebrates away. These tentacles are seldom seen but do come out when they are feeling threatened or when they are feeding.
This is your 6 month frame progress update. Unfortunately your frame is struggling!
Looking at your frame, we can notice lots of bleached corals as well as dead coral fragments. Unfortunately the warm months of March, April and May have been really rough on your frame. We are trying our best to keep the damage to a minimum by cleaning harmful algae off bleached corals. We also started moving extremely bleached frames under the Water Villa Restaurant to protect them from further damage through UV radiation. We hope to see some of your bleached corals recover over the next couple of months, but it will be a slow process. Now that the water temperatures are slightly decreasing the next step of action will be to replace dead coral fragments with new healthy fragments.
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 major signs of bleaching of around 90%. 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, those bleached on the surface (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.
Coral reefs for the most part appear to be static environments, despite the presence of ever busy fish life, that is because most of the activities happening within corals are invisible to our eyes. In fact, coral reefs are a dynamic environment where every cm2 may hide beauty or a fight for survival! Among the invisible, corals are surely the most active, by building the amazing structure which allow us to see paradise tropical islands! However, they are continuously fighting for the survival, against predators, disease and environmental changes, and even between them. They are supplied with microscopic needles and venomous tentacles to kill any other corals and ejecting their stomach to digest them. The battle-zones when two different corals are easy to spot, there is often a cleared band between the two where they’ve killed each other off. They use similar tactics when they are fighting off invading algae. On healthy reefs, corals can maintain their territory, often beating back and even killing various types of algae. Here you will notice the two types ….
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.
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.), it is very common in the Indo-Pacific area; but don’t worry, it’s not a threat for corals, they can live together in peace, however when they increase their biodiversity on the frames they are removed to minimize competition with corals. Ascidia is a filter-feeder, this means that it filters water looking for plankton to feed itself. The green color is given by some little green 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.
Acropora corals are among the most common genera of corlas in tropical reefs. Corals are composed of tiny individual polyps each that resembles 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 defence. 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.
We would like to give some more information about the particular coral colony that lives on your coral frame, Pavona varians. Colonies are sub-massive, laminar or encrusting or various combinations of these. The surface has many long ridges on it, which are close together, which may intersect or not. Colonies are yellow, greenish-brown, or cream in color. According to International Union for Conservation of Nature (IUCN), this is considered a native species in all Indian Ocean. This species occurs in most reef environments on shallow and deep reef slopes and on vertical walls.
