Do you know that even under the water we can find cobwebs? The invertebrate responsible for this mesh is not a spider, but rather a gastropod mollusk called Ceraesignum maximum. As all Vermeidae, this mollusk species is sessile and houses themselves within tubular shells. They are common dwellers of shallow water in coral reefs and rocky shores. These nets are called mucus nets that can expand around the individual up to 10 cm in diameter. Waves and currents fill the net with tiny particles. After a few hours the mollusk will inhale the net with all of its yummy goods caught inside.
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.
Why are coral reefs so important? For once, coral reef are said to be one of the most diverse ecosystem on the planet and provide shelter and habitat for many marine organisms. Furthermore coral reefs take an integral part in nitrogen and carbon fixing and are a source of essential nutrients for the marine food web. But not just marine organisms benefit from coral reefs, they also play a crucial role in protecting the coastline from wave action, tropical storms and coastal erosion. Economically coral reefs are important to foster healthy and abounded fishing grounds, tourism as well as the creation of soil and solid substrate for construction.
Here we would like to give some information about this nice looking Pocillopora meandrina branches collected from a broken 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
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’ve had another very warm spring this year; March, April and May have been consistently warm and lead to a lot of coral bleaching on many of our frames as well as the house reef. Because your frame has been showing extreme signs of bleaching, we decided to move it into the shade. Your coral frame will be under the Water Villa Restaurant until we see your corals recover.
Research shows that corals can display bleaching from high temperatures but also that UV light can damage already stressed corals. This is one of the reasons we moved your frame out of the direct sun light and into the shade. Furthermore the temperatures in the shade are a little lower than the exposed sunny spot your frame used to call home.
Over the next couple of months it is one of our priorities to clean your frame frequently to minimize harmful algae from smothering your coral frame.
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 intermediate bleaching (still some symbiotic algae present) 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.
Looking at this species of Acropora on your frame, you will notice the white tips on the branches. When corals are stressed by changes in water conditions such as temperature, light intensity, or nutrients, they expel the symbiotic algae called Zooxanthellae, 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 yet, but may soon starve if conditions persist, since the animals inside rely on this algae for its energy. 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 temperature is around March – June, when we also see some of the corals turn white, usually their colors return soon after if conditions don’t persist.
The coral on your frame is thriving. Here you will see the fragments attached at the beginning are growing very well near the base of your frame and the fragments of this digitate Acropora are now fused together. Here we applied the micro-fusion technique that has been described by the Mote Marine Laboratory in Florida. In particular, when putting fragments of the same genotype close to each other they can stimulate the fusion of these fragments, speeding up their growth rate. When doing coral frame restoration or maintenance we usually apply this technique when we find a huge broken colony. We cut off small branches and then we attach them very close to each other as you can see here.
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.
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.
We use plastic cable ties to attach fragments of corals to the iron frame. Stability is necessary for corals to grow. The branching Acropora living on your frame is slowly growing over the cable tie. You can see part of the light-brown skeleton partially covering the two cable ties. In fact, it will be part of its skeleton forever. Plastic cable ties are a good compromise for attaching corals to the structure, since material is cheap, resistant and the results are great. However, we are following the upcoming researchers to improve our technique in order to reduce the use of plastic.
