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.
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).
Relationships with beneficial consequences between different species such as mutualism or commensalism are common in the coral reefs. In this photo, we would like to show you an important association that has been recently discovered by the team of researchers from the University of Milan-Bicocca. It refers to tiny hairy-looking animals living on the surface of corals called Hydrozoans belonging to the genus Zanclea. Indeed, it seems that they have an important role for the protection of the corals since they also have powerful toxin that may represent a strong defense against predators.
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.
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 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 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 major signs of bleaching of around 50%. 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. We have also noticed that there is some “glowing corals” on your frame. Corals produce a fluorescent chemical which act like sunscreen to protect them against increasing heated waters caused by climate change and as a result produce the most vivid colors, although spectacular to look at, this is the ultimate warning that our oceans are in trouble.
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.
We would like to introduce you to this species of Hydnophora microcornus coral living on your frame. Hydnophora colonies are usually massive and rounded with a lumpy surface. The circular bumps are called moniticules, they are about 2-3 mm across and tall. The colors are usually dull cream, brown or green. This species is found in all reef environments, but primarily in lagoons and protected slopes in the Indian Ocean, and wave washed reef flats in the Red Sea.
Acropora corals are among the most common genera of corals in tropical reefs and this month we show you another species that is growing on your frame. 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 also appreciate the tiny polyps that covers the entire branch 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.
Looking at the top of your frame, you will see this amazing species of coral, they are classified as table corals because of their round and flat shapes. They all belong to the Acropora genus which is the fastest growing species with up to 145 species already described. The role of table corals in the reef is quite important as they provide vital sun protection for new and smaller corals but also larger fish. Some scientific evidence suggest that without this important shade (in which they escape strong UV-light), larger fish which include predatory species will ultimately leave the reef. Predatory fish such as groupers, emperors or even sharks are important to maintain a healthy balance within the ecosystem. Unfortunately due to their size and support base, they often tumble over due to strong seas or hurricanes and this species is put under more pressure. The addition of this table coral on your frame is doing really well as you can see and it will soon also start growing more outwards and start providing more necessary shelter for different species of fish
As you know we use plastic cable ties to attach fragments of corals to the iron bar structure in order to achieve the necessary stability corals need for survival. This 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 researches to improve our technique in order to reduce the use of plastic.
This beautiful creature known as the reeftop pipefish (Corythoichthys haematopterus) but is also known as the Bloodspot pipefish, Dragonface Pipefish or Yellowstreaked Pipefish. The Pipefish is in family with the Seahorse and has the same head and snout. Pipefish feeds on small animals on the bottom which they suck whole into their mouth. They are often difficult to see when they are on the sandy corals as their colors camouflage them very well. They are a common species around the coral frames and are often spotted moving in and out from the frame. They can grow up to 30 cm in length and usually found at depths of around 0 – 20 meters. Interesting fact is that the Pipefish are like seahorses in that the male gives birth! The female deposits their eggs after fertilisation into the males pouch located under their tail to incubate the eggs for one month before giving birth.
