Photograph by Randy O

Acropora

The Acropora is one of the six families of corals that dominate today’s reefs, both in terms of diversity – being in fact the most diverse family of corals in the ocean – and in terms of numbers. This species has been around for over 60 million years, but in the past decades their numbers have suffered a massive losses due to diseases, bleaching and storms of all kind.

The Acroporidae come in all manner of shapes and sizes, from plates to bushes of slender growths, to massive contructs of thick branches over 2 meters long. The Acropora are considered among of the most important reef building corals, often responsible of huge calcium carbonate structures that support and entire reef.
There are over 140 different species of this coral, including: Acropora Cervicornis, Acropora Echinata, Acropora Efforescens, and Acropora Palmata (which can grow to over 3 and a half meters in diameter). Most Acropora species are shades of either green or brown, although several are brightly colored, ranging from bright blue and yellow to deep purple and orange.

The Acroporidae inhabit the fore and back reef areas, preferring locations with strong currents of water, hugh oxygen content and access to plenty of food. Their favorite depth range appears to be between 0 and 12 meters, although several subtypes of Acropora can be found as far as 30 meters down. This coral can also be found to lesser extents in specific habitats like sandy lagoon floors, deep reef slopes and deepwater Halimeda banks.
From a global perspective, colonies can be found starting from the Florida coastline all the way to Venezuela and Curaçao, as well as in most Indo-Pacific reefs. Most of the species of Acropora inhabit the Carribean Sea, the Bahamas and Florida Keys, and the Gulf of Mexico. They favor waters with very low termperature variations of only a few degrees, usually in the range of 25 to 35 °C.
The continued survival of such a wide range of colonies of diverse species require very specific circumstances, relying upon a complex interplay of water quality and biological, chemical and physical conditions. Because of this, corals of the Acropora family are very succeptible to certain threats such as bleaching and and sedimentation, as well as diseases, even leading to some species being listed as endangered – meaning that our oceans may very well one day be robbed of these amazing corals.

Acropora Care

Acropora Care, Reef Corals
Photograph by Jez Tryner

Acropora care is deemed extremely difficult; many enthusiasts consider a thriving Acropora colony to be the holy grail of reef keeping. They require strict water quality and lighting conditions, but with enough care and patience the Acropora can become some of the most beautiful corals in your tank.

The general rule is ‘the larger your tank, the better’. A high volume of water goes a long to keeping pollution low, but be careful: the bigger your tank, the harder and more expensive it is to get things back on track if anything goes wrong.
Take regular measurements of the conditions present, from water temperature to lighting, so that you can make adjustments on time. Proper Acropora care can only be done if you know what’s happening in your tank, so keep a close eye on the environment.

Acropora love stability. In their natural habitat, temperature doesn’t change by more than 1 degree in a 24h period. Depending on what other corals you keep, your tank’s temperature can vary by up to 7 degrees in a day, which is usually too much for the Acropora to handle. Keeping the variance to 2-3 degrees is enough though, and can be done with the help of cooling fans and heaters coupled with timers and controllers.

Lighting is equally important. Metal Halider (MH) light bulbs are standard, but T5 lighting has been on the rise recently. T5s emit less heat than MH and can be placed closer to the water surface, but they emit as of yet untested UV radiation that has a suspected effect on coral colors. Some even use LED lighting. But whatever you use, you should always get a PAR meter and measure the lighting to avoid any damage to the corals.

Flow is vital to good Acropora care. A strong water current keeps the core clean of any debris and pesky algae. Strong pumps are required to move the water and create currents. The pumps are programmable and with a bit of tinkering you can achieve an almost naturally chaotic water flow that is ideal for Acropora growth. Testing the water thoroughly is a must. Salinity levels, along with nitrate, calcium, magnesium, and PH levels must be as consistent as possible. Check the web and ask other enthusiasts or specialists to find out the exact parameters matching natural sea water, or even collect some actual sea water to use in your tank.
Acropora care can be difficult, frustrating and quite expensive at times, but being able to enjoy the magnificent view of your flourishing coral colony is well worth the effort.

Acropora Cervicornis

Acropora Cervicornis, Reef Corals
Photograph by Nicole Helgason

Acropora Cervicornis is a stony coral with cylindrical branches in the shape of a male deer’s antlers, hence it’s more common name: the Staghorn Coral. The length of these branches can vary from a few centimiters to more than 2 meters in length and height. The Staghorn Coral is present at depths ranging from 0 to 30 meters, with the upper limit determinted by the force of the waves in the area and the lower limit depending on sediment and light availability. This species of coral exhibits the fastest growth of all western Atlantic corals, with branches growing as much as 20 centimetres per year.

The main reproduction manner of the Acropora Cervicornis is asexual fragmentation. New colonies of this coral type form from branches that break off and reattach themselves to the substrate in a different location. Sexual reproduction is also present, via the circulation of gemetes into the water annually, from August to September. The colonies themselves are simultaneous hermaphrodites (both male and female). Very few coral larvae survive to settle and form new colonies, and the predominance of asexual reproduction in the species results in very low genetic diversity.

Within a coral reef, the Staghorn Coral is present both in the back reed and the fore reef environments. On a global scale, colonies of the Acropora Cervicornis can be found in the Carribbean Sea predominantly, as well as the Atlantic Ocean and western parts of the Gulf of Mexico. Since the 1980s, Staghorn populations have been drastically reduced – by as much as 98% – as a result of an entire list of threats, including:
predation
bleaching
algae overgrowth
sedimentation
high salinity and temperature variations;
very low genetic diversity
hurricanes
diseases.

The biggest threat to this species has been the outbreak of diseases such as the white band disease. Due to the massive reduction in population, the Staghorn Coral has been place on the endangered species list, classified as Critically Endangered – only one step away from being extinct in the wild. Although the current population appears to be overall stable, with even some cases of recovery, the threat is still very real and in some areas their numbers are still dwindeling.
Great efforts are being made to prevent the extinction of the Acropora Cervicornis, with sanctuaries and programs to re-attach coral fragments being actively developed, but only time will tell if this magnificent coral will regain it’s former glory.

Acropora Coral

Acropora Coral, Reef Corals
Photograph by Chris Horne

Six families of corals make up the vast majority of modern day reef composition and out of these six the Acropora coral is by far the most numerous, diverse and arguably also the most successful. This coral family has been the backbone of reef structures across the Indo-Pacific and Atlantic areas for over 60 million years, erecting huge calcium carbonate construction that support entire reefs.

The skeletal structure of the Acropora coral is that of an open “synapticular” framework supporting a polyp, facilitating rapid growth while at the same time minimizing the required amount of calcium carbonate to increase efficiency. This has allowed them to dominate in terms of species variety. The skeletons themselves are made up of the crystal aragonite form of calcium carbonate, in various shapes and sizes dictaded by the individual species.
Corals are colonial organism comprised of thousands of individual polyps. These polyps have a simple structure, with a “mouth” encircled by tentacles which capture plankton for food, clean away debris and protect them. Inside the polyp’s gastrodermal cells, most corals have symbiotic algae called zooxanthellae, which provides them with the building blocks (CaCO3) needed to contruct the reefs.

The species of the Acropora coral reproduce both sexually and asexually. Their polyps are hermaphrodites (meaning they are both male and female at the same time), and they develop gemetes (eggs and sperm) with fertilization taking place externally. The fertilized eggs drift through the water for some days until finding a suitable spot to establish a new coral colony. Asexually they reproduce through mesenteries, fragments of coral that break of and settle somewhere else, starting a new colony.

While corals generally exhibit a very wide range of shapes and sizes, most can be classified into then general forms:
1. Branching corals with a few primary branches with many secondary ones;
2. Digitate: several large finger-like clumps with no secondary branches;
3. Table corals;
4. Elkhorn corals, which have large, flattened branches;
5. Foliose corals have wide plates on several levels;
6. Encrusting corals, which grow as a thin crust over the substrate;
7. Submassives have several large wedges of columns rising form an encrusting base;
8. Massive corals with their ball-shaped forms of widely different sizes;
9. Mushroom corals;
10. Cup corals, which look like squashed, elongated cups.

Acroporidae have the largest number of species of all corals, and so exhibit most of the above forms. However, despite their incredible diversity, the Acropora coral is extremely succeptible to diseases and changes in its habitat, which have even led to localized extinction – threatening the very existence of coral reef across the globe.

Acropora Echinata

Acropora Echinata, Reef Corals
Photograph by DBarsotti

One of the most intriguing aspects of the acropora family of corals is the huge amount of variety within the species, and the echinata corals are no exception. First discovered in the mid 1800s, the fast-growing species is native to the shallow waters of the Pacific Ocean.

Given the large number of acropora species currently identified (over 300); proper identification is not always easy. Even though the general name is defined as a porous stem or branch, the echinata specie of coral is further distinguished by corallites that grow outward in a bottle-brush pattern. The growth pattern of echinata is also beneficial to the fish that dwell near its reef systems, providing an excellent source of protection in its many interwoven branches.

Capitalizing on prime dwellings that consist of strong currents and easy access to strong natural light exposure, corals can quickly become the dominant coral species in a reef system. Although the branches of corals are fragile and easily damaged by natural storms and other systems, its growth rate is so accelerated that it quickly bounces back from most damage.

But even its fast growth rate hasn’t been able to overcome the negative impact that global warming has had on corals in the recent years. These warmer temperatures are not desired by the echinata species, and the disturbance causes the symbiotic algae to be expelled from the coral system, taking with it the acropora echinatas source of food. When this occurs, corals lose its coloring and turn completely white- a process known as bleaching. Bleaching has significantly decreased the numbers of corals that are currently in existence.

Acropora echinata corals that are brightly colored are extremely popular among reef enthusiasts. However, a considerable level of experience with reef systems will greatly benefit an aquarist who desired to maintain specimens in an artificial environment. Compared to other types of corals, echinata corals require more maintenance and attention to detail than its relatives.

These corals that are brightly colored are extremely popular among reef enthusiasts. However, a considerable level of experience with reef systems will greatly benefit an aquarist who desired to maintain specimens in an artificial environment. Compared to other types of corals, echinata corals require more maintenance and attention to detail than its relatives.

Acropora Florida

Acropora Florida, Reef Corals
Photograph by Tony Vargas

Generally known to be a hybrid species of coral which can be found in a variety of locations spanning across regions in the southern Atlantic and western Pacific Ocean, Acropora Florida has been spotted mainly in tropical climates, reaching significant depths in some areas.

Commonly referred to as “branch coral”, this species of Acropora has been known to occur in shallow reef environments. It was found in many cases either on walls, reef tops or slopes reaching depths of anything between 3 and 30 meters.
While widespread and common to a large number of locations, the species is also known to be under threat due mainly to its low tolerance to disease and bleaching, as well as its slow ability to recover which has lead to pessimistic habitat loss and population reduction estimations in recent years.

Acropora Florida is a species that can easily be located in a lot of of different areas. These include the East China Sea and Japan, Southeast Asia, Cook Island and the entire oceanic region of the western Pacific. Its native countries also include India, Indonesia, French Polynesia, the Philipines, Sri Lanka or even South Africa and Madagascar.
Although all these locations would suggest the abundant presence of this type of coral in many areas mainly across the Indian and Pacific Ocean, there is very little information available about its population statistics. Nevertheless, reef losses throughout the range of the entire species were recorded across three generations, and while it isn’t fully seen as a threatened species, its susceptibility to various threats have caused experts to consider it “near threatened”.

Current estimations seem to point to the loss or significant degradation of more than 21% of the reefs associated with this type of coral. The most significant threats come mainly from the species’ inability to withstand bleaching, as well as various predators, diseases and the considerable climate changes of the past 25-30 years.
Localized threats have also been known to include human infrastructure development, pollution, chemical fishing, sedimentation and changes in the dynamics of various competing species such as pathogens, predators or parasites.
While its “near threatened” status may cause some to believe that the species is rather safe from disappearance, predicted factors and threats such as climate change, ocean acidification and reef degradation may play a major part in its development during the next 10 years. Many experts consider that Acropora Florida should closely be observed in that period.

Acropora Formosa

Acropora Formosa, Reef Corals
Photograph by Guido Poppe

Also referred to as Staghorn Acropora, the species known as Acropora Formosa is a type of coral found often on slopes and fringes, although mainly observed to be a dominant presence in lagoons.
This variety of Acropora can generally be found in thickets, with a single member being able to reach out as far as 10 meters in areas more than 30 meters deep. The species are also known to be highly adaptable, their habitats ranging from turbid waters without much sunlight to low tide areas where they are fully exposed to the sun.

While most Acropora corals have dense bases and present porous, lightweight skeletons near the edges and the tips of their branches, Acropora Formosa is slightly unique in the sense that it has one of the densest types of skeletons ever observed in stony corals.
Formosa species mainly thrives in areas where the temperature is average and stable at around 70-78 F (22-26 C), some of its most prevalent locations including Madagascar, the Marshall Islands and Australia.
Also, while a notable trait about Acropora corals is that they have developed a symbiotic bond with a type of marine algae called zooxanthellae, through which they are able to receive most of their nutrients on a regular basis, Formosa polyps do not rely on these algae, and they are known to be fed by the rest of the colony.

Acropora Formosa has the unique characteristic of being able to outgrow many of the other corals on the reefs they populate. This is due mainly to their fast growing polyps found on the tips of their branches which constantly produce new, thicket-like growths.
Their life cycle also plays a significant role in this, as Formosa species can reach sexual maturity within 3-5 years, while their life span can stretch out to about 7 years in many cases. Despite this fact, however, the coral is very sensitive to various environment changes which can include sedimentation, insufficient water movement or the presence of various harmful chemicals in the waters surrounding it.
Also, potential problems have been found due to the species’ rapid deterioration as a result of bleaching or receding. They are known to be susceptible to almost all coral related diseases as well, including necrosis, white-band and black-band diseases.
Their inability to sustain themselves under a variety of challenging conditions along with the observations made throughout the past decades have brought the Acropora Formosa corals on the IUCN Red List for endangered species.

Acropora Granulosa

Acropora Granulosa, Reef Corals
Photograph by Leo Chen

While consistent with the main characteristics of Acropora corals, the species known as Acropora Granulosa can usually be found as a smooth branched coral, more or less short in size, which is dominant in southwestern Pacific and southeastern Indian Ocean waters.
Although the intensity of its color and size of its growth can be somewhat diverse, the species is usually found in formations of short, purple granular shapes with yellow tips and edges.

Acropora Granulosa is a commonly occurring species of coral found in the waters surrounding Australia and Indonesia, as well as in numerous different areas in the Indian Ocean. Known to thrive mainly in areas where water movement and waves are less prevalent, the species is found in abundance in the specific locations where it was spotted the most.
Colonies are usually found in circular or semi-circular plates, arranged in a horizontal fashion and located close to other Acropora-type corals. Populations of neatly stacked together horizontally inclined blue, crème, purple or yellowish branches along with smaller branches of a paler color largely define the unique visual characteristics of the Granulosa coral.
Their habitats mainly thrive in reef slopes that are undisturbed by intense wave action, although there have been exceptions to this rule based on the specific type of Granulosa found and the waters they inhabit. Also, it is worth mentioning that Acropora Granulosa is not shy from appearing in most types of reef environments, making it quite common in certain areas.
Although usual occurrences have been spotted mainly across the reefs of Australia, southern China and Indonesia, this species of coral has also been known to appear – although less prevalently – in areas surrounding Sri Lanka and northern Madagascar.

Although similar in its low tolerance and low resistance levels to many other Acropora species known to be sensitive when it comes to bleaching or the presence of chemicals in the water, the species also has a few important properties that makes it more capable of withstanding major threats.
Its maturity cycle can often reach 8 years, while the species can be located in shallow, tropical reef environments on slopes deeper than 15 meters. Its range has actually been observed at depths of 8-40 meters, although its occurrence in shallower waters is less notable.
Nevertheless, the Acropora Granulosa corals’ near threatened status is fully justified by its tendency to cope less easily with climate change and temperature shift, as well as by the destruction of more than 20% of the surrounding reefs in the areas where it is most prevalent which has lead to the species’ considerable population decrease since the 1970s.

Acropora Growth

Acropora Growth, Reef Corals
Photograph by Leonardo den Breejen

Acropora growth has been monitored closely for decades by scientists seeking to explore and understand the role that this species of coral plays in the various ecosystems it inhabits and, more recently, to account for the significant population decrease that coral reefs have sustained in the past 3-4 decades.
Acropora species are complex living organisms that require specific needs in order to grow or thrive. Many members of this family of corals are only able to survive at certain depths, while requiring particular nutrients, as well as ideal levels of sunlight and water movement.

Most species of Acropora will reach maturity within 5 years, although the statistics may vary depending on the specific types one would encounter. Also, some can grow in length, width and overall size to more than 10-20 inches within a period of one year or less.
Despite its rapid growth, Acropora has significant difficulty when it comes to growing in harsher environments or under controlled circumstances. While growing it in a tank may yield less favorable results in most cases, however, some scientists have observed positive response to certain kinds of treatments when applied to Acropora species in their natural habitats.
A new study analyzing the growth of a species known as Acropora Muriata in the wild, using controlled vs. natural means over a period of four months has even concluded that certain treatment methods used were able to increase growth by more than 50% in some cases.
It was presented that the species used showed favorable results even when exposed to slightly higher concentration levels of phosphate, although the study did also show that, despite the increased growth, skeletal integrity was reduced as well.

Acropora growth requires extreme care, especially when members of the species are taken from their natural environment. High lighting levels, variable water turbulence (which differs in the case of each sub-species in part) and higher levels of calcium define healthy growth in many areas where Acropora has been found to thrive.
Under these circumstances, maintaining a healthy environment under controlled circumstances can be quite difficult, and many of those who try to keep Acropora corals in tanks have found it to be extremely difficult.
Most scientists, therefore, advise that the species be kept under careful observation and that efforts should be made to preserve the integrity of the ecosystem for the purpose of encouraging Acropora growth, or at least avoiding its hindrance which could have significant negative effects in the next decades.

Acropora Hyacinthus

Acropora Hyacinthus, Reef Corals
Photograph by Jan Messersmith

Acropora Hyacinthus is known as a peaceful variety of coral thriving mainly in tropical zones where the waters are consistent with high levels of pH, calcium and alkalinity levels.
This saltwater species is normally characterized by thin, finely structured branches of a green or gray color, while their general area of occurrence spans across multiple regions in the Indian and Pacific Oceans.

A unique coral with fine, neatly shaped, vertically directed branchlets, Acropora Hyacinthus are known for their colorful appearance and distinct axial corallites. Aside from the most prevalent types of Hyacinthus specimens which are normally green, light blue or gray, the coral has also been found in brown or uniform cream shapes in various areas where it is known to grow.
In terms of depth, this species of coral can normally be found in areas where the reef stretches 5-20 meters beneath the surface of the water, and particular specimens have been located both at the top and bottom of reef slopes, with those found at lower depths being more flattened as a result of increased pressure.
Hyacintus corals spawn every year in the month of October in regions such as French Polynesia, and their increased life cycle often makes them the dominant species in most of the reefs they inhabit.
Mainly thriving in sheltered regions it has also been noted that some of the larger clusters can withstand difficult circumstances more easily, the growth of this tropical coral being sometimes observed on reef edges just as often as it is found on slopes, submerged reefs and outer reef flats.

This species of Acropora is considered by many scientists to be one of the most abundant corals prevalent in any outer reef slopes situated in western Pacific areas. Despite this fact, their occurrence is even more frequent in regions close to Australia, Indonesia, southwest China and the Philippines, with some populations spotted near Madagascar, the Red Sea, Sri Lanka and other locations in the western part of the Indian Ocean.
Their habitats often consist of upper reef slopes and flats as well, and they have often been associated with similar species, such as Acropora Spicifera and Acropora Tanegashimensis.
In spite of its widespread occurrence, this type of Acropora coral is still labeled as near threatened, mainly as a result of the extensive reef population reduction that has been a problem in recent years throughout south Asia and the northern part of the Indian Ocean.
Nevertheless, Acropora Hyacinthus boasts a level of superior genetic, which has had a significant effect in increasing its resilience to most of the elements that have caused population reduction in the case of other Acropora species.

Acropora Millepora

Acropora Millepora, Reef Corals
Photograph by Neville Coleman

Known to be native to the western Indo-Pacific area, Acropora Millepora is recognized as being a small, colonial coral that comes in bright blue, green and pink colors and can take on a variety of shapes and growth configurations depending on the specific type of species involved.
Millepora corals are unique in their appearance, featuring scaly, clustered forms and short, cylindrically shaped branches with projective lower rims that confer them their scaly look and rich configuration.

Found in many cases to exceed 5 mm in diameter in a period of less than 10 months, Acropora Millepora is a type of coral that features a relatively slow growth, and the coral reef it produces are made of materials which have their origins mainly in coral rubble, live coral, dead standing coral and coral-like stones.
With its polyps extending from its vertical branches to about 1.5 cm outward, the coral reproduces through a process called “mass spawning” once each year, for a period of about 3 nights during the full moon in the warmer seasons.
The unique requirements of Millepora habitats demand that the waters in which they thrive be abundant in elements such as calcium and strontium, while the preferred areas they thrive in will often include reef flats and upper reef slopes.
Despite its specific requirements, the species is considerably common in a wide range of regions, including the Red Sea, Kenya, South Africa, as well as Indonesia, Japan and Australia.

Due to their lower reproduction speed, Millepora species are prone to more rapid degradation and sensitive to sedimentation. This translates into diminished metabolism and growth size, as well as smaller coral populations.
Acropora Millepora requires adequate lighting which is essential to the species’ survival, as well as specific water conditions involving average temperatures of about 75-78 F and pH levels of 8.1-8.4.
Because of requiring increased lighting, the levels of depth in which these types of corals can thrive are significantly reduced in comparison with other Acropora species. Moreover, studies show that the light can also have a significant effect on the orientation of the coral growths, influencing whether the larvae will settle on the upper or lower levels.
A unique property that Millepora has also developed is its increased UV-ray blocking abilities. Secreting an agent that effectively helps them reduce the effects that prolonged exposure to UV light may have on the species, Acropora Millepora have at least one tool capable of maintaining their resilience and ensuring the less pronounced reduction of future populations within the next 40-50 years.

Acropora Palmata

Acropora Palmata, Reef Corals
Photograph by SEFSC

Seen as one among the most important types of endangered coral reefs in the Caribbean, Acropora Palmata – also referred to as Elkhorn coral – is a complex species featuring large, ramified branches that can reach lengths of up to 3 meters.
While the growth rate of this coral is significant, reaching 5-10 cm on average per year, it is estimated that more than 80% of the Elkhorn coral which existed in the Florida Keys and the Caribbean before 1980 has since been entirely destroyed.

Normally found in exposed reef crests and reef environments that are situated no deeper than about 20 meters under the surface, Acropora Palmata used to be the dominant shallow water coral species in the Caribbean, as well as the entire area of the Florida Reef Tract.
Because of its size and relatively fast growth based on an asexual process that – while ineffective in the case of diseased population – can assist with the rapid recovery of reefs after storms and other damaging natural catastrophes, this species of coral is one among three of the most important types of coral reefs responsible for inducing reef growth and producing extensive fish habitats in the Caribbean.
The most important role played by Elkhorn coral has been established in regions such as Puerto Rico, Florida and the islands of St. John and St. Thomas, where restoration efforts are currently underway to assist with population re-growth. Other areas where this species can be found also include areas such as the Bahamas and even sections of the region stretching south towards Venezuela.

Despite the area of the Caribbean being constantly bombarded with hurricanes and other natural disasters, climate change and the presence of increased sedimentation and disease outbreaks were identified as the main reasons for the decline of Acropora Palmata populations.
The species is significantly susceptible to bleaching and damage incurred from sedimentation, as well as the long term threat of ocean acidification which is known to reduce the skeletal integrity of a number of different coral reef varieties.
Among the diseases known to be a major threat to the species, some of the most notable are white band and black band disease, as well as white pox disease. Also, predators such as coral-eating snails and bearded fireworm species continue to contribute to the coral’s population decline to this day.
While conservation and restoration efforts continue to be funded for improving the status of Acropora Palmata, they have so far only presented mixed results, and attempts to conserve the corals or introduce herbivores to eliminate damaging algae in areas like the Virgin Islands and the Florida Keys have produced limiting success thus far.

Acropora Sp

Acropora Sp, Reef Corals

Although Acropora sp are known for having some of the fastest coral growing abilities and creating long lasting habitats for fish and other marine life, the populations of various species have been in rapid decline in the past 3-4 decades.
Ranging from near threatened to critically endangered, species such as Acropora Florida, Granulosa or Palmata have been continually monitored in recent years, as scientists attempt to preserve, conserve or even rejuvenate some of the colonies that are rapidly deteriorating in regions where the ecosystem would rely on future coral reef populations in order to survive.

The variety of Acropora species currently known to exist can be quite significantly diverse, ranging from long, stag horn shaped species that can reach up to 2 meters in length to small, delicate colonies in the shape of flat plates and tables ranging between a few centimeters and more than 3 meters in diameter.
Most of these corals also have a unique relationship with various types of algae which live inside the coral, providing it with food and nourishment and inducing, through the process of photosynthesis, the production and growth of coral reefs.
Naturally, the process requires sunlight, and depending on the depth at which they develop, different types of Acropora sp have evolved anything from highly sensitive photosensitive surfaces to UV blocking agents in order to adapt to their specific environments.
Even individual species building colonies throughout a variety of reef formations often show a remarkable variety in terms of their growth speed, size, shape, length and depth. Among the more than 360 different Acropora species, both similarities and differences can be difficult to point out, however, there are a few important common aspects that most of them share, one of the most significant of which is their sensitivity and diminishing population growth resulting from a variety of different threats.

Dwindling acropora populations have resulted because of a number of different reasons, the most significant of which are bleaching – due to the loss of the coral’s zooxanthellae – and the recent global climate changes which have not only caused abnormally severe weather, damaging more fragile and exposed corals, but have also increased water temperatures to hostile values, threatening entire colonies to extinction.
Other causes, such as sedimentation, ocean acidification and eutrophication have also lead to decimating Acropora sp populations, and while restoration efforts continue to be funded worldwide for the purpose of protecting the most endangered types, some scientists maintain that current results are still not enough to ensure the long term survival of these corals.

Blue Acropora

Blue Acropora, Reef Corals
Photograph by Dan Rigle

Blue Acropora coral species, such as the vivid blue Millepora species can be an essential contribution to the integrity of various ecosystems.
However, just as there are numerous benefits to the growth form and coloring of the various species of Acropora that can actually maintain constant blue coloring, this feat depends on precise factors such as the alkalinity and movement of the water, as well as on the intensity and nature of the light that feeds the corals.

Numerous species of blue corals exist that are associated with the Acropora category. Because of the high levels of natural sunlight, as well as the specific and stable content of elements such as calcium, strontium and other trace elements that need to be present in the water, however, these species are extremely picky about the environment they are able to cope with, and often do not do well in captivity, unless all their needs are met to the smallest detail.
Tropical environments, such as those found in the eastern Indian Ocean and the coasts of Indonesia are ideal for the growth of these types of blue coral.
Here, the amount of sunlight is not only optimal for maintaining the necessary (and stable) levels of lighting and water temperature to allow the corals to thrive, but the overall stability of the ecosystem is also a bonus, allowing for unique species of Acropora to maintain their constant growth in spite of global climate changes.

The somewhat rare occurrence of blue Acropora and its unique properties have made it an object of interests for many scientists across the globe. One of the problems they’ve had with this type of species, however, is that, in most cases, they tend to gradually lose their health and coloring during attempts of growing them indoors in an enclosed environment with artificial lighting.
It has been shown that blue varieties of acropora may actually turn brown and diminish their growth cycle if taken from their natural environments. While light can be one important contributing factor to this, researchers have also pointed out that the delicate balance between water pH and alkalinity, as well as the amount of calcium and magnesium contained by the water can play a major role as well.
Whether or not most species of blue Acropora can in fact be nurtured and influenced to maintain their color, structural integrity and health in controlled environments is still a topic of debate, however, further research in this area can be a significant step forward to clarifying the efforts that need to be made in order to reduce population decline and maintain steady acropora growth in future years.

Green Acropora

Green Acropora, Reef Corals
Photograph by Dan Rigle

When viewing the various shades of intense color associated with most green Acropora coral colonies, many would simply focus on the beauty of these complex life forms; however, the significance of the green color of these coral reef species goes well beyond appearance, playing a major role in their survival, reproduction and healthy growth.

There are about 368 different documented species of Acropora currently in existence, their colors ranging from bright pink to dark blue and purple. Green seems to be predominant in a number of corals that thrive near the surface of the water (at about 5-20 meters in depth, although this is not an extremely strict rule).
Green species of Acropora can range between wide variety of different shades of green, from the less intense color of Acropora Nasuta – a small sized, colonial coral that grows in clumps with branches of up to 0.5 inches in diameter – to the rich, vivid color of Elkhorn coral (or Acropora Palmata), an endangered species that predominantly inhabits the areas around Florida, Puerto Rico and the Bahamas.
The significance of the color can depend on multiple factors, including the depth at which the species thrives best and the amount of sunlight it usually benefits from in that particular region in order to enhance the photosynthesis process which allows it to survive.
Depending on the specific green Acropora species in question, some corals can change their color to adapt to their environment or grow tips and branches of other colors – such as blue, purple or brown – depending on the species’ particular needs.

Researchers have determined that most colors play a major role in protecting Acropora corals from intense UV radiation coming from the sun. Also, coral colors are widely responsible for attracting mates, being a sign of the coral’s health.
The most important reason behind green colored Acropora, however, is due to the allowance of zooxanthellae cells of converting light to chlorophyll and inducing the process that allows the coral to manufacture its necessary supply of oxygen.
Depending on the amount of light needed for this process, Acropora species have developed distinct color patterns to absorb precisely the amount of light required and protect their populations from excess light that would, for instance, be absorbed through the use of darker color pigmentation.
The chemical structure of the pigment used by green Acropora corals is what gives them their own distinct shades, and while their existence can in some cases still be prolonged without excessive amounts of their green pigment, the bleaching effect that results from various environmental unbalances can often lead to the degradation and death of that specific coral.

Pink Acropora

Pink Acropora, Reef Corals

Although it has been widely known or at least suspected in the scientific community that the GFP (green fluorescent protein) is the main element responsible for contributing to the protection of corals such as green, blue, purple or pink Acropora from intense UV and sunlight exposure, recent studies tend to point out that another type of protein, called chromoprotein – which is commonly found in pink and purple corals of this species – may also play a major role in acting as a sunscreen for the symbiotic corals.

Researchers now believe that Acropora species which use pink pigments often benefit from the resilient properties of chromoprotein. Discovered to be related to GFP, this protein, together with similar proteins that are closely connected to the same properties that make GFP so effective, plays the role of defending the coral from substantial amounts of sunlight.
An important difference between chemoprotein and GFP, however, is the fact that the former does not re-emit the light. Growing in exposed areas that contain basically no symbiotic algae, the development of the protein is cleverly triggered by the excess light itself, allowing it to practically “terraform” the areas of the coral that were not previously ripe to be colonized by the algae.

Although light is an important factor for maintaining the health of pink Acropora and various other colors and species of corals that rely on pigments for balancing their intake of UV rays, the changes in the water’s salinity, temperature and nutrient levels are also important to keep into account.
The process of bleaching, caused by these unbalances in the ecosystem, is basically a cry for help from colored corals, showing exactly how the simple change from pink to white can leave these otherwise resilient life forms completely lifeless.
Even though the use of chromoprotein has been observe to confer Acropora with additional protection which also ties in with the protein’s increased resilience in the face of environmental circumstances that would cause bleaching in other species, the fact remains that it will still not defend them from other harmful influences, such as water pollution, overfishing and coastal development.
According to scientists, despite the major threat that the elements presented here can pose for future Acropora coral populations, there is still hope. Efforts to understand the process through which the pigmentation process acts to prevent intense sunlight exposure for pink Acropora, as well as the role it plays in balancing the coral’s relationship with the environment, may provide important clues for improving the coral conservation and restoration processes already underway.

Purple Acropora

Purple Acropora, Reef Corals

Purple Acropora coral species have often been a subject of debate regarding the specific circumstances that allow them to develop their particular hues, as well as the reason for doing so.
While purple pigments, like pink and blue ones, are mainly considered to add a layer of protection between the coral and the excessive UV lights penetrating the ocean surface and being potentially dangerous for the corals’ survival, a variety of other factors also seem to have an impact on why the purple pigments are developed – including geographical location, depth and water content.

Acropora colonies that use purple pigments may vary depending on their species’ characteristics such as size and resilience, however, most of them will require a stable environment with temperatures that rarely fluctuate more than 5-6 degrees on average (while remaining in the 70-80 F range) and stable quantities of magnesium, water pH and trace elements.
A good example that falls in this category is the rare, purple colored Cerealis Acropora coral. Commonly found in areas such as Fiji, Indonesia, Australia and southern China, this coral is a bright purple color, ranging between 1 and 7 inches in height, and can normally be found on upper reef slopes, closer to the surface where fewer of the Sun’s UV rays are filtered by the ocean’s water.

Although it’s safe to say that purple Acropora species in general use their color to protect against dangerous levels of UV radiation, it may also be important to note exactly which types of UV light levels actually need to be reduced.
There are three essential varieties of UV radiation, known as UV-A, UV-B and UV-C. While the latter is not of consequence, since it rarely if ever penetrates the atmosphere of the Earth, UV-A and UV-B rays can constitute a destructive factor for coral DNA.
Corals such as the purple Cerealis species mentioned earlier develop various shades of purple pigment to protect against higher or lower levels of these UV rays. Deeper areas will generally filter these rays and require less protection. As a result, corals that use high frequency colors such as purple and pink will generally come from a shallow area where the need to protect against a higher amount of UV-A or UV-B sunrays is more pronounced.
It is important to note that corals such as purple Acropora may change color depending on climate or water level changes, and may even lose some of their pigments; however, this is not always cause for concern, since the coral may simply adapt its pigmentation in accordance with the newly altered amount of UV rays it needs to fend off or attract.

Red Acropora

Red Acropora, Reef Corals
Photograph by Frank Starmer

Red Acropora species, which are uncommonly rare compared to the various types of blue, purple or pink colored corals; when it comes to comparing these species, there are a variety of aspects that need to be taken into consideration.
The water composition in the area where the coral is known to thrive, as well as the amount of UV filtration the water is capable of and its overall temperature fluctuations are all important ingredients in determining the type of pigment that corals are most likely to use depending on their species and specific location on the reef slope.

Apart from the amount of UV light that makes its way to the coral in question, the differences between colors are actually influenced by a number of other factors as well. In corals, warmer, red pigment is actually either a more intense version of pink still required for high depths (where the water doesn’t fully filter UV rays to the point of making them harmless), or a lighter shade of brown normally adapted for corals located at lower depths.
Red Dragon Acropora is the perfect example of these types of corals. Ranging from orange and bright red to magenta, its pigments can change depending on the amount of oxygen it is required to produce and the amount of UV light it needs to protect itself from.
Its semi-aggressive temperament sets it somewhat apart from most types of Acropora, while the water content it requires is extremely specific, which make it prone to temperature fluctuations and adverse effects resulting from water iodine, magnesium and calcium concentrations.

For red Acropora species such as the Red Dragon Acropora usually light intensity has to be more specific in order for them to maintain their natural coloring and steady production of oxygen that would induce an adequate amount of growth.
Purple or blue Acropora colonies which are adapted to fending off a higher amount of sunlight on a regular basis and can thrive in a wider variety of environments – even doing well in tanks. Red varieties of Acropora, on the other hand, are significantly more sensitive and difficult to maintain, as well as more prone to environmental changes.
Aside from this, red Acropora is also found at much lower depths and requires less exposure when it comes to its placement on the reef slope surface, a fact that is in accordance with the main geographic locations they thrive in such as the areas to the north of Australia and south of Indonesia.

Staghorn Acropora

Staghorn Acropora, Reef Corals
Photograph by Franklin Viola

Staghorn Acropora corals include a large variety of coral species featuring lightweight, porous skeletons, as well as a varying number of colors and shapes.
From pale pink, blue and yellow shades to intense green and purple, these are among the most prevalent, as well as demanding types of corals on the planet, requiring significant amounts of sunlight and enough space to allow for free range considering their rapid growth cycles.

Also called branching corals, Staghorn Acropora species belong to the Scleractinia family and are considered to be semi-aggressive due to their fast growth properties. Colonies can reach heights of up to 60 cm, and for some of the species that expand to populations stacked in the shape of plates and tables, the diameter of the entire colony can increase to almost 300 cm.
One of the most important characteristics of this species that allows them to maintain and even increase their populations is the ability of taking over the space taken up by various other species of coral, enabling them to expand to significantly larger and often dominating populations.
The drawback of this rapid growth process, however, is also that Staghorn coral colonies tend to take up too many of their environment’s resources. This can and often does lead to significant stress and bleaching which makes some of the species prone to steep population declines, especially when growing in a more hostile environment or having to deal with rapidly fluctuating climate changes.
Also, since they get most of their nourishment from symbiotic algae, many of these species, although not all of them, require higher than average levels of sunlight to support their growth and allow them to thrive in a more stable fashion.

Unlike most types of Acropora coral colonies, Staghorn corals rely on a slightly higher temperature ranging between 77 and 82 F degrees. Also, they need fast water currents, and the pH of the water they thrive in has to remain constant around values of 8.3-8.4 for the species to survive.
While these highly specific requirements may suggest that they are unable to cope with most environments, this is not entirely so. There are numerous Staghorn species which can readily be located in the Indian and Pacific Ocean, as well as in the Red Sea.
Despite their somewhat frail skeleton structures and demanding environmental requirements, most Staghorn Acropora species feature a superior level of adaptability that allow them to survive quite well in hospitable environments and an active pigmentation process that allows for quick color changes to adapt to increased levels of UV rays.

Table Acropora

Table Acropora, Reef Corals
Photograph by Jan Messersmith

Shaped as its name would suggest, as a table, and taking up significant space on reef surfaces, Table Acropora colonies thrive basically by branching out horizontally in a way similar to flat bushes.
This approach and method of growth is entirely different from that of staghorn corals, which essentially branch out in a similar way as a tree would on the surface. Nevertheless, the way in which table corals expand helps them expose their branches in a more direct fashion to the sunlight that feeds their growth and allows them to thrive in a variety of different locations.

Table Acropora is known as a hard coral which creates skeletal structures built from calcium carbonate that are essential to the overall integrity of all coral reefs.
Depending on the environment, the amount of sunlight that reaches them and the intensity of water currents in the area, table corals can develop a variety of different reef shapes to serve for assisting the ecosystem’s development and continual conservation.
Table corals have numerous branches that are lined up by cup-shaped extensions from which polyps are extended to feed during the night. This configuration together with the number of polyps it allows to come into contact with vital nutrients makes the entire existence of these species of corals far easier and more stable due to their ability to capture more food.
The practical advantages of the structure associated with Table Acropora are exemplified by a specific type of Acropora coral species called Hyacinthus. This is an abundant and widespread species that not only serves itself, but also provides shelter for a wide variety of coral reef fish species which can take shelter and thrive underneath its large plates.

Most table corals are not considered to be very picky when it comes to the water conditions they can survive in. Nevertheless, researchers have observed that there are specific conditions which would allow them to maintain their health more successfully.
Some of the main concerns regarding the healthy growth of most table coral species are the levels of nitrate and phosphate compounds, as well as the temperature and salinity of the water they would attempt to survive in. Areas involving nitrate levels lower than 5 ppm and phorphate concentrations that don’t exceed 9-10 ppm are those where the species thrive best.
Also, a specific salinity level of about 1024-1025 is required, while the lighting and temperature conditions do not need to exceed normal levels.
Unfortunately, Table Acropora, like many other types of coral species, have also been influenced by global warming and coastal expansion, many scientists considering that conservation efforts should be intensified in future years for these species to survive.

Blane Perun

Diver - Photographer - Traveler

Whale in Ocean