Purple Sea Blade

Angular Sea Whip, Purple Ribbon

Purple Sea Blade Pterogorgia anceps, also known as Angular Sea Whip, and Purple RibbonPterogoria Sp.Photo © Animal-World: Courtesy Carrie McBirney

   The Purple Sea Blade is not only gorgeous in color, but can get really tall to spread that color out in your tank!

   True to its name, the Purple Sea Blade Pterogorgia anceps, is usually dark purple. They have a long reach, almost 3 feet (1 m) in height, and are the largest of the Pterogorgia genus. They are also known as the Angular Sea Whip or Purple Ribbon because they have 3 or 4 flanged, flat branches that look like a "Y" or an "X" when you look at a cross section.

   The Pterogorgia gorgonians come in several colors, from gray to purple, yellow, orange, brown and olive green. Their branches are flat and blade like, and can be triangular or straight. On the edges, there are raised calyces with openings or grooves where the white or tan polyps emerge. Different species can grow in a "Y" or "X" formation, which is a dichotomous growth structure.

   The Purple Sea Blade P. anceps is just one of these beautiful gorgonians. Another is the attractive Yellow Sea Whip or Yellow Ribbon P. citrina. It is a smaller species, typically only growing to about 12" tall (30 cm), though they have been seen up to 18" (46 cm), They can be yellow, green to olive green, or orange and possibly purple, with white or tan polyps. There is also the Grooved-Blade Sea Whip P. guadalupensis which can reach to 24" (60 cm) in height. Its polyps come from the edges of the blade also, but also from grooves. It is gray to olive green and light purple, with cream or white polyps.

   The Purple Sea Blade P. anceps is moderate to difficult to care for due to lighting, feeding, and water movement needs. All Pterogorgia corals have a secret weapon against algae! They will shed off a layer of their rind if it gets over taken by that or cyanobacteria. Found in shallow waters with a wide variety of water quality, it seems odd they would have a hard time in captivity. In the past, they were thought of as impossible to keep. They would ship well, but deteriorate over time. Now it is realized that they need not only strong light and good water movement to prevent algae growth, but a regular feeding schedule. Be sure to only buy a Pterogorgia coral with the root attached to substrate. Then provide the right environment and you will be rewarded with a beautifully colored Ptergorgia with open and happy polyps.

To learn more about these fascinating Octocorals see:
What Are Gorgonians?
Types of Gorgonians, Sea Fans and Sea Whips


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Scientific name    Suborder: Holaxonia
   Family: Gorgoniidae
   Species: Pterogorgia anceps

Distribution / Background    Gorgonian Information: The Pterogorgia genus was described by Ehrenberg in 1834. There are at least 13 species in this genus, the most common being P. anceps, P. citrina, and P. guadalupensis. Some common names these corals are known for are Sea Whip, Sea Blade, Angular Sea Whip, Yellow Sea Whip, Purple Sea Whip, and Grooved-Blade Sea Whip, as well as Purple Ribbon, Yellow Ribbon, and Gold Ribbon. They have been propagated in captivity, and interestingly, the Pterogorgia genus have pharmaceutical type compounds that are now being studied.

   The classification of gorgonians in general is done by some simple visual clues such as colony size, shape, axis structure, color, polyp placement, and pattern of branches. Getting a little more technical, they also look to see if the polyp is autozooid or siphonozooid. Then there is the more exacting use of chemotaxonomy, used to show the different terpenoids or other chemicals produced by each gorgonian species.

   Where Pterogorgia Corals Are Found: The Pterogorgia genus are found in the Western Atlantic Ocean near Florida, and in the Caribbean, Bahamas, and Colombia.

   Pterogorgia Coral Habitat: The Pterogorgia genus inhabit very shallow waters on in-shore reef flats with a very good current.

Status    The Pterogorgia genus is not on the IUCN Red List for Endangered Species.

Description    What do Pterogorgia Corals look like: Gorgonians in the Suborder Holaxonia have a rigid structure of branches that consist of a protein substance called gorgonin, thus the name. In this family, Gorgoniidae, there is a central "chord" that is the main branch from which the rest of the coral grows from. The structure is covered by a rind which is a tissue layer, and there are polyps on raised areas of the rind.

   The Pterogorgia genus comes in several colors, from gray to purple, yellow, orange, brown and olive green. Their branches are flat and blade like that can be triangular or straight. On the edges, there are raised calyces with openings or grooves where the white or tan polyps emerge. It is thought that the white polyp species are non-photosynthetic, thus being much more demanding, and in need of more feedings. Tan polyps are a better color to look for to keep in captivity, and can be found on all the colors. Different species can grow in a "Y" or "X" formation, which is a dichotomous growth structure. They do tend to shed their rind if the algae growth gets to be too much, but it is not a sign of decay necessarily.

  • P. anceps
    Purple Sea Blade, Angular Sea Whip, Purple Ribbon can reach almost 3 feet (1 m) in height and it is the largest of the genus. They have 3 or 4 flanged, flat branches that look like a "Y" or an "X" when you look at a cross section. They are usually dark purple.

  • P. citrina
    Yellow Sea Whip, Yellow Ribbon, Gold Ribbon are small and only typically grow to 12" tall (30 cm), though they have been seen in the range of 7" to 18" (17 - 46 cm). The polyps come from the edges of the blade also, but from individual openings, as opposed to a groove, like P. guadalupensis. They can be yellow, green to olive green, or orange and possibly purple with white or tan polyps. They can be difficult to keep in captivity, needing optimal conditions and rhythmic currents. They can take on a blue hue under strong metal halides.
    There is a picture in Anthony Calfo's Book of Coral Propagation on page 249 top right that shows a picture of this species, but oddly the tips are purple. This lends to the belief that the purple color is just a variation of P. citrina, although the purple is not as demanding and color may have something to do with depth.

  • P. guadalupensis
    Grooved-Blade Sea Whip an reach to 24" (60 cm) in height. The polyps come from the edges of the blade also, but from grooves, as opposed to individual openings like P. citrina. The branches are numerous, long and slightly tapering towards the tip. They color is gray to olive green and light purple, with cream or white polyps.

Difficulty of Care    Gorgonian Care: The Pterogorgia genus can be moderate to difficult to care for due to lighting, feeding, and water movement needs. It's best to only buy the Pterogorgia genus with the root attached to substrate. Lighting needs to be moderate to high and moving in a sideways direction. Plenty of water flow is to prevent algae or cyanobacteria growth on the blades. Also feed regularly.

Foods / Feeding    Gorgonian Feeding: In the wild, Pterogorgia corals have developed several feeding strategies. They capture planktonic organisms and microscopic food particles from the water column, and can absorb dissolved organic matter. Unlike a lot of other Gorgonians, many have a symbiotic relationship with a marine algae known as zooxanthellae, where they receive some of their nutrients. However it is thought that the white polyp species are non-photosynthetic, thus being much more demanding, and in need of more feedings.

   In captivity, the Purple Sea Blade P. anceps and other in this genus can be fed enriched Artemia nauplii, rotifers, dust-sized pellet food, Cyclopeeze, daphnia, and other similar sized foods. Frozen foods that dissolve into fine particulate in the water are a great choice, and you can try marine snow as well. Feed twice a week or more, depending on appearance.

Aquarium Care    Stable tank conditions are needed to keep the Pterogorgia genus. Doing water changes of 20% a month or 10% biweekly is needed, although it is suggested that doing 5% water changes once a week will replenish many of the needed additives. With higher concentrations of coral with calcareous skeletons, there may be a need put in additional additives to maintain proper levels for good growth. Trace elements and iodine may be added.

   Suggested levels for Pterogorgia species are:

  • Calcium:  400 - 450 ppm (Seachem makes a calcium additive that states 385 as sufficient)
  • Alkalinity:  3.2 - 4.8 MEQ/L (8 to 11 dKh - 10 is recommended)
  • Phosphates:  0, zero.
  • Magnesium:  1200 - 1350 ppm. (magnesium makes Calcium available, so if your calcium is low, check your magnesium levels before adding any more calcium.)
  • Strontium:  8 - 10

Aquarium Parameters

Quick Reference Chart
Lighting: Prefers Low Lighting Levels Prefers Medium Lighting Levels Prefers High Lighting Levels
Water Flow: Prefers Low Water Flow Levels Prefers Medium Water Flow Levels Prefers High Water Flow Levels
Temperament: Peaceful Temperament Semi-Aggressive Temperament Aggressive Temperament

   A typical live rock/reef environment is what is needed for the Purple Sea Blade, along with some fish for organic matter production. A mature tank (well over a year old) is advised to increase the successful keeping of Pterogorgia. Tank should be at least 18" high (50 cm) with a sandy bottom.

   Provide proper lighting and water movement, and they must be anchored down. A moderate to strong, and sideways water flow, along with medium to high lighting are needed for the Purple Sea Blade to do well. These Octocorals are very peaceful but can be overgrown by other gorgonians, so adequate space should be provided between the different species.

  • Minimum Tank Size / Length: 100 gallon (380 L) or larger. Pterogorgia gorgonians can be kept in a smaller tank, such as 40 to 50 gallons, that has high water quality.
  • Marine Lighting: Moderate to high
  • Temperature: 70° - 84° F (21° - 29° C)
  • Salinity / Specific Gravity: 1.023 - 1.025
  • Water Movement: Moderate and laminar
  • Water Region: Bottom of the aquarium

Compatibility and Social Behaviors    The Purple Sea Blade and other Pterogorgia corals are very peaceful and pose no threat to any other corals or gorgonians. Other gorgonians can over take the Pterogorgia corals, so they will need to be kept at a distance. They get along with their own species.

   Butterflyfish feed on gorgonian polyps or tissue. Butterfly fish will constantly chow, so they are not the best idea for a tank mate. Some angelfish will also pick at the polyps, but can be housed with them if the angelfish is well fed.

Sex - Sexual differences    No sexual difference in appearance is known.

Breeding and Reproduction   Gorgonians in general reproduce by by breakage, fragmentation. and they may also spawn for sexual reproduction. The Pterogorgia genus can reproduce sexually. The male releases sperm and the female takes it in, fertilizes the eggs, and allows the "young" to brood. The larva, called planula larva, can freely swim. As they mature they drop into the substrate to develop a primary polyp.

   Propagation of gorgonians consists of using severing or clean cuts. Tearing the coral will result in infection. Be cautious with the use of glues, as many gorgonians react badly to the chemicals. However an underwater epoxy has been suggested by some. They have a very hard time reattaching to a new base, and this may take a while. Containment is recommended if the frag survives. This involves keeping the frag in one spot, say a small piece of upright pvc, around the same height as the frag, with sand or rubble at the bottom. This will keep the frag from blowing over before it can take root. It is suggested to drill holes in the pvc to keep the water flowing. Allowing your Pterogorgia genus to just grow, and then cutting part of the base with the root is really the best way to go if you can do this.

Potential Problems   The Pterogorgia genus is susceptible to algae and cyanobacteria accumulating on its branches. This problem can lead to red band and black band infections. Keeping water flow strong will help prevent this. If your gorgonian does get this, you can at times cut off the bad part and hope the rest will recover. They are also a food source for Flamingo Tongue Snails Cyphoma spp., which also prey on many other photosynthetic gorgonians.

Availability    Gorgonians for Sale: The Purple Sea Blade P. anceps (and other Pterogorgia gorgonians) are very easy to find at pet shops and on line. Using common names, you may easily locate these gorgonians. The cost for online stores is around $8.00 USD or more, depending on size and/or color.

References

Author: Carrie McBirney, Clarice Brough CRS
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