‘Purple Forest’
Decorator Crab (Microphrys bicornuta) on Asparagopsis taxiformis algae
Music, Video, and Aquarium
2010 Morphologic Studios

This week’s video features an aquascape comprised of the beautiful purple macro algae  Asparagopsis taxiformis. However, if you pay close attention to the left 1/3 of the screen, you’ll notice something… moving with claws… Nestled amongst the algae is a perfectly camouflaged decorator crab (Microphrys bicornuta).  Keep paying attention… at 26 seconds into the clip you’ll notice a tiny isopod crustacean float by in the current and descend helicopter-style right onto the crab’s back. The unsuspecting isopod has no idea that it has landed upon an algae covered beast. Furthermore, it appears that the crab is not aware of the unexpected visitor until the isopod begins to explore its decorated exoskeleton.  50 seconds into the clip the isopod meets its fate with a few swift snatches of the crab’s claws.  Without missing a beat, the crab continues scavenging amongst the rocks and algae.  And life on the reef goes on…

Decorator crabs are amazing creatures in that they pick up pieces of their surrounding habitat and place them on their carapace (back, exoskeleton) in order to blend into their surroundings.  Decorator crabs that live amongst sponges decorate with sponges, those that live amongst zoanthids use zoanthids, and so on. This instinctual logic is truly remarkable.  The  crab in the video has attached small pieces of the Asparagopsis upon itself, and as a result is all but indistinguishable from its surroundings.

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‘Corynactis viridis’
The feeding of a Corynactis viridis corallimorph
Music, Video, and Aquarium
2010 Morphologic Studios

This past week we finally received our long awaited Corynactis viridis from our good friend Dr. Yvan Perez at the Institut Méditerranéen d’Ecologie in Marseilles, France. I collected these polyps this past June while diving in the Mediterranean, and Dr. Perez has been culturing them in his lab in the interim. Laurent Foure, the current curator of the Noumea Aquarium in New Caledonia, also collected us several stunning morphs from a different Mediterranean location before he left for the South Pacific.

Corynactis viridis is an archetypal corallimorph species found all along the cold, rocky coastlines of Western Europe. Its distribution across the Mediterranean is much more sporadic and considerably less common. They are frequently referred to as ‘jewel anemones’, which is a misnomer, as they are not anemones despite their superficial resemblance. Typically, polyps range in size from about 3-10mm in diameter and can be found in a seemingly limitless number of color morphs. What they lack in individual size, however, they make up for in colonial dominance. It is not uncommon for colonies to completely carpet large areas, frequently rocky outcrops and vertical surfaces. As these colonies are comprised of clones, this carpet will be of uniform coloration, creating the illusion of a singular connected organism. Multiple color morphs will often be found living in close proximity, creating a technicolor patchwork of tiny individuals. Their colors are often vibrant with fluorescent accents. Unlike most of our tropical corallimorphs, C. viridis are non-photosynthetic, relying entirely on the capture of plankton by their sticky tentacles. At the end of each tentacle is a small ball known as an acrosphere; a tell-tale characteristic of all non-photosynthetic corallimorphs.

In this video a single Corynactis viridis polyp (about 8mm in diameter) is seen capturing and digesting tiny plankton as they flow past in the current. As the tentacles capture food, they retract towards the animal’s mouth, located at the center of the polyp. The mouth is likewise transformable; capable of extending, expanding, and enveloping food items. The total elapsed time was roughly 12 minutes and sped up 1200% in order to demonstrate the hydraulic muscular contractions and contortions that the polyp goes through while feeding. 470nm LED light is used to highlight the fluorescent orange ring around the outer diameter of the polyp.

‘The Christmas Tree Worm’
Spirobranchus giganteus – Amber Morph
Music, Video, and Aquarium
2010 Morphologic Studios

Christmas tree worms (Spirobranchus giganteus) are an abundant creature on Floridian reefs, making their permanent homes encased inside the limestone skeletons of live coral. Found in a seemingly endless variety of colors and measuring 2-3 cm in diameter, dozens of these worms will typically adorn massive coral heads in local waters.

Using only the perception of light and vibration, these animals will retract at lighting speed at the first sense of something ominous approaching. Fortunately the worms come equipped with a a protective double-horned operculum that seals the worm safely inside the inpenetrable coral. A sharp, calcareous spike extends forward of the tube’s opening, acting as a further deterant to a would-be predator.

The spiraled, ‘branchial crown’ serves as both breathing and feeding apparatus for the worm, and is the only part of the worm’s body that is extended into the water column. The feathery appendages, known radioles, collect plankton that drift by in the current. The radioles are lined with cilia that direct the captured food down the spiral to the worm’s mouth.

‘Preener’
Mithraculus cinctimanus crab on Ricordea florida corallimorphs
Music, Video, and Aquarium
2010 Morphologic Studios

Shown above is a 1cm Mithraculus cinctimanus, commonly known as the banded clinging crab. Typically this species is known to live in association with a variety of Caribbean sea anemone species. However, several years ago we noticed that juvenile and sub-adult banded clinging crabs seemed to prefer the protection amongst Ricordea florida polyps in the wild. When they are small, like this one,  the carapace (shell) of the crab is nearly entirely covered by a fuzzy red algal camouflage. As they get larger (up to 25mm) they lose much of this hairy coat, revealing a striking white and maroon patterned exoskeleton.

The video shows the crab alternating between preening its own algae covered carapace and the fluorescent tentacles of the Ricordea florida on which it lives.  It is possible that the crab may ingest some of the polyps’ mucus as an occasional food source.  The video was sped up considerably (9x). At normal speed the polyps appear static, but at this speed the regular hydraulic undulations and contractions of the R. florida polyps are clearly visible.

An unusual colony of Discosoma sanctithomae with perfectly spherical vesicles from the Florida Keys at 10m of depth.  Note the turbid sea floor, characteristic of this species’ preferred habitat.

The unusual spherical vesicles of these Discosoma sanctithomae polyps once gave this morph a separate species designation Orinia torpida by Duchassaing & Michelotti in 1860.  Despite several other taxonomists re-examining the single preserved specimen in the Zoological Museum of Turin in the first half of the 20th century, it was the late great corallimorph taxonomist J. C. Den Hartog who finally corrected this error in 1980.   It is understandable that such confusion could occur.  Until the advent of scuba diving, many taxonomists would never actually observe the living marine animals they classified.  Instead these Euro-centric scientists would rely on preserved specimens sent back to them from various collection missions around the world.  With few specimen samples to compare with, morphologic oddities like the pictured polyps could easily be considered to be something entirely new.

A close-up of a staghorn coral (Acropora cervicornis) branch tip. Note the healthy coral polyp extension.

This past Saturday I took my friend Jeremy (of coralpedia.org) and his wife on a shore dive off Fort Lauderdale Beach.  I had heard rumors that decent stands of the endangered staghorn coral (Acropora cervicornis) were abundant in this area.  Despite (relatively) poor visibility, we found these rumors to be correct.  Acropora cervicornis was one of, if not the most, common stony corals only 250-350 meters offshore this popular sunbathing mecca in only 6-7 meters of water.  It is amazing to see how even a small ‘bush’ of A. cervicornis can attract dozens of small fish seeking refuge amongst its branches.  It is clear that the widespread die-off of this single species has had a detrimental impact on the entire ecosystem of the Florida’s coral reefs. I can only imagine what the reefs in the Florida Keys were like 30 years ago, as today most are just lumpy humps of rock dominated by massive coral heads,  gorgonians, and macroalgae.  The interstices of A. cervicornis branches provides a habitat that is unmatched.  Seeing an abundance of A. cervicornis so close to shore in Fort Lauderdale is encouraging…

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The spongy decorator crab (Marcocoeloma trispinosum) takes expert care in snipping off pieces of living sponge and attaching them to its carapace (exoskeleton shell).  Detritus and debris are added for additional camouflaging effect. This particular crab has taken the decoration to the next level by including some spectacular zoanthids (Zoanthus sp.) into its design. As you can imagine, the crab was living amongst a colony of the same zoanthid morph, rendering it nearly impossible to detect.  Furthermore, decorator crabs move very slowly and deliberately, quite unlike the unpredictable scurry of most other crabs.  The purposeful addition of  camouflaging marine life to the body of this crab highlights the evolution and subconscious intelligence of  ‘tool-use’ at such a ‘primitive’ level in the animal kingdom.