Posts Tagged ‘Natural History’

‘The Heart Urchin Pea Crab’

Monday, June 21st, 2010

‘The Heart Urchin Pea Crab’
Dissodactylus primitivus on Meoma ventricosa
Music, Video, and Aquarium
2010 Morphologic Studios

Barely 7mm in size, the aptly named heart urchin pea crab (Dissodactylus primitivus) lives its entire life as a passenger upon the slow-moving red heart urchin (Meoma ventricosa). It is an example of the unusual life that can be found by looking in unexpected places on Floridian coral reefs. The red heart urchin is an unusual member of the echinoderm clan (e.g. urchins, sea stars, sand dollars, sea cucumbers) that spends most of its time burrowing in the sand. It sifts through the grains of sand searching for organic detritus that constitutes its diet. Likewise, the heart urchin pea crab lives a well-protected life (usually below the sand) amongst the spines of this fist-sized urchin. While most crabs move swiftly, this pea crab moves slowly in order to navigate through the corridors of spines, even spending time inside the urchin’s mouth. It is likely that the crab feeds upon some of the food that would otherwise be consumed by the urchin. This commensal relationship appears mildly parasitic, as the urchin doesn’t seem to gain any sort of direct benefit from the crab living amongst its spines. Frequently, several heart urchin pea crabs will live communally without any noticeable negative impact to their host urchin’s health.

If you look closely, you’ll notice the rhythmic working of its gills and circulatory system within the heart urchin pea crab’s translucent, eggshell exoskeleton.

‘Cleaner’ Pt. 3

Tuesday, June 15th, 2010

‘Cleaner’ Pt. 3
Periclimenes rathbunae on Stichodactyla helianthus
Music, Video, and Aquarium
2010 Morphologic Studios

The sun anemone shrimp (Periclimenes rathbunae) is the least common of the three species of Floridian anemone shrimp. While the other two anemone shrimp (P. pedersoni and P. yucatanicus) act as cleaners to passing fish, the sun anemone shrimp doesn’t seem to engage in this behavior. Instead, it spends its time living almost exclusively upon its namesake sun anemone (Stichodactyla helianthus). Aquarium observations suggest that this shrimp may supplement its diet by occasionally nipping off and eating the tentacles of the anemone. This parasitism suggests a more complicated symbiotic relationship than the sort of simple mutualism that these shrimp are often categorized by.

In Floridian waters, the scarcity of this shrimp is likely related to the infrequency of its host sun anemone. However, where they are found, the sun anemone often lives in dense clonal colonies that can literally carpet shallow reefs. The tentacles, while short and stubby, are packed with powerful stinging nematocysts that act like microscopic harpoons to deliver their venom. The end result of all these nematocysts and tentacles, is an anemone that is very ‘sticky’, and capable of producing painful welts to the careless diver.

‘Sally Lightfoot’

Monday, April 26th, 2010

‘Sally Lightfoot’
Percnon gibbsi crab amongst Anemonia bermudensis anemone garden
Music, Video, and Aquarium
2010 Morphologic Studios

The sally lightfoot crab (Percnon gibbsi) is an agile maneuverer on the rocky shores of the Caribbean. These crabs are particularly well-suited to life on craggy limestone rock in shallow water. The rockwork is the result of sea urchins eroding the limestone as they rasp off the algae growing on the surface. The cumulative erosion by sea urchins over many years creates a jagged network of fissures and channels through the solid rock. The sally lightfoot crab’s pancake-flat body allows it to scuttle beneath the protective spines of a nearby urchin at a moment’s notice. Anemonia bermudensis sea anemones like the ones seen in the film can also be common on the rocks in this surf-washed zone. The sally lightfoot’s nimble legs allow it zig-zag harmlessly between the tentacles of these stinging animals. Between the crab’s eyes you’ll notice a pair of fast-flitting antennae that detect the ‘smell’ of food in the water. The turbulence of the environment requires accurate detection and nimble response.

‘The Florist’

Monday, April 12th, 2010

‘The Florist’
Leptopsia setirostris (Decorator Crab) scavenging amongst a Zoanthus polyp garden
Music, Video, and Aquarium
2010 Morphologic Studios

Once again we return to observe a cryptic red decorator crab (Leptopsia setirostris); this time living upon, and decorated with, zoanthid polyps (Zoanthus sociatus), close cousins to both sea anemones and corals.  Zoanthus in Latin literally means ‘animal flower’.  The species name sociatus refers to the fact they these flower animals live socially in dense groupings of identical polyps.

Decorator crabs demonstrate a remarkably prescient instinct to be able process the information required to successfully camouflage themselves to match their preferred habitat.Unlike the typically fast-scuttling crabs of the mainstream, decorator crabs move at a deliberately slow pace to reduce being noticed.

This particular decorator crab species boasts a brilliant red exoskeleton that it has disguised with the zoanthids.  The crab has carefully nipped individual zoanthid polyps from a larger colony and placed them upon its carapace (back) where they attach down on their own and continue growing.  My experience suggests that it takes at least two days for a polyp to begin attaching down to new substrate.  I have yet to observe the crab going through the whole process of zoanthid ‘decoration’, but clearly it is a very patient animal.

The crab uses it’s small claws to pick at and remove pieces of detritus between the polyps.  The animal nature of the zoanthids becomes especially apparent when the movements of the crab cause the polyps to close up in reaction.   If you look carefully at the bottom right of the screen you’ll notice the periodic movements of a barnacle that these zoanthids are growing upon.  Zoanthids are commonly called ‘sea mat’ due to their rubbery, encrusting morphology. They live together in interconnected colonies of cloned polyps, slowly expanding their colonies outward; growing over shells, in-between coral heads, and across shallow tide pools.

‘The Lynx Nudibranch’

Monday, March 29th, 2010

‘The Lynx Nudibranch’
Phidiana lynceus (Lynx Nudibranch) on Spondylus americanus oyster
Music, Video, and Aquarium
2010 Morphologic Studios

Last week we spent a moment making eyes with the oyster (Spondylus americanus). This week we’ll spend a moment with a diverse community of animals and plants that have colonized the upper shell of the very same oyster. Towards the left of the frame is a small colony of flower-like animals known as hydroids. Hydroids are most closely related to jellyfish, but instead remain attached to the reef their whole lives (unlike a jellyfish). But, like the jellyfish, hydroids can pack a powerful stinging punch. The brown, daisy-like creatures seen growing here on the oysters’s back are one such type of hydroid, Myrionema amboinense. This hydroid species derives its brown coloration from the symbiotic zooxanthellae (dinoflagellate ‘algae’) stored in its tissues. The ability to gain nutrition from both prey capture and photosynthesis, allows these hydroids to grow and colonize quickly. The sting from these hydroids is considerably more powerful than that of most corals. The gray, lumpy knobs on the back of the oyster shell are zoanthid polyps, close cousins of the sea anemones. However, these zoanthids are no match against the powerful sting of the hydroids. The zoanthids have all but acknowledged defeat by the encroaching stingers by simply closing up; effectively handing over control of the oyster shell to the hydroids.

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‘Oyster Vision’

Monday, March 22nd, 2010

‘Oyster Vision’
Spondylus americanus oyster
Music, Video, and Aquarium
2010 Morphologic Studios

Here we look into the face of the thorny oyster (Spondylus americanus).  Unlike most shallow-water oyster species, the thorny oyster is a solitary creature that lives permanently cemented to the deeper coral reef.  Its fleshy mantle is adorned with sepia-toned psychedelic camouflage that can vary widely from one individual to the next.   The rim of the mantle is lined with dozens of eyes that stare out into the depths.  These eyes are quite simple, only detecting changes in light that might suggest an incoming predator.  If a threat is detected, the oyster will quickly snap its two shells together, sealing the animal inside with its two powerful adductor muscles.  It is the adductor muscle that people eat when they eat ‘oysters on the half shell’.  Oysters are filter feeders, spending their time siphoning water through gills that strain out particulate matter. As seen in the film, the oyster periodically expels waste and water with a quick contraction of its adductor muscles.

In the second installment (next week) we will explore the upper shell of the oyster and the community of organisms that has colonized it.

‘Purple Forest’

Sunday, January 31st, 2010

‘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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