The sea-slug known as the Blue Chinese Dragon is a remarkable marine creature capable of surviving for long periods without food by using the nutrients provided by its own garden of unicellular plants growing and multiplying inside its body.
Previous articles on Digital Journal have introduced to interested readers some remarkable marine creatures. We have shown the amazing beauty of the Blue Dragon (Glaucus atlanticus), the charming cuteness of the splendid Chromodoris, and the elegance of an extraordinary fish known as the Weedy Sea Dragon.
In this occasion, I will share with Digital Journal readers
Juvenile (left) and adult Blue Chinese Dragon (Pteraeolidia ianthina). (The Sea Slug Forum).
another fascinating marine animal. Most divers in the distribution range of this underwater wonder know this organism as the “Blue Chinese Dragon”. Using the binomial nomenclature, scientists know it by its Latin name Pteraeolidia ianthina.
The Chinese Dragon
The Blue Chinese Dragon is a widely distributed sea creature belonging to the group generically known as nudibranchs or sea slugs. It is found in diverse habitats including sea-sponge patches and among shallow coral reefs throughout the Southwestern Pacific Ocean, from Hawaii to the Philippines, also extending to Northeast Australia and New Zealand waters.
Adult Pteraeolidia ianthina measures about 7 centimeters and have a rather elongated body with many clusters of blue-edged curved arches called cerata. Their general appearance resembles a Chinese Dragon. It also looks like a centipede. Their typical coloration is often translucent beige or brown, except the juveniles which are mostly white. As all nudibranchs (meaning “naked gills”), they have exposed respiratory organs protruding from their back end. The front end has two long cephalic tentacles with purple-blue rings, and two sensory organs, called rhinophores, with a purple-blue tip.
Adult Blue Chinese Dragon.
Blue Chinese Dragon. This is a juvenile who has not yet obtained the unicellular plants (zooxanthellae) which will multiply in its digestive system and provide nutrients to the slug.
Blue Chinese Dragon. Details of the clusters of blue-edged curved arches called cerata. The tips of the cerata contain nematocysts which can cause painful stings to humans.
A "solar-powered" organism
The most remarkable feature of the Blue Chinese Dragon is their capacity of going for long time without food intake. How do they do it? Most sea slugs are carnivorous, but the Blue Chinese Dragon has evolved the ability of capturing and “farming” in their digestive system a large number of unicellular algae (microscopic plants) known as Zooxanthellae.
The sea slug obtains an initial supply of the microscopic algae which they keep alive within their body. Both organisms, slug and zooxanthellae, establish a symbiotic relationship. The microalgae can multiply within the slug’s body and, as most plants do, they can transform the sun’s energy into Chlorophyll, sugars and other nutrients. They use some of the generated nutrients themselves and pass on a significant portion to the sea-slug for its own nourishment.
Blue Chinese Dragon. Details of the two long cephalic tentacles.
Blue Chinese Dragon. Details of the anterior chemosensory organs called rhinophores.
The photographs that illustrate this article were taken by Jason Shelley in waters off the Kurnell Peninsula, Botany Bay National Park, Sydney, New South Wales, Australia, where Blue Chinese Dragons are plentiful.
Although I know a few things about aquatic life, and I like photography of natural subjects, I am not a diver and I must admit that my camera is barely good enough to capture terrestrial landscapes and the occasional, moderately successful, macro photography. Thus, I have been particularly impressed by the high quality of Jason Shelley’s underwater images. I asked Jason to enlighten me on his technique and equipment.
Digital Journal: How difficult is it to capture small marine creatures?
Jason Shelley: Some slow moving creatures are not too difficult to photograph. However, the Blue Chinese Dragon has been one of the hardest to capture because besides being small, their body moves like kelp in the current, so good focus is always a challenge. This has motivated me to improve my equipment to obtain a better image.
D.J.: Which image of the Chinese Dragon do you consider your best shot?
J.S.: The last photo is my favourite. That is the one showing the close up of the rhinophores, the club-shaped sensory structures with a purple-blue tip. I have wanted to capture an image like that since I bought my first underwater camera.
D.J.: What kind of equipment do you use to capture such neat close-ups of marine organisms?
J.S.: I use an Olympus E520 10MP Digital SLR camera equipped with an Olympus PT E05 Underwater Housing. For macro photography I use an Olympus 50mm macro lens. I also use what's called a wet lens or wet diopter. The setup also includes an INON Strobe which is an underwater flash that can be moved around to different angles depending on how you wish to light the subject. I also use a Submersible LED Torch. It acts as a focus light. It lights the subject so the camera can focus quicker on the subject and also assists in the correct capture of colours.
For shooting very fast moving subjects, I use a GoPro HD. That is the component on top of the underwater casing in the front view of the system. The rig is attached to a homemade holder (best seen on the side view). The assemblage is fairly heavy to carry above water, but underwater I can use and maneuver it with one hand.
Underwater photographic equipment used to capture most of the images illustrating this report. Front view.
Underwater photographic equipment used to capture most of the images illustrating this report. Side view.
D.J.: Is this elaborated equipment very costly?
J.S.: I estimate that replacement cost of the entire underwater camera system may be about $4500.
I appreciate Jason Shelley’s contribution to this and previous articles by providing extraordinary images of interesting marine organisms not readily accessible to Digital Journal readers.