Everyone knows that some terrestrial animals are active primarily at night and sleep most of the day, while others go about their business during daylight hours and rest when it’s dark. For some reason, many people are surprised to learn that the same thing holds true for animals that live in the sea.
One of the many marine animals that works the night shift is the crinoid species pictured here: Lampometra klunzingeri, a member of the Mariametridae family. During daylight hours, these crinoids hide in crevices in the reef. Shortly before sunset, like clockwork, they emerge from their hiding places and laboriously crawl up onto the corals in search of a perch for feeding.
In the Red Sea, where these photos were taken, these crinoids are seen frequently among the branches of Millepora dichotoma, a calcareous reef-building Cnidarian commonly known as ‘fire coral’. At dusk, these crinoids crawl onto the branches and grasp the surface with their cirri, as you see in the first photo on this page. Then they unfold their segmented arms, spreading them widely to capture plankton. The whole process is quite a wonderful sight to witness.
The close-up photo above shows L. klunzingeri with its arms spread for feeding. You can see how this array could be a fairly efficient plankton sieve, but the next image is even more convincing.
The image above is a macro photo of a section of a single arm of L. klunzingeri. Clearly visible are the rows of fine hairlike structures on each pinnule. Once we have a look at an image like this, it is easier to understand how it is possible for the crinoid to capture enough food to sustain itself. All but the most microscopic bits that might be suspended in the water that passes over this crinoid’s arms will be caught.
I mentioned above that this crinoid species hides in the day and comes out at dusk. Clearly, the relative presence or absence of ambient light is an important regulator of this animal’s behavior. In fact, like many other nocturnal animals, this crinoid species is very sensitive to light. This photosensitivity can make it difficult to photograph. When exposed to bright light, the animal rapidly retracts its arms, curling them inward.
For the photographer, this means it is necessary to set up a shot of the animal with its arms extended in next to no ambient light! In order not to prematurely disturb the animal when photographing this species, I use a light with a narrow beam, like that of a penlight, to locate a likely subject. One of my camera strobes has a modeling light — also a very narrow beam — which I use to quickly aim and focus the camera lens. As soon as the strobes flash once, the crinoid will begin to curl in its arms. As a result, I have many more photos of these crinoids that look like the final one, below, than of the arms completely spread out.
Note: All of the photos on this page are the same species, Lamprometra klunzingeri, but each image is of a different individual. All of the photos were taken during night dives in the Red Sea, off the coast of the Sinai Peninsula.