The January sun streaming down, the light refracted against the hooded nudibranchs . . . the underwater rainbows?!
Hooded nudibranchs are already such ethereal, other-worldy creatures, to see the rainbows dancing against their translucent bodies made me catch my breath and desperately want to capture the beauty for you.
May you dream of underwater rainbows and – maybe- fall even a little bit deeper in love with the NE Pacific Ocean.
For information on hooded nubibranchs (includes images and video of them swimming and their eggs), please see my previous blogsat this link.
In late August, some of my Young Naturalists alerted me that they had already seen hooded nudibranchs (Melibe leonina) around Port Hardy (B.C., CANADA).
[It so wonderful that these local children know and greatly appreciate nudibranchs.]
Late August is earlier than we historically have seen the hooded sea slugs gather in large numbers. Usually this happens in late September / early October with them beginning to lay eggs in the spring.
Hooded nudibranchs back in very large numbers. Late August 2010.
This week, I had the opportunity to check how many are already in the area and, it’s official – the hooded nudibranchs are very much back.
To see the video from today, click here (2-minute video).
This week, I share video showing this remarkable sea slug when it is swimming.
When viewing the clip, try to identify the animal’s “rhinophores”, the structures coming off the animal’s head that allow it to smell its way around. These structures have the shape of mouse ears but they pick up on chemical signals, not sound. In last week’s posting I shared how the Hooded Nudibranchs come together to mate through being attracted by smell (pheromones).
Video from today of a swimming Hooded Nudibranch.
The lobed structures on the animal’s back are the naked (nudi) gills (branchs). They can detach if the hooded nudibranch is threatened and are sticky. Maybe this is so that the predator is distracted by the gills sticking to it allowing the hooded nudibranch to have a greater chance of getting away.
Hooded Nudibranchs (up to 17.5 cm) on Giant Kelp.
I have included a second clip this week too, taken on today’s dive. No Hooded Nudibranchs in it, but Bull Kelp forest visions while on my “safety stop”; a 3-minute rest at 15 feet to offload nitrogen before surfacing. Thought you might like to take a dip with me!
The remarkable-looking animals to the right are Hooded Nudibranchs (Melibe leonina up to 17.5 cm). A nudibranch is subgrouping of sea slugs whose characteristics include having naked (“nudi”) gills (“branchs”).
Typically, starting in the fall, around northeast Vancouver Island, Hooded Nudibranchs come together in the hundreds. It is awe-inspiring to see them clustered together just below the surface, delicate and ghost-like, clinging to kelp. Most are translucent white but some individuals are more green or orange.
Often, you can see them swimming on the surface and many people mistake them for jellyfish. But no, they are sea slugs.
The large oral hood (disc-like head) is used to feed on plankton and small crustaceans. The lobed structures on the animals’ backs are the naked gills (cerata). The cerata can pop off if the Hooded Nudibranch is threatened e.g. pinched by a crab. This “ceretal autonomy” and the ability to swim, are believed to be distractors for predator (Bickell-Page, 1989).
The two structures on the Hooded Nudibranch’s oral hood are their rhinophores by which they smell their way around. Hooded Nudibranchs are believed to signal one another by emitting a fruity scent. My personal experience after having picked up a dead Hooded Nudibranch on the beach, is that the smell is something like a mix of watermelon and grapefruit. The scent stayed on my hand for more than an hour.
The secretion is reported to serve as a repellent for predators but does not deter Northern Kelp Crabs.
After mating, as is the way with sea slugs, both individuals lay eggs and then, they die. You can find additional information about sea slugs being reciprocal hermaphrodites in this past blog posting.
In the area around northeast Vancouver Island, I have observed that they lay their egg masses between January and April. Each ribbon of eggs is only about one centimetre wide. Every dot is an egg capsule containing 15 to 25 eggs. After about 10 days, depending on temperature, the eggs will hatch into larvae that will be part of the zooplankton soup of the Ocean.
After 1 to 2 months, they settle to the ocean bottom and change body shape and even digestive tract to become small adult Hooded Nudibranchs
Hooded Nudibranchs do not have the rasping mouth structure of many other sea slugs (the radula). They feed by opening their oral hood to capture prey while standing on kelp or Eelgrass.
From Invertebrates of the Salish Sea: ” . . . diet includes copepods, amphipods, and ostracods, as well as small post-larval mollusks. The animal stands attached to the substrate and expands the oral hood. It then sweeps the hood left and right or downward. When the ventral surface of the hood contacts a small animal the hood rapidly closes and the fringing tentacles overlap, holding the prey in. The whole animal is then forced into the nudibranch’s mouth.”