Join me in the cold, dark, life-sustaining NE Pacific Ocean to discover the great beauty, mystery and fragility hidden there.

Posts tagged ‘nudibranch’

Bring in the Clowns

In having noted the recent “Creepy Clown” absurdity in the far off periphery of my life, I thought I would share the beauty of the clowns abundant below the surface at this time of year – Clown Dorids.

Clown Dorids are a species of nudibranch (Triopha catalinae to 7 cm).

Nudibranchs are sea slugs with naked gills and those in the dorid suborder most often have their plume of gills on their posterior (around the anus in fact). See the orange frills in the Clown Dorids in these images? Those are their gills.

Clown Dorid; gills on right @Jackie Hildering.

Clown Dorid with gills are on the right. It’s “rhinophores”, by which it smells its way around, are on the left, atop its head. ©2016 Jackie Hildering 

Many dorid species fully retract their gills when disturbed. Clown Dorids can only partial retract their gills.

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That’s all!  Clown Dorids cannot fully retract their gills like most other dorid species.
@2016 Jackie Hildering.

Note too the beautiful “oral veil” with papillae that aid Clown Dorids in finding food.

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Image allowing a good look at the Clown Dorid’s oral veil. ©2016 Jackie Hildering.

Also unlike many dorids, Clown Dorids do not feed on sponges. They feed exclusively on bryozoan species; those crusty colonies of organisms often found on kelp.

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Clown Dorid likely feeding on Kelp-Encrusting Bryozoan (Membranipora serrilamella).
©2016 Jackie Hildering.

There were a particularly large number of Clown Dorids on my dive this past weekend with many egg masses.

Sea slugs are reciprocal hermaphrodites. This of course makes good sense as a reproductive strategy when you are a slow slug and your offspring hatch out to be plankton. Reciprocal hermaphrodites have both male and female sex organs whereby both individuals are inseminated and lay eggs = way more eggs!

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Clown Dorids that have found one another (relying on smell and touch) and maneuvering into the mating position. ©2016 Jackie Hildering.

Nudibranchs mate right side to right side. If you look very carefully in the photo below, you can see a bump on the individuals’ right side. This structure is the “gonopore” and is usually retracted. They lock onto one another with their gonopores and both become inseminated.

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Clown Dorids extending their mating organs and about to lock on right side to right side.
(Ochre Star beside them.) ©2016 Jackie Hildering.

The gonopore may be easier to see in this image.

Clown Dorid - note the "gonopore" on the right near the nudibranch's head. ©2017 Jackie Hildering.

Clown Dorid – note the “gonopore” on the right near the nudibranch’s head. ©2017 Jackie Hildering.

The egg masses of each species of sea slug look different. However, it is very difficult to discern the eggs masses of some closely related dorids. The ideal is to find an individual laying the eggs.

Clown Dorid egg mass. Every little dot is an egg that will hatch as plankton into the sea. ©2017 Jackie Hildering.

Clown Dorid egg mass. Every little dot is an egg that will hatch as plankton into the sea.
©2017 Jackie Hildering.

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Another perspective on Clown Dorid egg masses. ©2016 Jackie Hildering.

However, in all these years, I have never managed to get a photo of a Clown Dorid laying eggs. Dive buddy Paul Sim has though. See his great image below.

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Clown Dorid laying an egg mass. Note each little dot? That’s an individual egg! ©Paul Sim.

How’s that for bringing in the clowns?!

For you to enjoy, below are more non-scary clowns from this past weekend.

Clown Dorid near White-Spotted Anemone. ©2016 Jackie Hildering.

Clown Dorid near White-Spotted Anemone. ©2016 Jackie Hildering.

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Clown Dorid just below the surface in less than 5 m depth. Appears to be feeding on bryozoans.
©2016 Jackie Hildering.

More information:

  • Reproductive structures of Clown Dorids from the Sea Slug Forum – click here.
  • Colour and diet in Clown Dorids from A Snail’s Odyssey – click here.

Nudibranchs on an Offshore Whale Survey?!

How does studying whale acoustics lead to increased knowledge about the depth range of nudibranchs?

Orange doto.

Just a little more is now known about the orange doto’s depth range. Photo: Hildering.

Let me take you deep and share an experience from my recent time offshore in the eastern North Pacific on a DFO cetacean survey.

This is the Canadian Coast Guard Ship – the J.P. Tully.

JP Tully.

CCGS J.P. Tully. Photo: Hildering

Among the offshore science expeditions undertaken upon the Tully, are surveys by DFO’s Cetacean Research Program.  These line transect studies provide an estimate of cetacean abundance, as well as an opportunity to ID individual whales and collect feeding and genetic information. The knowledge about abundance and location is of particular importance for the large whales that were hunted so intensely and require protection under Canada’s Species at Risk Act.

These are Autonomous Underwater Recorders for Acoustic Listening (AURAL-M2s).

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AURAL-M2s. Photo: Sheila Thornton.

AURALs are hydrophones that can be deployed to 300 m, making time-spaced recordings (e.g. 15 minutes every hour) for up to a year.  Such acoustic monitoring is a very important supplement to the cetacean vessel surveys. The AURALs are of course placed very strategically, in remote, offshore locations. By passively recording whale calls, the AURALs can provide information about the location and seasonality of whale species which may aid in determining critical habitat.

The AURALs are a wonder of technology. It is of course no problem to get something to the bottom of the ocean but, getting it back to the surface so you can retrieve your equipment and data is not so simple. It is achieved with an acoustic release (“D” in the diagram below). Once the vessel is positioned so that there is no chance of the device coming up under it, a sound signal is sent to the device and the AURAL releases from its anchor and floats to the surface thanks to the big yellow buoy.

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AURAL-M2. Click to see an enlarged, labeled schematic on the Multi-Electronique webpage.

These are two perplexed black-footed albatrosses! A big yellow orb has just popped up to the surface as a result of the acoustic release signal. This AURAL was at 226 m depth at the Bowie Seamount, 180 km west of Haida Gwaii. It had been there for a  year.

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Black-footed albatross just after the buoy with the AURAL recording device came up from 226 m.

Here, the highly skilled Coast Guard crew get the AURAL back aboard the ship so that the data can be retrieved and, ultimately, analyzed for whale vocals.

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Coast Guard deck crew expertly retrieves the AURAL. Photo: Hildering

But, there was also a year’s worth of growth on the buoy and who knows what you might find . . .

Nudibranchs! Three species found and even one species with eggs!

3 nudibranch species on the aural that had been at 226 m. Photo: Hildering.

3 nudibranch species on the AURAL that had been at 226 m. BC aeolid; bushy-backed nudibranch and orange doto. Click to enlarge. Photo: Hildering.

  • Top: BC aeolid (Catriona columbiana to 1.5 cm); eggs also found.
  • Left: Bushy-backed nudibranch (Dendronotus venustus to 3 cm; previously Dendronotus frondosus)
  • Right: Orange doto (Doto amyra to 1.4 cm)

By examining the AURAL that had been at 226 m, it confirms that these 3 species of nudibranch have a range to at least that depth.

BC aeolids + egg mass.

Sheila Thornton (marine mammal researcher and fellow nudibranch nut) providing a size comparison for the BC aeolids and their egg masses that were found on the AURAL. Click to enlarge. Photo: Hildering

I shared the find with those who have nudibranch expertise much greater than my own (Dave Behrens via Andy Lamb) and learned that for two of the species, there had been no previous record for them at this depth.

It has long been known that some nudibranch species range to depths of at least 700 m. However, you can imagine what a a challenge it is to get species specific depth information. We camera carrying scuba divers can’t help beyond 40 m depth (deeper if diving with mixed gases).

So it’s not a big scientific discovery.  Compared to the data the AURAL will reveal about endangered whales, it’s just a sea-slug-sized discovery.

This is me – back on survey duty looking for much bigger organisms but delighting in how collecting data to help save whales, led to learning a bit more about the little guys.

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Spotter duty on the DFO Cetacean Program’s offshore survey. July 2013. Christie McMillan photo.


 

See the CSAS technical report is by Linda Nichol and Dr. John Ford on the importance of the line transect surveys to the recovery of endangered cetaceans: Information relevant to the assessment of critical habitat for Blue, Fin, Sei and North Pacific Right Whales in British Columbia.

A few more photos from this DFO cetacean survey will soon be posted in this FaceBook album. 

Scroll down at this link to hear samples of marine mammal vocals recorded by AURALs.

Hooded Mystery – Hooded Nudibranchs and their eggs

©Jackie Hildering

Hooded Nudibranch – oral hood open to catch plankton. ©Jackie Hildering

The remarkable looking animals to the right are Hooded Nudibranchs (Melibe leonina up to 17.5 cm). A nudibranch is a type of sea slug that has naked (“nudi”) gills (“branchs”).

Starting in the fall, around NE Vancouver Island, they come together in order to mate and it is awe-inspiring to see 100s of them clustered together, delicate and ghost-like, clinging to kelp.

Often, you can see them swimming on the surface and many people mistake them for jellyfish. It is indeed one of the most alien looking of the 200+ sea slug species of our area. The large disc-like head lets it feed on plankton and small crustaceans and the lobed structures on the animals’ backs are the naked gills.

Hooded nudibranch swimming. ©Jackie Hildering

Hooded nudibranch swimming. ©Jackie Hildering

Since sea slugs can only sense light and dark, the way Hooded Nudibranchs signal one another is by emitting a fruity scent (pheromone) that attracts others of their kind. 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 and the scent stayed on my hand for more than an hour. 

After mating, both animals lay eggs (they are hermaphrodites) and then, they die. You can find additional information about why sea slugs are hermaphrodites at this past blog posting. 

Hooded Nudibranch eggs. ©Jackie Hildering

Hooded Nudibranch eggs. ©Jackie Hildering

Typically in our area they lay their egg masses between January and April. Each ribbon of eggs is only about one centimetre wide and contains thousands of eggs.

Every dot is an egg capsule contains 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. The larva are called “veligers” and look very different from the adult Hooded Nudibranchs.

They have a shell and a big flap on their head with which they swim and feed on smaller plankton. After 1 to 2 months, they settle to the ocean bottom and change body shape and even digestive tract to become small Hooded Nudibranchs. 

A few of my video clips of this species below.

Unusually coloured Lions Mane Jelly near kelp draped in Hooded Nudibranchs. ©Jackie Hildering

Unusually coloured Lions Mane Jelly near Giant Kelp draped in Hooded Nudibranchs. ©Jackie Hildering

Hooded Nudibranchs on a rotting piece of Bull Kelp. ©Jackie Hildering

Hooded Nudibranchs on a rotting piece of Bull Kelp. ©Jackie Hildering