2010 April | The Marine Detective

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Hooded Nudibranchs and their eggs

*Hooded Nudibranchs – oral hood open ©Jackie Hildering*

[Last updated on January 2, 2022]

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.

Hooded nudibranch swimming. ©Jackie Hildering — *Hooded nudibranch swimming* *©Jackie Hildering*.

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.

Hooded Nudibranch eggs. ©Jackie Hildering — *Hooded Nudibranch egg ribbons. ©Jackie Hildering*

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.

*Hooded Nudibranch on Eelgrass and yes, those little snails are part of their diet.*

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.”

*Hooded Nudibranchs on Giant Kelp. ©Jackie Hildering, 2022*

For more information:

Biodiversity of the Central Coast: Hooded Nudibranch

Deep Sea News: “This sea slug is like a cross between a dinosaur, a jellyfish, and a watermelon”

Lawrence, K. A. and Winsor H Watson. “Earth , Oceans , and Space ( EOS ) 10-1-2002 Swimming Behavior of the Nudibranch Melibe leonina.” (2017).

Newcomb, James M., et al. “Homology and Homoplasy of Swimming Behaviors and Neural Circuits in the Nudipleura (Mollusca, Gastropoda, Opisthobranchia).” Proceedings of the National Academy of Sciences of the United States of America, vol. 109, National Academy of Sciences, 2012, pp. 10669–76, http://www.jstor.org/stable/41601654.

*100s of Hooded Nudibranchs just below the surface in Telegraph Cove ©Jackie Hildering.*

*Dive buddy Jacqui Engel with Hooded Nudibranch ©Jackie Hildering.*

Whale Vomit?!

Mystery mass – ambergris? 3 inches wide (7.6 cm)

Recently, I was contacted by a local family about their very unique find on a beach on Southwest Vancouver Island. Their email had the entertaining subject line of “Whale Puke – Hopefully?” and contained pictures of what they had found.

I was amazed at how they had narrowed down what the strange looking masses might be . . . ambergris (pronounced “amber-grease”; from the French for gray amber), a substance produced in the intestines of sperm whales. And . . . ambergris is extremely valuable; apparently worth up to $20,000 USD per kg. It has a musky, very distinct odour and has been used in perfume as a fixative (to stop it all from evaporating quickly). It has also been used as food flavouring and medicine. Apparently it was even believed to cure the plague. Yes, sperm whales used to be intensely hunted and the hope of collecting ambergris was one of the reasons why.

The sperm whale is the largest toothed whale species. It has a head up to 1/3 of its body (Physeter macrocephalus = big head) and can dive to depths of 3,000 m. We humans have so much to learn about whales that are far less deep diving. You can imagine what knowledge gaps there are for an animal that dives to such great depths and for so long; up to about an hour. (Click here for a detailed “The Marine Detective” posting on the sperm whale).

So how and why do sperm whales create ambergris?

It is believed to be caused by the beaks of the giant squid irritating the sperm whale’s intestines. However, ambergris may not be “whale vomit” at all, but rather, it may come with “whale poop”. Apparently, when “fresh”, ambergris smells more like it comes from the anus. Some scientists believe it does get regurgitated (vomited up) if the piece is particularly large.

Was the family’s mysterious material the highly valuable ambergris? It seemed possible. We have sperm whales off the B.C. coast and the material was resinous, less dense than water and looked like some of the images of ambergris I could find online.

They found two masses, each about the size of a goose egg. They dropped one and it fragmented and crumbled, some pieces darker and clearer than others. But, there were no bits of squid beaks nor was there a really distinct musky odour.

I wanted to be sure, so I contacted the wonderful Dr. John Ford, DFO’s head of Cetacean Research at the Pacific Biological Station in Nanaimo. He very kindly relayed a test that would prove whether it was the highly prized ambergris – or not. If you heat a wire or needle to red hot and stick it into ambergris to about a centimetre’s depth, it melts into an opaque liquid the colour of dark chocolate and leaves a tacky residue on the wire/needle.

When I carried this out, the material did melt and leave a residue but it was a lighter brown material. It did not melt like chocolate. There was a distinct sizzling sound and a small puff of smoke. There was still no distinct musky odour.

So what could it be? I decided to take about a teaspoon of the crumbs and melt them down and, when I saw the result, I had an idea. The material was oily, it melted easily, it had small dark flecks in it. Why – it looked like used cooking oil!

Not ambergris but – cooking grease?!

It’s my best guess to date. That a boat somewhere out a sea, dumped cooking oil. It solidified and got rolled around on the beach, rounding it and pitting it. Why were there two masses of about the same size? I have absolutely no idea. Feel free to offer any hypotheses.

For further details to identify ambergris and where to sell it, go to http://www.ambergris.co.nz/identification

Click here for my bundling of links on B.C.’s sperm whales – includes video, sounds, information about the historical whaling of sperm whales and articles about ambergris.

Article related to finding a high-quality synthetic alternative for use in perfumes. UBC Press Release: April 5, 2012; “How to make high-end perfumes without whale barf”

Hakai Magazine, August 2021, Why We Can’t Shake Ambergris

July 2023, Pathologist finds €500,000 ‘floating gold’ in dead whale in Canary Islands – Team hope sale of block of rare ambergris, used by perfumers, will help victims of 2021 La Palma volcano

Journey Through Kelp

Bull Kelp is so beautiful, especially now in the early spring when the young “sporophyte” stage is growing at an insanely fast rate. The stipe (stem-like structure) of this kelp species, Nereocystis luetkeana, can grow to be up to 36 m long. The stipe would have to grow an average of 17 cm a day to reach this length in the 210-day growing period (source: Druel).

The growth rate of the stipe and fronds together (the leaf-like structures) has been documented to reach an average of 25 cm per day (source: Duncan).

Baby Bull Kelp

It is at this early stage of growth too that Bull Kelp is an intense colour green unlike anything else I know. When older, the colour darkens to an olive green.

Kelp is an alga, not a plant. However, like plants, algae also photosynthesize, converting the sun’s energy into food. Algae have simpler structures and different chemical pathways than plants.

Young Bull Kelp grows so fast to allow the leaf-like parts, called “fronds”, to be closer to the sun so that more food can be made.

Sun streaming through a Bull Kelp forest.

The round, floating part of the kelp, is the “pneumatocyst”. This bladder-like structure is completely hollow and is filled with carbon monoxide (NOT carbon dioxide), allowing the long fronds to drift at the surface to catch the sun’s rays.

Apparently, there is enough carbon monoxide in Bull Kelp to kill a chicken! Now that’s valuable information. See my blog “Enough Carbon Monoxide to Kill a Chicken” at this link.

The stipe is also hollow. I’m sure it is not what Nature had intended, but this allows we humans to play the stipe of Bull Kelp like a trumpet or didgeridoo! The stipe gets thinner and whip-like near the holdfast which is why Bull Kelp likely got its name because the stipe is shaped like a “bull whip”.

Bull Kelp does not have roots. Rather it is a “holdfast”, a tangle of woody structures, that anchors Bull Kelp onto rocks. However, if rocks are too light to counter the floatation of the pneumatocyst, the kelp will actually change the ocean bottom by carrying away smaller rocks, likely ending up washed onto the shore.

Bull Kelp holdfast. No roots. See my blog on holdfasts at this link.

Bull Kelp always grows in patches, truly forming an underwater forest that is life-giving for the same reasons as terrestrial forests: kelp forests buffer the climate change gas carbon dioxide; produce oxygen; and provide food and habitat for so many other organisms. Bull Kelp forests are, in fact, estimated to provide habitat for some 750 species of fish and invertebrates (animals without backbones).

Sea urchins are one of those invertebrates, living in the forest and grazing on a lot of Bull Kelp. If Sea Otters, Mink, Wolf-Eels and other predators of urchins did not keep urchins in check, there would be further reduced kelp forests. Sea Star Wasting Syndrome has devastated the world’s largest sea star species, the Sunflower Star (Pyncopodia helianthoides) which is a predator of Green Urchins. This has led to too many of these urchins and an increase in the number of urchin barrens. Please see my blog here for information on urchin barrens and Sea Star Wasting Syndrome.

Kelp forests are not what they used to be for reasons far beyond our foolishness in over-harvesting Sea Otters. There used to be such dense forests that it is theorized “Ancient humans from Asia may have entered the Americas following an ocean highway made of dense kelp.“

All coastal boaters still benefit from kelp. It is a navigational aid since, where it grows, you know you there is shallower water.

We divers have yet an additional reason to value kelp. Since it is so strong, we can hold onto it if we need to during our safety stop (3 minutes at 5 metres depth) or if needing to gradually pull ourselves down into the depths or back to the surface.

Oh – and you can eat it. (I love pickled young Bull Kelp!)

And yes, you could do puppet shows with Bull Kelp, cutting a face into the bladder like you would into a jack-o-lantern. The fronds even look like two pig-tails!

THEN there is how Bull Kelp reproduces. The offspring look nothing like their parents. Please see here for my blog on the remarkable phenomena that is “alternation of generations”.

But for now, come underwater with me. Come into the forest, breath in, breath out and worship the kelp!

My additional blog items on kelp include:

Sources:

Duncan, M. J. 1973. In situ studies of growth and pigmentation of the phaeophycean Nereocystis luetkeana. Helgolander Meere- € sun. 24:510–25.
Druehl, Louis and Clarkston, Bridgette. 2000. Pacific Seaweeds – a guide to common seaweeds of the west coast.

Sea Slug Easter Eggs For You!

Giant nudibranch's eggs laid at the base of its food, the tube-dwelling anemone. Each dot is an egg. © Jackie Hildering

To follow up on last week’s posting about the feeding of giant nudibranchs, “Who’s eating who”, I now share images of the giant nudibranch swimming and of its egg-laying behaviour.

I know that these are the strangest eggs you will see this Easter!

The story of how the eggs come to be is pretty unique too.

There are no girl or boy sea slugs. They are both male and female; they are hermaphrodites. This means that when sea slugs mate, both animals “get pregnant” and lay eggs.

Sea slugs need this adaptation because it is really difficult for them to find another of their kind. They are relatively slow moving animals that depend on feel and smell to get around.

They don’t search around aimlessly for a mate though. That would be a waste of energy. The chances of finding a member of their own kind are greater near their favourite food. To make this clearer, imagine that you were someone who really loved eating pizza and you wanted to find someone else who loved pizza. The best place to find them would be at . . . a pizza parlour!

For the giant nudibranch, you know from last week’s posting that they love to eat tube-dwelling anemones so they are likelier to meet a mate around this prey. They also may give off chemical signals (pheromones) to announce that they are in the area and “looking for love”.

Compared to faster animals that can see though, the chances of sea slugs finding one another are much smaller. So when they do meet, it is important that they really make it count and have as many babies as possible especially since the eggs will hatch into plankton. This means that many baby sea slugs will become dinner for filter feeders like anemones and barnacles.

How to have as many babies as possible? Both should lay eggs! This is why they are hermaphrodites; not just a male or female. The sea slugs line up right side to right side and exchange cells so that they can both lay eggs.

I will share much more about the love life of sea slugs in future postings. Every sea slug species lays eggs that look very different. One of the “cases” I have worked on the longest is to figure out what each species’ eggs look like. A great clue in trying to figure this out is that sea slugs most often lay eggs on their food.

You can imagine my delight when I found a big mass of eggs at the base of a tube-dwelling anemone! Knowing that the giant nudibranch preys on this species, the chances were very, very good that these were its eggs.

When you follow the link, you can see a larger picture of the eggs mass and get an idea of just how many eggs are in this string (each dot is an egg).

I have also included video of the giant nudibranch swimming for your Easter weekend pleasure. You’ll see that the nudibranch swims upwards but, when it wants to go down, it just stops moving and gently drifts back down to the ocean bottom. You’ll also see that I am pointing my dive light at the animal and how this makes colours look different underwater.