The Marine Detective

Who’s Eating Who?

Giant Nudibranch (Dendronotus iris) on the prowl for tube-dwelling anemones. This species of nudibranch has great variation in colour. © Jackie Hildering

Giant Nudibranch on the prowl for Tube-Dwelling Anemones. This species of nudibranch has great variation in colour. See photos at end of blog. ©Jackie Hildering

This “case” features the Giant Nudibranch (Dendronotus iris to 30 cm long) and the Tube-Dwelling Anemone (Pachycerianthus fimbriatus).

The Giant Nudibranch’s favourite snack is this anemone species. It is not impacted by the anemone’s stinging cells (nematocysts).

Giant Nudibranch launching into a Tube-Dwelling Anemone. © Jackie Hildering

The Tube-Dwelling Anemone is therefore adapted to be able to withdraw into its tube (which can be up to 1 m long) in an attempt to get away from the predator sea slug.

And the battle is on! The Giant Nudibranch patrols the sandy ocean plains “looking” for the Tube-Dwelling Anemone. When it finds one, it rears up and pounces, mouth parts extended in the hopes of grabbing onto the anemone. When the anemone senses the nudibranch’s attack, it withdraws into its tube.

Wait till you see what happens to the Giant Nudibranch!

See below for a short clip of such an attack.

[

But that’s not all, this nudibranch species also swims.

By lifting off, it may land somewhere with better chances for feeding and mating. See video below.

As is also generally the way with sea slugs, they also lay their eggs on their prey.

And oh the diversity in colour among Giant Nudibranchs. See photos below.

And here are a few more pouching on their prey.

Interspecies interaction: When this Giant Nudibranch touched the Leather Star, it touched it again and then recoiling with an acute change in direction. The diet of Leather Stars (Dermasterias imbricata) is omnivorous. From Neil McDaniel: “Eats a wide variety of prey, depending on the locale. On the open coast it consumes plumose anemones and tunicates; in sheltered areas it eats orange sea pens, sea vase tunicates, encrusting sponges and bryozoans.” So, Leather Stars are not likely to eat a Giant Nudibranch, especially because Leather Stars are not particularly fast sea stars (15 cm/min) and Giant Nudibranchs can swim away (yes, that’s right they swim). Leather Stars’ skin is known to contain a unique chemical “imbricatine” that does elicit an escape response form Swimming Anemones so . . . whether the Leather Star felt or “tasted” odd to the Giant Anemone, it did “decide” that distancing was the better way to go.

Note: Dendonotids are not known to utilize the stinging cells (nematocysts) of their prey. From the Sea Slug Forum “There has been some confusion in the literature concerning the presence of branches of the gut in the ‘gills’ or ‘cerata’ of species of Dendronotus. Firstly there is no evidence to suggest that any species of Dendronotus has cnidosacs at the tip of its dorsal processes in which to store nematocysts. In fact there is no evidence that they store nematocysts from their prey anemones in any part of their body.“

Manta Ray Magic – Fiji

In December of 2009, I had the extraordinary privilege of seeing manta rays while diving off Kaduva Island with the dive crew from the Matava Eco-Resort. It is thanks to the environmental ethic of this team that these dives are very controlled to make sure the animals are disturbed as little as possible.

The video allows us to share all the observations listed below as well as giving you the chance to laugh when you hear my underwater screams of joy when the mantas break from their feeding behaviour, get into a formation of 5 animals and swim by us 4 times! I didn’t even realize I was making these sounds but my dive buddy was there behind me, capturing it on video.

The video shows:

Holy manta rays are big! They are the biggest rays in fact; up to almost 7 m across and more than 1,000 kg. The ones we saw are probably about 4 m across.
They are very “alien” looking animals. They feed on plankton and small fish and can scoop more food using the two big paddle-shaped flaps (“cephalic lobes”) that are just to the inside of their eyes. You will see from the murkiness of the water that it is thick with plankton. The circular diving pattern of the mantas is believed to help them concentrate the plankton.
That manta rays have a relatively short tail for a ray, no stinging spine and you’ll see one animal in the video that has had their tail shredded off, likely by a tiger shark.
That sometimes there are remoras attached to the manta rays. These fish may help in removing parasites and have the benefit of transportation, being less visible to predators and possibly getting some scraps as snacks.
That mantas are incredibly graceful, having very flattened bodies and big wing-like fins.
They can be told apart as individuals. Of course the one with the shark injury is easy to tell apart from the others. There is also one that has had its left fin tip bitten off. But if you look even more closely, you’ll see that each animal has unique markings on their upper and undersides. We passed on our photographs and video for research but, even though they are easy to tell apart, so little is known about them.
They are intelligent and coordinate their movements. This is what I found the most fascinating of all, how they knew to all get into a line at the same time and as each of them came by, they were observing me. They pivoted their eyes back to get the longest look possible at the strange creature who couldn’t stop from screaming out in sheer amazement.

California Sea Lions Barking Underwater – video!

This posting is typical for why I set up this blog (and the identity of “The Marine Detective”). I want to share what I learn from my marine adventures.

I was diving off Northern Vancouver Island when my buddy and I had a “swim-by” from several male California Sea Lions and one male Steller Sea Lion.

Many of you know that the two species can be discerned very easily because California Sea Lions bark and Steller Sea Lions growl. Yep, you could be blind and determine which sea lions species is present.

You can’t miss the barking of California Sea Lions when they are on land.

What I hadn’t fully realized was . . . you can hear them bark underwater too!

See my video below./strong>

Please note that it is against my ethics (and the law) to target seal and sea lion haulouts for the purposes of diving with them. This certainly constitutes “disturbance” of marine mammals and also leads to the animals losing their wariness and becoming habituated to humans. This has led to significant human injury. It definitely does not help the seals and sea lions either to be habituated to people as there are those who believe there are “too many” and that they should be killed.

However, sometimes, as a result of being in their ocean, we have unexpected encounters like the one videoed here.

Update 2018: The amended Marine Mammal Regulations (federal law) now specifically include: “No person shall approach a marine mammal to, or to attempt to: (b) swim with it or interact with it.”