If A Whale Falls In The Ocean

“Are the animals that inhabit whale falls restricted to feeding and living on whale carcasses or will they also use the carcasses of other large animals like mola mola or large sharks?”

— Anonymous

In order to answer this question in all its complexity, I must first explain the three major stages of a whale fall community, as there are absolute boatloads of species that take advantage of them. And as with all good science, everybody and their dog is publishing papers arguing furiously on which species are where, for how long, and if they can be found anywhere else.

SO LET’S GET RIGHT TO IT THEN

The first stage of a whale fall is likely exactly what you’d expect - the mobile scavenger stage; hagfish, sharks, crustaceans, etc. Species that cruise around the hadal depths of the ocean looking for dead stuff that they can eat and/or expel horrifying amounts of deadly mucus onto (looking at you, mixinids). Whatever you’re in to, really.

Photo from Rothman Natural Science Illustration

There is zero contention on if these dudes have been found on other large cases of food falls - they’ve been documented on other falls such as on mobulid rays, whale sharks, Mola mola, etc. They eat the good meaty stuff, so any animal body that falls to the bottom of the ocean will quickly and easily be “colonized” by these dudes. It’s hypothesized that they can actually hear the sound of a large body hitting the sea floor up to several hundred metres away, (on top of the more normal “death smell coming from over here”) which is just about the most terrifying/amazing thing I’ve heard all day.

The second stage is the enrichment opportunist stage; Osedax and other polychaete worms, gastropods, more crustaceans - a more “sessile” stage of organisms coming to chow down on what’s left. These are the species that take advantage of the bones and all the delicious, delicious particles that melted off the skeleton and into the surrounding sand. Delightful

Now, this is the stage that is mostly up for contention - Osedax, after all, needs bone to colonize. Sharks and rays have cartilage, not bone, and fish, of course, have much flimsier skeletons than mammals. Osedax have been shown to colonize cow bones sunk for Science™, so they obviously aren’t specialists on only marine mammals, but examples of ray, shark, and fish falls have shown no sign of the extensive and typical second stage whale fall communities.

The third and final stage of a whale fall is the sulphophilic stage; Osedax is even more abundant, there are loads of anaerobic bacterial mats, crustaceans, and mollusks - the whole shebang. This stage has so much anaerobic, anoxic, and sulphuric action going on that it actually closely resembles the community that surrounds hydrothermal vents, which is actually quite ridiculous.

Mobulid ray carcasses have shown signs of similar bacterial mats, but it’s not quite enough to definitively say “this is a typical whale fall community”. Again, no other signs of this stage have been found on smaller, non-mammalian carcasses.

It could just be that since the second stage takes up to two years to form fully, and the third stage is at around 10, that with non-mammalian food falls there just isn’t enough there to support the entire complex community - or that the mobile predators take care of a smaller carcass before it can be colonized by further stages. It’s a got dan mystery, like basically everything else in the ocean that isn’t a Daphnia.

So as with all of my long-ass answers here, enjoy this explanation that likely did nothing but clarify points you didn’t actually want to know, and further muddy the ones you did. You’re welcome.

BONUS: A super gorgeous video showing the whole process. Look at it. Wow