Let me start with the squid “penis” and get to the mysterious grooves on the seafloor later.
Last April an ROV called Little Hercules, cruising around the seafloor in the northern Gulf of Mexico, spotted a distant, possibly cephalopod-like shape. As Little Hercules got closer, NOAA researcher Mike Vecchione reports in the mission log, “the apparition resolved into a pair of large squid, similar to the one from the previous day. One squid was holding on to the other.”
Mating deep-sea squids! So little is known about these squids that to stumble on a pair of them so entwined, 1400 meters below sea level, was incredible.
Clearly I’m just a cephalopod fan, not an expert—it would have taken me a while to figure out what was happening between these two squids if I hadn’t read about them in the December issue of Biological Bulletin. So I ask Henk-Jan Hoving, who co-authored a paper about the mating habits of Pholidoteuthis adami with Vecchione, what was going on.
That’s the male squid on top there, Hoving said, and he’s actually upside down and backward relative to the female—“pretty unexpected,” said Hoving, a post-doc at MBARI. Several other squid species are known to mate head-to-head. One of my favorite lines from the paper: pairs of Brachioteuthis beanii have been spotted in various positions, possibly mating… “However, alternative explanations (e.g., cannibalism) could not be excluded.”
Other squids, too, have a modified arm that they use for implanting packets of sperm in a female. This species has an “extended terminal organ” (“It’s not really a penis,” Hoving says) that it uses to deposit spermatophores—and it’s the first time researchers have seen squid with this kind of appendage mating in the ocean.
By looking at museum specimens and at a second ROV-captured mating video, they determined that the process must take a while. The male seems to be able to put out only one spermatophore at a time, and researchers found between 15 and 20 spermatangia, which the spermatophores release, in the muscles of a female specimen’s mantle. (Other squid species are known to mate for a long time, too—a study last year in Biology Letters reported that southern dumpling squid mate for up to three hours, and might be too tired to swim well for the following 30 minutes.)
So what about the whole upside-down thing? The researchers have a few ideas—one possibility, Hoving says, is that this position lets the male deposit his spermatophores where he needs to, and “the female won’t be able to grab him.”
Pholidoteuthis adami is a key species in the Gulf of Mexico’s food web. They’re prey for sharks, for tuna, and particularly for sperm whales. And researchers have wondered how sperm whales can take down wily, intelligent (and possibly ink-squirting) squid.
At one time, a popular hypothesis was that whales could blast their prey into submission with intense ultrasound clicks. But a study a few years ago in Biology Letters tested squid against deafening levels of whale echolocation, and the squid didn’t even seem to notice. Some of the researchers on that study had seen whales making acrobatic twists just before swallowing a squid—often snagging their prey while upside down, a method that suggests the spin might create suction to slurp an unsuspecting squid.
Little Hercules didn’t capture any squid v. sperm whale incidents last spring, but it did motor over something else interesting: giant furrows along the seafloor. Divots like these have also scar the underside of the Mediterranean and the North Sea.
One possible explanation: these furrows could be impact marks from sperm whales trying to snag squid that are hovering close to the bottom, like the mating pair. And although cephalopods have keen eyesight and cool self-camouflaging abilities, among other fascinating attributes, being human has some unexpected perks, too: No matter whether you’re worried that your kids or your parents will walk in on you, it’s very unlikely that you’ll be embarrassed by a sperm whale crashing down on your head.