A team of scientists from the Monterey Bay Aquarium Research Institute (MBARI) has filmed for the first time the deep-sea squid Grimalditeuthis bonplandi in its native habitat, at depths of 1,000 – 2,000 m.
Most squids have eight arms and two longer feeding tentacles. The tips of the tentacles, which are often broader and armed with suckers or hooks, are known as clubs. Such squids hunt by rapidly extending their tentacles and then grabbing prey with their clubs. The squids also use the tentacles to carry captured prey to their mouths.
The deep-sea squid Grimalditeuthis bonplandi seems to use a very different feeding strategy.
Using remotely operated vehicles, the MBARI scientists were able to study how these squids behave in their native habitat, about 1 mile below the ocean surface. Their findings appear in the journal Proceedings of the Royal Society B.
When the vehicles first approached, most of the squids were hanging motionless in the water with their eight arms spread wide and their two long, thin tentacles dangling below. What intrigued the researchers was that the Grimalditeuthis bonplandi‘s tentacles did not move on their own, but were propelled by fluttering and flapping motions of thin, fin-like membranes on the clubs. The clubs appeared to swim on their own, with the tentacles trailing behind.
Instead of using its muscles to extend its tentacles, like most squids, Grimalditeuthis bonplandi sends its clubs swimming away from its body, dragging the tentacles behind them. After the tentacles are extended, the clubs continue to wiggle independently of the tentacles.
When threatened, instead of retracting its tentacles as most squids would do, Grimalditeuthis bonplandi swims down toward its clubs. After swimming alongside its clubs, the squid coils both the tentacles and clubs and hides them within its arms before swimming away.
In short, all of the motions and activities of these squids appear to be directed toward giving the impression that their clubs are small, swimming animals, independent from the rest of the squids’ bodies.
The MBARI team speculates that the motion of the clubs may induce smaller squids and shrimp to approach close enough to be captured by Grimalditeuthis bonplandi‘s arms.
Because Grimalditeuthis bonplandi‘s clubs do not glow, they would be invisible in the inky darkness of the deep sea. However, the researchers proposed several other ways that these swimming clubs might attract prey.
One possibility is that the moving clubs could disturb glowing microscopic organisms in the surrounding water, causing the water to glow like a ship’s wake during a red-tide bloom. The clubs’ swimming motions would also create turbulence or vibrations in the water, which could be detected by their prey. Such vibrations might mimic the vibrations used by prey animals to attract mates.
Alternatively, they might be similar to the vibrations created by the even smaller animals eaten by Grimalditeuthis bonplandi‘s prey.
Bibliographic information: Hendrik J. T. Hoving et al. 2013. First in situ observations of the deep-sea squid Grimalditeuthis bonplandi reveal unique use of tentacles. Proc. R. Soc. B, vol. 280, no. 1769; doi: 10.1098/rspb.2013.1463