December 10, 2014

Juvenile squid avoids predators by imitating stinging jellies

nanomia siphonophore

Nanomia siphonophore (left) and juvenile Chiroteuthis calyx squid (right). The animals are about 20 to 30 centimeters (8 to 12 inches) long. Image: © 2014 MBARI

In the deep waters of the ocean, there are no places to hide. To avoid predators, many deep-sea animals have dark-colored, reflective, or transparent bodies. Others have evolved elaborate methods of deception. For example, some deep-sea fishes and worms curl their bodies so that they resemble jellies, which are generally less palatable to predators. This ruse is particularly effective in environments where jellies are abundant.

Scientists at MBARI recently documented the first known case of a squid mimicking a siphonophore (siphonophores are a common group of jellies that are distantly related to the Portuguese man-of-war). Because siphonophores consist mostly of water, they aren’t a very dense source of food. They also have numerous stinging cells.

Using video from MBARI’s remotely operated vehicles, Ben Burford, a collaborator and former MBARI intern, observed juveniles of the deep-sea squid Chiroteuthis calyx imitating siphophores in the genus Nanomia. Chiroteuthis calyx is known as the swordtail squid because juveniles of the species have ornate tails as long as their bodies. For years, marine biologists have speculated about the function of these tails. Some researchers have suggested that they provide buoyancy and stability, allowing the juvenile squid to conserve energy.

Chiroteuthis calyx squid

Subadult Chiroteuthis calyx squid extending a feeding tentacle. Image: © 2009 MBARI

In a recent article in the Journal of the Marine Biological Association of the United Kingdom, Burford and his coauthors suggest that the shape and color of their tails allows juvenile swordtail squids to mimic the elongated floats and stinging tentacles of Nanomia siphonophores. The young squids enhance this mimicry by curving their bodies and tails in the shape of a siphonophore.

As swordtail squids grow older and larger they apparently have less need for this deception. By the time they become subadults, they lose their tails, and can no longer mimic Nanomia.

As they grow toward adulthood, the squids develop long feeding tentacles tipped with glowing lures (perhaps an example of a different type of mimicry). The adults hover motionless in the water column and use these lures to attract crustaceans or small fish, which they seize using their arms and feeding tentacles.

This discovery adds to the amazing diversity of strategies (including body postures, colors, and bioluminescence) that deep-sea squids use to communicate, capture prey, and evade predation.


MBARI YouTube video on this research:


Original journal article:
Burford B. P., Robison B. H. and Sherlock R. E. (2014) Behaviour and mimicry in the juvenile and subadult life stages of the mesopelagic squid Chiroteuthis calyx. Journal of the Marine Biological Association of the United Kingdom, 1-15. DOI: http://dx.doi.org/10.1017/S0025315414001763

Researchers

Bruce Robison
Midwater Ecologist

For additional information or images relating to this article, please contact: Kim Fulton-Bennett
831-775-1835, kfb@mbari.org