Past Research and Ongoing Projects
Deep-sea squid ink release
Ink release by coleoid cephalopods (squids, octopuses, cuttlefishes) is familiar to many people and it’s obvious cloaking abilities has led to a long held assumption that it is primarily a visual defense. We assume the dark ink mass distracts and/or confuses a predator so a cephalopod can escape or hide within the ink. Scientists believed that ink release would be useless as a defense for deep-sea cephalopods because light is attenuated by water so that much of the deep sea is dark. A dark ink cloud must be useless. However, observations by the MBARI Midwater Ecology lab using Remotely Operated Vehicles indicated that midwater squid living below the photic zone do release ink throughout their depth range. I reviewed ROV dive footage and made directed observations to determine which species released ink, at what depths, and the concurrent behaviors (Bush and Robison, 2007).
Reactions to deep-sea squid ink
If we see a deep-sea squid release ink in response to another animal or watch midwater animals react to squid ink, we could better understand why squids release ink. Unfortunately, observations of species interactions in the deep sea are rare. To determine midwater animal reactions to squid ink, I have to create my own ‘interactions’. With the help of MBARI ROV pilots and technicians, I designed an ‘Ink Ejector’ to release collected deep-sea squid ink in the water column. Encounters with squid and fish allow us to observe whether animals behave differently when ink is released.
Deep-sea squid ink chemistry
Ink is used in different ways by different species; it is released in different forms, at different depths, even has subtle differences in color. One possible defensive function is that ink has important chemical properties. Ink may contain constituents that are distasteful to predators and/or attractive to predators. If ink is distasteful, and a predator mistakes an ink pseudomorph for a squid, it may then concentrate hunting efforts on another prey type, such as fish. If ink is attractive it may distract a predator while the squid escapes. I have collected ink from 15 species of deep-sea cephalopod and several shallow-dwelling species to compare their chemical composition using liquid chromatography-mass spectroscopy. This method separates molecules within a mixture, then gives the molecular mass of each, allowing comparisons of molecules present in inks from different species and us to pick out molecules of interest for further study.
Behaving in the dark
Shallow-water cephalopods are well-known for their body patterning, consisting of changes in skin coloration, skin texture, body posture, and body movement. These are used in visual communication with other cephalopods, potential prey, and predators. Scientists reasoned that body patterning in species living in low-light environments, such as the deep sea, would have limited body patterning. I made the first in-depth observations of a deep-sea squid species to test the hypothesis that deep-sea cephalopods have limited coloration, posturing, and movement. Octopoteuthis deletron is capable of many body patterns, comparable in number to shallow-water squids (Bush et al., 2009).
Squid arm autotomy
The midwater squid Octopoteuthis deletron’s eight arms are tipped with large bioluminescent photophores. In situ and laboratory observations of O. deletron and its congenerics O. neilseni and O. megaptera (Young & Vecchione 2006) indicate that these squids are able to autotomize, or voluntarily release, part of an arm. We have observed shed arms continue to move and the arm-tip photophores bioluminesce. This behavior is hypothesized to be defensive, whereby it startles, distracts, or confuses a potential predator. I am using data collected on MBARI Remotely Operated Vehicle expeditions as well as laboratory observations of collected specimens to determine how often individuals are observed with missing arms, what stimuli trigger arm loss, what are the associated behaviors, and whether the animal has control over arm loss. Histological sections of collected specimens’ arms are being examined to determine the breakage mechanism.
UC Berkeley webpage
Squid science: Field notes from Stephanie Bush – UC Museum of Paleontology feature
Bush, S. L., Robison, B. H., & R. L. Caldwell. 2009. Behaving in the dark: locomotor, chromatic, postural and bioluminescent behaviors of the deep-sea squid Octopoteuthis deletron Young 1972. Biol. Bull. 216: 7-22.
Bush, S. L., and B. H. Robison. 2007. Ink utilization by mesopelagic squid. Marine Biology. 152(3): 485-494.
Young, Richard E. and Vecchione, Michael. 2006. Octopoteuthis Ruppell 1844. Version 24 April 2006. http://tolweb.org/Octopoteuthis/19839/2006.04.24 in The Tree of Life Web Project, http://tolweb.org/