With our ROVs as platforms for in situ observation we have published a series of papers that define a new discipline of midwater research – animal behavior. Results from our behavioral studies include the first ethograms ever published for any deep pelagic species. Ethograms are catalogs of the behavioral components that a species can draw upon to create a behavior pattern in response to challenges or opportunities in the environment. Four of these papers show how squid species from different families all use pigmentation patterns, posture, locomotion, bioluminescence, and inking to communicate visually — this despite the low light levels in their environment. Specific combinations of these five components of communication are associated with particular behaviors. The observed communication patterns are like seeing the words in a text conversation but not knowing, yet, what the words mean. This is an intriguing area for future research in non-human communication, particularly because cephalopods are not known to communicate with each other acoustically.

Because we can learn very little about behavior from net-caught specimens, the ability to make detailed behavioral observations in situ has yielded a windfall of new kinds of information. In terrestrial behavior studies, different kinds of animals require different approaches to observe their behavior and the same applies in midwater. Over time, we have learned how best to deal with certain species to enable our behavioral observations and experimentation. Variable ballast systems on our ROVs allow them to be trimmed to neutral buoyancy, thus minimizing vertical thruster use to hold position, while also increasing vehicle stability and stealth. Likewise, the ROV’s control systems can be shifted to utilize only the aft thrusters for maneuvering when close to an animal, thereby reducing water disturbance around the target. The value of this new kind of information is that it allows a much better understanding of the complex ecological interactions between species. It also provides an index of activity levels, which is necessary to quantify carbon and energy flux through the world-ocean’s vast midwater ecosystem. As our access to the deep pelagic habitat has increased, the range of our behavioral observations has expanded, from escape responses and defensive behavior, to predator tactics, aggregation patterns, food selection, mimicry, symbiosis, and reproductive behavior.

In addition to species identifications and abundance, MBARI’s VARS annotations also include behavioral data (e.g. feeding, inking). Thus it is possible to search the database and accumulate observations from throughout our 25-year-long series of dive records. For example, the tails of juvenile squid Chiroteuthis calyx are typically oriented in the same direction as the siphosomes of the siphonophore Nanomia bijuga when they co-occur in the water column during periods of diel vertical migration. The squid tails closely resemble the nematocyst-laden siphosomes of the more numerous siphonophores, and statistical analyses strongly indicate that this behavior is a case of mimicry. Likewise, the curling behavior of some zoarcid midwater fishes, chaetognaths, and tomopterid worms has also been identified as Batesian mimicry of medusae, with the latter as unpalatable models because of their low nutritional value and their stinging cells.

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