Complex color-changing (chromogenic) behaviors in squid provide camouflage by mimicking benthic features such as rocks, coral or algae, and also serve in intra-specific signaling. However, few studies have been carried out under natural lighting conditions in the field, or without the presence of human observers or noisy remotely operated vehicles. This project will extend field studies of natural chromogenic behaviors to the family Ommastrephidae as exemplified by Dosidicus gigas (Humboldt squid). To accomplish the research under natural lighting conditions, the project will develop an improved low-light Crittercam and an improved Driftcam that can operate effectively at greater depths. These improved video platforms will lead to new understanding of the generation and regulation of camouflage and communication in the open-ocean environment. Little is known of predatory behavior in midwater region occupied by Humboldt squid, which in the eastern Pacific Ocean is associated with a vast volume of water that is naturally hypoxic called the oxygen minimum zone (OMZ). This OMZ is currently expanding and moving toward the surface, largely due to climate change. Observations of predatory activity in the upper OMZ will increase our understanding of how pelagic ecosystems might change as climate change progresses, and how these changes could impact economically and ecologically important species like the Humboldt squid.
Chromogenic behavior in squid and other cephalopods is generated by muscular organs called chromatophores that are controlled by neural activity in the brain, and this direct, descending motor-control for chromatophores is unique to cephalopods. Pilot studies with the National Geographic Remote Imaging (NGRI) "Crittercam" video-package deployed on free-swimming Humboldt under natural lighting have revealed static patterning-type displays, like those seen in loliginid species, as well as a unique "flashing" behavior, with the entire body rapidly alternating between pale white and deep red. Flashing appeared to occur only during interactions with conspecifics, strongly suggesting a communication role. These data also revealed a more subtle wave-like "flickering" of chromatophores that may emulate fluctuations of light in the water column and provide dynamic countershading or crypsis. Neither type of behavior has been described in the scientific literature. The generation and control of the flashing and flickering chromatophore signals is therefore of great interest. This project will increase our knowledge of chromatophore signals through in situ video observations and anatomic analyses of Humboldt squid that include electrophysiology assessments, and immunohistochemical analyses of mantle tissue. An improved version of an autonomous low-light drift-camera package ("Driftcam") that can operate at midwater depths to observe natural behaviors of Humboldt squid that are too small to carry a Crittercam will be developed during the course of the project. Stanford graduate and undergraduate students will benefit from direct involvement in all of the research activities, and the researchers will also participate in wider public science dissemination efforts through regional K-12 programs, international educational outreach programs, and collaboration with major public media outlets.
