O’DOR, R.K.: Telemetered cephalopod energetics: swimming, soaring and ballooning.

Cephalopods are uniquely suited to field energetic studies. Their hollow mantles that pump water for respiration and jetting also conveniently accommodate differential pressure transducer-transmitters that measure pressure-flow (PQ) power output and can be calibrated against oxygen consumption by swim-tunnel respirometry. Radio-acoustic positioning telemetry (RAPT) allows us to record PQ power and animal movements in nature with meter accuracy. Powerful oceanic squids and primitive nautilus are nearly pure jetters, so the picture is clearer than for large-finned squid and cuttlefish. However, our studies show that cephalopods use their complex nervous systems to reduce the high cost of jet propulsion by taking advantage of complex flow and density fields in nature. Buoyed up by evacuated shells, nautilus and cuttlefish live in boundary layers and use them like balloonists to navigate cheaply. Large-finned, negatively buoyant squid soar like eagles in rising currents, but are almost planktonic in currents above one body length per second. Many muscular squids have life histories linked to current systems. Direct observations of ammoniacal oceanic cephalopods in nature are limited, but the small density differential between seawater and isotonic ammonium chloride means that they are truly balloon-like and nearly planktonic, with very low power densities. This sufficiently restricts the habitats they can survive in that many species only develop neutral buoyancy late in their ontogeny, often as they approach semelparous reproduction, mobilizing the carbon from muscle protein for gametes and energy while retaining the ammonium ions for buoyancy.