Harmful algal blooms are increasing worldwide, including those of Pseudo-nitzschia spp. producing domoic acid off the California coast. This neurotoxin was first shown to cause mortality of marine mammals in 1998. A decade of monitoring California sea lion (Zalophus californianus) health since then has indicated that changes in the symptomatology and epidemiology of domoic acid toxicosis in this species are associated with the increase in toxigenic blooms. Two separate clinical syndromes now exist: acute domoic acid toxicosis as has been previously documented, and a second novel neurological syndrome characterized by epilepsy described here associated with chronic consequences of previous sub-lethal exposure to the toxin. This study indicates that domoic acid causes chronic damage to California sea lions and that these health effects are increasing.

Decompression sickness (DCS; ‘the bends’) is a disease associated with gas uptake at pressure. The basic pathology and cause are relatively well known to human divers. Breath-hold diving marine mammals were thought to be relatively immune to DCS owing to multiple anatomical, physiological and behavioural adaptations that reduce nitrogen gas (N2) loading during dives. However, recent observations have shown that gas bubbles may form and tissue injury may occur in marine mammals under certain circumstances. Gas kinetic models based on measured time-depth profiles further suggest the potential occurrence of high blood and tissue N2 tensions. We review evidence for gas-bubble incidence in marine mammal tissues and discuss the theory behind gas loading and bubble formation. We suggest that diving mammals vary their physiological responses according to multiple stressors, and that the perspective on marine mammal diving physiology should change from simply minimizing N2 loading to management of the N2 load. This suggests several avenues for further study, ranging from the effects of gas bubbles at molecular, cellular and organ function levels, to comparative studies relating the presence/absence of gas bubbles to diving behaviour. Technological advances in imaging and remote instrumentation are likely to advance this field in coming years.

The California sea lion (Zalophus californianus) has been a focal point for sensory, communication, cognition, and neurological disease studies in marine mammals. However, as a scientific community, we lack a noninvasive approach to investigate the anatomy and size of brain structures in this species and other free-ranging, live marine mammals. In this article, we provide the first anatomically labeled, magnetic resonance imagingbased atlas derived from a live marine mammal, the California sea lion. The brain of the California seal lion contained more secondary gyri and sulci than the brains of terrestrial carnivores. The olfactory bulb was present but small. The hippocampus of the California sea lion was found mostly in the ventral position with very little extension dorsally, quite unlike the canids and the mustelids, in which the hippocampus is present in the ventral position but extends dorsally above the thalamus. In contrast to the canids and the mustelids, the pineal gland of the California sea lion was strikingly large. In addition, we report three-dimensional reconstructions and volumes of cerebrospinal fluid, cerebral ventricles, total white matter (WM), total gray matter (GM), cerebral hemispheres (WM and GM), cerebellum and brainstem combined (WM and GM), and hippocampal structures all derived from magnetic resonance images. These measurements are the first to be determined for any pinniped species. In California sea lions, this approach can be used not only to relate cognitive and sensory capabilities to brain size but also to investigate the neurological effects of exposure to neurotoxins such as domoic acid. Anat Rec, 292:1523Rec, 292: -1547Rec, 292: , 2009

SUMMARY Lung compression of vertebrates as they dive poses anatomical and physiological challenges. There has been little direct observation of this. A harbor and a gray seal, a common dolphin and a harbor porpoise were each imaged post mortem under pressure using a radiolucent, fiberglass, water-filled pressure vessel rated to a depth equivalent of 170 m. The vessel was scanned using computed tomography (CT), and supported by a rail and counterweighted carriage magnetically linked to the CT table movement. As pressure increased, total buoyancy of the animals decreased and lung tissue CT attenuation increased, consistent with compression of air within the lower respiratory tract. Three-dimensional reconstructions of the external surface of the porpoise chest showed a marked contraction of the chest wall. Estimation of the volumes of different body compartments in the head and chest showed static values for all compartments except the lung, which showed a pressure-related compression. The depth of estimated lung compression ranged from 58 m in the gray seal with lungs inflated to 50% total lung capacity (TLC) to 133 m in the harbor porpoise with lungs at 100% TLC. These observations provide evidence for the possible behavior of gas within the chest of a live, diving mammal. The estimated depths of full compression of the lungs exceeds previous indirect estimates of the depth at which gas exchange ceases, and concurs with pulmonary shunt measurements. If these results are representative for living animals, they might suggest a potential for decompression sickness in diving mammals.