Thermoregulation in Florida manatees (Trichechus manatus latirostris) -Understanding the cold-stress syndrome in terms of physiology, morphology and early diagnosis

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The Florida manatee (Trichechus manatus latirostris) belongs to the sea cows or Sirenia, a group of fully aquatic mammals consisting of four recent species. As the only herbivorous marine mammals, sireneans live in tropical/subtropical habitats and are adapted to high water temperatures. Particularly the Florida manatees are extremely sensible to lower water temperatures. One of the major threats to this species is the so called cold-stress syndrome (CSS), occurring in manatees that are exposed to water temperatures <20°. In particular subadult animals are affected by CSS, failing to find the way to warm water refugees (warm fresh water springs, warm-water discharges from power plants) in time, when water temperatures decrease. Amongst others, CSS symptoms are immune suppression, organ failure, lesions of heart, skin and other organs, eventually causing the death of the animal. The proposed project comprises three major objectives: (a) The identification of indicators for early recognition of cold stress in a manatee prior to the appearance of life-threatening CSS symptoms. (b) The identification of environmental, physiological and morphological parameters influencing the susceptibility to thermal stress in Florida manatees on the basis of early-diagnosed animals (see (a)) as well as animals with CSS symptoms. (c) Based on (a), (b) and additional morphological studies in deceased animals, to generate well substantiated hypotheses on the physiological causation of CSS in manatees. My hypotheses are: (1) Incipient cold-stress can be recognized by changes in surface temperature of body parts above the water surface via infrared-thermography (IRT), in particular the open nostrils while breathing at the surface. (2) The amount and composition of biofouling on the skin are indicators for the susceptibility of a manatee to CSS. In this context also the role of the skin surface structure for biofouling will be investigated. By means of IRT and further non-invasive methods, an array of measurements, such as skin and core body temperature, heat flux and blubber thickness, will be conducted in manatees suffering from CSS, as well as comparatively in healthy animals. Amount and composition of biofouling on the skin as well as skin surface structure will be documented and analyzed. Histological postmortem examinations will provide further information concerning CSS susceptibility. In particular blubber thickness and composition, skin surface structure, and the presence or absence of arteriovenous anastomoses (AVAs), which are important structures for the regulation of peripheral heat loss, will be examined. This long-term study will lay a foundation to understanding manatee thermoregulation, in particular concerning thermal stress, with possible implications for other mammalian species as well.