Extremes of metabolic strategy in Antarctic Bryozoa

The physiology of many organisms in many places varies with seasonality of environment characteristics. Polar marine environments are amongst the least and most seasonal. For example, sea temperature varies by < 3 degrees C while light climate and primary productivity vary more than elsewhere. Polar nearshore invertebrates generally live life at a slow pace with recorded metabolic rates of 22-454 mu g O-2/g ash-free dry-mass/h. We measured oxygen uptake by three Antarctic cheilostomatid bryozoan species during summer and winter months. Our data suggest that, in many ways, bryozoans differ from other animals. They have enormous metabolic flexibility; more within the order Cheilostomatida than in all other polar marine animals measured to date. One species alone, Kymella polaris, had both the lowest (16.8) and highest (574.9 mu g O-2/g ash-free dry-mass/h levels recorded. Furthermore, Camptoplites bicornis showed no significant change in oxygen consumption with season whereas the final species, Isoseculiflustra tenuis, showed the highest winter to summer metabolic rise (ratio =3.45) reported for a polar species. They may not have a resting state analogous to other animals, but exhibit either full activity or 'dormancy' in which most organic tissues are reabsorbed. The concept of resting metabolism in this taxon may be inappropriate.