Meeting Abstract

28.5  Monday, Jan. 5  Polar Gigantism in Antarctic Invertebrates: Sizing up the Role of Temperature-Oxygen Interactions MORAN, A.L.**; WOODS, H.A.; Clemson Univ., SC; Univ. of Montana, Missoula moran@clemson.edu

Polar gigantism, the trend among some marine invertebrates towards large body sizes at high latitudes, is not clearly understood in ecological or evolutionary terms. One hypothesis is that in cold environments, ectotherms have low metabolic oxygen demands and thus are released from constraints placed on body size by the challenges of O2 transport and diffusion at higher temperatures. We tested this hypothesis in the Southern Ocean using a metabolically simple, diffusion-driven system, nudibranch egg masses. We developed biophysical models that predicted O2 dynamics and maximum possible sizes at different environmental temperatures. These models accurately described radial O2 profiles in the lab and field, and predicted that in the Antarctic, egg masses can reach larger sizes and/or higher densities of embryos without experiencing greater internal hypoxia. We measured the size of egg masses from 6 Antarctic species and compared them to masses of temperate relatives, and showed that Antarctic nudibranchs indeed lay significantly larger masses. However, Antarctic egg masses contained substantially fewer embryos per unit volume than temperate masses. Low embryo density was due to the unusually large size of Antarctic embryos, which averaged 10x larger than embryos of their temperate relatives. This, along with direct observations of hatching in some taxa, suggests the majority of Antarctic species in our study are nonplanktotrophic. Thus, predictions of the temperature-oxygen model must be considered in the light of dramatic differences in life histories between polar and temperate oceans.