In the Classroom
How do fish in the Southern Ocean keep from freezing?


Systematic & Evolutionary Studies

The taxonomy, relationships, distributions, and biology of many Sub-Antarctic fishes are poorly known due to the remoteness of the region and the difficulties of sampling there. In terms of weight ("biomass"), the fauna is dominated by the notothenioids, a perch-like suborder that evolved in the Southern Ocean (about 130 species). For many years, this group was thought to compose the majority of the species of the region. However, recent studies have shown that several other families also have many Sub-Antarctic species that may, in fact, outnumber those of the notothenioids. These include the Liparidae (snailfishes), Zoarcidae (eel pouts), and Rajidae (skates). This group (secondary families, about 120 species) did not originate in the region, but colonized it later. A result is that the notothenioids are distributed primarily at shallower depths (almost all above 1500 m depth) and the secondary families dominate at greater depths. ICEFISH participants will be collecting and studying representatives of all these families from the intertidal zone to the greatest depths we can sample (at least 7000 m in the South Sandwich Trench). These fresh specimens will allow genetic studies of relationships that have previously been impossible. This research will help clarify how today=s observed patterns of distribution came to exist.

Sub-Antarctic and South Temperate Zone notothenioids have been understudied compared with the High-Antarctic species. There is a pressing need to expand our knowledge of the morphology, physiology, and biochemistry of the basal, non-Antarctic notothenioids. With this data in hand, we will be able to evaluate more rigorously numerous questions regarding the origin of the High Antarctic notothenioids. Why do modern notothenioids contribute so heavily to Antarctic fish diversity at both the organismal and ecological levels? Are the adaptations described in Antarctic notothenioids truly advantageous, or are they simply traits that have persisted in this group? How did fish with reduced density (i.e., neutral buoyancy) evolve from ancestors who were heavy bottom dwellers? Are notothenioids an example of an adaptive radiation, a species flock or both? These and related questions will be addressed using both morphological and molecular approaches.

Among the non-notothenioid fishes, there are almost 70 species of liparids and about 30 species of zoarcids in the Antarctic. Many of these are known only from a few specimens (in some cases, only single individuals). We hope to collect many more specimens of these species, expand our knowledge of their morphology, geographical and depth distributions, and obtain good samples of tissues for genetic analysis. These data will allow us to form a clearer view of their evolution, relationships to one another, and their role in the Sub-Antarctic ecosystem. Some of the questions we will try to answer are "Why do the primary and secondary species groups have different depth distributions?"; "How closely related are the Antarctic and Sub-Antarctic species to one another?"; and "What is the relationship of these species to relatives farther North?" Although we cannot hope to answer these questions definitively, we can at least develop better hypotheses to allow us to ask more specific (and in some cases, better) questions!