Participants
John MacDonald, Phil Ross, & Shane Windsor
Marine Biology, School of Biological Sciences
University of Auckland, New Zealand
We shall be working as a team to collect and study examples of larval, juvenile and adult life stages of notothenioid fishes ('southern cod-icefishes') from the subantarctic region. This group of fishes has diversified extensively in the waters near the continent of Antarctica, where it has become the dominant group of fishes. The group is also well-represented in the subantarctic region. The high Antarctic species generally show a distinct change in life style when the pelagic larvae metamorphose into juvenile/adult forms living on the continental shelf, in relatively shallow water. A minority of species are neotenic, retaining larval features including a pelagic life style. In the subantarctic, where shallow water suitable for settlement is found only in widely distant isolated islands, a prolonged pelagic larval stage should be disadvantageous, as the larvae could easily be swept away from the islands. Thus the relationships between age, buoyancy and body form are expected to differ between the high latitude fishes and their subantarctic relatives.
Species of especial interest include the white-blooded icefishes Champsocephalus esox and C.gunnari, and the red-blooded Pseudotrematomus vicarius, which is closely related to the high Antarctic P.bernacchii. Eleginops maclovinus, more distantly related to high latitude species, will also be targeted. Small tissue samples from these species will be preserved for a study of evolutionary relationships based on mitochondrial DNA.
We plan to measure volume, mass and fin area for all fish collected, and collect otoliths and scales to estimate age. It may be possible to determine the age and size at metamorphosis by examining otoliths and comparing maximum larval size with that of the smallest juveniles.
Shane and Phil will set up small observation aquaria to record fin movements and water velocity for a kinematic study of swimming at different life stages.
Collections in the South Georgia region would target Trematomus vicarius, an offshoot of the high-Antarctic subgroup of trematomine nototheniids. This species has a peculiarly restricted distribution, being known only from S.Georgia, and no details are known of its larval life. Its closest relative, T.bernacchii, is very common on the Antarctic continental shelf, a distribution promoted by the long pelagic stage of its larvae. T.vicarius would seem a prime candidate for a reduction in pelagicism, as outlined above.
If circumstances permit (i.e. not too much vibration or electrical noise), John plans also to record electrical activity from the nerve-muscle junction of a few adult specimens, to see whether the subantarctic species show any signs of the adaptations to low temperatures found in species from the Ross Sea.