Food chain investigations at White Island: seal survey, seasonal trends in phytoplankton populations, ocean environmental factors, zooplankton biomass and fish diet, age and growth studies

A population of Weddell Seals at White Island (some 20km from the edge of the Ross Ice Shelf) was/is thought to be a sub-population that does not migrate to the pack ice in the non-breeding season but rather maintaining breathing holes in the pressure ridges over winter. The seals studied were always in excellent condition indicating under the shelf ice some considerable distance from the open sea a flourishing food chain. Studies were undertaken to study the food chain relationships under the permanent shelf ice. The area was surveyed for seals and 20 animals were located and tagged over the season. The weights and size increases were plotted for the two male pups. Six hourly weather observations were made of sky condition, visibility, temperature, wind atmospheric pressure and other conditions of interest. The water column was monitored through an ice hole in a depth of 70m at weekly intervals to follow seasonal trends in the phytoplankton population structure, to determine the level of primary productivity and to monitor the environmental factors which may influence the rate of photosynthesis. The water column was sampled at depths of 0, 3, 10, 25, 50, 65 and 70m for temperature, salinity, dissolved oxygen, light, chlorophyll (a,b and c) and phytoplankton. Water samples were collected for nutrient analysis. Estimations of seston was determined by the concentration of chlorophyll. ATP, particulate organic carbon, total nitrogen and measurements of dry weight from separate filtered volumetric samples. In addition, zooplankton was sampled with fine and coarse nets from the surface to 65m. The biomass and species present and their relative abundance was measured. A current/tide profile was measured. Quantitative benthos samples were collected from each area. Fish were of the area were trapped and the diets, age and growth of two species of Trematomus was studied.