Abstract:
Three key processes in the embryos and larvae of the sea urchin Sterechinus neumayeri were examined to determine how they respond to environmental changes. In situ experiments were carried out at Cape Evans and on the sea ice edge with the blastula/gastrula larval stage.
1. Genetic expression of the photolyase enzyme: Embryos were exposed to ambient UVR at varying depths (0.5,
... 2, 5, 10, 15 and 20m depth) under the sea ice and treating the larvae to one of three light treatments (Full UVR, No UVR and No UVB) and varying the number of days of exposure (5, 8 and 12 days). Embryos were examined for developmental abnormalities, subsamples removed for RNA and protein extraction and the remaining samples preserved for later DNA dimer quantification. Photolyase expression and DNA damage were analysed.
2. Quantification of oxidative stress: Embryos were exposed to ambient UVR in situ using the same experiments as above. The degree of oxidative stress was examined from the expression of the superoxide dismutase gene and protein transcription. At the same time, oxidative stress was also examined in vivo for anti-oxidant enzyme activities in embryos. Ambient concentrations of hydrogen peroxide and superoxide were quantified using flow injection analysis of the chemiluminescence reactions.
3. The effects of pH: Embryos were reared at densities of 10 per ml in airtight chambers containing seawater at either normal or at a lowered pH. During experiments regular samples were collected and survival rates, growth and development, and skeletal rod formation quantified. Samples of larvae were collected, bleached to remove tissue and viewed under SEM to quantify fine scale structures and skeletal density. Larvae were also reared in larger containers (20L) at experimental pH (8.0, 7.5) and after a predetermined period, concentrated, dried at 60°C for 2 days, weighted then ashed at 400°C for 5 hours and reweighed for ash content. Samples were also taken for x-ray defraction to quantify the Mg concentration in the calcite skeletons. 
