Question 1
Paper 2Hard16 marksScientists investigated the effects of carbon dioxide concentration and water temperature on coral fragments. Fragments were kept for 10 weeks under four conditions. Other conditions were kept constant, and each condition was tested in six replicate tanks. The table gives mean results.
| CO₂ condition | Seawater pH | Temperature / °C | Mean calcification rate / mg CaCO₃ g⁻¹ day⁻¹ | Fragments showing bleaching / % |
|---|---|---|---|---|
| Ambient | 8.1 | 27 | 4.0 | 5 |
| Elevated | 7.8 | 27 | 2.6 | 6 |
| Ambient | 8.1 | 30 | 3.9 | 48 |
| Elevated | 7.8 | 30 | 2.5 | 50 |
Calculate the percentage decrease in mean calcification rate when CO₂ is elevated at 27 °C.
Compare the effects of elevated CO₂ and increased temperature on calcification and bleaching.
A separate survey was carried out at one reef in Year 0 and again in Year 12. No comparison reef was surveyed. Fish species were grouped as those recorded using living coral for shelter and those not recorded doing so; the two groups together make up total fish species richness.
| Measure | Year 0 | Year 12 |
|---|---|---|
| Mean seawater pH | 8.1 | 7.8 |
| Maximum summer water temperature / °C | 27 | 30 |
| Live coral cover / % | 52 | 19 |
| Algal cover / % | 10 | 37 |
| Total reef fish species | 28 | 18 |
| Fish species using living coral for shelter | 16 | 7 |
| Fish species not recorded using living coral for shelter | 12 | 11 |
Compare the changes in the two fish groups from Year 0 to Year 12, using data.
Evaluate the claim that rising CO₂ and water temperature could cause coral loss and lead to collapse of the reef ecosystem. Use evidence from both studies and give one limitation of the evidence.