Question 1
Paper 2Medium16 marksA kelp-forest survey recorded the following data. Sea otters feed on sea urchins, which graze on kelp. Kelp forests provide food and habitat for many species.
| Year | Sea otters counted along a 10 km coastline | Sea urchins (individuals m⁻²) | Kelp cover (%) |
|---|---|---|---|
| 2018 | 40 | 8 | 82 |
| 2021 | 29 | 15 | 63 |
| 2024 | 16 | 24 | 43 |
Managers also estimated annual replacement and harvest for two renewable resources. Annual replacement is the number of individuals entering the harvestable stock during the year through growth or recruitment.
| Resource | Annual replacement | Annual harvest |
|---|---|---|
| Scots pine, a terrestrial plant | 150 trees year⁻¹ | 180 trees year⁻¹ |
| Atlantic cod, a marine fish | 30 000 fish year⁻¹ | 24 000 fish year⁻¹ |
Describe the patterns in the sea otter, sea urchin and kelp data between 2018 and 2024.
Using the data and feeding relationships, explain how a decline in sea otters could affect ecosystem stability and support identifying sea otters as a keystone species.
Calculate the percentage of annual replacement harvested for each resource. Show your working.
Using your results from (c), assess whether harvesting meets the sustainability criterion for each resource in the year shown.
Explain why the results for one year cannot by themselves establish whether each harvest is sustainable over the long term.