Question 20N.3.HL.TZ0.c
| Date | November 2020 | Marks available | [Maximum mark: 1] | Reference code | 20N.3.HL.TZ0.c |
| Level | HL | Paper | 3 | Time zone | TZ0 |
| Command term | Suggest | Question number | c | Adapted from | N/A |
Sea urchins (Strongylocentrotus) are echinoderms that consume large quantities of algae. Sea otters (Enhydra lutris) feed on sea urchins.
The graphs show the biomass of sea urchins in an area of 0.25 m2 plotted against their size. Data were collected in two Aleutian Islands, Amchitka and Shemya. In Amchitka the sea otter population is high while at Shemya there are no sea otters.
[Source: From Estes, J.A. and Palmisano, J.F., 1974. Sea Otters: Their Role in Structuring Nearshore Communities. Science,
185(4156), pp.1058–1060.16. DOI: 10.1126/science.185.4156.1058, https://science.sciencemag.org/content/185/4156/1058.
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Sea urchins are destroying the giant kelp alga (Macrocystis pyrifera) marine forests of South East Australia. Suggest a reason that sea urchins might be an invasive species in this environment.
[1]
the sea urchins’ limiting factors in their original habitat are missing
OR
lack of (natural) predators for sea urchins
Many suggested that sea urchins' predators were not present, but too many irrelevant or blank answers were seen.
