| Date | May 2015 | Marks available | 3 | Reference code | 15M.3.SL.TZ1.19 |
| Level | Standard level | Paper | Paper 3 | Time zone | Time zone 1 |
| Command term | Describe | Question number | 19 | Adapted from | N/A |
Question
The brown alga Sargassum muticum is a successful invasive species around the world. It grows attached to rocks in the intertidal zone and has large fronds that float in the water. It has recently become established in intertidal communities on the west coast of Scotland. The impact of this invasive species was investigated by measuring the composition of the animal community in the intertidal zone in an affected area. The data were compared to a control site with no invasive S. muticum which was located close by.
Identify the most abundant animal type at
the S. muticum site:
the control site:
Describe the impact of invasive S. muticum on the shoreline animal community.
Discuss possible reasons for the differences in the animal communities seen at the two sites.
Markscheme
S.muticum site: Corophiidae sp.
control site: S. squamata
Both needed for [1].
a. fewer different types of organism / smaller diversity at S. muticum site;
b. mean abundance at S. muticum site is higher for those organisms present;
c. Rissoidea sp. and P. maculata found at control site but not at S. muticum site;
d. C. pagurus only found at S. muticum site;
Comparisons are required but the control site does not need to be mentioned in each response.
a. S. muticum provide habitat/shelter/protection from predators for some species;
b. S. muticum change the environment to suit some species/example of a change;
c. some organisms more successful because less (inter-specific) competition;
d. more food may be available (for herbivores);
e. some herbivores may rely on native algae that have been displaced;
f. (other) conditions at the control site may not be identical to the test site;
Examiners report
19(a) was answered correctly.
Most candidates scored at least 2 marks for part (b), with some responses being too vague, for example not making it clear that Rissoidea sp and P. maculata were not present at all at the S. muticum site.
There was some confusion in part (c), where evidently the introduction to the data had not been properly read, as some candidates appeared to think that S. muticum was an animal.
