From the data, identify the depth along the transect where the greatest species richness is observed.

Outline the relationship between Zooxanthellae and reef-building coral reef species.

Suggest one way in which depth may act as a limiting factor for coral. 

6.5 m ✔

Unit required

a. a symbiotic/mutualistic relationship ✔

b. Zooxanthellae obtain shelter/habitat/exposure to light ✔

c. coral obtains energy/food through photosynthesis of the Zooxanthellae ✔

low light levels/lower temperatures cannot support growth/metabolism ✔

Requires the explanation for the mark

Richness appeared well understood but the depth unit was sometimes omitted.

This was a well-answered question with many candidates knowing the term symbiosis or mutualism. Protection provided by coral was often stated but the role of Zooxanthellae in providing nutrients from photosynthesis was less often seen.

The reduction in light or temperature with greater depth was recognized but not often linked to growth or photosynthesis.