A salt marsh is a highly dynamic coastal ecosystem containing specialized plant communities (halophytes) and various marine and terrestrial invertebrates. Succession on a salt marsh gradually leads to a more stable community with high animal species richness.
Describe a method that could be used to determine the mean percentage cover of cordgrass (Spartina anglica) on a salt marsh. Do not include information on the difficulties of working on a salt marsh.
Explain how succession results in a wide variety of animal species living on a salt marsh. Do not describe the process of succession in your answer.
Ecologists investigated the effect of two grazer species, the rough periwinkle (Littorina saxatilis) and the saltmarsh amphipod (Orchestia gammarellus), on cordgrass (Spartina anglica) growth on a salt marsh. They cleared experimental plots of vegetation on a salt marsh in North Wales at an elevation of 3.0–3.5 metres above chart datum. They attached four large mesh enclosures, W, X, Y and Z, to the ground in each plot and populated the enclosures as follows:
After 16 weeks, the ecologists measured the mean percentage cover of cordgrass within each set of enclosures. The ecologists used a statistical test to find out whether the mean for each set of enclosures was significantly lower than the mean for set W.
Table 3 shows the probability (PPP) values that the ecologists obtained using this statistical test.
| Set of enclosures | PPP value |
|---|---|
| X | =0.518= 0.518=0.518 |
| Y | =0.008= 0.008=0.008 |
| Z | =0.024= 0.024=0.024 |
Using all the information, evaluate the effect of the two grazer species on cordgrass growth on salt marshes.
