Answer:
A. counting the total number of different species
Step-by-step explanation:
The only way to calculate the species richness in the ecosystem is counting the total number of different species. This is basically what species richness is, therefore it would be the best way to calculate it. Species Richness does not require that the scientists take into account the population of each species instead, each unique species found is counted as 1 towards the calculation of species richness.