Answer:
When sensitive species are present, they indicate the marsh is healthy.
Step-by-step explanation:
Robert knows that, in the region where he lives, there is an increase in the level of the sea that is interfering with the functioning of the Salt marshes, which believe well at the sea level and are very sensitive to changes at that level. The sea level is rising very fast and Robert is concerned not only with the health of the Salt marshes, but also with the species that depend on it as a habitat.
Robert decided to assess the number of sensitive species that, even with the increase in sea level, continue to use Salt marshes as their habitat. Among these species, he observed sparrows. For Robert, the more sensitive species found in the Salt Marshes, the healthier the swamp is.