A low number of algal cells/in the presence of a high number of grazers/suggested, but did not prove, that the grazers had removed most of the algae.

• 译文：/在食草动物的数量很大时/却仅有少量的水藻细胞这一点暗示着（但却不能证明）是食草动物除去了大多数水藻。