The phrase in parentheses (to 200 feet) is a prepositional phrase.
The prepositions are the words which show the relationship between the pronoun and the nouns. On the other hand, the prepositional phrase starts with the prepositions and end with the object of a preposition, having one or more modifiers to describe.
The pattern of the prepositional phrase follows by the object of the preposition having one or more modifiers.
Therefore, the above parentheses phrase begins with a preposition 'to' and modifies Seaweed.
