At first glance, our speaker may sound like she's kind of all over the place with the constantly shifting moods, subjects, and imagery. But when we actually get through the entire poem, we see that all the transitions are happening for a reason and aren't caused by a personality disorder.
In fact, the dissolving images add to the wavy movement of her word choice that mimics the sound of the ocean and the swimming fish. After all, the ocean doesn't stand still, so why should the speaker's voice?
So the speaker is an omniscient observer that takes us from one setting to the next in a dispassionate sort of way. There isn't a whole lot of emotion behind her voice since she's just an observer, which only adds to the natural sound of the poem and speaker. Nature doesn't usually get worked up over things, right?
In that way, our speaker is also mimicking the somewhat indifferent and emotionally uninvolved way that nature does its thing. And all that indifference helps to emphasize some of the poem's themes that deal with life, perseverance, and the natural world. Sure it may sound cold, but nature doesn't take into consideration all the kind deeds you've done over the years when it's time to send a little hardship your way. Everyone lives, dies, and hopefully perseveres in the natural world. Cycles are maintained and life goes on, without any worked-up commentary or special treatment.