the mermaid whose dark hair streams black, the merman in his armored body (lines 72-73)
We've mentioned this before, but questioning the boundaries of gender is an important theme in this poem. It's not that uncommon for a poem to leave out the gender of the speaker. When that happens, we might just decide that the speaker is the same gender as the poet. So we might have a female diver in mind when we start this poem. As soon as we read this line though, our assumption is no longer possible. On one hand, this makes the poem's subject and its message easier to apply to people in general. On the other hand, it forces us to think about how much (and in what ways) gender matters in this poem.
I am she: I am he (line 77)
Here again, the poem is opening up. Do you feel how its reach gets wider? This echoes the change we felt in the mermaid/merman line. But it also points us forward to the next few lines when the speaker becomes one with the dead, and even with the objects in the ship. If we strung this line together with the next one it would read: "I am she: I am he whose drowned face still sleeps with open eyes" (lines 77-78). When the gender changes, the speaker becomes one with all of the people who died in this disaster. Eventually, it lets him/her become one with all the victims and survivors of wrecks everywhere. We think that's kind of exciting and moving.