When Pound mentions that the Greek poet Homer had an "ear for the sea-surge" (13), it's not just some throwaway comment. He's giving us a hint about the entire sound of "Canto II," which is supposed to remind us of the sea. Pound sets this up early on, when he makes up the sea-god "So-shu," whose name is really an onomatopoeia that is supposed to sound like the ocean surf. Pound follows this line with the even more sea-like, "Seal sports in the spray-whited circles of cliff wash" (6). Notice all that alliteration and consonance? Good, because throughout the rest of the poem, you're going to get a lot of hissing S sounds and shushing Sh sounds.
Not only does Pound use sound to remind us constantly of the setting (about which you can read more, over in… "Setting"), but he also uses sound to tie each line together. This poem is a nod to the Old English accentuated meter, which means that sound is totally wrapped up with form; they can't really be separated. The stressed syllables in each line are tied together through alliteration), internal rhyme, or both.
What in the Wide World of Sports are we talking about? Well, here's an example of an alliterative lines with internal rhyme:
And poor old Homer blind, blind, as a bat,
Ear, ear for the sea-surge, murmur of old men's voices: (12-13)
In line 12, we get a ton of alliteration with the B words (no, not that B word) and then in line 13 we get both alliteration (with the S and the M words) as well as internal rhyme ("surge" and "murmur"). In other words, the lines are held together with a sonic glue, echoing both their consonant and vowel sounds to create momentum and predictability in your mind's ear (if you can imagine that).