The song has the following lines:
"Beware, beware the Daughter of the Sea." "Beware," I heard him cry.
And, in the ending:
To his nation, with his last breath, cried, "Beware the Daughter of the Sea."
Is the meaning of these sentences to warn 'the Daughter of the Sea' (like in 'But beware, dear brother, ...') or to warn against her (like in 'Beware the dog')