Your excellent question points towards the way in which this brilliant poem presents supernatural elements in this poem as vital and inherent parts of a natural world. This is of course linked to the overall theme of the poem which is that every aspect of the natural world has a right to be respected and valued and that it is necessary for humans to recognise this fact to coexist happily with nature. Consider how this theme is expressed towards the end of this poem:
He prayeth best, who loveth best
All things both great and small;
For the dear God who loveth us,
He made and loveth all.
It is the Mariner's inability to recognise this at the start of the poem that plunges him into a maelstrom-like world where supernatural beings are presented as allegorical figures, representing respectively the powers of retribution, life, death, and nature. You might wish to consider "DEATH" and "LIFE-IN-DEATH" as examples of these kind of figures. The juxtaposition of these supernatural elements with the natural world of which the Mariner forms a part indicates the way in which nature in this poem is presented as containing elements of both the natural and supernatural. It is only when nature is offended that the supernatural elements manifest themselves and need, in turn, to be appeased, in order for the Mariner to mature, develop and gain a measure of freedom after committing his heinous crime.