I think that “La perla de la mora” means “The pearl owned by the moor”. A moor is a North African of mixed Arab and Berber descent. Also I “Googled” the phrase and found the poem by José Marti. The first two lines of the poem are:
Una mora de Trípoli tenía
Una perla rosada, una gran perla,

It seems to me “de Tripoli” is determinative in concluding “mora” must be a person. The first two lines would be;
A moor from Tripoli had (owned)
A large pink pearl

The problem is that our translators pick the most popular meanings when they do a translation. A peek at the dictionary definitions of “perla” and of “mora” gives many other options.

I hope this is a little help.

Recuerdos/Regards,

Moe

I think it means:

1)The pearl from the blackberry

2) The pearl's blackberry

3) The blackberry's pearl.

my suggestion would be similar, only adding: the pearl of the blackberry. have you read the story yet? and does it make any sense with the title?

I googled the poem:

LA PERLA DE LA MORA Una mora de Trípoli tenía Una perla rosada, una gran perla, Y la echó con desdén al mar un día: -«¡Siempre la misma! ¡Ya me cansa verla!»

Pocos años después, junto a la roca de Trípoli... ¡la gente llora al verla! Así le dice al mar la mora loca: -«¡Oh mar! ¡Oh mar! ¡Devuélveme mi perla!»

Maybe we could disect it and just figure out how the blackberry comes into this.

They throw the pearl of the blackberry into the sea and then it comes back?

i pasted the whole poem into the translator and it is really hard to decipher what it is saying.