If you are having a hard time trying to get pearl, etc, try mixing it up a bit...
EBS - level 15 snow & level 10 seaweed (mating pair 1)
EBC - level 15 seaweed & level 10 snow (mating pair 2)
Switch up which sanctuary/cave you put them in to breed & also which is on left & right. I've gotten 3 emerald & 3 pearl rotating mating pairs. (I always attempt with 2 pairs until I get 3 of each)
I also have much better luck if the "mating pair" are NOT the same level of dragon.
Park value over 2 billion & in top 5% of all GC players