Other powers they have:

Speed swimming: It allows all merpeople to swim at the speed of 600 km/h. Their body is encased in bubbles and use it as a jet stream to swim faster. 

(It's never been mentioned, but I think they should be able to communicate with aquatic life, mainly whales and dolphins. *shrugs* At least more so than a normal human can.)

Powers they can all learn (eventually) without an upgrade from the moon pool: (They're just natural powers mermaids should be able to learn)

Telekinesis 
It is the ability to move objects and people with the mind, often in ways not visible to the naked eye. 

Invisibility
Can be used while in mermaid or human form, but does not last very long. Can also be used to make anything the mermaid is touching invisible, including people.

Volume Reduction
Volume Reduction is the ability to shrink objects. (Can also un-shrink objects) [There was an episode in Mako Mermaid's where the mermaids used this power to manipulate someone's vocal cords, shrinking them, changing them until the person sang on perfect pitch.]

Also when you get wet, you have 10 seconds to dry off or you will turn into a mermaid.