Voyage Update 5: Salp parasites and micropredators

10 November 2018. By Voyage Leader Dr Moira Decima.

10 November 2018. By Voyage Leader Dr Moira Decima.

We know that some fish (like oreos, warehou and leatherjacket) and Bryde’s whales like to eat salps, but who else out there is taking advantage of all that food? 

It turns out that one of the main critters that we can see eating salps out here are hyperiid amphipods – small crustaceans that are usually smaller than the salp itself! You can see them clearly in the inside of the salp, since they are orange and the salp is clear. These particular amphipods are called ‘micropredators’ (since they are small), and they swim in and out of the animal through the siphons that pump water in and out.

Two hyperiid amphipods munch away at a S. thompsoni oozoid + close-up images of the amphipods.

However, there is one amphipod that is not just a micropredator, it is also a parasite. Meet the inspiration for the movie ‘Alien’: the amphipod Phronima!

Phronima! The black dots are part of its mouth, and the clear, giant spaces above are its eyes [Photo: Mike Stukel]  

Phronima carves its salp host into a barrel, eating it from the inside. Phronima makes a comfortable little home from the salp barrel, and when the right time comes, the female lays her eggs inside. 

Left: Phronima sitting in its salp barrel. Right: Momma Phronima is outside the house, and can you see the little amphipod babies inside of the barrel?
Left: Baby Phronima amphipods up close. Right: One baby Phronima! [Photos: Mike Stukel]  
But don’t be too afraid of this scary-looking parasite – it’s only about an inch long!

We've highlighted Phronima's special relationship with salps before as a Critter of the Week and just recently in a Halloween post on the NIWA Invertebrate Collection Facebook page.