Attack of the Amphipods

“They mostly come out at night, mostly”. Okay, that was a cheesy line from a great sci-fi movie, but so fitting in this case. A few weeks ago we introduced a topic that most hobbyists probably had doubts in. We discussed the possibility that amphipods, usually beneficial reef invertebrates that are mostly active at night, could potentially become a pest in the average home reef aquarium if their populations reached a certain size. The reason for the article was due to the fact that we witnessed, or at least thought we witnessed, a large Tridacna derasa clam being nibbled on by multiple amphipod crustceans. The clam was laying over on one side, having been blown over by the water current. It righted itself, as it usually does, but the side that was laying in the sand was retracted. The clam looked as if i had the dreaded Pinched Mantle Syndrome, so we began preparing a freshwater dip, the only known form of treatment. That is, until we noticed a very large “pod” sitting on the exposed portion of the shell where the mantle was a bit roughed up. We noticed this activity on a few other instances, and we’ve finally managed to get a video clip of the attack in action. The clam is obviously irritated, even closing up and expelling water so quickly that it moves several inches away from where it was sitting.