What are these bugs?

[dbati]

Late at night if I focus my vision on a single rock I’ll eventually notice these little critters. They kind of look like little bugs. Any clue as to what they are? Are they an issue or just beneficial biodiversity to the system?

https://youtube.com/shorts/RLRCAgm4sjw?feature=share

 

[ZombieEngineer]

Amphipods. They are beneficial.