These small, shrimp-like crustaceans are among the most ubiquitous organisms on Earth. They occur in nearly every aquatic environment, from deep ocean trenches to freshwater lakes and rivers. Any time you're near water, you're probably close to an amphipod.
To many ecologists, they’re best known for their role as fish food. Although small, amphipods are highly nutritious and often extremely abundant, making them one of the most readily available energy sources in aquatic food webs. They are like ecological popcorn: small, plentiful, and always being replenished.
But amphipods do much more than support fisheries. There are over 10,000 species. Some pollinate seagrass. Others build tube-like homes from surrounding material and function as ecosystem engineers, like tiny beavers of the invertebrate world.
Amphipods can do just about everything, except tolerate pollution.
That sensitivity is why they are widely used as ecological indicators. During spills, oil often accumulates in the wrack line along beaches, exactly where amphipods tend to concentrate. These areas provide moisture for respiration and a steady food supply of wrack delivered with each high tide.
After the 1978 Amoco Cadiz oil spill, dense amphipod populations that once dominated the wrack community disappeared almost immediately. Since then, similar observations and studies have confirmed their sensitivity relative to other organisms.
Public attention during spills often focuses on commercial species like salmon, or more charismatic wildlife like whales, turtles, and birds. But impacts to the unseen majority, including amphipods, can be the earliest signal of ecosystem-level effects.
In the Natural Resource Damage Assessment (NRDA) process, the entire ecosystem is considered. It’s not just counting oiled birds, it’s understanding how impacts to even the smallest organisms affect the whole system.
Photo credit to lpbateman via iNaturalist. Thank you!