Filter-Feeding of Hyalella montezuma, an Unusual Behavior for a Freshwater Amphipod

Hyalella montezuma, an endemic planktonicamphipod in Montezuma Well, Arizona, filtered suspensions of a green alga, Coccomyxa sp. (2-4µm) in the laboratory at rates averaging 7.9 ml/ day. A mixed suspension of phytoplankton (2-35µm) was filtered at average rates of 15.6 ml/ day. Both the unialgal culture of Coccomyxa and mixed suspension were collected from Montezuma Well. Hyalella azteca is a co-inhabitant in the littoral region in Montezuma Well. Under the same experimental design, H. azteca showed negligible uptake of phytoplankton. Increases in filtering rates for H. montezuma were significantly correlated with increases in amphipod body length. This is the first evidence, based on laboratory experiments, of a freshwater gammaridean amphipod displaying the ability to filter-feed.