Adam told us about the “functional feeding groups” into which creek animals are classified: scrapers, shredders, collectors, filterers, etc. Each group plays an important role in moving the nutrients in plant debris, algae, plankton, and the like up the food chain to larger and larger animals. We found scuds, for example, small 10-legged crustaceans that collect particles of suspended plant matter or graze on the thin film of algae, fungi and bacteria that forms on leaves, stems, and rocks.
One sample from the bucket-sieve produced a young white sucker. This fish, common in Maryland, has a mouth located on the underside of its head that helps with bottom feeding. At this early phase, it grazes on plants. Adults feed on aquatic insect larvae, crustaceans, small clams, and detritus.
We also found a female black-nosed dace, pregnant with eggs
that a male will fertilize just after they are laid.
Adam pointed out that, since fish can escape from poor-quality water by swimming up or downstream, they are not as useful for measuring stream quality as aquatic insect larvae, which have much more limited mobility.
Just below the confluence with Bree Tributary, we found attached to a rock what some of us thought might be a case-maker caddisfly larva, which would have been good news since they are less pollution tolerant and thus indicative of better-quality water. Unfortunately, Adam identified it as the pupal stage of a netspinner caddisfly in its cuccoon, an insect that is highly tolerant of unhealthy water. It creates a silk web that filters nutrients from the passing water.