The Aquatic Communities of Pennsylvania
Pennsylvania aquatic communities are classified according to fish, mussel and macroinvertebrate species indicative of each community type, and the stream habitats in which they are found. A formal characterization of these communities have been compiled into the Aquatic Community Classification (ACC) and are described in Chapters 4-7 of the ACC User's Manual. Information about community rarity, threats and conservation recommendations is also included.
Fish communities are characterized based on major drainages of Atlantic drainage basin (Delaware, Susquehanna and Potomac River watersheds) and the Ohio-Great Lakes basin (Ohio River, Genesee River and Lake Erie watersheds). Mussel communities are described from three areas: 1) Delaware River basin, 2) Susquehanna and Potomac River basins and 3) the Ohio River and Lake Erie basins.
Aquatic Communities and Watersheds: FAQ
All three of these types of organisms hold unique niches in Pennsylvania's streams and rivers. Macroinvertebrates include aquatic insects, worms and crustaceans (e.g., crayfish and scuds), which generally occupy the lower levels of food webs in aquatic systems. The presence of certain macroinvertebrates reflects differences among stream locations in food availability, water quality and habitat type. Perhaps most importantly, macroinvertebrate communities provide an overall picture of stream health; macroinvertebrate taxa generally respond to environmental stress in predictable ways, based on their levels of tolerance to different stressors.
Macroinvertebrates are an important prey source for many fish. Food resources and spawning habitats can be specific for different species of fish as different species will have different habitat requirements and habitat needs. Just like macroinvertebrates, fish are influenced by stream quality and the condition of the watershed. For example, sediment from erosion at a mismanaged construction site near a stream may cover substrates that are necessary for fish such as brook trout to lay their eggs. Layers of fine particles from sedimentation such as this can also smother the habitats that developing fish require, preventing them from reaching adult life stages.
Mussels are filter feeders, which means that they siphon water through internal gills to extract particles of food from the water column. They require relatively clean water to survive, and are particularly sensitive to industrial discharge, abandoned mine drainage and urban runoff pollution. Mussels generally require gravelly, sandy or muddy habitats where they can burrow into the stream bottom. They typically occur in larger streams and in rivers that contain sufficient nutrient levels to supply them with food.
Many factors influence the occurrence of aquatic communities, including natural variations in stream environments. Fast-flowing, cold streams flowing from ridgetops provide different habitat types than slow, warmer rivers meandering through valleys. Aquatic communities reflect these differences in stream type and environment. Geology also varies across Pennsylvania, and flowing water may have unique chemical compositions based on the types of rocks that it contacts.
Human alterations to aquatic environments can exert much stronger effects than any type of natural variation discussed above. Many changes within a watershed can be detected within its streams and rivers. If implemented improperly, timber harvest, agriculture, urban development and road management are among some watershed alterations that may cause changes in water quality and stream habitats from non-point source pollution. Additionally, a number of pollutants can enter aquatic systems from point sources, such as discharges from sewage treatment plants, abandoned mines and other industrial sources.