FISH-INDUCED BIOTURBATION ACROSS A STREAM PROFILE: IMPLICATIONS FOR ICHNODIVERSITY OF RIPARIAN PALEOSOLS

Intense biogeomorphic activity by native and invasive fish species have had profound impact on bottom sediments and slope stability in fluvial and lacustrine settings. Several catfish (Ictaluridae) and sucker (Catastomidae) genera have been observed as important agents of bottom sediment resuspension in Neshaminy Creek (Bucks County, Pennsylvania), with implications for substrate stability, macrophyte density, and nutrient cycling. However, more numerous than the former and much larger than the latter, the introduced species of cyprinids, especially the common carp (Cyprinus carpio), have a dramatically greater zoogeomorphic impact for this waterway. Lacking natural predators, subject to release by traditional fishing, and attaining up to 10 kg over a lifespan of several decades, these fish have the potential for substantial cumulative impact as landscape engineers, as they tend to persist along short channel segments. In addition to generating numerous Piscichnus-like feeding depressions in soft bottom sediments, recent findings reveal shallow tunneling into stream bank. Numerous intentations in muddy sediments are oval in shape and vary between 5-20 cm in width, penetrating >3 cm into the bank. At low water levels, a series of these scalloped structures become emergent and can persist along low muddy overhangs near gravel bars. Cutbank faces contain similar indentations up to 1 m above mean water level, suggesting that similar activity may take place during flood-level conditions, although this scenario requires additional corroboration. When preserved by subsequent deposition, feeding and escape traces produced by cyprinids and other bottom-feeding fish have the potential to be incorporated into riparian floodplain and, subsequently, paleosol sequences. Combined with vertical lungfish burrows and sub-horizontal catfish tunnels, these features should be considered as potential contributors to riparian sediment reworking, microtopography, and ichnodiversity.