Insights into the ecology of Cryptorchestia garbinii on the shores of the urban lake Tegel (Berlin, Germany)

Abstract

Talitrid amphipods find their optimal zonation in humid substrates, from the supralittoral of sandy beaches, to damp wracks cast up on river and lake banks, to the moist soil of gardens, and are known to adjust behavior in order to fit within a broad range of environmental constraints. The stones along urban shores of Lake Tegel offer shelter to a resident population of Cryptorchestia garbinii; while the stones can offer a stable shelter, the lakeshore undergoes seasonal changes. To investigate how C. garbinii responds and copes with changes in such urban habitat, we carried out a preliminary study to assess mobility and daily activity of a resident population. The population was sampled with pitfall traps, emptied in the morning and in the evening avoiding dusk and dawn. Sampling lasted 48 hours in each season, along one year. A test for survival in water on 14 adults was paired with the summer sampling. A consistent pattern of activity was found: only the traps closest to the stones contained talitrids (including in condition of 0 °C air temperature), except in winter when the soil was frozen, incorporating the stones. The night captures were consistently more numerous than the daylight ones. All individuals survived in water, with a female observed to release live offspring. The results indicate a steadily nocturnal mobility, yet limited to less than one meter on the land side. The connectivity potential of this riparian-hopper hence relies either on the alongshore dimension or via water.