A near-natural experiment on factors influencing larval drift in Salamandra salamandra.

The larval stage of the European fire salamander (Salamandra salamandra) inhabits both lentic and lotic habitats. In the latter, they are constantly exposed to unidirectional water flow, which has been shown to cause downstream drift in a variety of taxa. In this study, a closed artificial creek, which allowed us to keep the water flow constant over time and, at the same time, to simulates with predefined water quantities and durations, was used to examine the individual movement patterns of marked larval fire salamanders exposed to unidirectional flow. Movements were tracked by marking the larvae with VIAlpha tags individually and by using downstream and upstream traps. Most individuals showed stationarity, while downstream drift dominated the overall movement pattern. Upstream movements were rare and occurred only on small distances of about 30 cm; downstream drift distances exceeded 10 m (until next downstream trap). The simulated flood events increased drift rates significantly, even several days after the flood simulation experiments. Drift probability increased with decreasing body size and decreasing nutritional status. Our results support the production hypothesis as an explanation for the movements of European fire salamander larvae within creeks.

Non-destructive investigation of extracellular enzyme activities and kinetics in intact freshwater biofilms with mineral beads as carriers.

Current procedures for fluorometric detection of extracellular hydrolytic enzyme activities in intact aquatic biofilms are very laborious and insufficiently standardized. To facilitate the direct determination of a multitude of enzymatic parameters without biofilm disintegration, a new approach was followed. Beads made of different mineral materials were subjected to biofilm growth in various aquatic environments. After biofilm coating, the beads were singly placed in microplate wells, containing the required liquid analytical medium and a fluorogenic substrate. Based on fluorometric detection of the enzymatically generated reaction products, enzyme activities and kinetics were determined. Mean enzymatic activities of ceramic bead-attached biofilms grown in a natural stream followed the decreasing sequence L-alanine aminopeptidase > L-leucine aminopeptidase > phosphomonoesterase > ß-glucosidase > phosphodiesterase > α-glucosidase > sulfatase. After one week of exposure, the relative standard deviations of enzyme activities ranged from 21 to 67%. Sintered glass bead-associated biofilms displayed the lowest standard deviations ranging from 19 to 34% in all experiments. This material proved to be suitable for short-time experiments in stagnant media. Ceramic beads were stable during more than three weeks of exposure in a natural stream. Biofilm formation was inhomogeneous or poorly visible on glass and lava beads accompanied by high variations of enzyme activities. The applicability of the method to study enzyme inhibition reactions was successfully proven by the determination of inhibition effects of caffeine on biofilm-associated phosphodiesterase.Key points• Optimized method to determine enzymatic parameters in aquatic biofilms• Direct investigation of bead-bound biofilms without biofilm disintegration• Fluorometric detection offers high sensitivity and sample throughput.