Annelid sperm and fertilization biology

This paper provides data on fine particulate organic matter (FPOM) and macroinvertebrates associated to natural and artificial leaf packs in a small woodland stream (Schlaube, Brandenburg). Macroinvertebrate colonisation and the dynamics of FPOM were studied in oven-dried alder leaf packs, air-dried alder leaf packs and packs with artificial leafshaped substrate exposed in the stream during a 68-day period. The importance of FPOM as a potential food source for macroinvertebrates especially in artificial leaf packs was evaluated. Changes in the quantity as well as in the chemical composition of the accumulating FPOM (>63 and <63 μm) was determined using soluble carbohydrates, proteins and chlorophyll a as parameters of the nutritional quality. Mass loss and the chemical changes of alder leaves during the decompositional process were also described. The loss of soluble carbohydrates due to leaching was more rapid in oven-dried alder leaf packs than in air-dried ones. After 3 days of leaf pack exposure weight loss of oven-dried and air-dried leaf packs was nearly comparable, as the similar decay coefficients, k = 0.0228 (oven-dried leaf packs) and k = 0.0214 (air-dried leaf packs), respectively, show. The amount of FPOM per unit leaf area constantly increased in artificial packs, although it remained below that of alder leaf packs at all sampling dates. The nutritional quality of FPOM <63 μm was constantly greater than that of FPOM >63 μm and decreased in both size-fractions with length of exposure. Referring to leaf area the abundance of macroinvertebrates continually increased in all packs till the end of exposure, whereas the numbers in artificial packs remained below that in alder leaf packs. The taxonomic composition of all treatments was very similar with Gammarus pulex being the most abundant taxon in all packs until day 42, while afterwards the caddis fly genus Hydropsyche gained in importance. The amphipod Gammarus pulex in general did not show a preference for air-dried alder leaf packs compared to oven-dried alder leaf and artificial packs. Corresponding dynamics of macroinvertebrate colonisation and FPOM content in artificial packs support the hypothesis that FPOM functions not only as an important food source for macroinvertebrates including gammarideans but also as a control mechanism of macroinvertebrate abundance in stream habitats. Even if the accumulation of FPOM and drifting macroinvertebrates might be influenced by the same abiotic factor (e.g. by reduction in stream velocity inside the packs) it is quite unlikely that only physical properties caused the invertebrates to stay.