Analytical studies on benthic food webs of aquatic ecosystems using stable isotope analyses

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Investigations of benthic food webs were conducted in estuarine, riverine and lake ecosystems using carbon, nitrogen and sulfur stable isotopes.1. As a simple lake ecosystem, we examined the acidic volcanic Lake Katanuma, which has a very simple community structure. We conducted feeding experiments using a deposit-feeding chironimid larvae (Chironomus acerbiphilus) as the consumer and its potential diets (benthic diatom and phytoplankton). The results showed C. acerbiphilus larvae selectively assimilated phytoplankton and benthic diatoms as fresh deposits from bulk sediments, and assimilated phytoplankton more readily than benthic diatoms. The assimilation rate of benthic diatoms from sediments by the larvae tended to decrease with increasing water depth, while the rate of phytoplankton tended to increase with depth.2. Food sources of benthic consumer were investigated at two locations in a semi-enclosed estuarine lagoon (gamo Lagoon), the Nanakita-river estuary, and diet of the consum … More ers were elucidated from the isotopic values of potential food sources (riverine and terrestrial plant materials, participate matter, macroalgae, benthic and epiphytic diatoms). A 2-source mixing model revealed that benthic diatoms were the important diet of suspension feeders as well as surface-deposit feeders, suggesting the dietary importance of resuspended diatoms. In contrast, phytoplankton became an important diet in the inner lagoon where phytoplanktonic biomass was considerably high.3. We analyzed food sources of Trichoptera in two first-order mountain streams, which indicated that the main food of most Trichoptera species in both streams was benthic particulate organic matter derived from terrestrial plants, and that the food sources did not differ markedly between the streams. In addition, we estimated the food sources of macroinvertebrates in a headwater stream. The snail Semisulcospira libertina assimilated different food sources from other associated macroinvertebrates. The production by chemoautotrophic bacteria contributes to the food sources of a snail in a stream, even in mostly aerobic habitats. Less