A Source of Terrestrial Organic Carbon to Investigate the Browning of Aquatic Ecosystems

There is growing evidence that terrestrial ecosystems are exporting more dissolved organic carbon (DOC) to aquatic ecosystems than they did just a few decades ago. This “browning” phenomenon will alter the chemistry, physics, and biology of inland water bodies in complex and difficult-to-predict ways. Experiments provide an opportunity to elucidate how browning will affect the stability and functioning of aquatic ecosystems. However, it is challenging to obtain sources of DOC that can be used for manipulations at ecologically relevant scales. In this study, we evaluated a commercially available source of humic substances (“Super Hume”) as an analog for natural sources of terrestrial DOC. Based on chemical characterizations, comparative surveys, and whole-ecosystem manipulations, we found that the physical and chemical properties of Super Hume are similar to those of natural DOC in aquatic and terrestrial ecosystems. For example, Super Hume attenuated solar radiation in ways that will not only influence the physiology of aquatic taxa but also the metabolism of entire ecosystems. Based on its chemical properties (high lignin content, high quinone content, and low C:N and C:P ratios), Super Hume is a fairly recalcitrant, low-quality resource for aquatic consumers. Nevertheless, we demonstrate that Super Hume can subsidize aquatic food webs through 1) the uptake of dissolved organic constituents by microorganisms, and 2) the consumption of particulate fractions by larger organisms (i.e., Daphnia). After discussing some of the caveats of Super Hume, we conclude that commercial sources of humic substances can be used to help address pressing ecological questions concerning the increased export of terrestrial DOC to aquatic ecosystems

A metadata approach to documenting sex in phylum Rotifera: diapausing embryos, males, and hatchlings from sediments

We present a survey of the literature documenting sexuality in monogonont rotifers, including reports of diapausing embryos (DEs), males, and/or hatchlings from dry sediments. Of 30 families, 27 possess species with documented occurrences of sex. Information on DEs is lacking in 41 genera. Of ~300 species with evidence of sexuality (~20% of ~1500 monogononts), only 172 had direct observations of DEs; in the others, DE production was inferred from observations of males and/or hatchlings. DEs are sufficiently widespread to affirm that their presence is plesiomorphic, however few DE characteristics show a phylogenetic signature. They differ widely in volume (~0.11–100 × 105 µm3) and have a varied surface morphology (smooth to highly structured and ornamented). Some species retain DEs within their bodies; others carry them, deposit them on or attach them to surfaces, or release them free into the water. To better understand the evolutionary forces that influence monogonont sexuality and DE biology, a more comprehensive and uniform reporting scheme is needed. To enhance information dissemination, we propose that new and existing data on sex in monogonont rotifers (DEs, males, and hatchlings from dry sediments) be placed in an Internet-based repository