The ecology of chytrids in aquatic ecosystems: roles in food web dynamics

Epidermal changes caused by a chytridiomycete fungus (Chytridiomycota; Chytridiales) were found in sick and dead adult anurans collected from montane rain forests in Queensland (Australia) and Panama during mass mortality events associated with significant population declines. We also have found this new disease associated with morbidity and mortality in wild and captive anurans from additional locations in Australia and Central America. This is the first report of parasitism of a vertebrate by a member of the phylum Chytridiomycota. Experimental data support the conclusion that cutaneous chytridiomycosis is a fatal disease of anurans, and we hypothesize that it is the proximate cause of these recent amphibian declines.

Batrachochytrium dendrobatidis is a fungus belonging to the Phylum Chytridiomycota, Class Chytridiomycetes, Order Chytridiales, and is the highly infectious aetiological agent responsible for a potentially fatal disease, chytridiomycosis, which is currently decimating many of the world's amphibian populations. The fungus infects 2 amphibian orders (Anura and Caudata), 14 families and at least 200 species and is responsible for at least 1 species extinction. Whilst the origin of the agent and routes of transmission are being debated, it has been recognised that successful management of the disease will require effective sampling regimes and detection assays. We have developed a range of unique sampling protocols together with diagnostic assays for the detection of B. dendrobatidis in both living and deceased tadpoles and adults. Here, we formally present our data and discuss them in respect to assay sensitivity, specificity, repeatability and reproducibility. We suggest that compliance with the recommended protocols will avoid the generation of spurious results, thereby providing the international scientific and regulatory community with a set of validated procedures which will assist in the successful management of chytridiomycosis in the future.

The factors that regulate energy transfer between primary producers and consumers in aquatic ecosystems have been investigated for more than 50 years. Among all levels of the food web (plants, herbivores, carnivores), the plant-animal interface is the most variable and least predictable link. In hypereutrophic lakes, for example, biomass and energy transfer is often inhibited at the phytoplankton-zooplankton link, resulting in an accumulation of phytoplankton biomass instead of sustaining production at higher trophic levels, such as fish. Accumulation of phytoplankton (especially cyanobacteria) results in severe deterioration of water quality, with detrimental effects on the health of humans and domestic animals, and diminished recreational value of water bodies. We show here that low transfer efficiencies between primary producers and consumers during cyanobacteria bloom conditions are related to low relative eicosapentaenoic acid (20:5omega3) content of the primary producer community. Zooplankton growth and egg production were strongly related to the primary producer 20:5omega3 to carbon ratio. This indicates that limitation of zooplankton production by this essential fatty acid is of central importance at the pelagic producer-consumer interface.