Multiple drivers of decline in the global status of freshwater crayfish (Decapoda: Astacidea)

International audienceRates of biodiversity loss are higher in freshwater ecosystems than in most terrestrial or marine ecosystems, making freshwater conservation a priority. However, prioritization methods are impeded by insufficient knowledge on the distribution and conservation status of freshwater taxa, particularly invertebrates. We evaluated the extinction risk of the world's 590 freshwater crayfish species using the IUCN Categories and Criteria and found 32% of all species are threatened with extinction. The level of extinction risk differed between families, with proportionally more threatened species in the Parastacidae and Astacidae than in the Cambaridae. Four described species were Extinct and 21% were assessed as Data Deficient. There was geographical variation in the dominant threats affecting the main centres of crayfish diversity. The majority of threatened US and Mexican species face threats associated with urban development, pollution, damming and water management. Conversely, the majority of Australian threatened species are affected by climate change, harvesting, agriculture and invasive species. Only a small proportion of crayfish are found within the boundaries of protected areas, suggesting that alternative means of long-term protection will be required. Our study highlights many of the significant challenges yet to come for freshwater biodiversity unless conservation planning shifts from a reactive to proactive approach

Six new <i>Actinella</i> (Bacillariophyta) species from Papua New Guinea, Australia and New Zealand: further evidence for widespread diatom endemism, in the Australasian region

Examination of sediment samples from oligo-and dystrophic ponds, lakes and streams in Papua New Guinea. Australia and New Zealand revealed a hitherto unknown diversity of the diatom genus Actinella Lewis. Six new species are proposed, viz. Actinella aotearoaia sp. nov., A. giluwensis sp. nov., A. indistincta sp. nov., A. muylaertii sp, nov., A. parva sp. nov. and A. pulchella sp. nov. All species are heteropolar, both in girdle and valve view. Novel information on the genus Actinella includes the observations of two ribbon-shaped. valve-appressed plastids in A. aotearoaia and A. pulchella, and the presence of long mucilage stalks in A. aotearoaia. It is argued that, despite recent proposals to reduce the genera Actinella and Desmogonium Ehrenberg to the rank of subgenera of Eunotia, they should be kept separate until the taxonomic significance of their distinctive morphological features (such as heteropolarity) is fully assessed. The new species appear to be endemic to Australasia and have distinct biogeographies within this region. Except for A. aotearoaia, all species are present in Tasmania. A. indistincta and A. pulchella have also been found in New Zealand (Stewart Island). A. aotearoaia is common in several localities in New Zealand but was also found near Sydney on the Australian mainland. Actinella giluwensis has only been observed in material from Papua New Guinea. The record of A. punctata for the latter country constitutes the first confirmed record for this species outside North America and Europe. The discovery of the new Actinella species again confirms the importance of the Australasian region as a major centre of microalgal biodiversity and endemism

Climate change and diatoms

Climate change has triple-pronged effects – warming, deoxygenation, and acidification – in freshwater and marine environments, effects which have a full spectrum of impacts on primary producers. Diatoms are an appropriate model for indicating climate change effects because they are ubiquitous in aquatic ecosystems and are the most important primary producers in marine ecosystems (i.e., 40% of productivity) and contribute 20% of atmospheric oxygen, but have not been adequately studied in relation to climate change. Diatoms have numerous characteristics that can be used to measure the effects of climate change. For example, climate change may increase the relative abundance of dinoflagellates compared to diatoms, leading to more frequent occurrences of harmful algal blooms in marine ecosystems, where diatoms and dinoflagellates dominate blooms. Such blooms can have far-reaching impacts on ecosystems and can impact on humans by affecting fisheries, tourism, and other economic losses. These changing climatic scenarios may be accompanied by a change in the various life-forms of diatoms, such as a shift from mixed life-forms (undisturbed) to the dominance of pioneer and adnate diatoms (disturbed by an increase in carbon dioxide concentration) in the community. Diatoms store excess energy as lipids, and the number and biovolume of lipid bodies can be a valuable diagnostic tool for stress, including climate change. At the molecular level, organic lipid biomarkers can provide information to help decipher past and present climatic conditions, such as glaciation and deglaciation processes in polar regions. Reductions in diatom size and silica availability for frustule formation have been linked to increasing temperatures, such as those from global warming, in both freshwater and oceanic ecosystems – although not all studies are supportive. Finally, diatoms are excellent experimental organisms for indicating potential impacts of climate change on living organisms