Persist or perish: critical life stages determine the sensitivity of invertebrates to disturbances
Lee, Gea H. van der; Kraak, Michiel H.S. ; Verdonschot, Ralf C.M. ; Verdonschot, Piet F.M. - \ 2020
Aquatic Sciences 82 (2020)2. - ISSN 1015-1621
Agapetus fuscipes - Bioassessment - Discharge - Life cycle - Lowland streams
A large proportion of studies assessing the impact of disturbances on the invertebrate community composition focus on a single life stage, assuming that those are an adequate indicator of environmental conditions. The effect of a specific disturbance may, however, depend on the life stage of the exposed organism. Therefore, we focused on the effect of spates on the caddisfly Agapetus fuscipes CURTIS (Trichoptera: Glossosomatidae) during different larval stages. A 2 year field study was performed in which we measured the discharge dynamics and population development of A. fuscipes in four lowland streams in The Netherlands. A stage-structured population model (i.e. StagePop) was used to test the impact of peak discharge on the different life stages, as larval instars 1–4 were not effectively sampled in the field. Four different mortality rates in response to spates were simulated, including a constant low, a constant high, a decreasing and an increasing impact per larval stage. This way, we were able to show a potential association between spates and population declines, where the stage-population model including decreasing impact by spates with increasing larval life stage most accurately described the population development of the larval instars 5–8. Focusing only on late instars could thus potentially result in underestimation of the effects of spates on this species. In conclusion, determination of responses of critical life stages to specific disturbances may help to identify the causes of the presence and absence of species, and thereby aid more effective management and restoration of degraded aquatic systems.
Biomonitoring of intermittent rivers and ephemeral streams in Europe : Current practice and priorities to enhance ecological status assessments
Stubbington, Rachel ; Chadd, Richard ; Cid, Núria ; Csabai, Zoltán ; Miliša, Marko ; Morais, Manuela ; Munné, Antoni ; Pařil, Petr ; Pešić, Vladimir ; Tziortzis, Iakovos ; Verdonschot, Ralf C.M. ; Datry, Thibault - \ 2018
Science of the Total Environment 618 (2018). - ISSN 0048-9697 - p. 1096 - 1113.
Bioassessment - Bioindicators - River typology - Temporary rivers - Temporary streams - Water Framework Directive
Intermittent rivers and ephemeral streams (IRES) are common across Europe and dominate some Mediterranean river networks. In all climate zones, IRES support high biodiversity and provide ecosystem services. As dynamic ecosystems that transition between flowing, pool, and dry states, IRES are typically poorly represented in biomonitoring programmes implemented to characterize EU Water Framework Directive ecological status. We report the results of a survey completed by representatives from 20 European countries to identify current challenges to IRES status assessment, examples of best practice, and priorities for future research. We identify five major barriers to effective ecological status classification in IRES: 1. the exclusion of IRES from Water Framework Directive biomonitoring based on their small catchment size; 2. the lack of river typologies that distinguish between contrasting IRES; 3. difficulties in defining the 'reference conditions' that represent unimpacted dynamic ecosystems; 4. classification of IRES ecological status based on lotic communities sampled using methods developed for perennial rivers; and 5. a reliance on taxonomic characterization of local communities. Despite these challenges, we recognize examples of innovative practice that can inform modification of current biomonitoring activity to promote effective IRES status classification. Priorities for future research include reconceptualization of the reference condition approach to accommodate spatiotemporal fluctuations in community composition, and modification of indices of ecosystem health to recognize both taxon-specific sensitivities to intermittence and dispersal abilities, within a landscape context.