Persist or perish: critical life stages determine the sensitivity of invertebrates to disturbances

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.</p

Door de dam heen : Soort- en rivier specifieke effecten van dammen op Europese trekvissen

Dammen vormen wereldwijd de grootste bedreiging voor rivierecosystemen, wat vooral tot uitdrukking komt in de afname van de aantallen trekvissen. De mate waarin vissoorten worden beperkt in hun migratie verschilt echter van rivier tot rivier en van soort tot soort. Recent zijn de effecten van rivierfragmentatie op trekvissen door barrières op Europese schaal onderzocht

Sensitivity of phytoplankton, zooplankton and macroinvertebrates to hydrogen peroxide treatments of cyanobacterial blooms

Addition of hydrogen peroxide (H2O2) is a promising method to acutely suppress cyanobacterial blooms in lakes. However, a reliable H2O2 risk assessment to identify potential effects on non-target species is currently hampered by a lack of appropriate ecotoxicity data. The aim of the present study was therefore to quantify the responses of a wide diversity of freshwater phytoplankton, zooplankton and macroinvertebrates to H2O2 treatments of cyanobacterial blooms. To this end, we applied a multifaceted approach. First, we investigated the 24-h toxicity of H2O2 to three cyanobacteria (Planktothrix agardhii, Microcystis aeruginosa, Anabaena sp.) and 23 non-target species (six green algae, eight zooplankton and nine macroinvertebrate taxa), using EC50 values based on photosynthetic yield for phytoplankton and LC50 values based on mortality for the other organisms. The most sensitive species included all three cyanobacterial taxa, but also the rotifer Brachionus calyciflores and the cladocerans Ceriodaphnia dubia and Daphnia pulex. Next, the EC50 and LC50 values obtained from the laboratory toxicity tests were used to construct a species sensitivity distribution (SSD) for H2O2. Finally, the species predicted to be at risk by the SSD were compared with the responses of phytoplankton, zooplankton and macroinvertebrates to two whole-lake treatments with H2O2. The predictions of the laboratory-based SSD matched well with the responses of the different taxa to H2O2 in the lake. The first lake treatment, with a relatively low H2O2 concentration and short residence time, successfully suppressed cyanobacteria without major effects on non-target species. The second lake treatment had a higher H2O2 concentration with a longer residence time, which resulted in partial suppression of cyanobacteria, but also in a major collapse of rotifers and decreased abundance of small cladocerans. Our results thus revealed a trade-off between the successful suppression of cyanobacteria at the expense of adverse effects on part of the zooplankton community. This delicate balance strongly depends on the applied H2O2 dosage and may affect the decision whether to treat a lake or not.</p

Complementarity of community indices in characterizing aquatic macroinvertebrate assemblages

Community indices are commonly used in ecology to characterize and track species assemblages. However, their use is also critically discussed. Unclarities remain about what the various community indices actually represent, their appropriateness in representing ecological status, and their drawbacks. Therefore, the present study aimed to elucidate the context-specificity of aquatic macroinvertebrate community index scores in lotic and lentic water bodies. To this end, a large set of macroinvertebrate distribution data in surface waters of the Netherlands was analysed. Five indices were considered, including the diversity indices species richness, Shannon diversity, and Simpson diversity, and two diagnostic indices, the number of rare species and the number of indicator species. Patterns in index scores were compared between lotic waters, lentic waters, and the combined dataset. We observed that the correlation between index scores was not as strong as often assumed. In addition, patterns in index scores differed between lotic and lentic waters, with deviating ranges in scores. These results showed that the interpretation of the patterns in macroinvertebrate community indices scores is dependent on the water type. This highlights the importance of reporting multiple community index scores and of careful interpretation of their meaning within the appropriate context. This should be considered to make appropriate choices in the use of these indices in future water quality assessment and environmental management

Door de dam heen : Soort- en rivier specifieke effecten van dammen op Europese trekvissen

Dammen vormen wereldwijd de grootste bedreiging voor rivierecosystemen, wat vooral tot uitdrukking komt in de afname van de aantallen trekvissen. De mate waarin vissoorten worden beperkt in hun migratie verschilt echter van rivier tot rivier en van soort tot soort. Recent zijn de effecten van rivierfragmentatie op trekvissen door barrières op Europese schaal onderzocht

Species composition drives macroinvertebrate community classification

Community classification enables us to simplify, communicate, track and assess complex distribution patterns. Yet, the distribution of organisms may not coincide with predefined geographical and environmental boundaries, and therefore, biology itself should be leading the classification. In this study, we showed how to arrive at such a biology-based classification by clustering locations based on similarity in species composition. A hierarchical classification structure allowed for the selection of classification levels that suit multiple scales of analysis. We also showed how to objectively identify the number of clusters present in a dataset based on the distribution of specific indicator species, allowing to identify clear boundaries in species composition on multiple scales. The resulting biology-based clusters were identified and characterized by local and regional environmental conditions, showing the limited explanatory power of these environmental conditions and the added value of taking biology itself as a starting point of the classification. By departing community classification from species composition, the unknown environmental, geographical, and biotic drivers influencing species composition are accounted for.</p

Quantifying cumulative stress acting on macroinvertebrate assemblages in lowland streams

Macroinvertebrates in lowland streams are exposed to multiple stressors from the surrounding environment. Yet, quantifying how these multiple stressors impact macroinvertebrate assemblages is challenging. The aim of this study was to develop a novel method to quantify the cumulative stress acting on macroinvertebrate assemblages in lowland streams. To this purpose, we considered 22 stressors from different stressor categories such as hydrological, morphological and chemical stressors, acting over multiple spatial scales ranging from instream to the catchment scale. Stressor intensity was categorized into classes based on impact on the macroinvertebrate assemblages. The main stream was divided into segments, after which for each stream segment, the cumulative stressor contribution from headwater catchments, from the riparian zone and from upstream was calculated. To validate the cumulative stress quantification method, the lowland stream Tungelroyse Beek in the Netherlands was used as a case study. For this stream it was shown that independently derived ecological quality scores based on macroinvertebrate samples collected at multiple sites along the stream decreased with increasing calculated cumulative stress scores, supporting the design of the cumulative stress quantification method. Based on the contribution of each specific stressor to the cumulative stress scores, the reasons for the absence and presence of macroinvertebrate species may be elucidated. Hence, the cumulative stress quantification method may help to identify and localize the most stringent stressors limiting macroinvertebrate assemblages, and can thereby provide a better focus for management resources.</p