H.H. van Kleef

Biological traits successfully predict the effects of restoration management on macroinvertebrates in shallow softwater lakes

Many shallow softwater lakes are being affected by eutrophication and acidification. In these small lakes decaying organic material usually accumulates and characteristic plant and animal species disappear. In many degraded lakes organic matter and macrophytes are being removed in order to restore the lakes to their original state. To assess the effects of restoration management in softwater lakes on aquatic macroinvertebrates, changes in the species assemblages were studied in four degraded lakes in the Netherlands undergoing restoration measures. The degraded lakes still harboured species characteristic of pristine softwaters. However, most of these species were not recorded after restoration measures were taken. Species’ densities declined dramatically during the execution of restoration measures. Swimming and abundant species were more likely to survive the restoration measures than other species. The first years after restoration, the lakes did not meet the habitat requirements for a number of species. Species requiring vegetation for ovipositioning, animal food sources and swards of vegetation as habitat declined. Because recolonization is expected to be restricted, it is recommended to ensure the survival of relict populations when taking measures to restore degraded softwater lakes. This may be achieved by phasing restoration measures in space and time, hereby minimizing mortality during the execution of restoration measures and by preserving habitat conditions required by characteristic species.

The influence of environmental factors and dredging on chironomid larval diversity in urban drainage systems in polders strongly influenced by seepage from large rivers

Abstract.  Interest in the biodiversity value of urban waters is growing. Understanding key ecological processes is essential for effective management of these aquatic ecosystems. Our paper focuses on identifying the key factors that structure chironomid assemblages, such as water quality and dredging, in urban waters strongly influenced by seepage of large rivers. Chironomid assemblages were studied in urban surface-water systems (man-made drainage ditches) in polder areas along lowland reaches of the rivers Rhine–Meuse in The Netherlands. Multivariate analysis was used to identify the key environmental factors. Taxon richness, Shannon index (H′), rareness of species, and life-history strategies at urban locations were compared with available data from similar man-made water bodies in rural areas, and the effectiveness of dredging for restoring chironomid diversity in urban waters was tested. Three different chironomid associations were distinguished by Two-Way Indicator Species Analysis. Variation within and among chironomid associations were significantly related to substrate (sludge layer and substrate type: sand vs clay), % cover of lemnids, submerged vegetation, filamentous algae, and water transparency. Chironomid taxon richness and H′ were similar in urban and rural waters, probably because of their similar hydrologic, morphologic, and water-quality conditions and their similar dredging and weed-control regimes. Rareness was slightly higher in urban than in rural waters. In urban water systems, chironomid taxon richness was negatively related to sludge layer and % cover of lemnids. Dredging changed chironomid species composition, and increased taxon richness and life-history strategies indicative of good O2 conditions. Therefore, dredging can be regarded as an effective measure to restore diversity of chironomid communities in urban waters affected by nutrient-rich seepage or inlet of river water.

Larval development, metabolism and diet are possible key factors explaining the decline of the threatened Dytiscus latissimus

In Western Europe, the diving beetle Dytiscus latissimus (Coleoptera: Dytiscidae) has become rare and went extinct in several countries during the last century. This study investigated whether larval development rate, metabolism and feeding ecology differ between D. latissimus and the congeneric D. lapponicus to explore factors explaining its decline. During instar I and II, D. latissimus larvae developed faster and gained more weight than D. lapponicus larvae. In accordance, D. latissimus larvae had higher oxygen consumption rates than D. lapponicus larvae, which signifies a greater energy expenditure. Food preference tests showed that D. latissimus larvae strongly prefer caddisfly larvae (Trichoptera: Limnephilidae) with early instars being obligatory dependent on caddisfly larvae for their development. Only instar III larvae readily fed on alternative prey items. In contrast, D. lapponicus larvae had a broader diet and even rejected caddisfly larvae. Based on field observations, availability of caddisfly larvae strongly declined before the end of the larval development of D. latissimus, suggesting that time constraints on food availability limit completion of larval development. Our results suggest that food limitation during (early) larval stages is a possible bottle‐neck for this species, potentially explaining its disappearance from former localities. Promoting caddisfly larvae in the vicinity of D. latissimus oviposition sites, may possibly safeguard the present distribution of D. latissimus and support the species recovery. Although more research is needed, promoting leaf litter in shores may be beneficial to the shredding caddisfly larvae and in turn for their predator D. latissimus.