Sediments,not plants,offer the preferred refuge for Daphnia against fish predation in Mediterranean shallow lakes: an experimental demonstration

1. Different behavioural responses of planktonic animals to their main predators, fish, have been reported from shallow lakes. In north temperate lakes, large‐bodied zooplankton may seek refuge from predation among macrophytes, whereas in subtropical lakes, avoidance of macrophytes has been observed. The prevalent behaviour probably depends on the characteristics of the fish community, which in Mediterranean lakes is typically dispersed in both the open water zone and in the littoral, as in temperate lakes, and is dominated by small size classes, as in subtropical lakes. 2. We performed ‘habitat choice’ experiments to test the response of Daphnia magna to predation cues at both the horizontal and vertical level by mimicking a ‘shallow littoral’ zone with plants and a ‘deeper pelagic’ zone with sediments. 3. Initial separate response experiments showed that natural plants, artificial plants and predation cues all repelled D. magna in the absence of other stimuli, while sediments alone did not trigger any significant response by D. magna. 4. The habitat choice experiments showed that, in the presence of predation cues and absence of plants, Daphnia moved towards areas with sediment. In the presence of both plants and sediments, Daphnia moved away from the plants towards the sediments under both shallow and deep water treatment conditions. 5. Based on these results, we suggest that Daphnia in Mediterranean shallow lakes avoid submerged macrophytes and instead prefer to hide near the sediment when exposed to predation risk, as also observed in subtropical shallow lakes. This pattern is not likely to change with water level alterations, a common feature of lakes in the region, even if the effectiveness of the refuge may be reduced.     

Pathways of Increased Water Clarity After Fish Removal from Ventura Marsh; a Shallow, Eutrophic Wetland

We investigated the pathways by which water clarity increases following fish removal by evaluating the effects of a benthivorous fish reduction in a large, shallow, eutrophic, wetland in a predominately agricultural watershed in Iowa, U.S.A. Phytoplankton was phosphorus limited prior to manipulation. After a substantial fish removal was obtained, water clarity increased as a result of decreased suspended sediment and phytoplankton biomass. Trophic cascading, mitigated by release from fish predation and decreased physical interference from suspended sediments, appears to determine water clarity. Inorganic suspended solids declined immediately after fish were removed but the biomass of Daphnia and Ceriodaphnia did not increase until a few weeks after fish removal. High grazing by zooplankton likely reduced phytoplankton biomass during the height of the clear-water phase. Phytoplankton appeared to be limited by zooplankton grazing for approximately two months before reverting to bottom-up control. An increase in suspended sediment and/or increased predation pressure on zooplankton, due to the return of juvenile carp, appears to account for the decline of larger-bodied zooplankters and the switch back to bottom-up control. Macrophyte diversity and density increased substantially after the initiation of the clear-water phase.     

Shallow water predation risk for a juvenile flatfish (winter flounder; Pseudopleuronectes americanus, Walbaum) in a northwest Atlantic estuary

Many small fish, including several juvenile Atlantic flatfish, are most abundant in shallow areas presumable because these habitats enhance survivorship and/or growth. In this study, we investigated size-dependent depth distributions and the role of shallow habitats as predator refuges for age-0 winter flounder (Pseudopleuronectes americanus) in a northwest Atlantic estuarine nursery. Analysis of trawl surveys performed during the larval settlement period throughout the Navesink River and Sandy Hook Bay, New Jersey, showed that as fish increased in size, depth of occurrence gradually decreased, so that individuals >35 mm standard length (SL) were concentrated in habitats ∼1 m deep. Tethering in structurally simple and adjacent shallow and deep habitats showed that predation risk for flounder (30-50 mm SL) was low in shallow water (<1 m) and increased rapidly with depth. Summer flounder (Paralychthys dentatus), which were more abundant in trammel nets in deep habitats and included winter flounder in their diets, appeared to be important consumers of tethered fish. Our results indicate that following larval settlement, winter flounder emigrate from or suffer high mortality in deeper water to become concentrated in shallow habitats that can serve as predator refuges even when they lack complex physical structures. These results highlight the potential for functional habitat loss when natural and/or anthropogenic factors make shallow habitats unavailable to young fish.     

Migratory benthic fishes may induce regime shifts in a tropical floodplain pond

1. Alternative states are a widely recorded phenomenon in shallow lakes, which may shift between turbid‐ and clear‐water conditions. Here, we investigate whether such shifts in a tropical floodplain pond may be related to the effect of the flood pulse regime on the community structures of fish and macrophytes. 2. Using a long‐term data set, we demonstrate how benthic fish migration together with colonisation by submerged plants affected the transition from a turbid to a macrophyte‐dominated state in a floodplain pond without top‐down control. 3. In our study, the turbid state occurred mostly during low water phases and was largely characterised by high values for the biomass of benthic fish, chlorophyll‐a and total phosphorous. 4. During the period of rising water levels, the migration of benthic fish out of the pond occurs simultaneously with the establishment of submerged plants, while water turbidity decreases along with phytoplankton and nutrient concentrations, inducing a clear‐water phase. However, when submerged plants are absent and fish migration is low, a transient state is generated. 5. We suggest that, in contrast to temperate ponds and shallow lakes, where the main driving mechanisms establishing alternative states are related to cascading effects via the food chain, in tropical ponds and shallow lakes it is resuspension of sediments by benthic fish that plays the most significant role in establishing alternative states. However, the effect of the flood pulse regime plays an important role in the temporal dynamics of fish community structure by controlling benthic fish migration.     

High Meiofaunal and Nematodes Diversity around Mesophotic Coral Oases in the Mediterranean Sea

Although the mesophotic zone of the Mediterranean Sea has been poorly investigated, there is an increasing awareness about its ecological importance for its biodiversity, as fish nursery and for the recruitment of shallow water species. Along with coastal rocky cliffs, isolated coralligenous concretions emerging from muddy bottoms are typical structures of the Mediterranean Sea mesophotic zone. Coralligenous concretions at mesophotic depths in the South Tyrrhenian Sea were investigated to assess the role of these coralligenous oases in relation to the biodiversity of surrounding soft sediments. We show here that the complex structures of the coralligenous concretions at ca. 110 m depth influence the trophic conditions, the biodiversity and assemblage composition in the surrounding sediments even at considerable distances. Coral concretions not only represent deep oases of coral biodiversity but they also promote a higher biodiversity of the fauna inhabiting the surrounding soft sediments. Using the biodiversity of nematodes as a proxy of the total benthic biodiversity, a high turnover biodiversity within a 200 m distance from the coralligenous concretions was observed. Such turnover is even more evident when only rare taxa are considered and seems related to specific trophic conditions, which are influenced by the presence of the coralligenous structures. The presence of a high topographic complexity and the trophic enrichment make these habitats highly biodiverse, nowadays endangered by human activities (such as exploitation of commercial species such as Corallium rubrum, or trawling fisheries, which directly causes habitat destruction or indirectly causes modification in the sedimentation and re-suspension rates). We stress that the protection of the coralligenous sea concretions is a priority for future conservation policies at the scale of large marine ecosystems and that a complete census of these mesophotic oases of biodiversity should be a priority for future investigations in the Mediterranean Sea.     

The importance of drawdown and sediment removal for the restoration of the eutrophied shallow Lake Kraenepoel (Belgium)

Lake Kraenepoel (Belgium) is a shallow lake (22 ha), divided in two basins since 1957 by a shallow dike. The lake was used for fish farming until World War II and was drawn down about every 5 years to harvest fish. Despite its dense historical carp population, it had clear water and a rich Littorelletea vegetation. During the course of the 20th century, the lake became eutrophic and the Littorelletea vegetation degraded. The northern basin, which was still drawn down about every decade after 1957, retained its clear water and had a dense submerged macrophyte vegetation. The southern basin, which was never drawn down after 1957 and which received direct surface water inputs, had become a turbid shallow lake with phytoplankton blooms in summer. In 2000, efforts were taken to restore the lake: the entire lake was drawn down, the fish community was biomanipulated, nutrient-rich surface water inputs were diverted from the southern basin and sediments were removed (only in the northern basin). Fish biomanipulation and sediment removal were successful in the northern basin, as nutrient levels declined and the Littorelletea vegetation recovered. In the southern basin, sediment analyses indicated that drawdown resulted in sediments with a lower water and organic matter content and water column turbidity decreased after the drawdown. But pH in the southern basin declined to <4, probably because sulphides in the sediment were oxidized during drawdown and sediment desiccation. In contrast, desiccated sediments were removed from the northern basin and pH did not decline below 6 after restoration. In spite of the still high dissolved nutrient concentrations, phytoplankton biomass declined significantly in the southern basin, probably due to acidification. However, no Littorelletea species colonised the lake bottom in the southern basin. Thus, lake drawdown may be a useful management technique to promote clear water conditions in shallow lakes. However, acidification due to sulphide oxidation may be an undesirable outcome and should be considered in drawdown and sediment desiccation manipulations.     

Seasonal and spatial microhabitat selection and segregation in young Atlantic salmon, Salmo salar L., and brown trout, Salmo trutta L., in a Norwegian river

Seasonal microhabitat selection by sympatric young Atlantic salmon and brown trout was studied by diving. Both species, especially Atlantic salmon, showed seasonal variation with respect to surface and mean water velocities and depth. This variation is partly attributed to varying water flows and water temperatures. In winter the fish sought shelter in the substratum. A spatial variation in habitat use along the river due to different habitat availabilities was observed. Both species occupied habitats within the ranges of the microhabitat variables, rather than selecting narrow optima. It is hypothesized that the genetic basis allows a certain range to the behavioural response. Microhabitat segregation between the two species was pronounced, with brown trout inhabiting the more slow-flowing and partly more shallow stream areas. Atlantic salmon tolerated a wider range of water velocities and depths. Habitat suitability curves were produced from both species. It is suggested that habitat suitability curves that are based on observations of fish occupancy of habitat at median or base flow may not be suitable in habitat simulation models, where available habitat is projected at substantially greater water flows.     

鲤对浅水湖泊水质影响的围隔实验研究

鲤是我国浅水湖泊常见鱼类,鲤可以通过扰动底泥、牧食浮游动物、排泄营养盐等途径影响湖泊水质。为了研究鲤对浅水湖泊水质的影响,论文于2009年6月23日至8月18日在暨南大学明湖进行原位围隔实验。实验分为三个处理组(三组围隔):(1)在围隔中放养鲤(放鱼组);(2)在围隔底部放置塑料隔网,在隔网上部空间放养鲤(放鱼放网组);(3)围隔中不放隔网也不放鲤(空白对照组)。实验结果表明:鲤可以显著增加水体悬浮物、总氮、总磷和叶绿素a含量,显著降低了水体透明度。而鲤是否扰动底泥对水体悬浮物、总氮、总磷和叶绿素a含量等指标的影响不显著。 因此,该研究中鲤对浅水湖泊的影响可能主要是通过排泄等途径实现的,鲤扰动底泥对水质的影响不大。     

Diel and seasonal vertical distribution of meiobenthic copepods in muddy sediments of a eutrophic lagoon (fish ponds of Arcachon Bay)

The vertical distribution of meiobenthic copepods was investigated within muddy sediments of a eutrophic lagoon (fish ponds of Arcachon Bay, France). The aim of the study was to determine if in muddy sediments, as previously established in sandy sediments, meiobenthic copepods migrate vertically according to the seasons or diel periods. Two experimental approaches were used, viz: a three-season comparison was made of the diel vertical distribution of the harpacticoid Canuella perplexa T. & A. Scott (1893) and secondly the depth distribution of a meiobenthic copepod assemblage was followed for a 24 h period, in shallow water subtidal locations. The harpacticoid C. perplexa vertically migrated through the top three centimeters of the sediment, showing diel and seasonal variations in depth distribution. The differential vertical distributions shown by the dominant meiobenthic populations suggest that emergence into the water column may mainly concern surface dwelling copepods. The physical and biological factors affecting seasonal and diel changes in the copepod assemblage of the fish ponds are discussed.     

Physical habitat simulation for a fish community using the ANFIS method

This study presents physical habitat simulations for the fish community in a reach of the Dal River, Korea. The study reach is 2.3 km long, located downstream from the Goesan Dam. The reach is gravel-bed, including a bend. A riffle is present at the apex of the bend, and pools are located before and after the riffle. Field monitoring revealed that five fish species are dominant, namely Zacco platypus, Coreoleuciscus splendidus, Zacco temminckii, Pungfungia herzi, and Acheilognathus yamatsute, and account for 78% of the total fish community. These five fishes, which include both lotic and lentic fishes, were selected as target species. The Center for Computational Hydroscience and Engineering 2D (CCHE2D) model, a 2D shallow water equation solver, and the Adaptive Neuro Fuzzy Inference System (ANFIS) method were used for hydraulic and habitat simulations, respectively. The Mahalanobis distance method was used for identifying outliers in the monitoring data. It was shown that the ANFIS method combined with data quality assessment predicts the Composite Suitability Index (CSI) better than the method without it. The CSI distributions in the study reach are presented for various flows. It was found that the distributions of the combined CSI predicted by the ANFIS method are higher than those predicted by the conventional multiplicative aggregation method with Habitat Suitability Curves (HSCs). In addition, it was revealed that the discharge that yields the maximum Weighted Usable Area (WUA) for the whole fish community is more than twice the discharge yielding the maximum WUA for a single target species. This increased discharge leads to a 58% increase in the maximum WUA for the fish community.     

惠州西湖底泥中氮磷特征的初步研究

惠州西湖为典型的亚热带城市浅水湖泊.为了调查该湖泊底泥性质了解底泥对水质的影响.2004年8月在惠州西湖5个子湖(南湖、丰湖、平湖、菱湖和鳄湖)采集了6个底泥柱样,对其含水率、烧失量(LOI)、总氮(TN)、总磷(TP)、藻类可利用性磷(AAP)和粒度的垂向特征进行了初步研究.结果表明,各子湖中南湖内源负荷最大,底泥中的LOI、TN、TP和AAP含量高于其他湖区数倍以上,表层值较高,表明曾遭受过严重的污染,而其它湖区的垂向变化不明显.底泥成分以粘土、粉砂为主,水体混浊度高可能与底泥粒径较小以及鱼类和游船活动的强扰动性有关.     

Effects of temporary desiccation on the mobility of phosphorus and metals in sulphur-rich fens: differential responses of sediments and consequences for water table management

In the Netherlands, permanent damming of sulphate (SO₄ ^2–)-rich surface water, in order to rewet desiccated wetlands, has resulted in stagnation and eutrophication of surface water. Permanent damming of surface water prevents periodic drought during summer and leads to suppressed iron (Fe)-rich groundwater input and to stimulated SO₄ ^2– reduction, all likely stimulating depletion of reducible Fe in the sediment. A laboratory experiment was conducted to assess the importance of temporary desiccation, its differential effects on various sediment types and the consequences for water table management. Permanent high SO₄ ^2–-rich surface water tables above sediments that are indirectly affected by shallow groundwater flows, resulted in severe eutrophication. The effect of temporary desiccation on phosphorus (P) mobilization and immobilization strongly depended on the sediment Fe and P pools in combination with the buffering capacity of the sediment. Desiccation of sediment that is indirectly affected by shallow groundwater flows, led to a long-lasting reduction in phosphate (o-PO₄ ^3–) release from the sediment because a reduced Fe pool is present, resulting in the release of Fe upon oxidation. Formerly dry sediments that have not been influenced by groundwater for a long time do not possess such a reduced Fe pool and desiccation did not reduce P-release from these sediments resulting in considerable eutrophication of the water layer immediately after rewetting. In sediment of seepage zones that are directly and permanently influenced by deeper groundwater, reduced Fe and calcium levels are so high that o-PO₄ ^3– was effectively immobilized under oxidized as well as reduced conditions. The results indicate that restoration of desiccated wetlands can not be achieved by simply retaining water by means of constructed dams. If water retention is artificially increased, temporary drops in water level during the summer are necessary to recharge the reducible P-binding Fe pool in large zones of the wetlands in order to prevent eutrophication.     

Amphidromous fish school migration revealed by combining fixed sonar monitoring (horizontal beaming) with fishing data

Coastal and estuarine environments are particularly productive ecological systems and can provide protein and nutrient exports to adjacent marine ecosystems. In spite of this, studies of fish school migration patterns between lagoons and the sea are lacking. In 1999, fish samplings combining fishing and acoustic sonar field data collection were performed in two shallow water channel lagoons to monitor fish school diel migration (lagoon-sea). Lagoon fish assemblages included 15 species and 10 families. The estimated abundances and the fishes' swimming characteristics permit those detected by sonar to be selected according to 3 criteria. Direct sampling by cast net confirmed that Dicentrarchus labrax schools were present during the autumn migration period. In situ horizontal sonar observation in shallow water bodies constitutes a powerful tool for the study of fish behaviour. Fish school migration within the range of values recorded was not affected by current velocity (maximum 0.83 m/s). No relationships among school shape, surface area or migratory direction were found. The amphidromous schools were small (0.3 to 15 m²) and observed mainly at night. Migratory behaviour appeared to be determined to some extent by fluctuations in lagoon salinity and temperature. Consistent with the ‘multi-transit’ hypothesis, which states that schools pass several times in front of the sonar transducer before moving toward or away from the lagoon, the net flow of fish was less than that predicted by the sonar methodology. Thus the multi-transit behaviour hypothesis should be considered when interpreting fish population transfer data gathered with acoustic methods using a single transducer in rivers, estuaries, or channels. In addition, the exclusive use of echosounder could generate major biomass underestimation when the fish are grouped in schools.     

Bottom-up and cascading top-down control of macroalgae along a depth gradient

On marine rocky shores, macroalgal herbivory is often intense, such that the cascading effects of fish predation may contribute to the control of algal communities. To estimate the magnitudes of top-down and bottom-up control on a macroalgal community, we manipulated the access of carnivorous fish to macroalgal colonization substrates, as well as nutrient availability, at two sub-littoral depths. There were three levels of fish manipulation: natural fish community, no fish and the enclosure of one common species, the perch, Perca fluviatilis. We found a clear cascade effect of fish predation on both the total density and several individual species of macroalgae, which was more pronounced in deep than shallow water. The density of the dominant grazers, i.e. snails, increased in nutrient-enriched conditions; perch were inefficient in controlling herbivores, and had therefore no cascading effect on algal densities under such conditions. Although nutrients enhanced the growth of opportunistic algae, herbivores, in the absence of fish, inhibited this response. While algal diversity was higher in shallow than in deep water, the enrichment effect was opposite at the two depths with lowered diversity in the shallows and increased at depth. Our results indicate that fish predation is an efficient regulator of meso-herbivores and that its effect thereby cascades onto the producer trophic level such that both perennial and opportunistic algae benefit from the presence of fish. This cascade effect is probably stronger at depth where predation efficiency is less disturbed by wave motion.     

Effects of flow on lateral interactions of fish and shrimps with off-channel habitats in a large river-floodplain system

Off-channel habitats play a crucial role in the life-cycles of many riverine fish species, but lateral movements of fish into these habitats are poorly understood. We tested how flow dynamics affects the movement of fish and shrimps between the main river channel and different types of off-channel habitats: a riverine lake and a wetland. Our study site was the lower Waikato River, North Island, New Zealand, where there are numerous off-channel habitats. Fish were sampled using directional fyke nets. Shortfin eel (Anguilla australis) migrated mostly into the wetland at night, particularly during high river flows. Common bullies (Gobiomorphus cotidianus) were most abundant during the day and in low-discharge conditions, moving mostly into the riverine lake, whereas freshwater shrimp (Paratya curvirostris) moved mostly into the wetland. High numbers of non-native larval common carp (Cyprinus carpio) moved out of the wetland with retreating flood water. This study emphasises the importance of lateral connectivity and flooding in functioning of this river system where numerous native fish, but also exotic fish, used off-channel habitats. Floodplain management strategies should promote ‘controlled connectivity’ measures that provide access for native species at key times while limiting opportunities for introduced species to utilise their favoured off-channel habitats.     

Formation of manganese oxyhydroxides on the Dead Sea coast by alteration of Mn-enriched carbonates

Manganese enriched carbonates preferentially accumulate in near-shore, shallow water sediments of the Dead Sea. These carbonates are formed by coprecipitation of Mn with authigenic aragonite, as well as by direct precipitation of Mn-carbonate from the pore water of the shallow sediments. The primary source of the Mn that accumulates as carbonates is allochthonous Mn-enriched oxides that are eroded from the nearby coasts and become buried within the near-shore shallow water sediments. Due to the decline in the level of the Dead Sea between 1960–1990, bands of sediments (parallel to the current shoreline) which were previously submerged, became exposed to air and consequently desiccated. We suggest that in order to approach new hydraulic equilibrium in some of those coastal areas, the decline in the level of the lake was followed by a lakeward advance of fresher groundwater from the shallow coastal aquifer. Those fresher waters are characterized by a higher pH than the interstitial brine, and therefore a new state of water-rock interaction is established which results in oxidative alteration of Mn-carbonates to Mn-oxides. In addition, manganese-oxidizing bacteria, shown to be active in water with lower salinity than that of the Dead Sea, may also play a part in oxidation of divalent manganese released from the sediment. As a result, some segments of the Dead Sea coast are characterized by black Mn-enriched sediments that in places form crusts over the surface.     

Extreme water level decline effects sediment distribution and composition in Lake Alexandrina,South Australia

Water level decline affects the biophysical environment of shallow lakes. Unprecedented drought in Australia’s Murray–Darling Basin resulted in extreme water level drawdown in the large, shallow Lake Alexandrina at the end of the River Murray. Surface sediment was collected from 22 sites in the lake before and after water levels declined to assess the integrated limnological changes over the period of drawdown. Results indicate an increase in the proportion of organic particles in profundal sediments, as well as an increase of fine particles (<19.9 μm) in peripheral sediments. These changes to sediment composition corresponded to higher concentrations of suspended particles at low water levels. Increased autochthony and a shift in primary production from macrophytes to phytoplankton in Lake Alexandrina support these findings. Inorganic carbon and other nutrients were lost from sandy sediments most likely through carbonate dissolution driven by a localized decrease in pore water pH from increased mineralisation of organic matter.     

The importance of sediment phosphorus release in the restoration of very shallow lakes (The Norfolk Broads,England) and implications for biomanipulation

Phosphorus release from the sediments of very shallow lakes, the Norfolk Broads, can be as high as 278 mgP m^-2 d^-1. These high rates are associated with high total sediment Fe:P ratios and occur when sulphide from sulphate reduction removes Fe(II) from the pore water. There is also evidence that bioturbation from benthic chironomids can enhance phosphorus release rates, particularly in sediments low in total iron. The release of phosphorus from the sediments of these lakes is delaying restoration following the control of phosphorus from sewage discharges. Biomanipulation is being used in these lakes to create clear water and re-establish aquatic macrophytes. This removal of fish has allowed larger populations of benthic chironomid larvae to develop which may result in an increase in the rate of phosphorus release and changes to the pore profiles of dissolved phosphorus, soluble iron and free sulphide.     

Effects of Acid Mine Drainage on the Estuarine Food Web, Britannia Beach, Howe Sound, British Columbia, Canada

We investigated the effects of acid mine drainage (AMD) from Britannia Creek, BC, Canada, a stream contaminated by an abandoned copper mine, on the estuarine food web. Near the mouth of Britannia Creek, sediments and the water contained high concentrations of dissolved copper and the waters were highly acidic. Relative to a reference location, rockweed (Fucus gardneriSilva) cover was reduced, phytoplankton biomass was lower, chironomid larvae were less abundant, and fewer gammarid amphipods colonized basket traps. Laboratory toxicity tests confirmed that sediments and water from the lower reaches of Britannia Creek and its estuary were highly toxic to midge larvae (Chironomus tentansFabricius), the marine amphipod (Eohaustorius washingtonianusThorsteinson) and also impaired fertilization of sand dollars (Dendraster excentricusEschscholtz). Analyses of stomach contents of chum salmon fry (Oncorhynchus ketaWalbaum) indicated that they preferred to feed on chironomid larvae and gammarid amphipods at Britannia Creek estuary but these two taxa were less abundant at Britannia Creek estuary relative to the reference location. AMD from Britannia Mine disrupted the structure and function of the intertidal ecosystem resulting in loss of food production for fish including chum salmon fry and other species.     

Host-dependent genetic variation in freshwater pearl mussel (Margaritifera margaritifera L.)

Freshwater fishes are vulnerable to changes in water quality, physical habitat and connectivity resulting from drought, particularly in regulated rivers. When adequate river flows return, the recovery of populations might depend on the duration and consequences of drought. Rivers of the highly regulated Murray–Darling Basin in south-eastern Australia terminate at two large, shallow lakes that are separated from the estuary by tidal barrages. Over-abstraction of water and widespread prolonged drought (1997–2010) placed the lakes under severe environmental stress, culminating in critical water level recession from 2007 to 2010. Concurrently, most freshwater fish populations collapsed. We investigate shifts in fish assemblages resulting from habitat inundation in the lakes following the drought. The inundation and re-connection of the lakes and fringing habitats led to a substantial reduction of salinity throughout the region, and aquatic vegetation shifted from salt-tolerant to freshwater species. Fish assemblages became increasingly characterized by common freshwater taxa (ecological generalists), including high proportions of alien species. There were no indications of population recovery for three threatened species. The findings emphasize that short-lived fishes with specialized habitat requirements are vulnerable to severe population declines during prolonged drought in regulated rivers, which might restrict their recovery when adequate flows return.