Contrasting impacts of invasive engineers on freshwater ecosystems: an experiment and meta-analysis

Invasion by common carp (Cyprinus carpio) and red swamp crayfish (Procambarus clarkii) in shallow lakes have been followed by stable-state changes from a macrophyte-dominated clear water state to a phytoplankton-dominated turbid water state. Both invasive carp and crayfish are, therefore, possible drivers for catastrophic regime shifts. Despite these two species having been introduced into ecosystems world-wide, their relative significance on regime shifts remains largely unexplored. We compared the ecological impacts of carp and crayfish on submerged macrophytes, water quality, phytoplankton, nutrient dynamics, zooplankton and benthic macroinvertebrates by combining an enclosure experiment and a meta-analysis. The experiment was designed to examine how water quality and biological variables responded to increasing carp or crayfish biomass. We found that even at a low biomass, carp had large and positive impacts on suspended solids, phytoplankton and nutrients and negative impacts on benthic macroinvertebrates. In contrast, crayfish had a strong negative impact on submerged macrophytes. The impacts of crayfish on macrophytes were significantly greater than those of carp. The meta-analysis showed that both carp and crayfish have significant effects on submerged macrophytes, phytoplankton, nutrient dynamics and benthic macroinvertebrates, while zooplankton are affected by carp but not crayfish. It also indicated that crayfish have significantly greater impacts on macrophytes relative to carp. Overall, the meta-analysis largely supported the results of the experiment. Taken as a whole, our results show that both carp and crayfish have profound effects on community composition and ecosystem processes through combined consequences of bioturbation, excretion, consumption and non-consumptive destruction. However, key variables (e.g. macrophytes) relating to stable-state changes responded differently to increasing carp or crayfish biomass, indicating that they have differential ecosystem impacts.     

Design features of constructed floodplain ponds influence waterbird and fish communities in northern New Zealand

1. Ponds can provide important refuges for aquatic biota on developed floodplains and are increasingly being constructed in an effort to enhance native biodiversity and ecosystem services in degraded landscapes. This study examined 34 constructed ponds to investigate the influence of design features on community composition, native biodiversity, and the biomass or abundance of common fish and waterbirds on the lower Waikato River floodplain, northern New Zealand.
2. Inundation frequency appeared to be a key factor affecting biomass of the native shortfin eel Anguilla australis and three invasive fish species (common carp [Cyprinus carpio], brown bullhead [Ameiurus nebulosus], and goldfish [Carassius auratus]), suggesting that colonisation occurred during flooding by adjacent waterbodies. Linear models indicated that shortfin eel abundance and total eel biomass were positively associated with the biomass of potential fish prey, the area occupied by islands and cover by trees in the riparian zone.
3. Native waterbird species richness was strongly related to water area, edge length (including islands) and area:perimeter ratio, with little increase in richness for ponds >1 ha in area, perimeters longer than 800 m, and ratios over 20. The protected grey teal (Anas gracilis), and the recreationally hunted species phenotypically assigned as mallard (Anas platyrhynchos + hybrids) and grey duck (Anas superciliosa + hybrids) appeared most strongly influenced, respectively, by perimeter length, water depth, and biomass of potential macroinvertebrate food supplies, suggesting variable effects of pond design attributes among waterfowl species.
4. Overall, these results indicate that constructed ponds can be designed to promote native waterbird diversity, enhance eel fishery and waterfowl gamebird services, and also limit the proliferation of some non-native invasive fish species in degraded floodplain landscapes. A hierarchy of constructed pond design attributes was identified, involving landscape position and connectivity, pond morphology and complexity, and riparian maturity and buffering, which were associated with direct (habitat) and indirect (food supply, physicochemistry) effects on biodiversity and provisioning services.

     

Population genetics of pike,genus <Emphasis Type="Italic">Esox</Emphasis> (Actinopterygii,Esocidae), in Northern Italy: evidence for mosaic distribution of native,exotic and introgressed populations

Biomanipulation, or management actions aimed to structure biological communities to achieve certain goals, has often been used in the restoration of aquatic ecosystems. In 2000, The Nature Conservancy acquired the Emiquon Preserve, which included two former Illinois River floodplain lakes, to restore these ecosystems. Restoration included stocking to establish a native fish community commensurate with historical records. Largemouth bass (Micropterus salmoides, bass) were also introduced to control poor water clarity and invasive common carp (Cyprinus carpio, carp). We summarized fish community characteristics and tested whether bass contributed to water clarity maintenance and limited carp during 2007–2014. The fish community was dominated by species stocked in greatest abundance, 13 of 32 species initially stocked have not been collected, and species diversity increased. No carp were observed in bass diets, water clarity declined significantly, and carp relative abundance increased. Increasing water levels during 2008–2009 diffused bass predation potential upon zooplanktivorous fishes and carp and weakened potential trophic cascading interactions. Our findings suggest that water level management, greater stocking of piscivores to maintain predator densities, prevention of gizzard shad (Dorosoma cepedianum) introduction, and/or a more diverse fish community including other native piscivores may be required to achieve long-term restoration goals.     

Biomass-dependent effects of age-0 common carp on aquatic ecosystems

Fishes play a functional role in structuring aquatic ecosystems through top-down and bottom-up processes. Adult common carp (Cyprinus carpio) are well recognized for their middle-out effects on aquatic ecosystems that can shift shallow lakes from the clear- to turbid-water stable state through benthic foraging activities. However, less is known about ecosystem effects of age-0 common carp. Age-0 common carp are planktivorous and can be highly abundant, suggesting that large year classes may also produce undesirable ecosystem effects. We evaluated the effects of four age-0 common carp densities (0, 175, 475, and 812 kg/ha) on water quality (ammonium, total phosphorus, total Kjeldahl nitrogen, and turbidity) and primary (macrophytes and phytoplankton) and secondary (zooplankton and benthic invertebrates) production. Common carp increased nutrient availability and phytoplankton production and decreased water transparency with effects increasing with carp biomass. Common carp also reduced macrophyte coverage and cladocera density (through effects on chydorus and ceriodaphnia) and body size, but effects were not density dependent. In contrast, common carp did not appear to affect copepod, rotifer, chironomid, or gastropod densities. These results suggest that even relatively low age-0 common carp densities (>175 kg/ha) may have many comparable ecosystem effects as adult carp, although effects may be accrued through different pathways.     

Validation of eDNA Surveillance Sensitivity for Detection of Asian Carps in Controlled and Field Experiments

In many North American rivers, populations of multiple species of non-native cyprinid fishes are present, including black carp (Mylpharyngodon piceus), grass carp (Ctenopharyngodon idella), bighead carp (Hypophthalmichthys nobilis), silver carp (Hypophthalmichthys molitrix), common carp (Cyprinus carpio), and goldfish (Carassius auratus). All six of these species are found in the Mississippi River basin and tracking their invasion has proven difficult, particularly where abundance is low. Knowledge of the location of the invasion front is valuable to natural resource managers because future ecological and economic damages can be most effectively prevented when populations are low. To test the accuracy of environmental DNA (eDNA) as an early indicator of species occurrence and relative abundance, we applied eDNA technology to the six non-native cyprinid species putatively present in a 2.6 river mile stretch of the Chicago (IL, USA) canal system that was subsequently treated with piscicide. The proportion of water samples yielding positive detections increased with relative abundance of the six species, as indicated by the number of carcasses recovered after poisoning. New markers for black carp, grass carp, and a common carp/goldfish are reported and details of the marker testing to ensure specificity are provided.     

A metabolic theory of ecology applied to temperature and mass dependence of N and P excretion by common carp

Our study used a metabolic theory of ecology (MTE) to explore scaling of metabolic rates by body size and temperature, and to predict nutrient excretion by common carp (Cyprinus carpio). At high biomasses, common carp have negative impacts on water quality, and one mechanism is excretion of the nutrients N and P. We measured whole-body and mass-specific excretion rates during summer and winter for fish of different sizes (wet mass range 28–1,196 g) to produce an allometric scaling model capable of predicting excretion at different temperatures. We found positive relationships between both dissolved and total nutrient concentrations and fish wet mass in summer and winter, with greater excretion rates in summer (mean water temperature 24.2°C) than in winter (mean water temperature 9.2°C). Mass-specific excretion rates decreased with increasing fish size, consistent with the MTE, and the temperature-adjusted model explained more variation for N excretion than for P. The proportion of dissolved nutrients (NH₄ and PO₄) to total nutrients increased with increasing fish size. The significance of these models is that they can be used to predict population-based nutrient excretion by common carp when thermal history, fish density and size distribution in a water body are known.     

The role of periphytes in the shift between macrophyte and phytoplankton dominated systems in a shallow, eutrophic lake (Lake Taihu, China)

Based on experiments of periphyte response to different trophic levels and their impact on macrophyte production, it was found that the periphyte biomass increased with the nutrient concentrations. Increased trophic level and periphyte biomass resulted in decreased macrophyte photosynthesis. It was suggested that the periphytes could cause resilience and hysteresis in the system shifts between macrophyte and phytoplankton domination. Other factors, such as fish farming, storm induced waves and mechanical destruction, and high water levels could be the perturbations during the system shifts, but these are not the key factors. Instead, the nutrient loading and periphyte abundance could determine the shift in lake ecosystem between macrophyte and phytoplankton domination. This finding could theoretically elucidate the mechanism of ecosystem shifts between macrophyte and phytoplankton domination.     

Contrasting responses of black fly species (Diptera: Simuliidae) to experimental whole-stream warming

1. As global temperatures continue to rise, assessment of how species within ecological communities respond to shifts in temperature has become increasingly important. However, such assessments require detailed long-term observations or ecosystem-level manipulations that allow for interactions among species and the potential for species dispersal and exchange with the regional species pool.
2. We examined the effects of experimental whole-stream warming on a larval black fly assemblage in southwest Iceland. We used a paired-catchment design, in which we studied the warmed stream and a nearby reference stream for 1 year prior to warming and 2 years during warming and estimated population abundance, biomass, secondary production, and growth rates for larvae of three black fly species.
3. Experimental warming by 3.8°C had contrasting effects on the three black fly species in the assemblage. The abundance, biomass, growth, and production of Prosimulium ursinum decreased in the experimental stream during the warming manipulation. Despite increasing in the reference stream, the abundance, biomass, and production of another species, Simulium vernum, decreased in the experimental stream during warming.
4. In contrast, warming had an overall positive effect on Simulium vittatum. While warming had little effect on the growth of overwintering cohorts of S. vittatum, warming led to an additional cohort during the summer months and increased its abundance, biomass, and production. Overall, family-level production was enhanced by warming, despite variation in species-level responses.
5. Our study illustrates that the effects of climate warming are likely to differ even among closely related species. Moreover, our study highlights the need for further investigation into the uneven effects of warming on individual species and how those variable effects influence food web dynamics and ecosystem function.

     

Impact of moderate silver carp biomass gradient on zooplankton communities in a eutrophic reservoir. Consequences for the use of silver carp in biomanipulation.

We examined the impacts of moderate gradient silver carp biomass (five levels from 0 to 36 g.m-3, i.e. about 0-792 kg.ha-1) on zooplankton communities of the eutrophic Villerest reservoir (France). During our mesocosm experiment changes in zooplankton assemblages were dependent on silver carp biomass. In the fishless and low fish biomass treatments, zooplankton abundance increased through time, owing to a peak in cladoceran density, but decreased (mainly cladocerans) at highest fish biomass. Copepods and rotifers were less affected at the highest fish biomass and dominated zooplankton communities. We highlighted that the presence of high silver carp biomass could lead to changes in phytoplankton assemblage via the impact on herbivorous zooplankton. Since silver carp efficiently graze on particles > 20 microns, the suppression of herbivorous cladocerans could result in an increase in small size algae (< 20 microns) abundance since these species would be released from grazers as well as competitors (large algae grazed by silver carp) and nutrients levels would be enhanced by fish internal loading. Our results showed that the use of low silver carp biomass (< 200 kg.ha-1) would allow us to minimize these negative effects.     

Complex interactions among fish, snails and macrophytes: implications for biological control of an invasive snail

The golden apple snail (Pomacea canaliculata), a native of freshwater wetlands of South America, has invaded many Asian countries and grazed heavily in agricultural and wild areas. Common carp (Cyprinus carpio) has been proposed as a biological control agent against this snail, but little is known about its impact on non-target aquatic plants and animals. In a 8-week enclosure experiment, we quantified the impact of common carp on three species of aquatic macrophytes and nine species of snails, including the apple snail, in a shallow pond. The results showed that the apple snail or carp alone significantly reduced the plant biomass, although the apple snail had a stronger overall herbivorous effect than the carp. The carp completely removed juvenile apple snails, but had only a weak predatory effect on larger apple snails and no effect on the adults’ oviposition frequency. Furthermore, the carp significantly reduced the populations of most species of other snails that occurred naturally in the pond. Our results thus indicate that common carp can be an effective biological control agent against the invasive apple snail, but caution should be taken about its potential to reduce wetland floral and faunal diversity.     

Experimental study of the impacts of silver carp on plankton communities of eutrophic Villerest reservoir (France)

We examined the impact of five silver carp biomass levels (0, 8, 16, 20, and 32 g m⁻³) on plankton communities and water quality of Villerest eutrophic reservoir (France). We realized the experiments using outdoor mesocosms. The presence of silver carp led to changes in zooplankton and phytoplankton assemblages. High fish biomass strongly reduced cladoceran abundance (through predation). Silver carp inefficiently grazed down particles < 20 μm. More importantly, however, the suppression of herbivorous cladocerans resulted in the increase of small size algae which were relieved from grazing and benefit from high nutrient concentrations. In contrast, in mesocosms without fish, the dominance of cladocerans (mainly Daphnia) controlled small size algae and probably also larger size algae (colonial chlorophytes, cyanobacteria). Thus, the Secchi disc transparency increased markedly. Through cascade effects, the modification of grazers communities led to changes in the utilization patterns of the added nutrients by phytoplankton communities. In high fish biomass treatments, nutrients were more efficiently accumulated into particulate fractions compared with no-fish and low-fish biomass treatments that were characterized by higher dissolved nutrients concentrations. Zooplankton was an essential source of food for silver carp. The productivity of zooplankton sustained a moderate silver carp biomass (up to 16 g m⁻³). In the presence of the highest fish biomass, the productivity of zooplankton was not large enough and silver carps fed on additional phytoplankton. Although mesocosms with high fish biomass were characterized by a slight cyanobacteria development compared with other fish mesocosms, silver carp was not effective in reducing cyanobacteria dominance. This revised version was published online in August 2006 with corrections to the Cover Date.     

Effects of common carp (<Emphasis Type="Italic">Cyprinus carpio</Emphasis>) and bream (<Emphasis Type="Italic">Abramis brama</Emphasis>) on the structure of the littoral community in a mesotrophic lake (Mesocosm Experiments)

The effect of common carp and bream on hydrochemical parameters, abundance, and structure of phyto-, zooplankton, and macrozoobenthos has been studied in semienclosed mesocosms installed in the littoral zone of a mesotrophic lake. Significant differences in the biomass of different algal groups in mesocosms with fish in respect to the control were established only for diatoms and were not found for other phytoplankton groups. Common carp had a greater effect on the abundance of large zooplankton species (Diaphanosoma brachyurum) compared to bream. The abundance of the small Bosmina longirostris increased in mesocosms both with bream and common carp. The macrozoobenthos biomass reduced at higher rates in mesocosms with common carp than in those with bream, with the strongest effect of common carp on mayfly larvae. The differences between the consumption of chironomid and oligochaete larvae were not established in mesocosms with common carp. Bream mainly affected the larvae of mayflies and oligochaetes and, to a lesser degree, the chironomid larvae.     

Indirect effect of different fish communities on nutrient chlorophyll relationship in shallow hypertrophic water quality reservoirs

Effects of different fish communities on the proportion of different nitrogen and phosphorous forms and the amount of phytoplankton (chlorophyll a) were examined in two consecutive years (1992–1993) in three Hungarian shallow water reservoirs (Cassette and outer reservoir of the Kis–Balaton Water Protection System, and Marcali reservoir). Possible interactions between nutrient concentrations and the amount of phytoplankton in these reservoirs were also examined. Considerable differences in the proportions of different nutrient forms were observed between the three test sites, which could be explained by the presence of different fish stocks in these reservoirs. In the Cassette, the fish biomass necessary for a water quality improvement was around 50 kg ha⁻¹. Phytoplankton biomass was controlled by the zooplankton, consequently chlorophyll a concentrations decreased considerably, while those of dissolved nutrients significantly increased. In the outer reservoir, phytoplankton was controlled bottom-up, since the 250 kg ha⁻¹ fish biomass was larger than the critical value due to the high proportion of planktivorous species. Chlorophyll a concentrations were high, and nutrients were mainly in particulate form (in algal cells). In the Marcali reservoir, the recently introduced silver carp population could not control fully the phytoplankton. The biomass of phytoplankton decreased only slightly, while its composition changed considerably. Although biomanipulation with silver carp is suitable for ceasing cyanobacterial blooms, reduction of the amount of planktivorous fish seems to be a more adequate method for increasing water transparency, rather than introduction of phytoplankton feeding fish.

     

飞机草入侵种群和原产地种群生长和数量型化学防御物质含量差异的比较研究

增强竞争能力的进化假说认为,在入侵地外来植物逃离了原产地天敌的控制,把原来用于防御的资源分配到生长、生殖等,从而提高竞争力。为探讨进化在恶性外来入侵植物飞机草（Chromolaena odorata）入侵中的作用,在同质种植园中的两个养分条件下比较研究了飞机草原产地和入侵地各8个种群叶片单宁含量,茎和叶片总酚、半纤维素和纤维素含量以及总生物量的差异。结果表明,在两个养分条件下,飞机草入侵种群和原产地种群总生物量差异均不显著,入侵种群茎和叶片半纤维素含量均低于原产地种群;在高养分条件下,飞机草入侵种群叶片纤维素含量低于原产地种群;在低养分条件下,入侵种群茎和叶片总酚含量高于原产地种群。由此,我们得出结论：在入侵地,飞机草未发生加快生长的进化,但数量型化学防御物质发生了遗传变化;降低的半纤维素和纤维素含量可能是对入侵地专性天敌缺乏做出进化响应的结果,提高的总酚含量有利于飞机草防御入侵地的广谱天敌。     

Scavenger guild and consumption patterns of an invasive alien fish species in a Mediterranean wetland

Invasive Alien Species (IAS) alter ecosystems, disrupting ecological processes and driving the loss of ecosystem services. The common carp Cyprinus carpio is a hazardous and widespread IAS, becoming the most abundant species in many aquatic ecosystems. This species transforms ecosystems by accumulating biomass to the detriment of other species, thus altering food webs. However, some terrestrial species, such as vertebrate scavengers, may benefit from dead carps, by incorporating part of the carp biomass into the terrestrial environment. This study describes the terrestrial vertebrate scavenger assemblage that benefits from carp carcasses in a Mediterranean wetland. We also evaluate the seasonal differences in the scavenger assemblage composition and carrion consumption patterns. Eighty carp carcasses (20 per season) were placed in El Hondo Natural Park, a seminatural mesohaline wetland in south‐eastern Spain, and we monitored their consumption using camera traps. We recorded 14 scavenger species (10 birds and four mammals) consuming carp carcasses, including globally threatened species. Vertebrates consumed 73% of the carrion biomass and appeared consuming at 82% of the carcasses. Of these carcasses consumed, 75% were completely consumed and the mean consumption time of carcasses completely consumed by vertebrates was 44.4 h (SD = 42.1 h). We recorded differences in species richness, abundance, and assemblage composition among seasons, but we did not find seasonal differences in consumption patterns throughout the year. Our study recorded a rich and efficient terrestrial vertebrate scavenger assemblage benefitting from carp carcasses. We detected a seasonal replacement on the scavenger species, but a maintenance of the ecological function of carrion removal, as the most efficient carrion consumers were present throughout the year. The results highlight the importance of vertebrate scavengers in wetlands, removing possible infectious focus, and moving nutrients between aquatic and terrestrial environments.     

氮磷养分共同添加促进退化典型草原恢复的机制

土壤养分含量降低是我国草原退化的主要原因之一,养分添加是退化草原恢复的有效措施,但过量养分添加会导致物种多样性降低。为了探讨适宜的养分添加量以及养分添加促进退化草原恢复的机制,本研究选择内蒙古典型草原的退化群落,通过氮(N)磷(P)养分共同添加梯度试验,研究了退化典型草原在群落、功能群和物种3个组织水平上对养分添加的响应。结果表明: 在群落水平,养分添加显著促进了退化典型草原生物量,但没有降低物种多样性;群落生物量随养分添加水平表现为饱和曲线响应,在12.0 g N·m^-2、3.8 g P·m^-2水平趋于饱和;物种多样性在低养分添加水平(N<9.6 g·m^-2、P<3.0 g·m^-2)较对照显著增加,在其余养分添加水平未发生显著变化。在功能群水平,随着养分添加量的增加,多年生根茎禾草在群落中优势度增加,生物量和密度均显著提高;一年生植物生物量和密度在高养分水平添加下显著增加,多年生丛生禾草和杂类草无显著变化。在物种水平,6个物种对养分添加响应不同,羊草通过增加种群密度和个体大小显著增加了种群生物量;大针茅、冰草和糙隐子草种群生物量没有显著变化;星毛委陵菜和黄囊苔草分别因为降低个体大小和种群密度减少了种群生物量。养分添加作为草原恢复的措施,可以显著增加退化草原生物量和物种多样性,降低植物群落中退化指示种,增加多年生根茎禾草。     

Nutrient management and structural shifts in fish assemblages: Lessons learned from an Area of Concern in Lake Ontario

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The role of periphytes in the shift between macrophyte and phytoplankton dominated systems in a shallow, eutrophic lake (Lake Taihu, China)

Based on experiments of periphyte response to different trophic levels and their impact on macrophyte production,it was found that the periphyte biomass increased with the nutrient con-centrations. Increased trophic level and periphyte biomass resulted in decreased macrophyte photo-synthesis. It was suggested that the periphytes could cause resilience and hysteresis in the system shifts between macrophyte and phytoplankton domination. Other factors,such as fish farming,storm induced waves and mechanical destruction,and high water levels could be the perturbations during the system shifts,but these are not the key factors. Instead,the nutrient loading and periphyte abundance could determine the shift in lake ecosystem between macrophyte and phytoplankton domination. This finding could theoretically elucidate the mechanism of ecosystem shifts between macrophyte and phytoplankton domination.     

Feeding behavior of black carp Mylopharyngodon piceus (Pisces: Cyprinidae) on fry of other fish species and trematode transmitting snail species

Fish raised in aquaculture ponds may get infected with fishborne zoonotic trematodes (FZT) during the nursing stage. Freshwater snails serve as intermediate hosts for FZT and we wanted to explore the possibility of controlling snails by stocking nursery ponds with a few juvenile specimens of the mollusc-eating fish, black carp (Mylopharyngodon piceus). Obviously, the risk that black carp might also prey on the juvenile fishes in nursery ponds should first be assessed. Laboratory trials showed that all size classes of juvenile black carp consumed fry of common carp (Cyprinus carpio) even when offered snails as food; the odds of survival of fry from tanks with medium sized and large black carp was 5.6% and 39.9%, respectively of that of fry in tanks with small sized black carp. Since the large black carp also consumed fewer snails than medium sized fish, we believe that large specimens were stressed in the experimental aquaria. Under semi-field conditions, presence of the black carp had no effect on survival of fry of Oreochromis niloticus and C. carpio both in the absence and presence of snails as alternative food. The black carp consumed most snails offered with the exception of some of the large snails. We conclude that under field conditions, predation by black carp on fish fry is minimal and field trials in nursery ponds are warranted. Due to the risks that black carp pose to native imperiled snails and other molluscs, trials should be restricted to ponds within the fish’s native or existing range.