Artificial Mesocosms Research Articles

An experimental study to assess resistance and resilience strategies of freshwater diatoms to cope with drying in Mediterranean temporary rivers

Temporary rivers are aquatic ecosystems that alternate periods of water flow with dry periods. Diatoms are a group of unicellular microalgae with a high colonizing ability, but little is known about their responses to drying. We carried out different resistance and resilience experiments to evaluate temporal and spatial dispersal capacity of diatoms during the dry period. The resistance was tested experimentally by rehydrating dried biofilms and sediments from temporary rivers, whereas resilience was tested by installing artificial mesocosms along a dry river section. Disconnected pools were also sampled to evaluate their propagule emission capacity. In turn, dogs from the area were sampled to test potential zoochory dispersal capacity. In the resistance experiment, we found living diatoms in all the rehydrated sediments but not in biofilms. Diatoms with mobility traits, high ecological plasticity, and resistance spores presented high, along with typical soil diatoms. In the resilience experiment, all mesocosms hosted living diatoms, which were low-profile, pioneering, and small species. Diatoms found in the mesocosms were also common in the disconnected pools, underscoring the potential role of the latter as a propagule emission zone. Dogs' paws also had living diatoms, which evidences that wild fauna could potentially act as passive diatom vectors.

Alien invasive macrophyte put into the shade: The native floating‐leaved macrophyte Nymphoides indica reduces Cabomba caroliniana growth performance through competition for light

Abstract Alien invasive aquatic macrophytes tend to displace native species and transform diverse macrophyte communities into monospecific stands. It is often thought that superior competitiveness allows alien invaders to achieve this. Cabomba caroliniana is a submersed macrophyte that is highly invasive worldwide and frequently monopolises habitats. However, field observations in Queensland, Australia, found that the native floating attached Nymphoides indica can co‐exist with C. caroliniana, highlighting N. indica as a potential candidate for habitat restoration. To identify factors and processes that regulate the coexistence of these species, we conducted a field survey and two experiments in artificial mesocosms. We found that N. indica leaf areal coverage of the water surface significantly reduced C. caroliniana standing crop biomass in the field. C. caroliniana growth was also linked to water depth; N. indica was not able to grow beyond 2 m depth. There was a small reduction in N. indica root and shoot biomass when co‐cultured with C. caroliniana in our experiment. Therefore, there was reciprocal competitive inhibition between the two species. However, the effect of N. indica on C. caroliniana was much larger. There was evidence that a reduction of C. caroliniana biomass below a threshold of c. 300 g dry mass/m is critical for protecting native submersed macrophyte diversity and abundance. Once C. caroliniana biomass exceeds this threshold, it dominates plant communities and forms high biomass monocultures. The experimental work identified shading as the most important factor that reduces C. caroliniana biomass, corroborating the relationship between leaf areal cover and C. caroliniana biomass found in the field. Based on these findings, N. indica could be useful for restoring the shallow lake littoral habitat, because it suppresses biomass of the invasive species to a level that allows other macrophytes to coexist and additionally increases habitat heterogeneity. Similarly, N. indica could be suitable to restore areas where C. caroliniana was previously removed to reduce the likelihood of future habitat monopolisation by C. caroliniana and realise long‐term ecological benefits from invasive macrophyte management.

Digestive gland microbiome of Pleurobema cordatum: mesocosms induce dysbiosis

ABSTRACT Herein, we characterized the digestive gland (‘gut’) bacterial community (microbiome) of the Ohio pigtoe, Pleurobema cordatum (Rafinesque, 1820), using 16S rRNA gene sequencing. Two populations were compared: wild P. cordatum (n = 5) from the Tennessee River and P. cordatum (n = 9) relocated to artificial mesocosms and exposed to various thermal regimes for 2 weeks. We also characterized the bacterial communities from the habitat (water and sediment) of these wild and mesocosm-held populations. The gut microbiome of wild P. cordatum was dominated by members of the bacterial phylum Tenericutes (72%). By contrast, the gut microbiome of mesocosm-held P. cordatum was dominated by members of the bacterial phylum Proteobacteria (64%). We found no temperature-associated difference in the gut microbiome of mesocosm-held P. cordatum. The bacterial communities of water and sediment from the Tennessee River were diverse and distinct from those of the studied mussels. By contrast, the bacterial communities of water and sediment in the mesocosms were dominated by Proteobacteria. These results suggest that when the studied mussels were moved into artificial rearing environments, their gut microbiome shifted to reflect that of their habitat (i.e. an increase in Proteobacteria). Moreover, the abundance of Tenericutes (also previously reported in other unionids) was reduced from 72% in wild mussels to 3% in mesocosm-held mussels. As a result, we think that mesocosm-held P. cordatum became dysbiotic, which could explain the observed wasting syndrome and associated trickling mortalities in captive P. cordatum.

No support for purported effects of salt-tolerant stream invertebrates on the salinity responses of salt-sensitive stream invertebrates

Increases in salinity can severely affect freshwater ecosystems, and research on the salt tolerances of freshwater species, and factors that modify tolerance, can improve our understanding and prediction of the effects of salinity. In order to test the hypothesis that salt-tolerant freshwater invertebrates can alter the salinity responses of salt-sensitive freshwater invertebrates, publicly available data from a recent study of artificial mesocosms that claimed to confirm this hypothesis were analysed in the present study. No supporting evidence was found for the hypothesis, with apparent salinity responses of salt-sensitive invertebrates varying no more with greater or lesser exposure to salt-tolerant invertebrates than expected merely by chance. The original findings were apparently misguided through unrecognised confounding of the experimental design, inadequate statistical hypothesis testing and accepting ostensible effects without considering their biological and ecological plausibility.

Prey colonization in freshwater landscapes can be stimulated or inhibited by the proximity of remote predators.

Recent findings suggest that the colonization of habitat patches may be affected by the quality of surrounding patches. For instance, patches that lack predators may be avoided when located near others with predators, a pattern known as risk contagion. Alternatively, predator avoidance might also redirect dispersal towards nearby predator-free patches resulting in so-called habitat compression. However, it is largely unknown how predators continue to influence these habitat selection behaviours at increasing distances from outside of their own habitat patch. In addition, current information is derived from artificial mesocosm experiments, while support from natural ecosystems is lacking. This study used bromeliad landscapes as a natural model system to study how oviposition habitat selection of Diptera responds to the cues of a distant predator, the carnivorous elephant mosquito larva. We established landscapes containing predator-free bromeliad habitat patches placed at increasing distances from a predator-containing patch, along with replicate control landscapes. These patches were then left to be colonized by ovipositing bromeliad insects. We found that distance to predators modulates habitat selection decisions. Moreover, different dipteran families had different responses suggesting different habitat selection strategies. In some families, predator-free patches at certain distances from the predator patch were avoided, confirming risk contagion. In other families, these patches received higher numbers of colonists providing evidence of predator-induced habitat compression. We confirm that effects of predators in a natural ecosystem can extend beyond the patch in which the predator is present and that the presence or absence of remote predator effects on habitat selection depends on the distance to predators. The notion that perceived habitat quality can depend on conditions in neighbouring patches forces habitat selection studies to adopt a landscape perspective and account for the effects of both present and remote predators when explaining community assembly in metacommunities.

Effect of different ecological treatment methods on microbial community in black and odorous sediment of urban river

底泥细菌代谢是城市河道底泥代谢物的主要来源，最终决定城市河道的生态状况.本文研究了黑臭河道底泥经添加硝酸钙、生物促生剂和种植沉水植物处理后底泥中细菌群落结构的响应，以期为城市黑臭河道细菌群落的改善和综合治理提供理论依据.实验结果表明：经过不同生态处理后，上覆水中，添加硝酸钙组总氮（TN）含量显著高于对照组，添加生物促生剂组溶解氧浓度显著高于对照组.沉积物中，所有处理组的氧化还原电位值（ORP）均显著高于对照组，种植沉水植物组和添加硝酸钙组TN含量均显著低于对照组，沉积物理化性质得到一定改善.对不同生态处理组底泥细菌群落的研究发现，处理组底泥细菌群落产生了较大变化，且不同处理组细菌群落变化不同，生物促生剂组底泥中细菌的Sobs指数和Chao 1指数显著高于对照组和硝酸钙组，且生物促生剂组Shannon指数和PD指数显著高于硝酸钙组.Proteobacteria（Deltaproteobacteria、Betaproteobacteria、Gammaproteobacteria）、Chloroflexi、Firmicutes、Bacteroidetes和Spirochaetae是各实验组的主要优势菌门；非度量多维尺度分析表明：硝酸钙和生物促生剂的投加可明显改变底泥细菌群落结构组成.在属水平上，uncultured_Anaerolineaceae、Ferribacterium、uncultured_Xanthomonadales_Incertae_Sedis是导致底泥细菌群落发生变化的主要菌属.冗余分析结果表明，底泥ORP的变化是驱动细菌群落结构变化的关键环境因素.;Sediment microorganisms are the main source of sediment metabolism in urban rivers, which ultimately determine the ecological status of the rivers. In this paper, to analyze the effect of different ecological treatments on sediment microbial community, we established artificial mesocosms to mimic sediment status of the black-stinking river with different ecological treatments as calcium nitrate, bio-energizer addition, and submerged macrophytes transplantation. Illumina Miseq sequencing was applied to reveal the bacteria community variations of all treated and untreated sediments. The results showed that in the overlying water, the total nitrogen (TN) content of calcium nitrate addition group was significantly higher than that in the control group, dissolved oxygen concentration in the bio-energizer addition group was significantly higher than that in the control group. In the sediment, the oxidation reduction potential (ORP) values of all the treatment groups were significantly higher than those in the control group; TN content of calcium nitrate addition group and submerged macrophytes transplantation group were both significantly lower than those in the control group, which indicate the improvement of sediment status of treatment group. Bacterial communities were also varied in treatment group, and showed diverse variations with different treatments. The Sobs and Chao 1 microbial diversity indices in the bio-energizer addition group were both significantly higher than those in the control group and calcium nitrate addition group; the Shannon and PD diversity indices for microbes in the bio-energizer addition sediment were both significantly higher than those in calcium nitrate addition group. All sediment microbial communities were dominated by Proteobacteria (Deltaproteobacteria, Betaproteobacteria, Gammaproteobacteria), Chloroflexi, Firmicutes, Bacteroidetes and Spirochaetae phyla. Nonmetric multidimensional scaling analysis showed that the addition of calcium nitrate and bio-energizer can significantly alter the composition of bacterial community structure. Uncultured_Anaerolineaceae, Ferribacterium and uncultured_Xanthomonadales_Incertaeae_Sedis were the main genus causing variations in the bacterial community. Redundancy analysis indicated that the change of sediment ORP is a key environmental factor driving the variation of bacterial community structure.

Adverse effects of mosquito control using Bacillus thuringiensis var. israelensis: Reduced chironomid abundances in mesocosm, semi-field and field studies

The ecological consequences of mosquito control using the larvicide Bacillus thuringiensis israelensis (Bti) are still a matter of debate especially when it comes to adverse effects on non-target but susceptible non-biting midges (Chironomidae). Our work aimed to assess the effects of Bti applied in operational mosquito control rates on chironomid abundances in seasonal flooded freshwater wetlands. We assessed the invertebrate community alongside with aquatic insect emergence rates in studies with increasing ecotoxicological complexity, ranging from artificial mesocosms, over a semi-field approach using enclosures to natural conditions in field studies. Study sites represented different habitats (forest, meadow, floodplain) with regularly Bti treated and untreated temporal wetlands that are located in the Upper Rhine Valley, Germany. Larval chironomids were the most affected group of organism in the altered aquatic invertebrate communities of the Bti treated pond mesocosms. The larvae of the chironomid subfamilies Chironominae and Orthocladiinae were affected by Bti field concentrations while emergence rates of Tanypodinae did not change. The Bti treatment significantly reduced the targeted mosquitoes in the mesocosm and in the field studies. At the same time, however, the application of operational Bti field rates reduced overall chironomid emergence rates to about half of the control rates. The observed abundance reductions occurred independently of the ecological complexity in the study design in artificial mesocosms as well as realistic field conditions. The considerable reduction of the abundant non-target chironomids along with mosquitoes may subsequently lead to unwanted indirect negative effects for birds, bats and other aquatic organisms feeding on midges. Hence, large-scale applications of Bti for mosquito control in seasonal wetlands should be considered more carefully. This is of special importance when these wetlands are parts of national parks, nature reserves or Natura 2000 sites that were created for the protection of nature and environmental health.

Inducing broadcast coral spawning ex situ: Closed system mesocosm design and husbandry protocol.

For many corals, the timing of broadcast spawning correlates strongly with a number of environmental signals (seasonal temperature, lunar, and diel cycles). Robust experimental studies examining the role of these putative cues in triggering spawning have been lacking until recently because it has not been possible to predictably induce spawning in fully closed artificial mesocosms. Here, we present a closed system mesocosm aquarium design that utilizes microprocessor technology to accurately replicate environmental conditions, including photoperiod, seasonal insolation, lunar cycles, and seasonal temperature from Singapore and the Great Barrier Reef (GBR), Australia. Coupled with appropriate coral husbandry, these mesocosms were successful in inducing, for the first time, broadcast coral spawning in a fully closed artificial ex situ environment. Four Acropora species (A. hyacinthus, A. tenuis, A. millepora, and A. microclados) from two geographical locations, kept for over 1 year, completed full gametogenic cycles ex situ. The percentage of colonies developing oocytes varied from ~29% for A. hyacinthus to 100% for A. millepora and A. microclados. Within the Singapore mesocosm, A. hyacinthus exhibited the closest synchronization to wild spawning, with all four gravid colonies releasing gametes in the same lunar month as wild predicted dates. Spawning within the GBR mesocosm commenced at the predicted wild spawn date but extended over a period of 3 months. Gamete release in relation to the time postsunset for A. hyacinthus, A. millepora, and A. tenuis was consistent with time windows previously described in the wild. Spawn date in relation to full moon, however, was delayed in all species, possibly as a result of external light pollution. The system described here could broaden the number of institutions on a global scale, that can access material for broadcast coral spawning research, providing opportunities for institutions distant from coral reefs to produce large numbers of coral larvae and juveniles for research purposes and reef restoration efforts.

Vertical movements through subsurface stream sediments by benthic macroinvertebrates during experimental drying are influenced by sediment characteristics and species traits

Abstract Streambed drying is becoming more common due to climate change and increasing anthropogenic water resource pressures. Subsurface sediments are a potential refuge for benthic macroinvertebrates during drying events in temporary streams. Sediment characteristics are important controls on the distribution of macroinvertebrates in subsurface habitats, but difficulties making observations impedes quantification of vertical movements. Species traits (e.g. subsurface habitat affinity) also influence vertical movements of macroinvertebrates into the subsurface sediments, but most species‐specific responses remain uncharacterised. Transparent artificial mesocosms were used to directly observe the vertical movements of individuals of three aquatic insect nymphs and two crustaceans. Mixtures of three types of transparent sediment of varying particle size were combined to produce six treatments with differing interstitial pore volumes and, hence, differing subsurface porosity. Macroinvertebrate vertical movements were measured during incremental reductions in water level from 5 cm above to 20 cm below the sediment surface. These species comprised a variety of trait categories including feeding group, species affinity to temporary streams and subsurface habitats. Active and passive vertical movements were determined by conducting experiments with both live individuals and their cadavers. Sediment treatment influenced the vertical movements of individuals as reducing subsurface porosity decreased vertical movements for most species. Vertical movement into subsurface sediments in response to water level reduction was the result of active, not passive, movements for all species. Species identity influenced the vertical movements made by individuals. Nemoura cambrica had the highest affinity for temporary streams and subsurface habitats and its vertical movements were unaffected by sediment treatment, generally reaching depths between 20 and 25 cm. Most individuals of species with a weaker subsurface affinity (i.e. the benthic grazer Heptagenia sulphurea and the filter‐feeder Hydropsyche siltalai) became stranded as water levels were reduced in all sediment treatments. Vertical movements of Gammarus pulex and Asellus aquaticus were restricted primarily by pore volume, these taxa becoming stranded most commonly in sediments with smaller interstitial volumes. Our results highlight the need for the development and implementation of river management strategies that increase streambed porosity, allowing macroinvertebrates to access to the saturated subsurface habitat during stream drying.

Efficacy of Labeling Wetlands with Enriched 15N to Determine Amphibian Dispersal

Stable isotope enrichment techniques can aid in understanding dispersal of animals. Pond-breeding amphibians often have spatially disjunct populations that depend on immigration for persistence, yet obtaining direct estimates of dispersal rates among wetlands is challenging. We enriched aquatic mesocosms with 15N to “mark” amphibian larvae and determine the feasibility of using enrichment techniques to study dispersal in pond-breeding amphibians. Because newly metamorphosed amphibians in mark-release-recapture studies may not be recaptured until adulthood, we estimated persistence of the 15N enrichment signature up to 3 years post-metamorphosis. We reared larval marbled salamanders (Ambystoma opacum) in artificial mesocosms dosed with 15NH4Cl, and maintained metamorphs on unlabeled prey for 7 months to estimate the biological half life (BHL) of 15N in tissue. Metamorphs in spiked treatments attained δ15N levels >1000 times higher than reference animals (5 ± 1‰), and levels remained ~225 times higher than controls after 7 months. The average 15N BHL was 2.49 ± 0.24 months, indicating that the elevated signature should be discernible for a minimum of 20–28 months after metamorphosis. Our results suggest that 15N enrichment is feasible for field studies of amphibian dispersal, as metamorphs will retain isotope-enriched tissues that persist until at least the second year of breeding.

The Fate of Endosulfan in Water

Although the use of endosulfan to control cotton pests has declined, this insecticide still has widespread application in agriculture and can contaminate riverine systems as runoff from soil or by aerial deposition. The degradation of endosulfan in pure water at different pH values of 5, 7 and 9 and in river water from the Namoi and the Hawkesbury rivers of New South Wales (NSW), Australia, was studied in the laboratory. Endosulfan transformation into endosulfan sulfate in river water using artificial mesocosms was also investigated. The results show endosulfan is stable at pH 5, with increasing rates of disappearance at pH 7 and pH 9 by chemical hydrolysis. Incubation of endosulfan with river water at pH 8.3 resulted in the disappearance of endosulfan and the formation of endosulfan diol due to the alkaline pH as well as formation of endosulfan sulfate. Although the degradation of endosulfan by Anabaena, a blue-green alga, did not result in the transformation of endosulfan to endosulfan sulfate, we conclude that other microorganisms catalyzed the formation of the sulfate. Significant conversions of endosulfan into endosulfan sulfate were also reported from associated field studies using artificial mesocoms containing irrigation water from rivers inhabitated by micro-macro fauna. From these results, we conclude that the presence of endosulfan sulfate in river water cannot be used to distinguish contamination by runoff from soil from contamination by aerial drift or redeposition.

Effects of the Herbicide Metazachlor on Phytoplankton and Periphyton Communities in Outdoor Mesocosms

AbstractThe effects of the chloroacetanilide herbicide metazachlor have been investigated in outdoor artificial mesocosms. Decreasing phytoplankton densities were caused by the application, however, the communities recovered after 30 to 35 days. Periphyton growth was found to be affected not only by the herbicide application but by the presence of species with different ability to grow on artificial substrates. Zooplankton diversity was small due to low density of ingestible algae species. Oxygen saturation was found to be correlated with the dosage levels of the herbicide in the second half of the study.

Influence of daylight on potential biodegradation of diesel and crude oil in Antarctic seawater

The effects of daylight exposure on Antarctic coastal bacterial communities contaminated by diesel fuel and ‘Arabian light’ crude oil addition were studied in artificial mesocosms during the austral summers of 1991–1992, 1992–1993 and 1993–1994 in the Terre Adelie land area. In order to study the possible influence of photo-oxidation, two sets of experiments were conducted in covered and noncovered batches. Daily sampling allowed regular surveys of the changes of total bacterial abundance, mean cell volumes, saprophytic and hydrocarbon-utilizing bacterial communities. The results clearly revealed a significant response of the Antarctic bacterial community to crude oil addition. Two orders of magnitude increases were observed after contamination. Concomitant enrichments of saprophytic and hydrocarbon-utilizing bacteria occurred during these periods. Hydrocarbon-utilizing bacteria ranged from 0.001% of the total community before contamination to more than 80% after 2 weeks of contamination with crude oil. Chemical analysis of the residual hydrocarbon fraction after 5 weeks of contamination confirmed this potential biodegradation. Solar radiation had no measurable effect upon crude oil-contaminated seawater. In contrast, there was a clear toxic effect upon bacterial communities contaminated with diesel. Data suggest that the initial state of the bacterial communities can play a major role in the potential biodegradation. Some surface bacterial assemblages seem to demonstrate a better resistance to solar radiation than deeper ones.