Decrease In Total Abundance Research Articles

Insight into the impact of air flow rate on algal-bacterial granules: Reactor performance, hydrodynamics by Computational Fluid Dynamics (CFD) and microbial community analysis

This study evaluated the impact of air flow rates on nitrogen removal and the formation of algal-bacterial granules in domestic wastewater treatment, revealing that sodium acetate addition and aeration shifted the microbial community composition. Two separate feedings and the addition of external organic carbon significantly enhanced inorganic nitrogen removal efficiency (over 90 %), which might have contributed to the increased microbial diversity and the relative abundance of denitrifiers such as Acinetobacter. This study also demonstrates that the higher air flow rate (0.5 LPM) resulted in higher nitrification rates (up to 6.4 mg N/L/h) and produced smaller and denser granules. The higher air flow rate also led to the increasing relative abundances of nitrogen-related genera (such as Nitrospira) and the decreasing relative abundances of cyanobacteria and Chlorella. Computational Fluid Dynamics (CFD) simulations revealed that mechanical mixing predominantly generated shear force. Increasing the air flow rate from 0.2 LPM to 0.5 LPM only yielded a 12 % increment in the volume-averaged strain rate, suggesting diminishing returns from higher air flow rates in terms of shear force enhancement. Moreover, the decrease in total abundance of grazers and pathogens along with the operation, including Chytridiomycetes, Sessilida, and Operculariidae, might result from the shear force and the decrease of Chlorella spp.. This study underscores the critical roles of aeration and carbon source management in optimizing the performance and microbial ecology of algal-bacterial systems in wastewater treatment while minimizing energy inputs.

Evaluation of the economic crisis on the conservation of the ichthyofauna in Marine Protected Areas

The use of marine protected areas can be an effective way to simultaneously achieve both conservation and fisheries management objectives. The creation of marine protected areas, in addition to many benefits, also entails several costs, including the need for financing to maintain adequate surveillance and conservation. The recent economic crisis significantly lowered budgets for the maintenance of Spanish Marine Protected Areas, that may have had serious consequences for the marine resources sustainability. In this study we evaluated the indirect impact of the 2008 economic crisis on the conservation of fish stocks in Marine Protected Areas. We compared the number of species, abundance and biomass levels of the ichthyofauna, and abundance and biomass of selected species in two marine reserves (Cabo de San Antonio and Tabarca Island) with control areas, two years before (2008 and 2010) and two years after (2014 and 2015) the budget cut. Results in San Antonio revealed a decrease in total abundance, total biomass and number of species after the crisis, which translates into a decrease in the reserve effect. While in Tabarca no reduction has been observed in these variables, so the reserve effect was maintained after the crisis. We have found that of the 18 species analyzed, in San Antonio the abundance and biomass of 8 and 6 species respectively have decreased after the crisis, while in Tabarca the abundance and biomass of 6 and 8 species respectively have decreased after the crisis. Therefore, surveillance in marine reserves is necessary for the conservation of the species.

Stream Mesocosm Experiments Show no Protective Effects of Calcium on Copper Toxicity to Macroinvertebrates.

Although the concept and modeling of metal bioavailability and toxicity have been well developed based largely on laboratory experiments with standard test species, additional evidence is required to demonstrate their applicability for macroinvertebrates typically found in natural lotic ecosystems. We conducted 10‐day stream mesocosm experiments to test the hypothesis that increased water hardness (in the present study, the calcium [Ca] concentration was increased by adding CaCl2) would mitigate the effects of copper (Cu) on natural benthic macroinvertebrate communities. Exposure of macroinvertebrate communities to 25 μg/L Cu for 10 days in stream mesocosm experiments resulted in significant decreases in total abundance, in number of taxa, and in abundance of many macroinvertebrate taxa. However, the addition of Ca to stream mesocosms and the associated increase in water hardness up to 250 mg/L CaCO3 did not mitigate these effects of Cu on macroinvertebrate communities. The results showed that the hardness‐based water quality criteria for Cu of the US Environmental Protection Agency were not protective under the conditions of relatively high hardness, low alkalinity, and circumneutral pH. In contrast, the water quality criteria based on the biotic ligand model predicted little protective effects of Ca on Cu toxicity, which is consistent with our results. Additional experiments are required to understand the influence of modifying factors on the toxicity of metals to macroinvertebrate communities. Environ Toxicol Chem 2022;41:1304–1310. © 2022 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

Increasing temperatures, diversity loss and reorganization of deep-sea fish communities east of Greenland

In recent years, Arctic and sub-Arctic fish communities have shown extensive reorganization on shelves and in shallow waters, but little is known about the ecological impact of environmental changes in deeper waters. We examined temporal changes (1998-2016) in fish diversity and community structure based on research survey data from East Greenland, over a depth gradient spanning 400 to 1500 m. A northern and a southern continental slope region, 360 km apart, were analysed for temporal changes in water temperature and fish community structure. The bottom water temperature increased by up to 0.2 and 0.5°C, respectively. Contrary to expectations, there was a concomitant loss of species richness of up to 3 and 5 species, respectively, and a decrease in total abundance in both regions. Abundances of individual species displayed different trends between regions, with 3 species of wolf fishes (Anarhichas spp.) and American plaice Hippoglossoides platessoides decreasing in the north and blue antimora Antimora rostrata, Agassiz’ slickhead Alepocephalus agassizii and the roundnose grenadier Coryphaenoides rupestris decreasing in the south. The regional differences may reflect different oceanographic characteristics, as the northern region is more influenced by colder Arctic water, whereas the southern region is primarily influenced by the Subpolar Gyre (SPG). However, the observed temperature increase is expected to be due to an intensifying Atlantic Multidecadal Oscillation and/or anthropogenic climate change and not to SPG changes. The observed changes in biodiversity and community structure associated with warming are likely to affect community dynamics and alter ecosystem functioning.

Richness–abundance relationships for zooplankton in ballast water: temperate versus Arctic comparisons

Abstract Species richness and abundance are two commonly measured parameters used to characterize invasion risk associated with transport vectors, especially those capable of transferring large species assemblages. Understanding the relationship between these two variables can further improve our ability to predict future invasions by identifying conditions where high-risk (i.e. species-rich or high abundance or both) and low-risk (i.e. species-poor and low abundance) introduction events are expected. While ballast water is one of the best characterized transport vectors of aquatic non-indigenous species, very few studies have assessed its magnitude at high latitudes. We assessed the arrival potential of zooplankton via ballast water in the Canadian Arctic by examining species richness, total abundance, and the relationship between the two parameters for zooplankton in ships from Europe destined for the Arctic, in comparison with the same parameters for ships bound for Atlantic Canada and the Great Lakes. In addition, we examined whether species richness and/or total abundance were influenced by temperature change and/or ballast water age for each shipping route. We found that species richness and total abundance for Arctic and Great Lakes ships were significantly lower than those for Atlantic ships. Differences in species richness and total abundance for ships utilizing different shipping routes were mostly related to ballast water age. A significant species richness–total abundance relationship for Arctic and Great Lakes ships suggests that these parameters decreased proportionately as ballast water aged. In contrast, the absence of such a relationship for Atlantic ships suggests that decreases in total abundance were accompanied by little to no reduction in species richness. Collectively, our results indicate that the arrival potential of zooplankton in ballast water of Arctic ships may be lower than or similar to that of Atlantic and Great Lakes ships, respectively.

Effects of sympatric predatory crabs Romaleon polyodon and Cancer plebejus (Decapoda, Brachyura, Cancridae) on sublittoral macrobenthic communities

Although large crabs are recognized as important sediment disturbers influencing the structure of benthic communities, the role of dominant predatory crabs in soft-bottom habitats along the Humboldt Current Ecosystem, remains largely unknown. A field study was conducted, hypothesizing that the digging activity of these predators disturbs the habitat thereby leading to a reduction in individual abundance, biomass and species richness; these changes result in a modified structure of macrobenthic communities. A directed sampling (crab pits vs. reference areas) showed significant reductions in total abundances in pits compared to reference areas, but no differences were observed in taxonomic richness or benthic biomass. Short-term cage experiment showed significant decreases in total abundance and biomass of macroinvertebrates in predator inclusion treatments compared to exclusions and controls. In consequence, our results confirmed that burrowing activities and the generation of small disturbed sediment patches influence the community structure. These results highlight the importance of large cancrid crabs in soft-bottom habitats, where their modification of the physical configuration of the sediment affects community structure over small spatial scales. Crabs are thus an important source of spatial heterogeneity of the sea-floor landscape. This ecological role must be considered in management strategies of the extensive artisanal fishery for these crabs, as current evidence is showing increasing populations of intermediate predators (like cancrid crabs) in many benthic habitats in response to the depletion of top predators.

Differences in elimination efficiencies of Escherichia coli in freshwater and seawater as a result of TiO2 photocatalysis

The effects of UV irradiation on the respiration and survival of Escherichia coli in various concentrations of aqueous NaCl were investigated in the presence of a photocatalyst. In this study, we anticipated that the photocatalysis of residual chlorine generated in a solution containing Cl− would result in bacterial elimination. Our results indicated a gradual reduction in the E. coli survival ratio in freshwater; however, no decrease in total abundance was observed during 8 h of photocatalysis with UV irradiation. Conversely, the survival ratio of E. coli in the artificial seawater decreased drastically as a consequence of photocatalysis, with a concomitant decrease in total abundance. These results revealed that the chlorinated active species that formed on the photocatalyst surface influenced the observed inactivation.

Trophic and functional cascades in tropical versus temperate aquatic microcosms

Inverse trophic cascades are a well explored and common consequence of the local depletion or extinction of top predators in natural ecosystems. Despite a large body of research, the cascading effects of predator removal on ecosystem functions are not as well understood. Developing microcosm experiments, we explored food web changes in trophic structure and ecosystem functioning following biomass removal of top predators in representative temperate and tropical rock pool communities that contained similar assemblages of zooplankton and benthic invertebrates. We observed changes in species abundances following predator removal in both temperate and tropical communities, in line with expected inverse effects of a trophic cascade, where predation release benefits the predator’s preys and competitors and impacts the preys of the latter. We also observed several changes at the community and ecosystem levels including a decrease in total abundance and mean trophic level of the community, and changes in chlorophyll-a and total dissolved particles. Our results also showed an increase in variability of both community and ecosystem processes following the removal of predators. These results illustrate how predator removal can lead to inverse trophic cascades both in structural and functioning properties, and can increase variability of ecosystem processes. Although observed patterns were consistent between tropical and temperate communities following an inverse cascade pattern, changes were more pronounced in the temperate community. Therefore, aquatic food webs may have inherent traits that condition ecosystem responses to changes in top-down trophic control and render some aquatic ecosystems especially sensitive to the removals of top predators.

A review of the spatial extent of fishery effects and species vulnerability of the deep-sea demersal fish assemblage of the Porcupine Seabight, Northeast Atlantic Ocean (ICES Subarea VII)

Abstract Priede, I. G., Godbold, J. A., Niedzielski, T., Collins, M. A., Bailey, D. M., Gordon, J. D. M., and Zuur, A. F. 2011. A review of the spatial extent of fishery effects and species vulnerability of the deep-sea demersal fish assemblage of the Porcupine Seabight, Northeast Atlantic Ocean (ICES Subarea VII). – ICES Journal of Marine Science, 68: 281–289. We review information from scientific trawl surveys carried out between 1977 and 2002 in the Porcupine Seabight and Abyssal Plain area of the Northeast Atlantic (240–4865 m water depth). Since the late 1980s, commercial bottom-trawl fisheries targeting mainly roundnose grenadier (Coryphaenoides rupestris), black scabbardfish (Aphanopus carbo), and orange roughy (Hoplostethus atlanticus) have been operating at depths of 500–1500 m, intersecting the depth ranges of 77 demersal fish species that would therefore be vulnerable to fishery effects. Comparisons of trawls pre-1989 and post-1997 indicate a significant decrease in total abundance of demersal fish down to 2500 m. Detailed analyses of the 15 most-abundant species showed that nine species with depth ranges within the commercial fishing depth have decreased in abundance. Other species were either not affected (Bathypterois dubius) or only affected at the shallow end of their range (Coryphaenoides guentheri). Species with a minimum depth of occurrence >1500 m (Coryphaenoides armatus and Coryphaenoides leptolepis) increased in abundance over part of their depth range. Decreases in abundance are probably caused by commercial fishing activities, an effect that is transmitted downslope by removal of fish at the shallow end of their depth range, resulting in declines at the deeper end of the depth range. The estimated fishery area is ca. 52 000 km2, but the potential impact probably extends to ca. 142 000 km2 and to many non-target species.

Loss of Ribosomal Protein L11 Affects Zebrafish Embryonic Development through a p53-Dependent Apoptotic Response

Ribosome is responsible for protein synthesis in all organisms and ribosomal proteins (RPs) play important roles in the formation of a functional ribosome. L11 was recently shown to regulate p53 activity through a direct binding with MDM2 and abrogating the MDM2-induced p53 degradation in response to ribosomal stress. However, the studies were performed in cell lines and the significance of this tumor suppressor function of L11 has yet to be explored in animal models. To investigate the effects of the deletion of L11 and its physiological relevance to p53 activity, we knocked down the rpl11 gene in zebrafish and analyzed the p53 response. Contrary to the cell line-based results, our data indicate that an L11 deficiency in a model organism activates the p53 pathway. The L11-deficient embryos (morphants) displayed developmental abnormalities primarily in the brain, leading to embryonic lethality within 6–7 days post fertilization. Extensive apoptosis was observed in the head region of the morphants, thus correlating the morphological defects with apparent cell death. A decrease in total abundance of genes involved in neural patterning of the brain was observed in the morphants, suggesting a reduction in neural progenitor cells. Upregulation of the genes involved in the p53 pathway were observed in the morphants. Simultaneous knockdown of the p53 gene rescued the developmental defects and apoptosis in the morphants. These results suggest that ribosomal dysfunction due to the loss of L11 activates a p53-dependent checkpoint response to prevent improper embryonic development.

The influence of a Hawaiian seamount on mesopelagic micronekton

The distribution of mesopelagic micronekton (small fishes, crustaceans, and cephalopods) is not uniform throughout the oceans. Seamounts are a feature that may influence the abundance, biomass, diversity, and taxonomic composition of a community of mesopelagic micronekton by introducing a hard substrate and benthic predators into a realm normally devoid of these. Cross Seamount, located roughly 295 km south of the island of Oahu, Hawaii, has a summit that is 330 m below sea surface and has a diameter of approximately 8 km. Using a large, modified Cobb trawl, samples were taken both directly over and away from the summit of Cross Seamount to sample the deep scattering layer during the day and the shallow scattering layer during the night. Trawls were conducted during two cruises in the spring of 2005 and 2007. All organisms collected were identified to the lowest taxonomic level possible resulting in a description of the local assemblage of mesopelagic micronekton over and around Cross Seamount. Results indicate that there is a significant decrease in total abundance of organisms and an absence of certain diel vertically migrating taxa directly over the summit as opposed to away. While predation might be partly the cause, the taxa that are absent from the summit all have daytime depths that are deeper than the depth of the summit indicating that avoidance may be a major reason for the low abundance. The overall taxonomic composition of the community over the summit is dominated numerically by epipelagic juvenile fishes and stomatopod larvae. This is in opposition to that found away from the summit where the community is dominated numerically by mesopelagic fishes, mostly myctophid fishes, with the epipelagic juvenile fishes and stomatopod larvae contributing little to the overall taxonomic composition. The community over the summit also contains two species that appear to be found in higher abundance over the summit as opposed to away and may be considered as seamount-associated species. These are a cranchiid squid, Liocranchia reinhardti, and a myctophid fish, Benthosema fibulatum. This seamount is known to impact the mesopelagic micronekton community and tuna community, but the mechanisms behind these impacts are largely unknown at this time.

Changes in relative abundance of phytoplankton in arsenic contaminated waters at the Ron Phibun district of Nakhon Si Thammarat province, Thailand

This research project examines the changes in relative abundance of phytoplankton in arsenic contaminated waters at the Ron Phibun district of Nakhon Si Thammarat Province during July 2004 to June 2005. The chosen locations were four dredge ponds (abandoned tin mines) at Ron Phibun and Hintok sub-districts and two in dug ponds for community use at Saothong and Khuankoey sub-districts. The dominant phytoplankton in all study locations were cyanobacteria except for one location in the Saothong sub-district. The results demonstrated that there were major seasonal variations in phytoplankton abundance and in dominant genera associated with all sampling locations, and these were particularly evident during the rainy period. In general, all sampling locations showed a decrease in total abundance during the rainy season, but changes to the dominant population at any one location were different from all the others.

Evidence of population genetic effects of long-term exposure to contaminated sediments—A multi-endpoint study with copepods

In the environment, pollution generally acts over long time scales and exerts exposure of multiple toxicants on the organisms living there. Recent findings show that pollution can alter the genetics of populations. However, few of these studies have focused on long-term exposure of mixtures of substances. The relatively short generation time (ca. 4–5 weeks in sediments) of the harpacticoid copepod Attheyella crassa makes it suitable for multigenerational exposure studies. Here, A. crassa copepods were exposed for 60 and 120 days to naturally contaminated sediments (i.e., Svindersviken and Trosa; each in a concentration series including 50% contaminated sediment mixed with 50% control sediment and 100% contaminated sediment), and for 120 days to control sediment spiked with copper. We assayed changes in F ST (fixation index), which indicates if there is any population subdivision (i.e., structure) between the samples, expected heterozygosity, percent polymorphic loci, as well as abundance. There was a significant decrease in total abundance after 60 days in both of the 100% naturally contaminated sediments. This abundance bottleneck recovered in the Trosa treatment after 120 days but not in the Svindersviken treatment. After 120 days, there were fewer males in the 100% naturally contaminated sediments compared to the control, possibly caused by smaller size of males resulting in higher surface: body volume ratio in contact with toxic chemicals. In the copper treatment there was a significant decrease in genetic diversity after 120 days, although abundance remained unchanged. Neither of the naturally contaminated sediments (50 and 100%) affected genetic diversity after 120 days but they all had high within treatment F ST values, with highest F ST in both 100% treatments. This indicates differentiation between the replicates and seems to be a consequence of multi-toxicant exposure, which likely caused selective mortality against highly sensitive genotypes. We further assayed two growth-related measures, i.e., RNA content and cephalothorax length, but none of these endpoints differed between any of the treatments and the control. In conclusion, the results of the present study support the hypothesis that toxicant exposure can reduce genetic diversity and cause population differentiation. Loss of genetic diversity is of great concern since it implies reduced adaptive potential of populations in the face of future environmental change.

Impacts of a Toxic Microcystis Bloom on the Macroinvertebrate Fauna of Lake Elphinstone, Central Queensland, Australia

The biological, physical and chemical properties of Lake Elphinstone were studied during a dense, toxic cyanoprokaryote bloom dominated by Microcystis. Decreases in total abundance and richness in macroinvertebrate communities coincided with increases in Microcystis toxicity. Water quality was characterized by high light attenuation values caused by abiogenic turbidity and shading and absorbance from thick algal scums. The study highlights the potential for multidimensional environmental impacts associated with toxic cyanoprokaryote blooms, and the consequent implications for the management of shallow, inland and tropical lakes that are susceptible to toxic blooms.