Can heterotrophic uptake of dissolved organic carbon and zooplankton mitigate carbon budget deficits in annually bleached corals?

Annual coral bleaching events due to increasing sea surface temperatures are predicted to occur globally by the mid-century and as early as 2025 in the Caribbean, and severely impact coral reefs. We hypothesize that heterotrophic carbon (C) in the form of zooplankton and dissolved organic carbon (DOC) is a significant source of C to bleached corals. Thus, the ability to utilize multiple pools of fixed carbon and/or increase the amount of fixed carbon acquired from one or more pools of fixed carbon (defined here as heterotrophic plasticity) could underlie coral acclimatization and persistence under future ocean-warming scenarios. Here, three species of Caribbean coral—Porites divaricata, P. astreoides, and Orbicella faveolata—were experimentally bleached for 2.5 weeks in two successive years and allowed to recover in the field. Zooplankton feeding was assessed after single and repeat bleaching, while DOC fluxes and the contribution of DOC to the total C budget were determined after single bleaching, 11 months on the reef, and repeat bleaching. Zooplankton was a large C source for P. astreoides, but only following single bleaching. DOC was a source of C for single-bleached corals and accounted for 11–36 % of daily metabolic demand (CHAR_DOC), but represented a net loss of C in repeat-bleached corals. In repeat-bleached corals, DOC loss exacerbated the negative C budgets in all three species. Thus, the capacity for heterotrophic plasticity in corals is compromised under annual bleaching, and heterotrophic uptake of DOC and zooplankton does not mitigate C budget deficits in annually bleached corals. Overall, these findings suggest that some Caribbean corals may be more susceptible to repeat bleaching than to single bleaching due to a lack of heterotrophic plasticity, and coral persistence under increasing bleaching frequency may ultimately depend on other factors such as energy reserves and symbiont shuffling.     

Experimental studies of the effect of beaver (<Emphasis Type="Italic">Castor fiber</Emphasis> L.) vital activity products on the formation of zooplankton structure (by the example of growth of two cladoceran species of different sizes)

Experiments in microcosms have demonstrated that beaver vital activity products (BVAPs) promote an increase in concentrations of total nitrogen (N) and total phosphorus (P), a decrease in the N/P value in water, and an increase in the abundance and biomass of bacterioplankton. Under such conditions, the abundance and biomass of small Ceriodaphnia dubia Richard and large Daphnia (Ctenodaphnia) magna Straus, which live separately, increase. The coexistence of these cladocerans in microcosms under the BVAP influences results in a high increase in the abundance and biomass of D. magna; in similar experiments without the influence of BVAP, Ceriodaphnia dubia becomes more abundant. The results of bioassay demonstrate that the number of newborns of Ceriodaphnia dubia decreases in water where Daphnia magna is numerous owing to BVAPs. It is suggested that the vital activity products of large representatives of the genus Daphnia inhibit the fecundity of small species of Cladocera. This fact, along with the high competitiveness of large cladoceran species under conditions of a high level of nutritive base, determine the formation of zooplankton communities in beaver ponds which are characterized by a high abundance and biomass and low uniformity     

Changes in the structural parameters of the summer zooplankton in the pelagic zone of Lake Sevan (Armenia) during an increase in fish abundance and biomass

Features of the composition and structure of the summer zooplankton in the pelagic zone of Lake Sevan in years that were characterized by different abundances and biomasses of fish are described. It is shown that the species diversity of the community and the specific number of species of zooplankteurs, the quantity of Copepods in the total abundance and biomass of zooplankton, as well as the value of the Shannon index and the trophic coefficient, increased upon an increase in the fish abundance. At the same time, the total biomass of zooplankton and biomass of cladocerans decreased, among which the density and biomass of the larger and more colored Daphnia (Ctenodaphnia) magna Straus decreased, but the density and biomass of D. (Daphnia) hyalina Leydig and Diaphаnosoma brachyurum Lievin increased.     

Zooplankton of the Patagonian slope and adjacent waters in the autumn

In autumn, from March until May 1988 in the Patagonian shelf and slope zones, the system of the water current was modified and water temperature decreased. The biomass of seston and abundance of zooplankton decreased simultaneously, especially those of the subantactric species Calanus simillimus. Zooplankton organisms started their descent to deeper waters. The Antarctic species Rhincalanus gigas was common in the upper layers in March. In May, R. gigas was rare and occurred in deeper layers. Subtropical zooplankton species dominated in the shelf zone, while subantartic species dominated in the slope zone within the Falkland current. In May, the abundance of shelf species in the slope zone increased due to weakening of the Falkland current and its dislocation to the east. The zooplankton biomass and abundance increased at the zone of water divergence in the east and at the slope frontal zone in the west.     

Numerical Modeling of Vertical Distribution of Living and Dead Copepods <Emphasis Type="Italic">Arctodiaptomus salinus</Emphasis> in Salt Lake Shira

In deep stratified lakes, the processes of growth and mortality of zooplankton populations result in uneven vertical distributions of living and dead organisms in a water column. The carcasses in the water are removed by sinking, degradation due to microbial decomposition and detritivory, etc. In the case of the epilimnion maximum of zooplankton, provided that the degradation prevails over the sinking, the downward flux of carcasses exponentially decays with depth. This vertical profile of dead organisms, demonstrating the decline in meta- and hypoliminon, can be described by the numerical model presented in this paper. The model approximation of the field data makes it possible to determine non-predator mortality rate m and degradation rate D in relative terms (m/v and D/v, v—sinking velocity) or absolute values (with defined v). For the case of the copepod population of Arctodiaptomus salinus in Lake Shira, the calculated m and D (medians of 0.13 and 0.26 day^–1, respectively) were in a good agreement with the literature data. This method also gives the advantage of using the depth-dependent sinking velocity v.     

Influence of Aquatic Plants of Different Ecological Groups on Zooplankton Distribution and Abundance

The distribution of zooplankton has been studied in a waterbody whose entire area is occupied by phytocenoses with the dominance of plants of different ecological groups. It is shown that, in the phytocoenosis of the submerged hydrophyte Elodea canadensis, zooplankton is involved in the classical grazing trophic web. The zooplankton community in this phytocoenosis is mainly made up by algaephagous species. In the habitats occupied by emergent plant Carex riparia, zooplankton is more closely associated with the components of the “microbial loop,” where the most abundant groups are predators and bacterio-detritophagous species.     

Effect of the vital activity products of beaver (<Emphasis Type="Italic">Castor fiber</Emphasis> L.) on the formation of zooplankton structure: Changes in the quantitative parameters of two cladocera species of different sizes in a beaver pound (in situ experiment)

The experiments were performed in microcosms situated on a control site and on a site regulated by beavers. Two cladoceran species of different sizes were placed in microcosms in different proportions. It was found that the vital activity products of Castor fiber L. promote an increase in the concentration of total phosphorus (P), a decrease in the N/P ratio in water, and an increase in the chlorophyll a concentration and the abundance and biomass of bacterioplankton. In such conditions, the abundance and biomass of the large species Daphnia (Ctenodaphnia) magna Straus was increased to the greatest extent when compared with background values when it was placed in combination with Ceriodaphnia dubia Richard or without it. Moreover, in the case of the combination of two crustacean species in microcosms, the abundance of C. dubia was lower when compared with the control site, while the abundance of D. magna was higher. The results of a bioassay showed that the productivity of C. dubia decreases in waters where D. magna is most abundant. We concluded that the formation of zooplankton in beaver ponds with specific features determined by the presence of large cladoceran species is provided by changes in the quantitative and qualitative parameters of food resources. This contributes to the massive distribution of large D. magna and its competitive relations with small C. dubia. According to the results of a bioassay, the vital activity products of D. magna can inhibit the fecundity of C. dubia.     

Studies on the zooplankton community of a shallow lagoon of the Southern Baltic Sea: long-term trends,seasonal changes,and relations with physical and chemical parameters

The Darß-Zingst Lagoon, a coastal inlet of the southern Baltic Sea, was subject to extended monitoring. The biomass data of zooplankton from 1969 to 2001 were used to analyze long-term trends and to correlate zooplankton biomass with abiotic factors. The dominant species in the lagoon were the calanoid copepods Eurytemora affinis and Acartia tonsa, and the rotifer Keratella cochlearis f. tecta. In the long-term trend, two pronounced changes in zooplankton biomass and species composition were observed. They are discussed in connection with a shift in dominance from macrophytes to phytoplankton and the invasion of a polychaet species into the lagoon. Significant relations between zooplankton data and abiotic parameters were found. While temperature, precipitation and NAO winter index correlated positively with copepods and negatively with rotifers, the relationships were inversely for pH-value and duration of ice cover.     

Evidence for Changes in Estuarine Zooplankton Fostered by Increased Climate Variance

Estuaries are among the most valuable aquatic systems in terms of their services to human welfare. They offer an ideal framework to assess multiscale processes linking climate and food web dynamics through the hydrological cycle. Resolving food web responses to climate change is fundamental to resilience management of these threatened ecosystems under global change scenarios. Here, we examined the temporal variability of the plankton food web in the Mondego Estuary, central Iberian Peninsula, over the period 2003 to 2012. The results pointed out a cascading effect from climate to plankton communities that follow a non-stationary behavior shaped by the climate variance envelope. Concurrent changes in hydrographic processes at the regional, that is, upwelling intensity, and local, that is, estuarine hydrology, scales were driven by climatic forcing promoted by the North Atlantic Oscillation; the influence of which permeated the physical environment in the estuary affecting both autotrophic and heterotrophic communities. The most conspicuous change arose around 2008 and consisted of an obvious decrease in freshwater taxa along with a noticeable increase in marine organisms, mainly driven by gelatinous zooplankton. The observed increase in small-sized cosmopolitan copepods, that is, Clausocalanus arcuicornis, Oithona plumifera, thermophilic species, that is, Penilia avirostris, and gelatinous zooplankton suggests a structural change in the Mondego plankton community. These results provide empirical support to the expectation that expanding climate variance changes plankton structure and functioning, likely fostering trophic interactions in pelagic food webs.     

The Plankton Community of Sevan Lake (Armenia) after Invasion of <Emphasis Type="Italic">Daphnia</Emphasis> (<Emphasis Type="Italic">Ctenodaphnia</Emphasis>) <Emphasis Type="Italic">magna</Emphasis> Straus, 1820

The appearance of Daphnia (Ctenodaphnia) magna Straus, 1820 in the pelagial of Sevan Lake caused significant changes in the communities of planktonic algae, bacteria, and heterotrophic nanoflagellates. Phytoplankton and nanoflagellates were the most affected by the direct impact of D. magna, and the number and biomass of bacteria increased due to the reduction in the trophic pressure of the protists. It was also facilitated by the increased supply of phosphorus as a result of the activity of the cladocerans, as well as the decrease in the number and biomass of phytoplankton, which competes with heterotrophic bacteria for the nutrients.     

Different thermal stimuli initiate hatching of <Emphasis Type="Italic">Daphnia</Emphasis> diapausing eggs originating from lakes and temporary waters

The simultaneous hatching of Daphnia resting eggs from a number of different lakes and ponds using one set of hatching cues can be difficult to achieve as environmental conditions differ considerably between water bodies. Therefore, optimal hatching conditions for ephippial eggs originating from shallow temporary waters may differ from those found in large lakes. The aim of our study was to compare the optimal thermal conditions for hatching ephippial eggs of Daphnia found in permanent lakes and those from shallow temporary ponds. We used ephippial eggs of Daphnia from the longispina species complex originating from two temporary city ponds and two deep lakes in Poland. The ephippia were protected against overheating at all stages of the field and laboratory work to prevent activation or killing of the eggs. After a refractory period (imposed storage in cool and dark conditions), ephippia were incubated at six different temperatures (6, 9, 12, 15, 18 and 21 °C) under a 16:8 L:D light regime. Our results indicate that hatching of resting eggs of Daphnia that inhabit lakes or ponds may require different thermal conditions. The hatching success of ephippial eggs originating from temporary waters was relatively high (30–56%) at all tested incubation temperatures, while for the ephippial eggs from the deep lakes it was lower (7–37%) and inversely related to water temperature. The divergent hatching responses of the ephippial eggs originating from temporary pools and lakes may reflect the typical thermal conditions during hatching in their native habitats. While in the deep lakes of the temperate zone Daphnia hatching typically occurs during the low water temperatures of early spring, in shallow ponds Daphnia hatching may occur throughout the year at varying water temperatures, from a few to over a dozen degrees Celsius.     

The metagenomic approach to characterization of the microbial community shift during the long-term cultivation of anammox-enriched granular sludge

A metagenomic approach was used to investigate how the microbial community composition changes when an anammox-based granular sludge reactor is seeded with nitritation-anammox biomass from a wastewater treatment plant. In the seed sample, the abundance of Candidatus Kuenenia stuttgartiensis was similar to Candidatus Jettenia caeni (12.63 vs. 11.68%). This biomass was typical in terms of microbial nitrogen conversion; both ammonia (Nitrosomonas sp.) and nitrite (Nitrospira sp.) oxidizing bacteria were detected. In the lab-scale reactor, Candidatus Kuenenia stuttgartiensis and Candidatus Jettenia caeni bacteria were also present in equal proportions (18.57 vs. 20.89%). On the contrary, Candidatus Nitrospira defluvii bacteria were highly abundant in this reactor, but no known ammonia-oxidizing bacteria were detected. In light of recent studies showing that Nitrospira sp. are capable of complete nitrification, the results presented here may well indicate that both stages of nitrification in the anammox-based granular sludge reactor were performed by this bacteria.     

Phylogenetic and functional prokaryotic diversity in the Hoito-Gol mesothermal mineral spring (Eastern Sayan Mountains,Buryat Republic)

High-throughput sequencing was used for comparative analysis of microbial communities of the water and mat from the Hoito-Gol mesothermal mineral sulfide spring (Eastern Sayan Mountains, Buryat Republic). Activity of microbial communities was determined. While both spring biotopes were dominated by members of three bacterial phyla—Proteobacteria, Bacteroidetes, and Firmicutes—they differed drastically in the composition of predominant phylotypes (at the genus level). In the water, the organisms widespread in aquatic environments were predominant, mostly aerobic chemoorganotrophs of the genera Acinetobacter, Pedobacter, and Flavobacterium. In the microbial mat, the organisms actively involved in the sulfur cycle predominated, including sulfur-reducing bacteria Sulfurospirillum, sulfate-reducing deltaproteobacteria, sulfuroxidizing chemoautotrophic bacteria, anoxygenic phototrophic bacteria of the phyla Chloroflexi and Chlorobi, as well as purple bacteria belonging to the α-, ß-, and γ-Proteobacteria. Microbial mats of the spring exhibited higher phylogenetic diversity compared to high-temperature mats containing photosynthetic microorganisms.     

Microbial community of freshwater sponges in Lake Baikal

The microbial community of Baikal sponges has been studied in five species belonging to the genera Swartschewskia, Baicalospongia, and Lubomirskia of the endemic family Lubomirskiidae. The results show that the total numbers of bacteria and bacterioplankton production have an effect on the growth of L. baicalensis body. Bacteria of the genera Pseudomonas, Bacillus, Micrococcus, Sarcina, Flavobacterium, Arthrobacter, and Acinetobacter living in the sponges are representatives of the Baikal bacterioplankton. Actinomycetes of the genera Streptomyces and Micromonospora are a permanent component of the cultivable sponge microbial community. The numbers and enzyme activities of heterotrophic, oligotrophic, and psychrophilic bacteria isolated from different sponge species and from the ambient water in autumn and in winter have been estimated.     

An analysis of long-term winter data on phytoplankton and zooplankton in Neusiedler See,a shallow temperate lake,Austria

In the last 40 years, the shallow steppe lake, Neusiedler See, was ice covered between 0 and 97 days. The North Atlantic Oscillation (NAO) as well as the Mediterranean Oscillation affected the lake and its conditions during winter. Both climate indices correlated negatively with the duration of ice cover and the timing of ice-out. Average winter phytoplankton biomass increased from less than 0.2 (0.05–0.84) mg FM l^?1 in the late 1960s/beginning of 1970s to 3.1 (1.72–5.61) mg FM l^?1 in the years 2001–2004. The increase in annual winter biomass of phytoplankton was associated with a significant shift in the composition of the algal assemblage. In the winter 1997/1998, diatoms contributed between 40 and 80% to the phytoplankton biomass while in 2006/2007 cyanoprokaryotes contributed 46%. Mean chlorophyll-a concentrations during winter were significantly correlated with those of total phosphorus (P_tot). Together with cold-water species (rotifer Rhinoglena fertöensis), perennial, eurythermal ones (copepod Arctodiaptomus spinosus) contributed to the zooplankton community. High zooplankton numbers were encountered when rotifers, particularly when densities of Rhinoglena fertöensis were high (r ² = 0.928). Zooplankton abundance and biomass varied from year to year but correlated positively with Chl-a (biomass ? r ² = 0.69; numbers ? r ² = 0.536). Winter zooplankton populations were primarily influenced by winter conditions, but in early winter also by survival of autumn populations, i.e., the more adults of Arctodiaptomus spinosus survived into winter, the higher was the zooplankton biomass in early winter. Phyto- and zooplankton dynamics in shallow lakes of the temperate region seem to critically depend on the biomass in autumn and on winter conditions, specifically on ice conditions and thus are related to climate signals such as the NAO.     

Potential Outdoor Cultivation of Green Microalgae Based on Response to Changing Temperatures and by Combining with Air Temperature Occurrence

In this study, our working hypothesis was to examine whether temperature alters biomass and metabolite production by microalgae according to strain. We also addressed whether it is possible to choose a strain suitable for growing in each season of a given region. A factorial experiment revealed a significant interaction between chlorophylls a and b (Chl a and Chl b), carotenoid/Chl (a?+?b) ratio, biomass and total lipid productivity of six green microalgae (four Chlorella spp., Chlorella sorokiniana and Neochloris oleoabundans) after 15 days at four temperatures. At 39/35 °C, two Chlorella sp. strains (IPR7115 and IPR7117) showed higher total carotenoids/Chl (a?+?b) (0.578 and 0.830), respectively. N. oleoabundans had the highest Chl a (8210 μg L^?1) and Chl b (1909 μg L^?1) at 19/15 °C and highest maximum dry biomass (2900 mg L^?1), specific growth rate (0.538 day^?1) and total lipids (1003 mg L^?1) at 15/8 °C. We applied a method to infer the growth of these six green microalgae in outdoor ponds, as based on their response to changing temperatures and by combining with historical data on day/night air temperature occurrence for a given region. We conclude that the use of regionalized maps based on air temperature is a good strategy for predicting microalgal cultivation in outdoor ponds based on their features and tolerance to changing temperature.     

Native and exotic foundation grasses differ in traits and responses to belowground tri-trophic interactions

A plant’s growth and fitness are influenced by species interactions, including those belowground. In primary successional systems, belowground organisms are known to have particularly important control over plant growth. Exotic plant invasions in these and other habitats may in part be explained by altered associations with belowground organisms compared to native plants. We investigated the growth responses of two foundation grasses on Great Lakes sand dunes, the native grass Ammophila breviligulata and the exotic grass Leymus arenarius, to two groups of soil organisms with important roles in dune succession: arbuscular mycorrhizal fungi (AMF) and plant-parasitic nematodes (PPN). We manipulated the presence/absence of two generalist belowground species known to occur in Great Lakes dunes, Rhizophagus intraradices (AMF) and Pratylenchus penetrans (PPN) in a factorial greenhouse experiment and assessed the biomass production and root architectural traits of the plants. There were clear differences in growth and above- and belowground architecture between Ammophila and Leymus, with Leymus plants being bigger, taller, and having longer roots than Ammophila. Inoculation with Rhizophagus increased above- and belowground biomass production by ~32% for both plant species. Inoculation with Pratylenchus decreased aboveground biomass production by ~36% for both plant species. However belowground, the exotic Leymus was significantly more resistant to PPN than the native Ammophila, and gained more benefits from AMF in belowground tri-trophic interactions than Ammophila. Overall, our results indicate that differences in plant architecture coupled with altered belowground interactions with AMF and PPN have the potential to promote exotic plant invasion.     

Study of ectoparasitism of ultramicrobacteria of the genus <Emphasis Type="Italic">Kaistia</Emphasis>, strains NF1 and NF3 by electron and fluorescence microscopy

Transmission electron and fluorescence microscopy was used to study the character of the interaction of free-living ultramicrobacterial (UMB) strains NF1 and NF3, affiliated with the genus Kaistia, and seven species of gram-positive and gram-negative heterotrophic bacteria. Strains NF1 and NF3 were found to exhibit parasitic activity against gram-positive Bacillus subtilis and gram-negative Acidovorax delafildii. UMB cells are tightly attached to the envelopes of the victim cells and induce their lysis, thus demonstrating the features of typical ectoparasitism. The selectivity of parasitism of the studied UMB to the victim bacteria has been shown: only two soil microorganisms of the seven test objects, B. subtilis ATCC 6633 and an aerobic gramnegative bacterium A. delafildii 39, were found to be sensitive to UMB attack. Other bacteria (Micrococcus luteus VKM Ac-2230, Staphylococcus aureus 209-P, Pseudomonas putida BS394, Escherichia coli C 600, and Pantoea agglomerans ATCC 27155) were not attacked by UMB. It was established for the first time that free-living UMB may be facultative parasites not only of phototrophic bacteria, as we have previously demonstrated [1], but of heterotrophic bacteria as well. The UMB under study seem to play an important role in the regulation of the quantity of microorganisms and in the functioning of microbial communities in some natural ecotopes.     

Artificial reefs for sea cucumber aquaculture confirmed as settlement substrates of the moon jellyfish <Emphasis Type="Italic">Aurelia coerulea</Emphasis>

In coastal areas with a high intensity of human activities, expansion of artificial structures may enhance Aurelia spp. blooms because these constructions may provide additional substrates for the settlement and proliferation of the polyps. In the present study, the possible occurrence and distribution of Aurelia coerulea ephyrae and polyps were investigated in sea cucumber (Apostichopus japonicus) culture ponds that contain huge amounts of artificial structures. Our results showed that A. coerulea ephyrae were widely distributed in the A. japonicus culture ponds along the Bohai and Yellow Seas. Furthermore, underwater photography revealed that polyps of A. coerulea mainly occurred on the undersides of the artificial reefs made by plastic sunshade nets, tiles and substrate cages. The artificial reefs may decrease the time A. coerulea planulae spend settling, provide more hidden, calm and shady places for the settlement and proliferation of A. coerulea planulae, and thus were suitable substrates for the moon jellyfish A. coerulea. Our study suggests that the A. japonicus culture ponds may act as nursery grounds for the jellyfish A. coerulea and may potentially enhance the blooms of this species in the coastal waters along the Bohai and Yellow Seas.     

The plankton community of Lake Matano: factors regulating plankton composition and relative abundance in an ancient,tropical lake of Indonesia

Recent evidence reveals that food webs within the Malili Lakes, Sulawesi, Indonesia, support community assemblages that are made up primarily of endemic species. It has been suggested that many of the species radiations, as well as the paucity of cosmopolitan species in the lakes, are related to resource limitation. In order to substantiate the possibility that resource limitation is playing such an important role, a study of the phytoplankton and zooplankton communities of Lake Matano was implemented between 2000 and 2004. We determined species diversity, relative abundances, size ranges, and total biomass for the phytoplankton and zooplankton, including the distribution of ovigerous individuals throughout the epilimnion of Lake Matano in three field seasons. The phytoplankton community exhibited very low biomass (<15 μg l^?1) and species richness was depressed. The zooplankton assemblage was also limited in biomass (2.5 mg l^?1) and consisted only of three taxa including the endemic calanoid Eodiaptomus wolterecki var. matanensis, the endemic cyclopoid, Tropocyclops matanensis and the rotifer Horaella brehmi. Zooplankton were very small (<600 μm body length), and spatial habitat partitioning was observed, with Tropocylops being confined to below 80 m, while rotifer and calanoid species were consistently observed above 80 m. Less than 0.1% of the calanoid copepods in each year were egg-bearing, suggesting very low population turnover rates. It was concluded that chemical factors as opposed to physical or biological processes were regulating the observed very low standing crops of phytoplankton which in turn supports a very minimal zooplankton community restricted in both species composition and abundance. As chemical factors are a function of the catchment basin of Lake Matano, it is predicted that resource limitation has long played an important role in shaping the unique endemic assemblages currently observed in the food web of the lake.