Secondary Productivity Research Articles

Biodiversity and Species Change in the Arctic Ocean: A View Through the Lens of Nares Strait

Nares Strait is the Northern most outflow gateway of the Arctic Ocean, with a direct connection to the remaining multi-year ice covered central Arctic Ocean. Nares Strait itself flows into the historically highly productive North Water Polynya (Pikialasorsuaq). Satellite data shows that Nares Strait ice is retreating earlier in the season. The early season surface chlorophyll signal, which was a characteristic of the North Water, has also moved north into Nares Strait. However, given the vast differences in the hydrography and physical oceanographic structure of the North Water and Nares Strait there is no a priori reason to assume that the species assemblages and overall productivity this region between Greenland and Canada will be maintained in the face of ongoing sea ice decline. The North Water’s high marine mammal and bird populations are dependent on seasonally persistent diatom dominated phytoplankton productivity, and although there have been several studies on North Water phytoplankton, virtually nothing is known about the communities in Nares Strait. Here we investigated the microbial eukaryotes, including phytoplankton in Nares Strait using high throughput amplicon sequencing. Samples were collected from Kennedy Channel below the northern ice edge of Nares Strait through the Kane Basin and into the northern limit of the North Water. The physical oceanographic structure and initial community rapidly changed between the faster flowing Kennedy Channel and the comparatively wider shallower Kane Basin. The community changes were evident in both the upper euphotic zone and the deeper aphotic zone. Heterotrophic taxa were found in the deeper waters along with ice algae that would have originated further to the north following release from the ice. Although there was a high proportion of pan-arctic species throughout, the Nares Strait system showed little in common with the Northern North Water station, suggesting a lack of connectivity. We surmise that a direct displacement of the rich North Water ecosystem is not likely to occur. Overall our study supported the notion that the microbial eukaryotic community, which supports ecosystem function and secondary productivity is shaped by a balance of historic and current processes, which differed by seascape.

Elicitation with methyl jasmonate combined with cultivation in the Plantform™ temporary immersion bioreactor highly increases the accumulation of selected centellosides and phenolics in Centella asiatica (L.) Urban shoot culture.

Centella asiatica (L.) Urban is an important pharmacopoeial plant used not only in medicine but also in cosmetology. C. asiatica agitated shoot cultures were established to study the influence of ethephon, methyl jasmonate, l-phenylalanine (Eth 50µM, MeJa 50µM, L-Phe 2.4g/L of medium, respectively; seven variants of the supplementation) on the accumulation of secondary metabolites: the main centellosides (asiaticoside and madecassoside) and selected phenolic acids, and flavonoids in the biomass. Microshoots were harvested two and six days after the supplementation. Secondary metabolites were analyzed in methanolic extracts by UPLC-MS/MS (centellosides) and by HPLC-DAD (phenolics). In comparison with the reference cultures, the concentrations of individual secondary metabolites increased as follows: centellosides up to 5.6-fold (asiaticoside), phenolic acids up to 122-fold (p-coumaric acid) and flavonoids up to 22.4-fold (kaempherol). The highest production increase of individual compounds was observed for different variants of supplementation. Variant C (50µM MeJa), the most optimal for centellosides and flavonoid accumulation, was selected for the experiment with bioreactors. Bioreactor Plantform™, compared to RITA® system and agitated cultures, appeared to be the most advantageous for secondary metabolites production in C. asiatica shoot cultures. The phenolic acid, flavonoid, centelloside, and total secondary metabolite productivity in Plantform™ system is 1.8-fold, 1.7-fold, 2.8-fold, 2.1-fold, respectively, higher than in MeJa elicitated agitated cultures, and 4.3-fold, 7.3-fold, 12.2-fold, 7.2-fold, respectively, higher than in control agitated cultures.

Changes of energy fluxes in marine animal forests of the Anthropocene: factors shaping the future seascape

AbstractClimate change is already transforming the seascapes of our oceans by changing the energy availability and the metabolic rates of the organisms. Among the ecosystem-engineering species that structure the seascape, marine animal forests (MAFs) are the most widespread. These habitats, mainly composed of suspension feeding organisms, provide structural complexity to the sea floor, analogous to terrestrial forests. Because primary and secondary productivity is responding to different impacts, in particular to the rapid ongoing environmental changes driven by climate change, this paper presents some directions about what could happen to different MAFs depending on these fast changes. Climate change could modify the resistance or resilience of MAFs, potentially making them more sensitive to impacts from anthropic activities (i.e. fisheries and coastal management), and vice versa, direct impacts may amplify climate change constraints in MAFs. Such changes will have knock-on effects on the energy budgets of active and passive suspension feeding organisms, as well as on their phenology, larval nutritional condition, and population viability. How the future seascape will be shaped by the new energy fluxes is a crucial question that has to be urgently addressed to mitigate and adapt to the diverse impacts on natural systems.

Dynamic spatial heterogeneity reveals interdependence of marine faunal density and fishery removals

Abstract The spatial structure and dynamics of populations, their environment, interacting species, and anthropogenic stressors influences community stability and ecological resilience. Despite the importance of spatial processes in ecological outcomes and increasing desire to implement ecosystem-based management, fine-scale spatial dynamics have been rarely incorporated in marine fisheries management. However, advances in population modeling and data availability provide the necessary ingredients to address this disconnect between the fields of ecology and fisheries. We used random forests and spatial indices to quantify spatial heterogeneity and dynamics of US west coast demersal marine faunal density (biomass of a community or assemblage per unit area) and the total removals (catches plus discards) from the system by the groundfish bottom trawl fishery from 2002 to 2017. We expected spatial heterogeneity of removals and density to increase following implementation of depth and habitat closures – due to proximally increasing density gradients and fishing-the-line – and following catch shares because of fleet consolidation and behavioral consequences of eliminating the race to fish. However, we found mixed responses, where at the broadest community levels spatial variation in removals and density declined with habitat closures, while spatial autocorrelation of removals increased with habitat closures and declined with catch shares. Our results reveal a complex interdependence between spatial distributions of faunal density and fishery removals that has been absent in previous studies focusing on catch only, and shows how these patterns are shaped by marine policy. Values of spatial variation of density and removals were positively correlated within year (i.e., each responded with the same sign and timescale), while there was also evidence that interannual changes in the spatial variation of removals among years led those of density by one year (i.e., increases in patchiness of removals were followed by increased patchiness of density). These results hint at the presence of a stronger than expected top-down effect of fishing, given that this system is considered to be dominated by strong bottom-up effects of environmental variation on primary and secondary productivity.

Atmospheric wet deposition of dissolved organic carbon to a typical anthropogenic-influenced semi-enclosed bay in the western Yellow Sea, China: Flux, sources and potential ecological environmental effects

Dissolved Organic Carbon (DOC) is a key organic compound in wet precipitation, but few data are available in China marginal seas. To probe the concentration, deposition flux, seasonality, source and potential ecological environmental effects of precipitation DOC, in this study, one-year precipitation samples were collected at Jiaozhou Bay (JZB), a typical anthropogenic-influenced semi-enclosed bay in the western Yellow Sea for the first time from June 2015 to May 2016. The concentrations of DOC in precipitation were highly variable with a volume-weighted mean (VWM) concentration of 3.63 mg C L−1, which was mostly higher than those in other areas. DOC concentrations were lower in wet season than that in dry season due to the dilution from more amount of rainfall. The wet deposition flux of DOC was calculated to be 3.15 g C m−2 yr−1 with 68.7% of which occurred in wet season mainly owing to the promoting of more rainfall amount. Besides, local emissions together with the long-range transport of pollutants were other factors controlling precipitation DOC. Fossil fuel combustion particularly coal burning was considered to be the leading source of precipitation DOC based on correlation analysis with some generally accepted indicators. Wet deposition dominates the external input of DOC at JZB by comparison with riverine input with a percentage of 54%. Heavy storm may exert enrichment effect on DOC levels in the surface water of JZB, and then promote the secondary productivity. This study emphasizes that wet deposition is an important process that should be seriously considered in the models of global/regional carbon biogeochemical cycling.

Secondary Growth Control in Garlic With Post Emergency Herbicides

This study aimed to verify the effect of the herbicides in the secondary growth control, productivity, and quality in garlic. The treatments were 5 herbicides: Glyphosate; Etoxissulfurom; 2-nicotinic acid; Halossulfurom and Metsulfurom-methyl and 5 doses (0; 10; 15; 20 and 25% of the smallest dose recommended for control of the weed). The experimental design was a randomized block, with 3 repetitions. The following evaluations were made: the total and marketable yield of bulbs, a percentage of secondary growth in bulbs, the medium mass of commercial bulbs and the number of bulbils per bulb of the commercial production. Larger productivities total and marketable was observed for the herbicide Glyphosate, 13.93 t ha-1, and 13.16 t ha-1, with doses of 10.81% and 13.12% of the commercial dose, respectively. The smallest incidence of secondary growth 4.05% was observed for Glyphosate with 15.58% of the dose. The largest medium mass of commercial bulbs 35.75 g were observed for the herbicide Glyphosate with 15.83% of the dose. The herbicides 2-nicotínic acid and Metsulfurom-methyl reduced the total productivity in relation to the control treatment without herbicide application and they promoted little gain in commercial productivity. Some herbicides can control the secondary growth in vernalized garlic, however, are necessary appropriate doses applied 50 days after the planting.

Mapping the spatial and temporal variability of the upwelling systems of the Australian south-eastern coast using 14-year of MODIS data

Coastal upwelling is important for marine ecosystems and the economy, because of its elevated primary and secondary productivity and large potential for fish catch. This study developed a scale-independent and semi-automatic image processing technique to map the upwelling areas along the 4500 km south-eastern coast of Australia from 14-year monthly MODIS Sea Surface Temperature (SST) data. The results show that there is significant spatial variability in the mapped upwelling areas, month to month, season to season and year to year. There is also strong temporal (month to month, seasonal and inter-annual) variability of the upwelling characteristics in area of influence, SST anomaly, chlorophyll-a concentrations and upwelling speed. This study identifies two prominent upwelling systems, the NSW system along the coast of New South Wales and the WVIC/SA system along the coast of western Victoria and adjacent South Australia. The NSW coastal upwelling system occurs more or less continuously from austral spring to autumn. The WVIC/SA coastal upwelling system is a seasonal upwelling system occurring in the austral summer. The NSW coastal upwelling system has a stronger upwelling intensity than the WVIC/SA system, in terms of area of influence, SST anomaly, chlorophyll-a concentrations and upwelling speed. We believe that the NSW coastal upwelling system, especially the northern and central parts, is mainly driven by the East Australian Current (EAC) and its eddies; while, the WVIC/SA coastal upwelling is a typical wind-driven system. In addition, the results indicate that the El Nino Southern Oscillation (ENSO) events are likely to have a low-to-moderate impact on both the NSW and the WVIC/SA coastal upwelling systems. The El Nino (La Nina) events tend to strengthen (weaken) upwelling intensity.

Circumpolar Deep Water Impacts Glacial Meltwater Export and Coastal Biogeochemical Cycling Along the West Antarctic Peninsula

Warming along the Antarctic Peninsula has led to an increase in the export of glacial meltwater to the coastal ocean. While observations to date suggest that this freshwater export acts as an important forcing on the marine ecosystem, the processes linking ice-ocean interactions to lower trophic-level growth, particularly in coastal bays and fjords, are poorly understood. Here, we identify salient hydrographic features in Barilari Bay, a west Antarctic Peninsula fjord influenced by warm modified Upper Circumpolar Deep Water. In this fjord, interactions between the glaciers and ocean act as a control on coastal circulation, contributing to the redistribution of water masses in an upwelling plume and a vertical flux of nutrients towards the euphotic zone. This nutrient-rich plume, containing glacial meltwater but primarily composed of ambient ocean waters including modified Upper Circumpolar Deep Water, spreads through the fjord as a 150-m thick layer in the upper water column. The combination of meltwater-driven stratification, long residence time of the surface plume owing to weak circulation, and nutrient enrichment promotes phytoplankton growth within the fjord, as evidenced by shallow phytoplankton blooms and concomitant nutrient drawdown at the fjord mouth in late February. Gradients in meltwater distributions are further paralleled by gradients in phytoplankton and benthic community composition. While glacial meltwater export and upwelling of ambient waters in this way contribute to elevated primary and secondary productivity, subsurface nutrient enhancement of glacially-modified ocean waters suggests that a portion of these macronutrients, as well any iron upwelled or input in meltwater, are exported to the continental shelf. Sustained atmospheric warming in the coming decades, contributing to greater runoff, would invigorate the marine circulation with consequences for glacier dynamics and biogeochemical cycling within the fjord. We conclude that ice-ocean interactions along the Antarctic Peninsula margins act as an important control on coastal marine ecosystems, with repercussions for carbon cycling along the west Antarctic Peninsula shelf as a whole.

Effects of grazing regimes on the temporal dynamics of grassland communities

AbstractQuestionsGrazing management influences grassland community dynamics, but few studies exist on the effects of specific management regimes in subtropical grasslands. Here, we ask how rotational and continuous grazing influences the composition, diversity, and biomass production of natural grasslands in southern Brazil.LocationThe study was conducted at four cattle farms within the south Brazilian grassland region (Campos Sulinos), in the upper area of the Camaquã river basin of Rio Grande do Sul, Brazil.MethodsOn each farm, grassland that had previously been subjected to continuous grazing (freely grazed by cattle) was divided into two experimental units; one managed by rotational grazing and the other maintained under continuous grazing. In each experimental unit, 14 permanent plots were monitored over six years for species composition and species biomass. Data were analyzed using linear mixed models to evaluate the effects of grazing management strategies on composition dissimilarity, diversity indices, and plant biomass.ResultsGrasslands under a rotational grazing regime changed steadily over the period of evaluation. Total biomass and species distribution patterns greatly differed from those in plots subjected to continuous grazing, leading to changes in species richness, dominance, and composition, as well as to an increase in overall plant biomass.ConclusionsCommunity changes during the six‐year study period as a consequence of the distinct grazing treatments were evident. Grasslands under rotational grazing management benefitted from less selective grazing, enabling a more uniform growth of species within the communities, which in turn were richer at the end of the six‐year experiment. In contrast, the proportion of grazing‐resistant species or less‐consumed species was higher under continuous grazing, where foraging by cattle appears to be more selective. Rotational grazing thus not only leads to higher species richness and diversity, but also to higher primary and, in consequence, secondary productivity.

Form and function of tropical macroalgal reefs in the Anthropocene

Abstract Tropical reefs have been subjected to a range of anthropogenic pressures such as global climate change, overfishing and eutrophication that have raised questions about the prominence of macroalgae on tropical reefs, whether they pose a threat to biodiversity, and how they may influence the function of tropical marine ecosystems. We synthesise current understanding of the structure and function of tropical macroalgal reefs and how they may support various ecosystem goods and services. We then forecast how key stressors may alter the role of macroalgal reefs in tropical seascapes of the Anthropocene. High levels of primary productivity from tropical canopy macroalgae, which rivals that of other key producers (e.g., corals and turf algae), can be widely dispersed across tropical seascapes to provide a boost of secondary productivity in a range of biomes that include coral reefs, and support periodic harvests of macroalgal biomass for industrial and agricultural uses. Complex macroalgal reefs that comprise a mixture of canopy and understorey taxa can also provide key habitats for a diverse community of epifauna, as well as juvenile and adult fishes that are the basis for important tropical fisheries. Key macroalgal taxa (e.g., Sargassum) that form complex macroalgal reefs are likely to be sensitive to future climate change. Increases in maximum sea temperature, in particular, could depress biomass production and/or drive phenological shifts in canopy formation that will affect their capacity to support tropical marine ecosystems. Macroalgal reefs can support a suite of tropical marine ecosystem functions when embedded within an interconnected mosaic of habitat types. Habitat connectivity is, therefore, essential if we are to maintain tropical marine biodiversity alongside key ecosystem goods and services. Consequently, complex macroalgal reefs should be treated as a key ecological asset in strategies for the conservation and management of diverse tropical seascapes. A plain language summary is available for this article.

AN application of a dynamical model with ecological predator-prey approach to extensive livestock farming in uruguay: Economical assessment on forage deficiency

Extensive livestock farmers have to manage climate risk. Therefore, there is a need to generate quantitative tools to evaluate the biophysical and economic impacts on extensive farming based on native grasslands. We present an ecological model based on the predator-prey approach, used to simulate the effect of forage deficiency on the farm's economic performance. Different scenarios of animal stocking rate and carrying capacity of grassland are considered to assess the impact of forage deficiency in spring. Results suggest a cubic response of Gross product per hectare as function of Gross margin, according Mott's theoretical model for meat production on grassland systems in response to stocking rate. The maximum value of this cubic response function strongly depends on the initial grass height and climate scenarios. The initial grass height is critical to maximize secondary productivity and farm economic results. Scenarios including grass reserves can buffer the deficiency on grass growth rates and pasture offer, as occurs in drought periods at the time when farmers try to make animals gain liveweight. Our analysis reinforces the usefulness of forage assignment adjustment by modulating stocking rate to improve liveweight gain and economic results under climate change conditions.

DESIGN AND CONSTRUCTION OF A LIVING SHORELINE PROJECT ALONG THE GULF COAST

The Hancock County Marsh Living Shoreline Project (project) was developed as an NRDA Early Restoration project. NRDA Early Restoration projects are intended to accelerate meaningful restoration of injured natural resources, and their services, resulting from the Deepwater Horizon oil spill. The Mississippi Department of Environmental Quality and National Oceanic and Atmospheric Administration (the federal and co-implementing trustee) worked cooperatively to develop a project along the Hancock County, Mississippi, shoreline. This project would partially offset injuries by preserving and protecting existing marsh and providing for increased secondary productivity. Currently, it is the largest restoration project to be designed and constructed in Mississippi.

The relationship between zooplankton distribution and hydrography in oceanic waters of the Southern Gulf of Mexico

Zooplankton was sampled in the Southern Gulf of Mexico, during autumn 2010, summer 2011 and winter 2013. Hydrographic data, dynamic topography and geostrophic velocities showed the presence of alternating cyclonic and anticyclonic gyres in the area, and a quasi-permanent gyre in the Bay of Campeche, with higher surface temperatures and lower salinities during autumn and summer, than in winter. Stronger rainfall was present during summer, which coincided with a strong salps “bloom” that considerably increased biovolumes. A significant difference in biovolumes was found for the three seasons, with highest zooplankton biovolumes during summer, and lowest during autumn. A shoaling of higher fluorescence and higher nutrients (Nitrate + Nitrite) was found in the BOC, in coincidence with higher biovolumes during the three seasons sampled. Multivariate analysis showed that the variables controlling the productivity were mainly fluorescence and nutrients for summer 2011 and winter 2013. Higher biovolumes were present in autumn, summer and winter at the same stations, being higher during summer. Data obtained show that the Bay of Campeche is a high productivity area, all year round, particularly inside the quasi-permanent gyre where high biovolumes were present in autumn, summer and winter, but with considerable seasonal variations in primary and secondary productivity, probably dependent in great measure from river discharge and rainfall.

Identifying environmental drivers of chlorophyll-a dynamics in Austral subtropical ephemeral ecosystems

Environmental and biological features of Austral subtropical pan types were assessed, along with the drivers of chlorophyll-a (chl-a) concentrations. Chl-a biomass varied considerably across seasons and endorheic pans had elevated chl-a concentrations compared to floodplain pans. The major driver of chl-a concentration based on generalised linear/non-linear models (GLZ) was total phosphorous and total suspended solids for all pan types and seasons combined. These results are discussed within the context of secondary productivity, aquatic ecosystem heterogeneity and endorheic pan conservation.

Epifaunal diversity patterns within and among seagrass meadows suggest landscape‐scale biodiversity processes

AbstractCoastal seascapes can support high animal diversity and secondary productivity that attracts conservation interest and provides ecosystem services. Though the importance of spatial structure in marine habitats is well known, determining the dominant spatial scale for biodiversity patterns is an often‐overlooked dimension of the ecological and conservation value of seagrass meadows. We estimated biodiversity patterns at fine (0.28 m2), meadow and seascape scales to explore whether seagrass‐associated biodiversity patterns are consistent with spatial processes such as abiotic habitat filtering or metacommunity dynamics in a northeast Pacific seascape. In Barkley Sound, British Columbia, we quantified epifaunal biodiversity on eelgrass (Zostera marina) to test three hypotheses: Taxonomic diversity and composition (1) vary randomly within meadows but (2) vary systematically among meadows reflecting meadow location or environmental conditions, and (3) spatial patterns are stable over time. We sampled epifaunal invertebrates in a systematic spatial grid within nine eelgrass meadows. We found that epifaunal community composition varied as much over a few meters within the same meadow as among meadows separated by kilometers and of different sizes and wave exposures. In each meadow, we observed less than three‐quarters of the species in the regional species pool, and we observed non‐random spatial aggregation within many species. Even with spatial turnover, assemblages were more similar than predicted by null models based on random species distributions, suggesting that some species tend to co‐occur in high abundance. These spatial biodiversity patterns were not clearly explained by meadow location, area, or abiotic conditions, except that there were differences in clusters of meadows distinguished by their salinity (more marine vs. more fresh). Our results indicate that effective conservation and understanding of how seagrass can support high biodiversity and ecosystem function may require consideration of spatial connections among meadows, and not just the condition of the meadows themselves.

Loss of seagrass results in changes to benthic infaunal community structure and decreased secondary production

Seagrass beds have decreased in abundance and areal coverage over the past several decades. Although previous studies have examined the importance of seagrass for benthic community assemblages and abundances, the effect of seagrass on deep-dwelling, large (high-biomass) infauna and the importance for benthic secondary production in Chesapeake Bay have not been addressed. Using benthic suctions and push cores, we compared density, diversity, and secondary productivity of benthic communities in seagrass to those in other shallow-water habitats and estimated benthic secondary productivity lost in the York River due to loss of seagrass from 1971 to 2016. We examined four habitat types in the York River: unvegetated, Gracilaria spp., mixed seagrass (multiple seagrass species), and Zostera marina L. seagrass. Physical characteristics of habitat types and biomass of organisms were assessed, and annual secondary productivity was calculated using biomass and production-to-biomass ratios. Benthic density, diversity, secondary productivity, sedimentary chlorophyll a, and percent sand were all highest in seagrass beds with Z. marina alone. Approximately 35% of benthic secondary productivity, or 1.51 × 108 g C yr–1, was lost in the York River in 1971–2016 due to the loss of seagrass beds to unvegetated substrate. The loss of seagrass in the York River over time and the associated decrease in benthic secondary productivity that we estimated could have negative consequences for the productivity of epibenthic predators. Our data emphasize the importance of conservation and restoration of seagrass.

Effects of nutrient enrichment on primary and secondary productivity in a subtropical floodplain system: an experimental approach

In this study, we evaluated the effects of nutrient enrichment on primary and secondary productivity, the relationship between these ecosystem processes, and the relationship between the resources of zooplankton community in response to ecosystem processes, experimentally. The experimental design was randomized, with three levels of nutrient replicated three times, giving a total of nine experimental units, for a period of 30 days (November–December, 2013). We measured primary productivity, secondary productivity, and zooplankton community structure, at the beginning and after every seven days of the experiment. Primary and secondary productivity increased with nutrient enrichment. Secondary productivity was supported by a few dominant species with ecologically selected traits, especially large-bodied zooplankton (copepods and large cladocerans). Nutrient enrichment turned the relationship between primary and secondary productivity from positive to negative and intensified the biotic process of competition because of exploitation by zooplankton populations, favoring an increase in the dominance of large microcrustaceans. This reflects the initial effects of a moderate eutrophication. At a larger temporal scale and at higher nutrient concentrations, effects of higher magnitude are expected, which may disrupt the whole community, resulting in the loss of ecosystem processes.

Seasonal variation in the predatory impact of myctophids on zooplankton in the Scotia Sea (Southern Ocean)

Myctophids are the biomass-dominant mesopelagic fishes in the Southern Ocean, but their trophic role within the pelagic food web south of the Antarctic Polar Front is poorly resolved from a seasonal perspective at the ocean-basin scale. In this study, the predatory impact of the predominant Southern Ocean myctophid community (Electrona antarctica, Electrona carlsbergi, Gymnoscopelus braueri, Gymnoscopelus fraseri, Gymnoscopelus nicholsi, Protomyctophum bolini, Protomyctophum tenisoni, Protomyctophum choriodon, Krefftichthys anderssoni and Nannobrachium achirus) on their zooplankton prey was examined during austral spring, summer and autumn in the Scotia Sea, one of the most productive regions of the Southern Ocean. Seasonal variations in diet and predation rates were apparent for all species. Based on the percentage index of relative importance, myctophids had high overlap in their diets, with all species mostly consuming copepods, small euphausiids and amphipods. Myctophid size was a key determinant of diet in the region, with larger species and intra-specific size classes consuming larger prey. Cluster analyses revealed myctophid feeding guilds that appeared to change seasonally, although there was little evidence of dietary specialisation. Myctophid predation on the daily productivity of most copepod species was relatively low across seasons (<7%), except for Calanus simillimus that was predated upon highly in summer (∼26%). From the macrozooplankton component of the prey field, the myctophid community consumed substantial proportions of the euphausiid Thysanoessa spp. in each season (∼7 to 76% daily productivity), particularly in summer. Relatively high proportions of the daily Antarctic krill (Euphausia superba) productivity (∼8–58%) were also consumed by the larger myctophid species, particularly in summer by Electrona antarctica, suggesting increased competition for krill resources during the higher predator breeding season and possible reductions in food web stability during periods of reduced krill availability at this time. The amphipod Themisto gaudichaudii formed an important part of the larger myctophid species’ diet in all seasons, with between 10 and 38% of its daily productivity being consumed. Myctophid predation on the daily productivity of salps was up to 4%, whilst their impact on ostracods and pteropods was negligible (<0.1% of daily productivity) in all seasons. This study demonstrates that Southern Ocean myctophids link secondary productivity to higher predators through both krill-independent and krill-dependent trophic pathways across seasons, with myctophids comprising a more krill-dependent pathway during austral summer.

Response of Secondary Metabolism of Hypogean Actinobacterial Genera to Chemical and Biological Stimuli.

Microorganisms within microbial communities respond to environmental challenges by producing biologically active secondary metabolites, yet the majority of these small molecules remain unidentified. We have previously demonstrated that secondary metabolite biosynthesis in actinomycetes can be activated by model environmental chemical and biological stimuli, and metabolites can be identified by comparative metabolomics analyses under different stimulus conditions. Here, we surveyed the secondary metabolite productivity of a group of 20 phylogenetically diverse actinobacteria isolated from hypogean (cave) environments by applying a battery of stimuli consisting of exposure to antibiotics, metals, and mixed microbial culture. Comparative metabolomics was used to reveal secondary metabolite responses from stimuli. These analyses revealed substantial changes in global metabolomic dynamics, with over 30% of metabolomic features increasing more than 10-fold under at least one stimulus condition. Selected features were isolated and identified via nuclear magnetic resonance (NMR), revealing several known secondary metabolite families, including the tetarimycins, aloesaponarins, hypogeamicins, actinomycins, and propeptins. One prioritized metabolite was identified to be a previously unreported aminopolyol polyketide, funisamine, produced by a cave isolate of Streptosporangium when exposed to mixed culture. The production of funisamine was most significantly increased in mixed culture with Bacillus species. The biosynthetic gene cluster responsible for the production of funisamine was identified via genomic sequencing of the producing strain, Streptosporangium sp. strain KDCAGE35, which facilitated a deduction of its biosynthesis. Together, these data demonstrate that comparative metabolomics can reveal the stimulus-induced production of natural products from diverse microbial phylogenies.IMPORTANCE Microbial secondary metabolites are an important source of biologically active and therapeutically relevant small molecules. However, much of this active molecular diversity is challenging to access due to low production levels or difficulty in discerning secondary metabolites within complex microbial extracts prior to isolation. Here, we demonstrate that ecological stimuli increase secondary metabolite production in phylogenetically diverse actinobacteria isolated from understudied hypogean environments. Additionally, we show that comparative metabolomics linking stimuli to metabolite response data can effectively reveal secondary metabolites within complex biological extracts. This approach highlighted secondary metabolites in almost all observed natural product classes, including low-abundance analogs of biologically relevant metabolites, as well as a new linear aminopolyol polyketide, funisamine. This study demonstrates the generality of activating stimuli to potentiate secondary metabolite production across diverse actinobacterial genera.

Do microplastics affect marine ecosystem productivity?

Marine and coastal ecosystems are among the largest contributors to the Earth's productivity. Experimental studies have shown negative impacts of microplastics on individual algae or zooplankton organisms. Consequently, primary and secondary productivity may be negatively affected as well. In this study we attempted to estimate the impacts on productivity at ecosystem level based on reported laboratory findings with a modelling approach, using our biogeochemical model for the North Sea (Delft3D-GEM). Although the model predicted that microplastics do not affect the total primary or secondary production of the North Sea as a whole, the spatial patterns of secondary production were altered, showing local changes of ±10%. However, relevant field data on microplastics are scarce, and strong assumptions were required to include the plastic concentrations and their impacts under field conditions into the model. These assumptions reveal the main knowledge gaps that have to be resolved to improve the first estimate above.