Effects Of Nutrient Enrichment Research Articles

Environmental and biological cues for spawning in the crown-of-thorns starfish.

Sporadic outbreaks of the coral-eating crown-of-thorns starfish are likely to be due, at least in part, to spatial and temporal variation in reproductive and settlement success. For gonochoric and broadcast spawning species such as crown-of-thorns starfish, spawning synchrony is fundamental for achieving high rates of fertilization. Highly synchronized gamete release within and among distinct populations is typically the result of the entrainment of neurohormonal endogenous rhythms by cues from the environment. In this study, we conducted multiple spawning assays to test the effects of temperature change, reduced salinity and nutrient enrichment of seawater, phytoplankton, gametes (sperm and eggs), and the combined effect of sperm and phytoplankton on the likelihood of spawning in male and female crown-of-thorns starfish. We also investigated sex-specific responses to each of these potential spawning cues. We found that (1) abrupt temperature change (an increase of 4°C) induced spawning in males, but less so in females; (2) males often spawned in response to the presence of phytoplankton, but none of the females spawned in response to these cues; (3) the presence of sperm in the water column induced males and females to spawn, although additive and synergistic effects of sperm and phytoplankton were not significant; and (4) males are more sensitive to the spawning cues tested and most likely spawn prior to females. We propose that environmental cues act as spawning ‘inducers’ by causing the release of hormones (gonad stimulating substance) in sensitive males, while biological cues (pheromones) from released sperm, in turn, act as spawning ‘synchronizers’ by triggering a hormonal cascade resulting in gamete shedding by conspecifics. Given the immediate temporal linkage between the timing of spawning and fertilization events, variability in the extent and synchronicity of gamete release will significantly influence reproductive success and may account for fluctuations in the abundance of crown-of-thorns starfish.

The role of above-ground competition and nitrogen vs. phosphorus enrichment in seedling survival of common European plant species of semi-natural grasslands.

Anthropogenic activities have severely altered fluxes of nitrogen and phosphorus in ecosystems worldwide. In grasslands, subsequent negative effects are commonly attributed to competitive exclusion of plant species following increased above-ground biomass production. However, some studies have shown that this does not fully account for nutrient enrichment effects, questioning whether lowering competition by reducing grassland productivity through mowing or herbivory can mitigate the environmental impact of nutrient pollution. Furthermore, few studies so far discriminate between nitrogen and phosphorus pollution. We performed a full factorial experiment in greenhouse mesocosms combining nitrogen and phosphorus addition with two clipping regimes designed to relax above-ground competition. Next, we studied the survival and growth of seedlings of eight common European grassland species and found that five out of eight species showed higher survival under the clipping regime with the lowest above-ground competition. Phosphorus addition negatively affected seven plant species and nitrogen addition negatively affected four plant species. Importantly, the negative effects of nutrient addition and higher above-ground competition were independent of each other for all but one species. Our results suggest that at any given level of soil nutrients, relaxation of above-ground competition allows for higher seedling survival in grasslands. At the same time, even at low levels of above-ground competition, nutrient enrichment negatively affects survival as compared to nutrient-poor conditions. Therefore, although maintaining low above-ground competition appears essential for species’ recruitment, for instance through mowing or herbivory, these management efforts are likely to be insufficient and we conclude that environmental policies aimed to reduce both excess nitrogen and particularly phosphorus inputs are also necessary.

Effects of predation and nutrient enrichment on the success and microbiome of a foundational coral.

By inflicting damage to prey tissues, consumer species may increase stress in prey hosts and reduce overall fitness (i.e., primary effects, such as growth or reproduction) or cause secondary effects by affecting prey interactions with other species such as microbes. However, little is known about how abiotic conditions affect the outcomes of these biotic interactions. In coral reef communities, both nutrient enrichment and predation have been linked to reduced fitness and disease facilitation in corals, yet no study to date has tested their combined effects on corals or their associated microbial communities (i.e., microbiomes). Here, we assess the effects of grazing by a prevalent coral predator (the short coral snail, Coralliophila abbreviata) and nutrient enrichment on staghorn coral, Acropora cervicornis, and its microbiomes using a factorial experiment and high-throughput DNA sequencing. We found that predation, but not nutrients, significantly reduced coral growth and increased mortality, tissue loss, and turf algae colonization. Partial predation and nutrient enrichment both independently altered coral microbiomes such that one bacterial genus came to dominate the microbial community. Nutrient-enriched corals were associated with significant increases in Rickettsia-like organisms, which are currently one of several microbial groups being investigated as a disease agent in this coral species. However, we found no effects of nutrient enrichment on coral health, disease, or their predators. This research suggests that in the several months following coral transplantation (i.e., restoration) or disturbance (i.e., recovery), Caribbean acroporid corals appear to be highly susceptible to negative effects caused by predators, but not or not yet susceptible to nutrient enrichment despite changes to their microbial communities.

Impact of an experimental eutrophication on the processes of bioerosion on the reef: One Tree Island, Great Barrier Reef, Australia

The components of bioerosion were investigated during ENCORE (The Effect of Nutrient Enrichment on Coral Reefs) over 2years of controlled additions of dissolved inorganic nitrogen and phosphorus. The study was carried out at One Tree Island, southern Great Barrier Reef, Australia. Rates of microbioerosion and external erosion by grazing were significantly higher at the enriched sites than at the control sites. Rates of accretion by coralline algae were also significantly higher at enriched sites. In contrast, rates of macroboring were not significantly different between enriched and control sites.This study highlights the importance of improving water quality on the reef to reduce rates of bioerosion given that quantities of dead coral substrates have recently substantially increased as a result of coral bleaching (Hughes et al., 2015) and several Crown of Thorns plagues (Fabricius et al., 2010; De'ath et al., 2012), on the Great Barrier Reef.

Carry over effects of nutrient addition on the recovery of an invasive seaweed from the winter die-back

Nutrient enrichment of coastal waters can enhance the invasibility and regrowth of non-native species. The invasive alga Caulerpa cylindracea has two distinct phases: a well-studied fast-growing summer phase, and a winter latent phase. To investigate the effects of nutrient enrichment on the regrowth of the seaweed after the winter resting-phase, a manipulative experiment was carried out in intertidal rockpools in the North-western Mediterranean. Nutrients were supplied under different temporal regimes: press (constant release from January to May), winter pulse (January to March) and spring pulse (March to May). Independently from the temporal characteristics of their addition, nutrients accelerated the re-growth of C. cylindracea after the winter die-back, resulting in increased percentage covers at the peak of the growing season. Nutrient addition did not influence the number and length of fronds and the biomass. Native components of the algal community did not respond to nutrient additions. Our results show that nutrient supply can favour the spread of C. cylindracea even when occurring at a time of the year at which the seaweed is not actively growing.

The contrasting effects of nutrient enrichment on growth, biomass allocation and decomposition of plant tissue in coastal wetlands

Eutrophication of coastal waters can have consequences for the growth, function and soil processes of coastal wetlands. Our aims were to assess how nutrient enrichment affects growth, biomass allocation and decomposition of plant tissues of a common and widespread mangrove, Avicennia marina, and how eutrophication drives changes in below-ground carbon sequestration. We assessed this through the measurement of above- and belowground growth and decomposition rates of plants and plant tissue in unenriched or nutrient enriched treatments. Nutrient enrichment increased biomass allocation above-ground compared to below-ground in seedlings but not in fully developed, mature trees where we observed the opposite pattern. Experiments to assess root decomposition found that 40–50% of biomass was lost within six months with little change between 12 and 18 months, indicating a high potential for accumulation of organic matter over time. We estimate root-derived carbon sequestration rates of 53, 250 and 94 g C m−2 year−1 for unenriched control, N and P enriched treatments, respectively. These results show coastal eutrophication can be beneficial and detrimental to ecosystem function of coastal plants. Eutrophication stimulates root growth in fully developed trees, increasing organic matter input to soils. Our data suggests that organic matter accumulation will increase in areas with high nutrient availability where root growth is increased and rates of decomposition are low.

Tardigrada in Svalbard lichens: diversity, densities and habitat heterogeneity

Tardigrades in lichens have been poorly studied with few papers published on their ecology and diversity so far. The aims of our study are to determine the (1) influence of habitat heterogeneity on the densities and species diversity of tardigrade communities in lichens as well as the (2) effect of nutrient enrichment by seabirds on tardigrade densities in lichens. Forty-five lichen samples were collected from Spitsbergen, Nordaustlandet, Prins Karls Forland, Danskøya, Fuglesongen, Phippsøya and Parrøya in the Svalbard archipelago. In 26 samples, 23 taxa of Tardigrada (17 identified to species level) were found. Twelve samples consisted of more than one lichen species per sample (with up to five species). Tardigrade densities and taxa diversity were not correlated with the number of lichen species in a single sample. Moreover, the densities of tardigrades was not significantly higher in lichens collected from areas enriched with nutrients by seabirds in comparison to those not enriched. The incorporation of previously published data on the tardigrades of Spitsbergen into the analysis showed that tardigrade densities was significantly higher in moss than it was in lichen samples. We propose that one of the most important factors influencing tardigrade densities is the cortex layer, which is a barrier for food sources, such as live photosynthetic algal cells in lichens. Finally, the new records of Tardigrada and the first and new records of lichens in Svalbard archipelago are presented.

Synergistic effects of nutrients and light favor Nostocales over non-heterocystous cyanobacteria

Blooms of Nostocales (Cyanobacteria) are thought to be invading subtropical and temperate water bodies. According to nutrient stoichiometry and physiological differences between cyanobacterial groups, the replacement of non-heterocystous species by Nostocales is favored when dissolved inorganic nitrogen decreases. However, some studies have shown different trends. We used laboratory bioassays to evaluate the concomitant effects of light and nutrient enrichment on phytoplankton assemblages dominated by non-heterocystous filamentous cyanobacteria. Three nutrient conditions (no addition, addition of phosphate, and addition of nitrate and phosphate) and two light intensities (40 and 80 µmol photon m−2 s−1) were assayed. Nostocales replaced or co-dominated with non-heterocystous species in all treatments by the end of the study. The shift in community composition towards Nostocales dominance led to an increase in species richness, which suggests that species with different eco-physiological traits may have differential impacts on diversity. The highest saxitoxin concentrations were measured in no addition treatments, which could link production to nutritional stress. Nostocales featured high phenotypic plasticity in terms of changes in average trichome volume and growth rates. These results help to have a better understanding of the conditions under which Nostocales predominance can occur.

The combined effects of sediment accretion (burial) and nutrient enrichment on the growth and propagation of Phalaris arundinacea

Sediment accretion (burial) and nutrient enrichment occur concurrently in lacustrine wetlands, but the role of these two aspects of sedimentation on macrophyte performance has rarely been examined. Here, we investigated the concurrent effects of sediment accretion and nutrient enrichment on the growth and propagation of Phalaris arundinacea L. using a factorial sediment burial by nutrient addition experimental design. Regardless of burial depth, nutrient addition increased biomass accumulation, shoot mass ratio, the number of rhizomes, and the length of ramets and rhizomes. While burial had little effect on plant growth and propagation, it had an interactive effect with nutrient addition on belowground growth and ramet production. These results indicate that P. arundinacea is tolerant to burial, which allows it to grow in habitats with high sedimentation rates. However, the enhanced growth and propagation of P. arundinacea following sedimentation were primarily related to nutrient enrichment. This suggests that nutrient enrichment of sediments, which occurs in many lacustrine wetlands, increases the risk of invasion by P. arundinacea.

Bryophyte communities’ responses to environmental factors in highly seasonal rivers

Historically, in river ecosystems close attention has been paid to aquatic vascular macrophytes, but recent literature shows the important role of bryophytes, especially in undisturbed conditions. For this reason, we explore whether aquatic bryophyte patterns change in altered physical habitats and in eutrophication along highly seasonal streams in Bulgaria. Specifically, we hypothesize that: (i) bryophyte assemblage patterns change in conditions of hydromorphological degradation and eutrophication; and (ii) bryophyte assemblage patterns can serve as a signal in assessing effects of nutrient enrichment and hydromorphological degradation. Biological data were collected for 30 river sites together with catchment land use, hydromorphological alterations (e.g. channelization, alteration of habitat and riparian vegetation, dykes), main abiotic characteristics of each site (flow velocity, substrate type, shading and mean depth) and water chemistry parameters.The data set mentioned above was used to describe the responses of bryophyte communities to two major pressures in rivers resulting in habitat destruction: hydromorphological alterations and eutrophication. The results clearly reflected that habitat degradation led to particular changes in the species-abundance patterns of bryophyte communities. Both studied pressure types resulted in loss of species and decreased bryophyte abundance. Hydromorphological degradation could be distinguished by morphological growth forms: presence of mosses of a more plastic shape (creeping pleurocarps), whereas eutrophication favours only the mesotrophic preferential Leptodictyum riparium. This moss should be applied as a conceptual signal species, the abundance of which indicates ranges of hydromorphological and nutrient pressure in seasonal rivers.

Interactive effects of nutrient availability, temperature, and irradiance on photosynthetic pigments and color of the brown alga Undaria pinnatifida

Color is one of the important factors that determine the commercial value of cultivated marine macroalgae such as the brown alga Undaria pinnatifida (Laminariales; Phaeophyta) in Japan. Macroalgal color is fundamentally derived from the algal photosynthetic pigment content, which is affected by abiotic factors. However, little is known about the quantitative relationship between pigment content and color and the direct effects of abiotic factors on the color of marine macroalgae. We conducted a 24-day indoor culture experiment to assess the combined effects of nutrient availability (enriched and nonenriched seawater), seawater temperature (15 and 5 °C), and irradiance (180 and 30 μmol photons m−2 s−1) on the concentrations of six pigments (chlorophyll (Chl) a, Chl c 1, Chl c 2, fucoxanthin, violaxanthin, and zeaxanthin) and three color values (lightness L*, redness a*, and yellowness b*) of U. pinnatifida sporophytes. Negative correlations between pigment content and color values of the cultured algae were detected. Reduced nutrient availability, decrease in temperature, and elevated irradiance resulted in decreased pigment contents and increased color values. Moreover, a significant interaction between nutrient availability and temperature indicated that the positive effect of nutrient enrichment was antagonized by a decrease in temperature. These results suggest that U. pinnatifida can discolor under nutrient-poor, winter temperature, and saturated irradiance conditions. To increase the commercial value of this species, artificial nutrient enrichment during spring or cultivation from a deeper depth may be effective.

Response of benthic assemblages to multiple stressors: comparative effects of nutrient enrichment and physical disturbance

J.M.K. was supported by an International Macquarie University Research Excellence Scholarship during this research. Research funding was provided through the Department of Biological Sciences Macquarie University and an ARC Discovery Project DP1093444 to MJB. D.M.P. received funding from the MASTS pooling initiative (The Marine Alliance for Science and Technology for Scotland) and their support is gratefully acknowledged. MASTS is funded by the Scottish Funding Council (grant reference HR09011) and contributing institutions.

Light asymmetry explains the effect of nutrient enrichment on grassland diversity.

One of the most ubiquitous patterns in plant ecology is species loss following nutrient enrichment. A common explanation for this universal pattern is an increase in the size asymmetry of light partitioning (the degree to which large plants receive more light per unit biomass than smaller plants), which accelerates the rates of competitive exclusions. This 'light asymmetry hypothesis' has been confirmed by mathematical models, but has never been tested in natural communities due to the lack of appropriate methodology for measuring the size asymmetry of light partitioning in natural communities. Here, we use a novel approach for quantifying the asymmetry of light competition which is based on measurements of the vertical distribution of light below the canopy. Using our approach, we demonstrate that an increase in light asymmetry is the main mechanism behind the negative effect of nutrient enrichment on species richness. Our results provide a possible explanation for one of the main sources of contemporary species loss in terrestrial plant communities.

Warming and nutrient enrichment in combination increase stochasticity and beta diversity of bacterioplankton assemblages across freshwater mesocosms.

The current climate warming and eutrophication are known to interactively threaten freshwater biodiversity; however, the interactive effects on lacustrine bacterioplankton diversity remain to be determined. Here, we analyzed the spring bacterioplankton community composition (BCC) in 24 outdoor, flow-through mesocosms (mimicking shallow lake environments) under 3 temperature scenarios and 2 nutrient regimes. Our results revealed that neither long-term warming (8.5 years) nor nutrient enrichment had significant effects on bacterioplankton alpha diversity, whereas long-term enhanced warming (elevated 50% above the IPCC A2 climate scenario) and nutrient enrichment in combination increased bacterioplankton beta diversity. We also found that BCC shifted significantly under enhanced warming and nutrient-enriched conditions towards decreased relative abundances of Actinobacteria, Bacteroidetes and Betaproteobacteria, whereas the percentages of Cyanobacteria, total rare phyla and unclassified phyla significantly increased. Null-model tests indicated that deterministic processes played a more important role than stochastic processes in determining BCC. However, the relative importance of stochasticity, primarily ecological drift, was enhanced and contributed to the increased beta diversity of BCC under enhanced warming and nutrient-enriched conditions. Overall, our study suggests that the synergetic effects of warming and nutrient enrichment may result in high variability in the composition of bacterioplankton communities in lacustrine water bodies.

Nutrient enrichment effects on mycorrhizal fungi in an Andean tropical montane Forest.

Nitrogen (N) and phosphorus (P) deposition are increasing worldwide largely due to increased fertilizer use and fossil fuel combustion. Most work with N and P deposition in natural ecosystems has focused on temperate, highly industrialized, regions. Tropical regions are becoming more developed, releasing large amounts of these nutrients into the atmosphere. Nutrient enrichment in nutrient-poor systems such as tropical montane forest can represent a relatively large shift in nutrient availability, especially for sensitive microorganisms such as arbuscular mycorrhizal fungi (AMF). These symbiotic fungi are particularly critical, given their key role in ecosystem processes affecting plant community structure and function.To better understand the consequences of nutrient deposition in plant communities, a long-term nutrient addition experiment was set up in a tropical montane forest in the Andes of southern Ecuador. In this study, we investigated the impacts of 7years of elevated N and P on AMF root colonization potential (AMF-RCP) through a greenhouse bait plant method in which we quantified root colonization. We also examined the relationship between AMF-RCP and rarefied tree diversity.After 7years of nutrient addition, AMF-RCP was negatively correlated with soil P, positively correlated with soil N, and positively correlated with rarefied tree diversity. Our results show that AMF in this tropical montane forest are directly affected by soil N and P concentrations, but may also be indirectly impacted by shifts in rarefied tree diversity. Our research also highlights the need to fully understand the benefits and drawbacks of using different sampling methods (e.g., AMF-RCP versus direct root sampling) to robustly examine AMF-plant interactions in the future.

Nutrient enrichment and flow regulation impair structure and function of a large river as revealed by aquatic hyphomycete species richness, biomass, and decomposition rates

AbstractDiversity, sporulation rates, and biomass of aquatic hyphomycetes (Kingdom Fungi) on leaf litter were examined to assess the effects of nutrient enrichment and flow regulation on the ecological integrity of the Saint John River, New Brunswick, Canada. Leaf decomposition rate was used as an indicator of ecological function, whereas fungal abundance and diversity were chosen as structural indicators. Leaf-litter bags of yellow birch (Betula alleghaniensis) were deployed at 8 sites, periodically retrieved, and analyzed during 2 consecutive years in unregulated and regulated reaches. The interaction between nutrient enrichment and flow regulation regime significantly affected leaf decomposition rate and fungal sporulation during summer and autumn and fungal diversity during autumn. Flow regulation regime was the primary driver for fungal diversity during summer. In contrast, nutrient enrichment significantly affected fungal biomass. In general, this large 7th-order river responded to flow regulation a...

Cumulative effects of multiple stressors: An invasive oyster and nutrient enrichment reduce subsequent invasive barnacle recruitment

Studies identifying interactions between biological invasions and other stressors have generally focussed on quantifying their cumulative effects on mature species assemblages. In benthic systems, however, early life history processes are key determinants of assemblage structure and functioning. This study tested whether the presence of an invasive species affected early life history processes of two common barnacle species and whether this was affected by a second common stressor, nutrient enrichment. The results of a field experiment identified and characterised the effects of an invasive oyster, Crassostrea gigas, on the early life history processes of the two barnacle species under ambient and enriched nutrient conditions. In the presence C. gigas, the invasive barnacle Austrominius modestus, had a lower recruitment rate, however, there was no effect of the presence of C. gigas on native barnacle, Semibalanus balanoides, recruitment. Nutrient enrichment also reduced the recruitment rate of A. modestus, however, there was no evidence of synergistic or antagonistic interactions between these stressors, indicating their cumulative effects were additive. There was no effect of nutrient enrichment on native barnacle recruitment. Our results show that the presence of an invasive oyster and nutrient enrichment altered the recruitment of another non-native benthic species. These findings emphasise the importance of considering early life history processes when assessing effects of multiple stressors on communities.

Seasonal regulation of herbivory and nutrient effects on macroalgal recruitment and succession in a Florida coral reef.

Herbivory and nutrient enrichment are drivers of benthic dynamics of coral reef macroalgae; however, their impact may vary seasonally. In this study we evaluated the effects of herbivore pressure, nutrient availability and potential propagule supply on seasonal recruitment and succession of macroalgal communities on a Florida coral reef. Recruitment tiles, replaced every three months, and succession tiles, kept in the field for nine months, were established in an ongoing factorial nutrient enrichment-herbivore exclusion experiment. The ongoing experiment had already created very different algal communities across the different herbivory and nutrient treatments. We tracked algal recruitment, species richness, and species abundance through time. Our results show seasonal variation in the effect of herbivory and nutrient availability on recruitment of coral reef macroalgae. In the spring, when there was higher macroalgal species richness and abundance of recruits, herbivory appeared to have more control on macroalgal community structure than did nutrients. In contrast, there was no effect of either herbivory or nutrient enrichment on macroalgal communities on recruitment tiles in cooler seasons. The abundance of recruits on tiles was positively correlated with the abundance of algal in the ongoing, established experiment, suggesting that propagule abundance is likely a strong influence on algal recruitment and early succession. Results of the present study suggest that abundant herbivorous fishes control recruitment and succession of macroalgae, particularly in the warm season when macroalgal growth is higher. However, herbivory appears less impactful on algal recruitment and community dynamics in cooler seasons. Ultimately, our data suggest that the timing of coral mortality (e.g., summer vs. winter mortality) and freeing of benthic space may strongly influence the dynamics of algae that colonize open space.

Biotic resistance buffers the effects of nutrient enrichment on the success of a highly invasive aquatic plant

Summary Biotic resistance theory predicts that the presence of a species‐rich native community is able to inhibit the establishment of invasive species. On the other hand, disturbed environments, for example, through eutrophication, tend to be more easily invaded. We investigated the effect of biotic resistance on the establishment success of the aquatic grass Urochloa arrecta in nutrient‐enriched and non‐enriched mesocosms so as to test the hypothesis that the effects of biotic resistance on invader success depend on ecosystem trophic state. Invader success, measured as plant biomass and length, increased with nutrient enrichment in treatments without biotic resistance, whereas there was no difference between the success of the invader in enriched or non‐enriched mesocosms in the presence of biotic resistance. Our results suggest that eutrophication enhanced the resistance offered by the native community and thereby reduced the establishment of invaders. The results underscore the importance of native communities as biotic filters to invasion, especially in environments that are subjected to anthropogenic impacts such as nutrient enrichment.

Impact of contaminated sediment elutriate on coastal phytoplankton community (Thau lagoon, Mediterranean Sea, France)

Effects of sediment-released contaminants and nitrogen were assessed on phytoplankton communities sampled from Thau lagoon (France, Mediterranean Sea) and one close offshore marine station. Phytoplankton was exposed to sediment elutriate (seawater containing a mix of metals, organic chemicals, and nutrients) or to ammonium enrichment for four days using immersed microcosms exposed to natural conditions of light and temperature. Functional (production - respiration balance) and structural (taxonomy and cell densities) responses of the phytoplankton community were assessed. In the lagoon, both treatments stimulated phytoplankton growth, compare to controls. Conversely in the offshore station, the phytoplankton growth was stimulated only with the sediment elutriate addition. In offshore and lagoon stations, both treatments caused a shift in the taxonomic composition of the phytoplankton. Proliferation of potentially toxic diatoms and dinoflagellates resulted from the addition of elutriate. Correspondence analysis determined that phytoplankton from the offshore station was more sensitive to both treatments compared to the lagoon community. According to daily production and respiration balance, lagoon community metabolism remained heterotrophic (P<R) for all treatments, whereas only transient shifts to net autotrophy (P>R) were observed in the offshore community. Direct toxicity of contaminants released from sediment, if any, was therefore masked by nutrient enrichment effects, whereas indirect evidence of contaminant pressure was highlighted by changes in community composition and metabolism.