Direct and Indirect Effects of Consumers on Benthic Algae in Isolated Pools of an Ephemeral Stream

1990 ◽  
Vol 47 (10) ◽  
pp. 2057-2065 ◽  
Author(s):  
Paul V. McCormick
Keyword(s):  
Algal Biomass ◽  
Algal Species ◽  
Algal Growth ◽  
Benthic Algae ◽  
Nitrogen Enrichment ◽  
Direct And Indirect Effects ◽  
Ephemeral Stream ◽  
Positive Effects ◽  
Algal Assemblages ◽  
Trophic Connections

Artificial pools were used to test for interactions among dominant consumer and producer populations that coexist in isolated pools of an ephemeral stream each summer. Nitrogen and/or phosphorus were supplied to one set of pools; herbivorous snails and crayfish and a predaceous centrarchid were added in different combinations to other pools. Algal growth was measured inside and outside wire cages placed in pools to exclude herbivores and/or predators. Algal biomass and the abundance of most algal species were increased by nitrogen enrichment. Algal biomass was also enhanced by addition of consumers. There were few differences in structure between algal assemblages inside and outside cages in any treatment. Under conditions of nitrogen limitation, moderate levels of herbivory can enhance algal growth. Positive effects are greatest at the microsite level and may depend on the ability of algal species to resist digestion by grazers. Predators may affect the algal assemblage indirectly by reducing herbivore survival or activity and directly by converting nutrients stored in herbivore biomass into a form available for algal growth. Because the importance of different trophic connections may vary among ecosystems, experimentation must consider all those that are potentially important.

scholarly journals Ecosystem engineering alters density-dependent feedbacks in an aquatic insect population

2021 ◽  
Author(s):  
Joseph S. Phillips ◽  
Amanda R. McCormick ◽  
Jamieson C. Botsch ◽  
Anthony R. Ives
Keyword(s):  
Primary Production ◽  
Aquatic Insect ◽  
Algal Growth ◽  
Adult Emergence ◽  
Benthic Algae ◽  
Ecosystem Engineering ◽  
Benthic Primary Production ◽  
Density Dependent ◽  
Benthic Production ◽  
Positive Effects

AbstractEcosystem engineers have large impacts on the communities in which they live, and these impacts may feed back to populations of engineers themselves. In this study, we assessed the effect of ecosystem engineering on density-dependent feedbacks for midges in Lake Mývatn, Iceland. The midge larvae reside in the sediment and build silk tubes that provide a substrate for algal growth, thereby elevating benthic primary production. Benthic algae are in turn the primary food source for the midge larvae, setting the stage for the effects of engineering to feed back to the midges themselves. Using a field mesocosm experiment manipulating larval midge densities, we found a generally positive but nonlinear relationship between density and benthic production. Furthermore, adult emergence increased with the primary production per midge larva. By combining these two relationships in a simple model, we found that the positive effect of midges on benthic production weakened the negative density dependence at low to intermediate larval densities. However, this benefit disappeared at high densities when midge consumption of primary producers exceeded their positive effects on primary production through ecosystem engineering. Our results illustrate how ecosystem engineering can alter density-dependent feedbacks for engineer populations.

scholarly journals Confounding factors in algal phosphorus limitation experiments

2018 ◽  
Author(s):  
Whitney S. Beck ◽  
Ed K. Hall
Keyword(s):  
Algal Biomass ◽  
Field Experiments ◽  
Meta Analysis ◽  
Algal Growth ◽  
Benthic Algae ◽  
Cost Effective ◽  
Phosphorus Limitation ◽  
Significant Inhibition ◽  
Selective Grazing ◽  
Phosphate Salts

AbstractAssessing algal nutrient limitation is critical for understanding the interaction of primary production and nutrient cycling in streams, and nutrient diffusing substrate (NDS) experiments are often used to determine limiting nutrients such as nitrogen (N) and phosphorus (P). Unexpectedly, many experiments have also shown decreased algal biomass on NDS P treatments compared to controls. To address whether inhibition of algal growth results from direct P toxicity, NDS preparation artifacts, or environmental covariates, we first quantified the frequency of nutrient inhibition in published experiments. We also conducted a meta-analysis to determine whether heterotrophic microbial competition or selective grazing could explain decreases in algal biomass with P additions. We then deployed field experiments to determine whether P-inhibition of algal growth could be explained by P toxicity, differences in phosphate cation (K vs. Na), differences in phosphate form (monobasic vs. dibasic), or production of H2O2during NDS preparation. We found significant inhibition of algal growth in 12.9% of published NDS P experiments as compared to 4.7% and 3.6% of N and NP experiments. The meta-analysis did not show enhanced heterotrophy on NDS P treatments or selective grazing of P-rich algae. Our field experiments did not show inhibition of autotrophic growth with P additions, but we found significantly lower gross primary productivity (GPP) and biomass-specific GPP of benthic algae on monobasic phosphate salts as compared to dibasic phosphate salts, likely because of reduced pH levels. Additionally, we note that past field experiments and meta-analyses support the plausibility of direct P toxicity or phosphate form (monobasic vs. dibasic) leading to inhibition of algal growth, particularly when other resources such as N or light are limiting. Given that multiple mechanisms may be acting simultaneously, we recommend practical, cost-effective steps to minimize the potential for P-inhibition of algal growth as an artifact of NDS experimental design.

scholarly journals The fractionation of nitrogen and oxygen isotopes in macroalgae during the assimilation of nitrate

2014 ◽  
Vol 11 (21) ◽  
pp. 6147-6157 ◽  
Author(s):  
P. K. Swart ◽  
S. Evans ◽  
T. Capo ◽  
M. A. Altabet
Keyword(s):  
Algal Biomass ◽  
Isotope Fractionation ◽  
Algal Growth ◽  
Benthic Algae ◽  
Syringe Pump ◽  
Stable Isotope Fractionation ◽  
Wide Range ◽  
Nitrogen And Oxygen Isotopes ◽  
Fractionation Mechanism ◽  
Residual Solution

Abstract. In order to determine and understand the stable isotope fractionation of 18O and 15N manifested during assimilation of NO3− in marine macro-benthic algae, two species (Ulva sp. and Agardhiella sp.) have been grown in a wide range of NO3− concentrations (2–500 μM). Two types of experiments were performed. The first was one in which the concentration of the NO3− was allowed to drift downward as it was assimilated by the algae, between 24 hour replacements of media. These experiments proceeded for periods of between 7 and 10 days. A second set of experiments maintained the NO3− concentration at a low steady-state value by means of a syringe pump. The effective fractionation during the assimilation of the NO3− was determined by measuring the δ15N of both the (i) new algal growth and (ii) residual NO3− in the free-drift experiments after 0, 12, 24 and 48 h. Modelling these data show that the fractionation during assimilation is dependent upon the concentration of NO3− and is effectively 0 at concentrations of less than ~2 μM. The change in the fractionation with respect to concentration is the greatest at lower concentrations (2–10 μM). The fractionation stablizes between 4 and 6‰ at concentrations of between 50 and 500 μM. Although the δ18O and δ15N values of NO3− in the residual solution were correlated, the slope of relationship also varied with respect to NO3− concentration, with slopes of greater than unity at low concentration. These results suggest shifts in the dominant fractionation mechanism of 15N and 18O between concentrations of 1 and 10 μM NO3−. At higher NO3− concentrations (>10–50 μM), fractionation during assimilation will lead to δ15N values in algal biomass lower than the ambient NO3− and 15N enrichments in the residual NO3−.

scholarly journals Hyperspectral analysis of algal biomass in northern lakes, Churchill, MB, Canada

2019 ◽  
Vol 5 (4) ◽  
pp. 240-256
Author(s):  
Kimisha Ghunowa ◽  
Andrew Scott Medeiros ◽  
Richard Bello
Keyword(s):  
Algal Biomass ◽  
Regional Scale ◽  
Benthic Algae ◽  
Algal Community ◽  
Total Biomass ◽  
Dominant Component ◽  
Sensing Technology ◽  
Algal Groups ◽  
Algal Assemblages

A hyperspectral approach to quantify algal biomass was studied across 30 shallow ponds in the Hudson Bay Lowlands near Churchill, MB. Normalized difference algal indices (NDAI) were calculated based on hyperspectral measurements of the reflectance collected on shore with a hand-held spectrometer in parallel to estimations of biomass with an in vivo fluorometer designed for benthic algae. Algal biomass and coarse assemblages were differentiated through their spectral reflectance as a demonstration of concept for future upscaling that would be necessary for regional monitoring using remote sensing technology. Results indicated strong agreements between the calculated NDAI for measured reflectance from each pond and that of the isolated benthic zone. Cyanobacteria were the dominant component of the algal community for most ponds. As such, measures of reflectance and use of simple NDAIs may be able to characterize the total biomass of northern ponds. However, the distinction between algal groups may require independent validation of algal assemblages for estimations beyond total biomass. Nonetheless, hyperspectral analysis could provide a strong potential for monitoring northern freshwater systems at a regional scale.

scholarly journals Trophic control of cryptic coralline algal diversity

2019 ◽  
Vol 116 (30) ◽  
pp. 15080-15085 ◽  
Author(s):  
Katharine R. Hind ◽  
Samuel Starko ◽  
Jenn M. Burt ◽  
Matthew A. Lemay ◽  
Anne K. Salomon ◽  
...  
Keyword(s):  
Algal Species ◽  
Trophic Dynamics ◽  
Kelp Forests ◽  
Negative Consequences ◽  
Food Web Structure ◽  
Nearshore Ecosystems ◽  
Keystone Predation ◽  
Ecological Patterns ◽  
Ecosystem Level ◽  
Algal Assemblages

Understanding how trophic dynamics drive variation in biodiversity is essential for predicting the outcomes of trophic downgrading across the world’s ecosystems. However, assessing the biodiversity of morphologically cryptic lineages can be problematic, yet may be crucial to understanding ecological patterns. Shifts in keystone predation that favor increases in herbivore abundance tend to have negative consequences for the biodiversity of primary producers. However, in nearshore ecosystems, coralline algal cover increases when herbivory is intense, suggesting that corallines may uniquely benefit from trophic downgrading. Because many coralline algal species are morphologically cryptic and their diversity has been globally underestimated, increasing the resolution at which we distinguish species could dramatically alter our conclusions about the consequences of trophic dynamics for this group. In this study, we used DNA barcoding to compare the diversity and composition of cryptic coralline algal assemblages at sites that differ in urchin biomass and keystone predation by sea otters. We show that while coralline cover is greater in urchin-dominated sites (or “barrens”), which are subject to intense grazing, coralline assemblages in these urchin barrens are significantly less diverse than in kelp forests and are dominated by only 1 or 2 species. These findings clarify how food web structure relates to coralline community composition and reconcile patterns of total coralline cover with the widely documented pattern that keystone predation promotes biodiversity. Shifts in coralline diversity and distribution associated with transitions from kelp forests to urchin barrens could have ecosystem-level effects that would be missed by ignoring cryptic species’ identities.

Response of Lake Michigan Benthic Algae to in situ Enrichment with Si, N, and P

1988 ◽  
Vol 45 (2) ◽  
pp. 271-279 ◽  
Author(s):  
Hunter J. Carrick ◽  
Rex L. Lowe
Keyword(s):  
Chlorophyll A ◽  
Algal Biomass ◽  
Lake Michigan ◽  
Benthic Algae ◽  
Benthic Diatoms ◽  
Nearshore Area

The possibility that benthic algae in the nearshore area of Lake Michigan might be growth limited by Si was tested using nutrient-releasing substrata. Nutrient treatments were Si, N + P, Si + N + P, and controls (CONT) and were sampled after 7, 14, and 31 d of exposure. Addition of Si alone had little stimulatory effect on algal biomass, while enrichment with Si + N + P led to the greatest increase in chlorophyll a, particulate Si, total biovolume, and diatom biovolume after 14 d of incubation (P < 0.0001). By day 31, communities on CONT and Si substrata exhibited little change in biomass and remained dominated by diatoms (98% of total biovolume), while algal biomass on both N + P and Si + N + P substrata increased more than eightfold (P < 0.0001) and consisted mainly of Stigeoclonium tenue (Chlorophyta) and Schizothrix calcicolas (Cyanophyta). These results indicate that benthic diatoms in Lake Michigan are not currently limited by Si, but may become Si limited following enrichment with N + P.

scholarly journals A macro-tidal freshwater ecosystem recovering from hypereutrophication: the Schelde case study

2009 ◽  
Vol 6 (12) ◽  
pp. 2935-2948 ◽  
Author(s):  
T. J. S. Cox ◽  
T. Maris ◽  
K. Soetaert ◽  
D. J. Conley ◽  
S. Van Damme ◽  
...  
Keyword(s):  
Growth Inhibition ◽  
Algal Biomass ◽  
Alternative Stable States ◽  
Algal Growth ◽  
Nutrient Concentrations ◽  
Freshwater Ecosystem ◽  
Nutrient Inputs ◽  
Stable States ◽  
Estuarine Ecosystem ◽  
Algal Growth Inhibition

Abstract. We report a 40 year record of eutrophication and hypoxia on an estuarine ecosystem and its recovery from hypereutrophication. After decades of high inorganic nutrient concentrations and recurring anoxia and hypoxia, we observe a paradoxical increase in chlorophyll-a concentrations with decreasing nutrient inputs. We hypothesise that algal growth was inhibited due to hypereutrophication, either by elevated ammonium concentrations, severe hypoxia or the production of harmful substances in such a reduced environment. We study the dynamics of a simple but realistic mathematical model, incorporating the assumption of algal growth inhibition. It shows a high algal biomass, net oxygen production equilibrium with low ammonia inputs, and a low algal biomass, net oxygen consumption equilibrium with high ammonia inputs. At intermediate ammonia inputs it displays two alternative stable states. Although not intentional, the numerical output of this model corresponds to observations, giving extra support for assumption of algal growth inhibition. Due to potential algal growth inhibition, the recovery of hypereutrophied systems towards a classical eutrophied state, will need reduction of waste loads below certain thresholds and will be accompanied by large fluctuations in oxygen concentrations. We conclude that also flow-through systems, heavily influenced by external forcings which partly mask internal system dynamics, can display multiple stable states.

The effects of water-level changes on periphytic algal assemblages in Poyang Lake

2020 ◽  
Author(s):  
Kuimei Qian ◽  
Martin Dokulil ◽  
Wan Lei ◽  
Yuwei Chen
Keyword(s):  
Water Level ◽  
Algal Biomass ◽  
Environmental Changes ◽  
Poyang Lake ◽  
Temporal Variations ◽  
Algal Community ◽  
Temperature Conductivity ◽  
Periphytic Algae ◽  
Water Level Changes ◽  
Algal Assemblages

Poyang Lake, which is the largest freshwater lake in China, has a seasonal flooding cycle that significantlychanges the water level every year. The aim of this study was to research the effects of water-level changeson periphytic algal assemblages in Poyang Lake. Dynamic shift of periphytic algal biomass were studied fromNovember 2016 to July 2019. Periphytic algal biomass and species composition were analyzed microscopically, andphysicochemical conditions were measured. There were significant seasonal variations in the community distributionof periphytic algae. The biomass of the periphyton ranged from 8 to 22,636 mg m-2. Periphytic algal biomassranged from 30 to 622 mg m-2 with the average of 204 mg m-2 in the LWL phase; periphytic algal biomass rangedfrom 8 to 21,839 mg m-2, with the average of 3,399 mg m-2 in the IWL phase. It ranged from 166 to 22,636 mgm-2, with the average 4,320 mg m-2 in the HWL phase and from 16 to 3,231 mg m-2 with the average of 585 mgm-2 in the DWL phase. There were temporal variations in periphytic algal community structure in Poyang Lake.Cryptophyceae dominated in algal periphyton from November 2016 to February 2017. Bacillariophyceae dominatedfrom March to July 2017 (increasing water-level phases). Pyrrophyceae and Euglenophyceae were dominant fromAugust and September (high-water-level phase) in 2017. Bacillariophyceae dominated through 2018 with occasionaldominance of Cryptophyceae from January to June and the occasional dominance of Chlorophyceae fromJuly to December. Chlorophyceae dominated from January to July in 2019 with occasional dominance of Bacillariophyceae.The water-level variations led to environmental heterogeneity in Poyang Lake, creating heterogeneoushabitats for algal periphyton. Our study revealed the primary importance of water level, water temperature, conductivity,total nitrogen, nitrite and total phosphorus as abiotic local factors structuring the periphytic algal communityin Poyang Lake. The water-level changes did not prevent growth of periphytic algae, but it did change the periphyticalgal community assemblages. This research provides data on the periphytic algae in Poyang Lake and will beuseful for establishing biological indicators of environmental changes and protecting Poyang Lake in the future.

Nutrient-related selection mechanisms in marine phytoplankton communities and the impact of eutrophication on the planktonic food web

1995 ◽  
Vol 32 (4) ◽  
pp. 63-75 ◽  
Author(s):  
R. Riegman
Keyword(s):  
Algal Blooms ◽  
Algal Biomass ◽  
Resource Competition ◽  
Water Quality Management ◽  
Algal Species ◽  
Marine Phytoplankton ◽  
Commercial Fish ◽  
N Limitation ◽  
Phytoplankton Communities ◽  
The Impact

A general increase in nutrient discharges during the last few decades has caused various changes in the algal community structure along the European continental coast. Coincidentally and maybe consequently, the foodweb structure and functioning has altered in local areas causing various phenomena like oxygen depletion, mortality of groups of organisms, foam on beaches, and an increase in the productivity of benthic communities and some commercial fish species. The observed increases in algal biomass and shifts in species composition are discussed in relation to the involved key mechanisms: resource competition and selective grazing. Along the Dutch coastal zone of the North Sea eutrophication has caused a doubling of the yearly averaged algal biomass during the past three decades. The sudden appearance of Phaeocystis summer blooms coincided with a shift from P-limitation towards N-limitation in the Dutch coastal area due to a stronger increase in P-discharge relative to the increase in N-discharge. Competition experiments in continuous cultures showed Phaeocystis to become dominant under N-limitation. Additionally, the large Phaeocystis colonies, which can reach a diameter up to one centimetre, escape from microzooplankton grazing. A computer model is presented which demonstrates a shift from bottom-up towards top-down control if the pelagic environment becomes eutrophicated. Implementation of this concept in a size-differential phytoplankton control model generates the prediction that algal blooms are dominated by species that escape from grazing by those zooplankton species which have a high potential numerical response. In marine environments these are microzooplankton species. These organisms mainly feed on cyanobacteria, prochlorophytes and some nano-algal species. One of the consequences for foodweb structure and the carbon fluxes in marine foodwebs is that eutrophication will lead to the dominance of poorly edible algal species. Eutrophication favours the downward transport of carbon and nutrients towards the sediments not only due to higher algal biomasses but also as a consequence of a shift towards larger algal species with higher sedimentation characteristics. An example is given how these new insights can be used for water quality management purposes.

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