scholarly journals Nutrient enrichment stimulates herbivory and alters epibiont assemblages at the edge but not inside subtidal macroalgal forests

2020 ◽  
Vol 167 (12) ◽  
Author(s):  
Fabio Bulleri ◽  
Giuseppina Pardi ◽  
Laura Tamburello ◽  
Chiara Ravaglioli
Keyword(s):  
Nutrient Enrichment ◽  
Algal Species ◽  
Experimental Studies ◽  
Forest Edges ◽  
Nutrient Inputs ◽  
Complex Species ◽  
Competitive Effects ◽  
Sessile Invertebrates ◽  
Herbivore Consumption ◽  
Suitable Substratum

AbstractNutrient enrichment is a major threat to subtidal macroalgal forests. Several studies have shown that nutrient inputs can enhance the ability of opportunistic algal species to acquire space freed by disturbance, at the expense of architecturally complex species that form forests. However, competition between canopy- and turf-forming macroalgae is not limited to the aftermath of disturbance. Canopy-forming macroalgae can provide suitable substratum for diverse epibiont assemblages, including both algae (epiphytes) and sessile invertebrates (epizoans). Despite evidence of enhanced epiphyte loading under eutrophic conditions, few experimental studies have assessed how nutrient enrichment influences the structure of epibiont assemblages on canopy-forming macroalgae at the edge versus inside forests. In oligotrophic waters of the NW Mediterranean, we experimentally tested the hypothesis that nutrient-driven proliferation of opportunistic epiphytic algae would affect the performance of the fucoid, Carpodesmia brachycarpa, and reduce the richness and abundance of the epizoan species they support. We predicted negative effects of nutrient enrichment to be greater at the edge than inside forests and on thalli that had recovered in cleared areas than on those within undisturbed canopy stands. Nutrient enrichment did not affect the photosynthetic efficiency and reproductive output of C. brachycarpa. By contrast, it enhanced herbivore consumption and decreased the cover and diversity of epizoans at forest edges, likely by stimulating the foraging activity of Arbacia lixula, the most abundant sea urchin in adjacent encrusting coralline barrens. Fertilization of areas inside forests had no effect on either C. brachycarpa or epibiont assemblages. Finally, nutrient enrichment effects did not vary between cleared and undisturbed areas. Our results show that moderate nutrient enrichment of oligotrophic waters does not necessarily cause the proliferation of epiphytes and, hence, a strengthening of their competitive effects on canopy-forming macroalgae. Nevertheless, enhanced herbivory damage to fertilized thalli at forest edges suggests that fragmentation could reduce the resilience of macroalgal forests and associated epibiont assemblages to nutrient enrichment.

scholarly journals Review of Harmful Algal Blooms in the Coastal Mediterranean Sea, with a Focus on Greek Waters

Diversity ◽  
2021 ◽  
Vol 13 (8) ◽  
pp. 396
Author(s):  
Christina Tsikoti ◽  
Savvas Genitsaris
Keyword(s):  
Mediterranean Sea ◽  
Harmful Algal Blooms ◽  
Algal Blooms ◽  
Ecosystem Health ◽  
Algal Species ◽  
Coastal Areas ◽  
Population Increase ◽  
Nutrient Inputs ◽  
Environmental Pressures ◽  
Marine Eutrophication

Anthropogenic marine eutrophication has been recognized as one of the major threats to aquatic ecosystem health. In recent years, eutrophication phenomena, prompted by global warming and population increase, have stimulated the proliferation of potentially harmful algal taxa resulting in the prevalence of frequent and intense harmful algal blooms (HABs) in coastal areas. Numerous coastal areas of the Mediterranean Sea (MS) are under environmental pressures arising from human activities that are driving ecosystem degradation and resulting in the increase of the supply of nutrient inputs. In this review, we aim to present the recent situation regarding the appearance of HABs in Mediterranean coastal areas linked to anthropogenic eutrophication, to highlight the features and particularities of the MS, and to summarize the harmful phytoplankton outbreaks along the length of coastal areas of many localities. Furthermore, we focus on HABs documented in Greek coastal areas according to the causative algal species, the period of occurrence, and the induced damage in human and ecosystem health. The occurrence of eutrophication-induced HAB incidents during the past two decades is emphasized.

scholarly journals Aerosol inputs affect the optical signatures of dissolved organic matter in NW Mediterranean coastal waters

2016 ◽  
Vol 80 (4) ◽  
pp. 437 ◽  
Author(s):  
E. Denisse Sánchez-Pérez ◽  
Isabel Marín ◽  
Sdena Nunes ◽  
Fran L. Aparicio ◽  
Laura Fernández-González ◽  
...  
Keyword(s):  
Organic Matter ◽  
Dissolved Organic Matter ◽  
Experimental Studies ◽  
Saharan Dust ◽  
Series Data ◽  
Nutrient Inputs ◽  
Data Set ◽  
Nw Mediterranean ◽  
The Mediterranean

Aeolian inputs of organic and inorganic nutrients to the ocean are important as they can enhance biological production in surface waters, especially in oligotrophic areas like the Mediterranean. The Mediterranean littoral is particularly exposed to both anthropogenic and Saharan aerosol depositions on a more or less regular basis. During the last few decades experimental studies have been devoted to examining the effect of inorganic nutrient inputs from dust on microbial activity. In this study, we performed experiments at two different locations of the NW Mediterranean, where we evaluated the changes in the quality and quantity of dissolved organic matter due to atmospheric inputs of different origin (Saharan and anthropogenic) and its subsequent transformations mediated by microbial activities. In both experiments the humic-like and protein-like substances, and the fluorescence quantum yield increased after addition. In general, these changes in the quality of dissolved organic matter did not significantly affect the prokaryotes. The recalcitrant character of the fluorescent dissolved organic matter (FDOM) associated with aerosols was confirmed, as we found negligible utilization of chromophoric compounds over the experimental period. We framed these experiments within a two-year time series data set of atmospheric deposition and coastal surface water analyses. These observations showed that both Saharan and anthropogenic inputs induced changes in the quality of organic matter, increasing the proportion of FDOM substances. This increase was larger during Saharan dust events than in the absence of Saharan influence.

Periphyton response to long-term nutrient enrichment in a shaded headwater stream

2005 ◽  
Vol 62 (9) ◽  
pp. 2033-2045 ◽  
Author(s):  
Jennifer L Greenwood ◽  
Amy D Rosemond
Keyword(s):  
Growth Rates ◽  
Nutrient Enrichment ◽  
Algal Species ◽  
Light Availability ◽  
Algal Growth ◽  
Detectable Effect ◽  
Long Term Effects ◽  
Tree Canopies ◽  
Periphyton Biomass

We maintained elevated but moderate concentrations of nitrogen and phosphorus continuously for 2 years in a heavily shaded headwater stream and compared effects on stream periphyton with a reference stream. Both streams were sampled for 1 year before treatment. Some measures of periphyton biomass (ash-free dry mass and chlorophyll a) responded positively to enrichment. Increased chlorophyll a was likely a result of higher chlorophyll per cell, as total algal biovolume did not change with enrichment. These differences were greatest during high-light months (November-May), when cellular growth rates (a proxy for production) were also highest with enrichment. Algal assemblages were dominated by diatoms and remained similar between the treatment and reference streams throughout the enrichment period. Although nutrients stimulated algal growth rates, the long-term effects of nutrient addition on periphyton biomass were small in magnitude compared with other published values and were potentially suppressed by light availability and invertebrate consumption. These and other factors may have also been important in limiting the algal species pool and thus a taxonomic response to enrichment. Our results indicate that in headwater streams with intact tree canopies, chronic nutrient enrichment at moderate concentrations may have little detectable effect on benthic algal composition or periphyton biomass. Although nutrients stimulated algal growth rates, the long-term effects of nutrient addition on periphyton biomass were small in magnitude compared with other published values and were potentially suppressed by light availability and invertebrate consumption. These and other factors may have also been important in limiting the algal species pool and thus a taxonomic response to enrichment. Our results indicate that in headwater streams with intact tree canopies, chronic nutrient enrichment at moderate concentrations may have little detectable effect on benthic algal composition or periphyton biomass.

Eutrophication in the High Arctic — Meretta Lake, Cornwallis Island (75° N Lat.)

1974 ◽  
Vol 31 (5) ◽  
pp. 647-662 ◽  
Author(s):  
D. W. Schindler ◽  
J. Kalff ◽  
H. E. Welch ◽  
G. J. Brunskill ◽  
H. Kling ◽  
...  
Keyword(s):  
Algal Species ◽  
Oxygen Depletion ◽  
High Arctic ◽  
Arctic Lakes ◽  
Nutrient Inputs ◽  
Lake Surface ◽  
Annual Cycles ◽  
High Nutrient ◽  
Resolute Bay ◽  
Cornwallis Island

Sewage from the Department of Transport Airport Base at Resolute Bay has caused increases in phytoplankton standing crop, changes in algal species composition, oxygen depletion, and disappearance of Limnocalanus in Meretta Lake. The annual cycles of chemical and physical events associated with these changes are described. Minimum annual input of phosphorus to Meretta Lake was 0.24–0.29 g/m2 of lake surface per year in 1971, with 66–80% supplied by sewage. Nitrogen input was 0.55–0.78 g/m2 during the same year, with 41 to 58% from sewage. Results show that severe eutrophication problems may be expected to develop in response to high nutrient inputs, even at arctic latitudes. Arctic lakes, which are sealed under ice for several months of the year, appear to be particularly vulnerable to increased oxygen depletion which accompanies eutrophication.

scholarly journals Plants cause ecosystem nutrient depletion via the interruption of bird-derived spatial subsidies

2010 ◽  
Vol 107 (5) ◽  
pp. 2072-2077 ◽  
Author(s):  
Hillary S. Young ◽  
Douglas J. McCauley ◽  
Robert B. Dunbar ◽  
Rodolfo Dirzo
Keyword(s):  
Plant Community ◽  
Nutrient Enrichment ◽  
Cocos Nucifera ◽  
Terrestrial Ecosystems ◽  
Coconut Palm ◽  
Nutrient Depletion ◽  
Nutrient Inputs ◽  
Plant Introductions ◽  
Marine Subsidies ◽  
Community Shifts

Plant introductions and subsequent community shifts are known to affect nutrient cycling, but most such studies have focused on nutrient enrichment effects. The nature of plant-driven nutrient depletions and the mechanisms by which these might occur are relatively poorly understood. In this study we demonstrate that the proliferation of the commonly introduced coconut palm, Cocos nucifera, interrupts the flow of allochthonous marine subsidies to terrestrial ecosystems via an indirect effect: impact on birds. Birds avoid nesting or roosting in C. nucifera, thus reducing the critical nutrient inputs they bring from the marine environment. These decreases in marine subsidies then lead to reductions in available soil nutrients, decreases in leaf nutrient quality, diminished leaf palatability, and reduced herbivory. This nutrient depletion pathway contrasts the more typical patterns of nutrient enrichment that follow plant species introductions. Research on the effects of spatial subsidy disruptions on ecosystems has not yet examined interruptions driven by changes within the recipient community, such as plant community shifts. The ubiquity of coconut palm introductions across the tropics and subtropics makes these observations particularly noteworthy. Equally important, the case of C. nucifera provides a strong demonstration of how plant community changes can dramatically impact the supply of allochthonous nutrients and thereby reshape energy flow in ecosystems.

Competitive effects on the structure of subalpine meadow communities

1985 ◽  
Vol 63 (8) ◽  
pp. 1444-1452 ◽  
Author(s):  
Roger del Moral
Keyword(s):  
Community Structure ◽  
Dominant Species ◽  
Experimental Studies ◽  
Experimental Methods ◽  
Niche Width ◽  
Competitive Effects ◽  
Structure And Dynamics ◽  
Subalpine Meadow ◽  
Species Overlap ◽  
Meadow Communities

The effects of competition in a subalpine meadow environment were investigated by comparing within-habitat distributions and species overlap in four communities. Based on experimental studies of these communities, it was hypothesized that structural patterns should be affected by productivity changes. It was determined that such changes are nonlinear and that the most stressed and the most competitive communities share many similar properties. Among closed, relatively productive communities, mean niche width, niche width of competitively inferior species, total overlap, and overlap among weak competitors all declined with increased competitive intensity. In contrast, niche width of dominant species changed little and overlap among space-holding species increased. The use of comparative pattern measures can complement and enhance the analysis of community structure and dynamics based on experimental methods.

Photochemical Evolution of Interstellar/Precometary Organic Material

1997 ◽  
Vol 161 ◽  
pp. 23-47 ◽  
Author(s):  
Louis J. Allamandola ◽  
Max P. Bernstein ◽  
Scott A. Sandford
Keyword(s):  
Origin Of Life ◽  
Building Blocks ◽  
Complex Species ◽  
Infrared Observations ◽  
Interstellar Ice ◽  
Polycyclic Aromatic ◽  
Ultraviolet Photolysis ◽  
The Origin Of Life ◽  
Simple Molecules ◽  
Complex Organic

AbstractInfrared observations, combined with realistic laboratory simulations, have revolutionized our understanding of interstellar ice and dust, the building blocks of comets. Since comets are thought to be a major source of the volatiles on the primative earth, their organic inventory is of central importance to questions concerning the origin of life. Ices in molecular clouds contain the very simple molecules H2O, CH3OH, CO, CO2, CH4, H2, and probably some NH3and H2CO, as well as more complex species including nitriles, ketones, and esters. The evidence for these, as well as carbonrich materials such as polycyclic aromatic hydrocarbons (PAHs), microdiamonds, and amorphous carbon is briefly reviewed. This is followed by a detailed summary of interstellar/precometary ice photochemical evolution based on laboratory studies of realistic polar ice analogs. Ultraviolet photolysis of these ices produces H2, H2CO, CO2, CO, CH4, HCO, and the moderately complex organic molecules: CH3CH2OH (ethanol), HC(= O)NH2(formamide), CH3C(= O)NH2(acetamide), R-CN (nitriles), and hexamethylenetetramine (HMT, C6H12N4), as well as more complex species including polyoxymethylene and related species (POMs), amides, and ketones. The ready formation of these organic species from simple starting mixtures, the ice chemistry that ensues when these ices are mildly warmed, plus the observation that the more complex refractory photoproducts show lipid-like behavior and readily self organize into droplets upon exposure to liquid water suggest that comets may have played an important role in the origin of life.

3-D reconstruction and analysis of mammalian mitotic spindle structure

1992 ◽  
Vol 50 (1) ◽  
pp. 578-579
Author(s):  
Kent McDonald ◽  
David Mastronarde ◽  
Rubai Ding ◽  
Eileen O'Toole ◽  
J. Richard McIntosh
Keyword(s):  
Cross Sections ◽  
Mitotic Spindle ◽  
Experimental Studies ◽  
Video Camera ◽  
Three Dimensions ◽  
Mitotic Spindles ◽  
Black And White ◽  
Reconstruction Methods ◽  
Spindle Structure ◽  
Tissue Culture Line

Mammalian spindles are generally large and may contain over a thousand microtubules (MTs). For this reason they are difficult to reconstruct in three dimensions and many researchers have chosen to study the smaller and simpler spindles of lower eukaryotes. Nevertheless, the mammalian spindle is used for many experimental studies and it would be useful to know its detailed structure.We have been using serial cross sections and computer reconstruction methods to analyze MT distributions in mitotic spindles of PtK cells, a mammalian tissue culture line. Images from EM negatives are digtized on a light box by a Dage MTI video camera containing a black and white Saticon tube. The signal is digitized by a Parallax 1280 graphics device in a MicroVax III computer. Microtubules are digitized at a magnification such that each is 10-12 pixels in diameter.

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