1,720,993 research outputs found
Forecasting ocean acidification impacts on kelp forest ecosystems
Get PDFAbstractOcean acidification is one the biggest threats to marine ecosystems worldwide, but its ecosystem wide responses are still poorly understood. This study integrates field and experimental data into a mass balance food web model of a temperate coastal ecosystem to determine the impacts of specific OA forcing mechanisms as well as how they interact with one another. Specifically, we forced a food web model of a kelp forest ecosystem near its southern distribution limit in the California large marine ecosystem to a 0.5 pH drop over the course of 50 years. This study utilizes a modeling approach to determine the impacts of specific OA forcing mechanisms as well as how they interact. Isolating OA impacts on growth (Production), mortality (Other Mortality), and predation interactions (Vulnerability) or combining all three mechanisms together leads to a variety of ecosystem responses, with some taxa increasing in abundance and other decreasing. Results suggest that carbonate mineralizing groups such as coralline algae, abalone, snails, and lobsters display the largest decreases in biomass while macroalgae, urchins, and some larger fish species display the largest increases. Low trophic level groups such as giant kelp and brown algae increase in biomass by 16% and 71%, respectively. Due to the diverse way in which OA stress manifests at both individual and population levels, ecosystem-level effects can vary and display nonlinear patterns. Combined OA forcing leads to initial increases in ecosystem and commercial biomasses followed by a decrease in commercial biomass below initial values over time, while ecosystem biomass remains high. Both biodiversity and average trophic level decrease over time. These projections indicate that the kelp forest community would maintain high productivity with a 0.5 drop in pH, but with a substantially different community structure characterized by lower biodiversity and relatively greater dominance by lower trophic level organisms
Seawater carbonate chemistry and fertilization rate of Mytilus galloprovincialis
No full textOcean acidification (OA) poses a major threat to marine organisms, particularly during reproduction when externally shed gametes are vulnerable to changes in seawater pH. Accordingly, several studies on OA have focused on how changes in seawater pH influence sperm behavior and/or rates of in vitro fertilization. By contrast, few studies have examined how pH influences prefertilization gamete interactions, which are crucial during natural spawning events in most externally fertilizing taxa. One mechanism of gamete interaction that forms an important component of fertilization in most taxa is communication between sperm and egg‐derived chemicals. These chemical signals, along with the physiological responses in sperm they elicit, are likely to be highly sensitive to changes in seawater chemistry. In this study, we experimentally tested this possibility using the blue mussel, Mytilus galloprovincialis, a species in which females have been shown to use egg‐derived chemicals to promote the success of sperm from genetically compatible males. We conducted trials in which sperm were allowed to swim in gradients of egg‐derived chemicals under different seawater CO2 (and therefore pH) treatments. We found that sperm had elevated fertilization rates after swimming in the presence of egg‐derived chemicals in low pH (pH 7.6) compared with ambient (pH 8.0) seawater. This observed effect could have important implications for the reproductive fitness of external fertilizers, where gamete compatibility plays a critical role in modulating reproduction in many species. For example, elevated sperm fertilization rates might disrupt the eggs' capacity to avoid fertilizations by genetically incompatible sperm. Our findings highlight the need to understand how OA affects the multiple stages of sperm‐egg interactions and to develop approaches that disentangle the implications of OA for female, male, and population fitness
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Coral calcifying fluid chemistry at CO2 seeps
No full textCoral reefs are iconic ecosystems with immense ecological, economic and cultural value, but globally their carbonate-based skeletal construction is threatened by ocean acidification (OA). Identifying coral species that have specialised mechanisms to maintain high rates of calcification in the face of declining seawater pH is of paramount importance in predicting future species composition, and growth of coral reefs. Here, we studied multiple coral species from two distinct volcanic CO2 seeps in Papua New Guinea to assess their capacity to control their calcifying fluid (CF) chemistry. Several coral species living under conditions of low mean seawater pH, but with either low or high variability in seawater pH, were examined and compared with those living in 'normal' (non-seep) ambient seawater pH. We show that when mean seawater pH is low but highly variable, corals have a greater ability to maintain constant pHcf in their CF, but this characteristic was not linked with changes in abundance. Within less variable low pH seawater, corals with limited reductions in pHcf at the seep sites compared with controls tended to be more abundant at the seep site than at the control site. However, this finding was strongly influenced by a single species (Montipora foliosa), which was able to maintain complete pHcf homeostasis. Overall, although our findings indicate that there might be an association between ecological success and greater pHcf homeostasis, further research with additional species and at more sites with differing seawater pH regimes is required to solidify inferences regarding coral ecological success under future OA
Macroalgae as ecosystem engineers and the implications for ocean acidification
No full textOcean acidification (hereafter OA) is the process of increasing surface seawater CO2 and decreasing pH. OA is predicted to negatively impact many calcareous species, including coralline macroalgae. However, pH also varies in seawater surrounding macroalgae due to their metabolic activity. Research within this thesis examined how larger canopy-forming macroalgae (Carpophyllum maschalocarpum) and smaller articulate coralline macroalgae (ACA) altered the pH microenvironment at the surface of crustose coralline macroalgae (CCA). Larger canopy-forming macroalgae reduced the velocity of seawater through their canopies, which magnified changes in pH occurring at the surface of CCA (pH increasing in the light and decreasing in the dark) through increasing the concentration boundary layer (CBL) thickness. Smaller ACA Corallina officinalis also reduced seawater velocity through their canopies, but not to the same extent as Carpophyllum maschalocarpum, resulting in smaller changes in pH and thinner CBLs. Further research confirmed that these changes in pH also occur when pH in the bulk seawater is reduced to levels comparable to that expected to occur by 2100 due to OA. CCA under the ACA species Arthrocardia corymbosa increased pH at their surface under slow seawater velocities (0 – 1.5 cm s-1) up to ambient seawater pH in the light (8.00) when placed in seawater with a bulk pH of 7.65.
pH measured within a kelp (Macrocystis pyrifera) bed around Otago, New Zealand (the collection site of A. corymbosa) showed that pH variability within macroalgal beds can be high, with pH varying between 7.5 and 9.1 units. To investigate the impacts of OA and variability in pH on coralline macroalgae, A. corymbosa was grown under 4 different pH treatments for 40 days (2 means: pH 8.05 and 7.65; and two levels of variability: <0.01 and increasing by 0.40 units from the mean during the day and decreasing by 0.40 units from the mean at night). A. corymbosa growth was reduced by both decreases in mean pH and by increases in pH variability. However, the recruitment of juvenile coralline macroalgae, and all other measured aspects of the physiology of adults were not impacted by pH. During this experiment the CBL was reduced by high flow rates, but in a subsequent experiment the effects of the absence and presence of a thick CBL at pH 8.05 and 7.65 was investigated by modifying the flow conditions that A. corymbosa was grown under. Seawater velocity and pH interacted to influence the growth and calcification of A. corymbosa. At pH 8.05 growth and calcification rates was higher at fast velocities, but at pH 7.65 growth and calcification rates was significantly higher under slow seawater velocity. This means that the effects of OA could be ameliorated at slow flows for calcareous organisms that are capable of photosynthesizing, where the pH micro-environment is altered favouring higher calcification rates during the day.
The work in this thesis emphasizes that macroalgae are capable of acting as ecosystem engineers, altering both their chemical and physical environment in a way not previous examined. Also, their ability to alter their physical micro-environment has flow on effects for their chemical micro-environment. This alteration of their micro-environment has implications for both coralline macroalgae, and potentially other species that live within macroalgal beds. Organisms inhabiting macroalgal beds will encounter both flower flow rates and a more variable pH environment, which will likely modulate their response to OA
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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