1,720,972 research outputs found
A synthesis of growth rates in marine epipelagic invertebrate zooplankton
No full textWe present the most extensive study to date of globally compiled and analysed weight-specific growth rates in marine epi-pelagic invertebrate metazoan zooplankton. Using specified selection criteria, we analyse growth rates from a variety of zooplanktonic taxa, including both holo- and mero-planktonic forms, from over 110 published studies. Nine principal taxonomic groups are considered, the copepods (number of individual data points (n) - 2,528); crustaceans other than copepods (n - 253); cnidarians (n = 77); ctenophores (n = 27); chaetognaths (n = 87); pteropods (n = 8);polychaetes (n = 12); thaliaceans (n = 88); and larvaceans (n = 91). The copepods are further examined by subdividing them into broadcasters or sac-spawning species, and as nauplii (N1–N6), copepodities (C1–C5) and adults (C6).
For each taxonomic group relationships between growth, temperature and body weight are examined using a variety of methods. Weight-specific growth tends to increase with increasing temperature and with decreasing body weight in the crustacean group. Growth does nor relate to body weight in the case of chaetognaths and larvaceans, but does increase with temperature. In the cnidarian and ctenophore groups growth does not relate to temperature, but is negatively related to body size. For the thaliaceans growth increases with both increasing body weight and temperature. In the entire broadcasting copepod data set, weight-specific growth increases with increasing temperature and decreasing body weight. In sac-spawners, growth increase with increasing temperature, and increases with decreasing body weight at temperatures below 20°C, but decrease with body weight at temperatures above this.
Comparison between the different taxa shows important differences and similarities. Our extensive synthesis of data generally confirms that larvaceans, pteropods, cnidarians and ctenophores have rates of weigth-specific growth that are typically greater than the copepods, chaetognaths and other crustaceans of similar carbon weight. For the cnidarians, ctenophores adn larvaceans groth rates are almost always greater than the general relationship describing copepod growth, and are also at the upper limits or beyond the maximum rates for copepods of a similar weight. For the pteropods, growth rates are generally greater than those of copepods, although the data set was limited to a single carnivorous species in a single study (i.e. Clione limacina). The thaliaceans have the highest growth rates for animals with body weights greater than around 1mg C ind−1, with rates of up to 2.1 d−1 for Pegea bicaudata. Whilst the larvaceans can achieve rates
of 2 d−1 in warm tropical waters (28°C), and as high as > 3 d−1 for < 0.2 mg C individual−1 animals of Oikopleura diocia. These are possibly the highest rates every recorded in epi-pelagic metazoans. Reasons for the differences between taxonomic groups are discussed in relation to intrinsic and extrinsic factors and limitations.
The importance of this investigation not only lies in it being the most comprehensive overview of patterns of growth to date, but because the data set highlight the gaps in measurements and current knowledge. We examine the inadequacies in the current data sets, and in the methods being used to measure growth and production. Most of the data are for animals collected from coastal and estuarine waters, and it is clear that for a fuller understanding there is an urgent need for work in the open ocean, and for investigations outside temperature regions. There is also a need to explore the role of food availability, and how food concentrations in incubations, and under food saturation, relate to those experienced in the natural environment
Development and production of planktonic crustaceans: A test of the "frequency of animals in apolysis" method
No full textThe duration of the molt cycle (DMC) was determined for three larval stages of the tropical decapod 'Lucifer faxoni' in Kingston Harbour, Jamaica using the "frequency of animals in apolysis" method (FAA). The DMC for each larval stage observed in a live rearing experiment (17.75 ± 1.95 h, 32.98 ± 1.75 h and 55.17 ± 7.88 h respectively) closely resembled those predicted by the cohort model (24 h, 34.5 h, 55 h), indicating the existence of a relationship between FAA and DMC for this organism. An unsuccessful attempt was made to adapt the FAA model to cladocerans in temperate systems. Since neither 'Holopedium gibberum' nor ' Daphnia catawba' exhibit a diel pattern in molting, critical model assumptions were violated resulting in an infinite number of possible model solutions. A diel pattern in FAA was noted in 'Diaphanosoma birgei '. Unfortunately, the maximum number in apolysis was low which also has the affect of increasing the number of model solutions. A further attempt to apply the FAA method to the marine cladoceran, ' Penilia avirostris' in Kingston Harbour, Jamaica also failed. The lack of both distinct size classes and diel preference in molting indicates these cladocerans are not suitable organisms for FAA analysis. Production of 'P. avirostris' was estimated as 190.76 KJ m-2 yr-1 using the instantaneous growth rate method which is comparable to the third largest contribution by a copepod species (191.41 KJ m-2 yr-1) and represents 16%-21% of total larvacean production (586 KJ m -2 y-1 with an additional 300-600 KJ m-2 y-1 for house production). Compared to the instantaneous growth rate method, the egg ratio method overestimated ' P. avirostris' production by approximately 66%. Estimates obtained equaled 317.38 KJ m-2 yr-1 when all egg and neonate stages were considered and 328.53 KJ m-2 yr-1 when only neonate stage 3 was used
The activity of chitobiase in the medium: A biochemical estimate of development rate in planktonic crustacea
No full textThe activity of the molting enzyme chitobiase in the medium surrounding individuals and populations of planktonic crustacea was investigated. Two applications of this enzyme assay are presented as methods of estimating development rates in crustacean zooplankton. The correspondence between elevated chitobiase activity in the medium and the presence of exuviae was confirmed in seven freshwater cladoceran, and one freshwater and six marine copepod species. This biochemical cue of the molting event was applied as a method of estimating the proportion of animals molting in a defined period of time (development time). An estimate of 'Daphnia magna' (2,000-2,100 [mu]m size class) development time was in close agreement with that derived by conventional incubations (70.3 versus 75.1 hours respectively). Chitobiase activity in the medium was found to vary with body length in six freshwater cladocerans and six marine copepod species. Although the slopes of species specific regressions differed, a significant common relationship was found (log10 [chitobiase activity] = -1.19 + 0.89 log 10 [body length], r2 = 0.79, p < 0.0001). Under steady state conditions in laboratory cultures, the rate of decay of chitobiase in the medium was balanced by its rate of production by molting animals. The rate of decay of the enzyme in the absence of animals was therefore also its rate of production, which is a measure of the average rate of development of the crustacean zooplankton community. Development times for a ' Daphnia magna' culture (2 determinations) and a 'Ceriodaphnia ' sp. - 'D. magna' mixed culture were 65.4 vs. 62 hours, 59 vs. 67 hours and 46.6 vs. 50 hours, as measured by this application of the chitobiase assay versus conventional molt rate determinations respectively
Size-related patterns in growth rate and production of tropical marine planktonic communities along a trophic gradient
No full textThe size-dependence of growth rates and possible ramifications on structure and regulation of planktonic communities were investigated in tropical marine ecosystems. Manipulations of nutrient, predator and prey concentrations were conducted using 21 litre microcosms in oligotrophic, mesotrophic and eutrophic waters surrounding Jamaica. Responses of size-fractionated chlorophyll, copepods and larvaceans were followed over 5 days. In all environments, there was a pronounced increase of chlorophyll in response to addition of nutrients, response being greatest in oligotrophic waters, and in the netplankton (20 m) size-fraction. Microcosms not receiving nutrients showed a decline in chlorophyll as a function of cell-size and grazing pressure. Sedimentation was most pronounced in the netplankton, and insignificant in the picoplankton (m). Grazing effects were less pronounced than nutrient effects. Phytoplankton biomass was more strongly controlled by nutrient supply (bottom-up) than by metazoan zooplankton grazing in areas of lower productivity, but may be strongly controlled by grazing (top-down) in areas of higher productivity. Growth rates of copepods and larvaceans were also size-dependent. Smaller species and/or earlier developmental stages displayed higher growth rates than larger species and/or later developmental stages. This pattern arises due to interaction of both intrinsic effects of size and progressive growth limitation by resources, with increasing size. Within the copepods, naupliar growth rates appear relatively uninfluenced, copepodites were mildly influenced, and egg production was highly influenced by resource concentration. Diel patterns were observed in molting and copepod egg production. Larvacean instantaneous growth rates averaged 2 d\sp{-1}, more than 3 times those of the average copepod. Applying these growth rates to a monitoring program in outer Kingston Harbour, secondary productivity was estimated as 1679 kJ \rm m\sp{-2}\ y\sp{-1} for the copepods and 544 kJ \rm m\sp{-2}\ y\sp{-1} for the larvaceans (excluding larvacean house production). Secondary production was 681 kJ \rm m\sp{-2}\ y\sp{-1} for the copepods and 323 kJ \rm m\sp{-2}\ y\sp{-1} for the larvaceans at mesotrophic Lime Cay, and 304 kJ \rm m\sp{-2}\ y\sp{-1} for the copepods in oligotrophic offshore waters. These production estimates indicate that the importance of tropical waters and larvaceans in global estimates of secondary production has been previously under-appreciated
Selecting candidate marine reserves: a test of the efficacy of current approaches
Get PDFIn an attempt to understand the relationship between the 'species-based' and 'spaces-based' approaches to marine conservation, this thesis examined: first, their relative efficiencies at selecting a set of marine reserves and second, the influence spatial aggregation had on the shape of the reserve system. Results demonstrated that: (a) a reserve system designed with a moderate degree of spatial aggregation most minimised the area, number of reserves and perimeter of the system most effectively; (b) neither focal species nor habitats alone were capable of capturing the desired level of representation; but (c) habitats acted as a better surrogate for capturing conservation features than do species; (d) 'species-based' and 'spaces-based' approaches can be combined to create an efficient reserve system designed to capture the full range of biodiversity; and, (e) when that approach was taken, reserve designs built using benthic habitat data, were more efficient at meeting the representation targets than species or other habitats alone
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
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
- …
