Virr Biovolume has to be calculated for every ex- quire a reexamination of the equation to be applied. Some results from phytoplankton counting intercalibrations. The bias will be high if, for exam- biovolume determination should be as close to the ple, Ditylum is the dominant species in a pelagic sam- real shape of the organism but at the same time ple. Wiley-Liss, New York, pp.

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In comparison such as particulate organic carbon, ATP, or chl a, with automated methods, the use of microscopical are known to vary dramatically with environmental measurements allows high taxonomic resolution, up conditions, such as light and nutrient availability to the species level, and has fewer sources of error. Verity et al. Furthermore, We present a set of geometric shapes and mathe- these parameters do not allow differentiation be- matical equations for calculating biovolumes of tween the contribution of different taxonomic.

The equations are designed to min- species in a mixed assemblage or the same species imize the effort of microscopic measurement. The under different environmental conditions. The similarities and differences between our proposal most commonly used traditional biomass estimate for standardization and previously published pro- for microalgae is cell biovolume, which is calculated posals are discussed and recommendations for qual- from microscopically measured linear dimensions ity standards given.

Steinman et al. Automated or els; microphytobenthos; microscopy; phytoplankton semiautomated techniques for estimating algal bio- volume using sophisticated laser- or image-analysis Abbreviations: PV, plasma volume; CLT, cytoplas- technologies are becoming increasingly available.

Calculating mm in diameter Reynolds In mixed-species phytoplankton carbon from biovolume rather than samples, high numbers of small-sized species might from particulate organic carbon eliminates the error actually contribute only a minor fraction of the over- due to detrital particulate matter contained in par- all biomass, whereas other, larger-sized species that ticulate organic carbon Mullin et al.

Thus, cell counts per se are in- , Montagnes et al. A standard ize the calculation of algal biovolume. As a result, biomass estimate is essential for comparing the rel- different sets of equations were used by different ative contribution of different microalgae in mixed- researchers Rott The selection of the equiv- alent geometric shapes requires careful attention 1 Received 20 March Accepted 7 December Smayda The problem was especially pro- 2 Author for reprint requests; e-mail hhillebrand ifm.

However, bacteria exhibit far less Larrance and Edler Whereas Edler morphological variability than microalgae. To our applied fairly simple methods that might not accu- knowledge, none of the existing image analysis sys- rately represent cell shape, Kovala and Larrance tems is capable of providing reasonable biovolume used a more accurate but complex approach. Both estimates of natural algal assemblages of even mod- works were published in journals of regional avail- erate species complexity.

Recently, Sieracki et al. Although hardware algal biovolume. As it is usually necessary to com- and morphometric software are likely to undergo fur- promise between accuracy and practicality, the given ther developments in the near future Verity and equations are designed to minimize the effort of mi- Sieracki , these systems will remain expensive.

These equations are ap- Light microscopy is the most commonly used plied to. Light halos around the to the analysis of benthic microalgae. We propose cell can mask the actual dimensions, especially in that this set of equations be adopted by algologists the case of small cells. However, these errors are to standardize biovolume calculations between re- generally less than 1 mm Montagnes et al.

Measurement variability can also Methods of measurement. Several automated and arise from the subjective judgment of the micros- semiautomated methods for biovolume estimation copist Leslie , subsampling error Hallegraeff are discussed in the literature, including electronic , and uneven distribution of cells in the count- particle counting Boyd and Johnson , flow cy- ing chambers.

Thus, the measurement procedure tometry Steen , microscopical image analysis should strictly conform to high, reproducible quality Krambeck et al. Other tech- Leslie compared three analysis methods of niques, such as computer tomography of single cells freshwater particulates microscopy, image analysis, Gordon , Gordon, pers. When applied to heteroge- cable for routine measurements. Besides requiring neous samples from lakes, the correlations between expensive equipment, these methods have several the results of the different methods were poor.

Les- drawbacks that render them unsuitable in many re- lie attributed this lack of correlation to detritus par- search areas. The taxonomic resolution with auto- ticles, which could be avoided only by visual exam- mated counting devices or flow cytometry is limited ination, and the presence of small algal particles, to the level of easily discernible groups e.

The different size classes or pigment composition in flow use of electron microscope images has been rec- cytometry. Thus, those methods do not allow the ommended as a means to overcome errors due to distinction of species or genera that is often necessary variability in cell components Sicko-Goad et al.

Benthic calculated by subtracting inert cell structures, such samples, which are often cohesive and contaminated as cell wall and vacuole, from the total cell volume. The results from cell counters are is an accurate estimate for biomass for detecting especially erroneous in determining biovolume of changes in morphometry e.

However, because the proportions of samples Montagnes et al. Thus, it becomes obvious and Johnson Cunningham and as direct microscopical measurements cf. Krambeck Buonnacorsi , Verity and Sieracki , Sieracki et al. Automated image analysis is applied et al. Automated methods are al- were already proposed by Kononen et al. Nevertheless, cinodiscus granii.

Kovala and Larrance cal- Allocating geometric shapes to microalgal taxa. Pub- culated dinophyte biovolumes with complex com- lished geometric models tend to have a distinct re- binations of shapes, but we decided to apply simpler gional e. Baltic Sea; Edler or environmen- shapes.

For some common freshwater phytoplank- tal focus e. In general, tions leads to biased results depends on the impor- the calculation of biovolume is based on geometric tance of the respective species in the whole com- approximations.

The geometric shapes used for munity studied. The bias will be high if, for exam- biovolume determination should be as close to the ple, Ditylum is the dominant species in a pelagic sam- real shape of the organism but at the same time ple.

On the other hand, in a sample with high easily discernible and conveniently measurable dur- proportions of simple centric diatoms e.

Coscinod- ing routine analysis Kononen et al. Discrep- iscus , the different geometric models will lead to ancies often exist between these two constraints. In almost the same results because of the high agree- such cases, the available dimensions, the abundance ment about these shapes.

In summary, the different and the importance of the species, and the question sets of equations published to date do not cover to be answered should all be taken into account. We studied the morphometry of pelagic and ben- Hillebrand and Sommer studied the re- thic microalgae with samples obtained from a num- sponse of epilithic microphytobenthos to nutrient ber of our projects and sources.

These included Pol- enrichment in the Kiel Fjord. The dominant microalgal species present ings for genera that are uncommon or absent from were mostly diatoms. The linear dimensions of all our material for cyanobacteria, Anagnostidis and species were measured with a Leitz DMR micro- Komarek , , Komarek and Anagnostidis scope at magnification and with an ocular , ; for diatoms, Krammer and Lange-Ber- scale that was calibrated with an object micrometer.

It becomes obvious that, for the gellates, Popovsky and Pfiester , Pollingher and several genera, no equation for biovolume calcula- Hickel , Steidinger and Tangen ; and for tion was given at all, whereas for others the results other microalgae, Leedale , Ettl , , Ko- show tremendous variation.

These differences might marek and Fott , Starmach , Heimdal be explained by less accuracy allocated to the ben- , Throndsen The application of these the approach to groups of organisms that have not shapes at the genus level is presented in Table 2. As been considered so far.

Furthermore, we attempted a general rule, these shapes should be applied to to eliminate sources of error detected in the previ- individual cells, even in coenobial, colonial, or fila- ously proposed models.

However, in some cases it is diffi- gested equations, especially for complex genera cult to identify the single cells e. In these cases, a shape can shape. Also, the fit of a cylinder to the triangular be applied to the entire colony or filament.

Volume of single cells of several diatom taxa dominant in the epilithic microphytobenthos in Kiel Fjord, calculated from the same linear di- mensions but with different equations proposed by Kovala and Larrance , Edler , and Rott Biovolume has to be calculated for every ex- quire a reexamination of the equation to be applied. Comprehensive rec- cells; see Round et al.

Subba Rao and Wohlgeschaffen , on the measurement of dimensions and calculation. Hillebrand and Sommer These deviations Smayda suggested an examination of 25 were not considered in our taxa list. Agardh Williams Measurement accuracy. Agardh, and Achnanthes lon- render it inaccurate to use average biovolume data gipes C. Geometric shapes and equations for the calculation of biovolume. Shapes are drawn in a three-dimensional version and in cross sections.

Equations are given, using standard abbreviations for the linear dimensions to be measured. Abbreviations: A 5 surface area; V 5 volume; r 5 radius; d 5 diameter; h 5 height; a 5 apical axis length ; b 5 transapical axis width ; c 5 pervalvar axis height ; z 5 height of cone; l 5 length of one side; m 5 height of a triangle.

TABLE 1. Annotations as in Table 1. Application of geometric models for biovolume calculations of microalgal taxa. The table is sorted according to higher taxonomic groups and lists the genera alphabetically. The annotations A are given at the end of the table according to their numbers.

We do not claim completeness for the genera or for the annotations. There may be significant deviations from this generic approach. The applied shapes should be checked carefully.

TABLE 2. Biovolume should be calculated from the me- scopically as described previously. For T. Sokal and Rohlf Microscopical measurements of linear dimensions in four diatom species. The graphs show the error coefficient standard error expressed as the percentage of the mean as a function of the number of measured cells.

For Melosira moniliformis, the diameter was measured; for Navicula perminuta, Achnanthes longipes, and Tabularia fasciculata, the apical axis was measured. However, these should to give lower values for fixed cells, even though not be measured in one chain or colony because the these cells did not shrink in an optically measurable variation within a filament is generally lower than way Boyd and Johnson



JoJolabar Hillebrand and Sommer It becomes obvious that, for the gellates, Popovsky and PfiesterPollingher and several genera, no equation for biovolume calcula- HickelSteidinger and Tangen ; and for tion was given at all, whereas for others the results other microalgae, LeedaleEttl, Ko- show tremendous variation. Log In Sign Up. An estimation of diatom area: We propose cell can mask the actual dimensions, especially in that this set of equations be adopted by algologists the case of small cells. Whereas Edler morphological variability than microalgae.



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