Differences in performance among four indices used to evaluate diversity in planktonic ecosystems

The performance of four common estimators of diversity are investigated using calanoid copepod data from the Continuous Plankton Recorder (CPR) survey. The region of the North Atlantic and the North Sea was divided into squares of 400 nautical miles for each 2-month period. For each 144 possible cases, Pielou's pooled quadrat method was performed with the aims of determining asymptotic diversity and investigating the CPR sample-size dependence of diversity estimators. It is shown that the performance of diversity indices may greatly vary in space and time (at a seasonal scale). This dependence is more pronounced in higher diverse environments and when the sample size is small. Despite results showing that all estimators underestimate the `actual' diversity, comparison of sites remained reliable from a few pooled CPR samples. Using more than one CPR sample, the Gini coefficient appears to be a better diversity estimator than any other indices and spatial or temporal comparisons are highly satisfactory. In situations where comparative studies are needed but only one CPR sample is available, taxonomic richness was the preferred method of estimating diversity. Recommendations are proposed to maximise the efficiency of diversity estimations with the CPR data.

The CPR Survey (1948-1997): a gridded database browser of plankton abundance in the North Sea.

The Continuous Plankton Recorder (CPR) survey provides a unique multi- decadal dataset on the abundance of plankton in the North Sea and North Atlantic and is one of only a few monitoring programmes operating at a large spatio- temporal scale. The results of all samples analysed from the survey since 1946 are stored on an Access Database at the Sir Alister Hardy Foundation for Ocean Science (SAHFOS) in Plymouth. The database is large, containing more than two million records (~80 million data points, if zero results are added) for more than 450 taxonomic entities. An open data policy is operated by SAHFOS. However, the data are not on-line and so access by scientists and others wishing to use the results is not interactive. Requests for data are dealt with by the Database Manager. To facilitate access to the data from the North Sea, which is an area of high research interest, a selected set of data for key phytoplankton and zooplankton species has been processed in a form that makes them readily available on CD for research and other applications. A set of MATLAB tools has been developed to provide an interpolated spatio-temporal description of plankton sampled by the CPR in the North Sea, as well as easy and fast access to users in the form of a browser. Using geostatistical techniques, plankton abundance values have been interpolated on a regular grid covering the North Sea. The grid is established on centres of 1 degree longitude x 0.5 degree latitude (~32 x 30 nautical miles). Based on a monthly temporal resolution over a fifty-year period (1948-1997), 600 distribution maps have been produced for 54 zooplankton species, and 480 distribution maps for 57 phytoplankton species over the shorter period 1958-1997. The gridded database has been developed in a user-friendly form and incorporates, as a package on a CD, a set of options for visualisation and interpretation, including the facility to plot maps for selected species by month, year, groups of months or years, long-term means or as time series and contour plots. This study constitutes the first application of an easily accessed and interactive gridded database of plankton abundance in the North Sea. As a further development the MATLAB browser is being converted to a user- friendly Windows-compatible format (WinCPR) for release on CD and via the Web in 2003.

Macro-ecology of plankton–seabird associations in the North Pacific Ocean

In conjunction with the North Pacific Continuous Plankton Recorder program, we conducted surveys of seabirds from June 2002 to June 2007. Here, we tested the hypotheses of (i) east–west variations in coupled plankton and seabird abundance, and (ii) that surface-feeding and diving seabirds vary in their relationships to primary productivity and mesozooplankton species abundance and diversity. To test these hypotheses, we developed statistical models for 20 species of seabirds and 12 zooplankton taxonomic groups. Seabird density was highly variable between seasons, but was consistently higher in the western than eastern North Pacific. Seabird diversity was greater in the east. Zooplankton abundance did not differ between regions. We found associations at the “bulk” level between seabird density and net primary productivity, but only one association between seabirds and total zooplankton abundance or diversity. However, we found many relationships between seabird species and the abundance of different zooplankton summarized at the genus or family level. Some of these taxonomic relationships reflect direct predator–prey interactions, while others may reflect zooplankton that serve as ecological indicators of other prey, such as micronekton, upon which the birds may feed. Surface or near-surface feeding, mostly piscivorous seabirds, did not differ systematically from diving, mainly planktivorous seabirds in their zooplankton associations. Seabirds apparently respond to zooplankton taxonomic groupings more so than bulk zooplankton characteristics, such as abundance or diversity. Macro-ecological studies of remote marine ecosystems using zooplankton and seabirds as ecological indicators provide a framework for understanding and assessing spatial and temporal variations in these difficult-to-study pelagic environments.

The emergence of automated high-frequency flow cytometry: revealing temporal and spatial phytoplankton variability

Phytoplankton observation is the product of a number of trade-offs related to sampling processes, required level of diversity and size spectrum analysis capabilities of the techniques involved. Instruments combining the morphological and high-frequency analysis for phytoplankton cells are now available. This paper presents an application of the automated high-resolution flow cytometer Cytosub as a tool for analysing phytoplanktonic cells in their natural environment. High resolution data from a temporal study in the Bay of Marseille (analysis every 30 min over 1 month) and a spatial study in the Southern Indian Ocean (analysis every 5 min at 10 knots over 5 days) are presented to illustrate the capabilities and limitations of the instrument. Automated high-frequency flow cytometry revealed the spatial and temporal variability of phytoplankton in the size range 1−∼50 μm that could not be resolved otherwise. Due to some limitations (instrumental memory, volume analysed per sample), recorded counts could be statistically too low. By combining high-frequency consecutive samples, it is possible to decrease the counting error, following Poisson’s law, and to retain the main features of phytoplankton variability. With this technique, the analysis of phytoplankton variability combines adequate sampling frequency and effective monitoring of community changes.