Spatial structure of planktonic ciliate patches in a tropical coastal lagoon: an application of geostatistical methods

Abstract

The distribution of ciliates in a Mexican coastal lagoon was studied. The 4 goals were to: examine small-scale (<100 m) patches; indicate how geostatistical techniques can be used to examine these patches; make inferences concerning ciliate distribution and behaviour in the lagoon using geostatistical techniques; and assess geostatistics as a method for modelling ciliate distributions. Underlying these goals we attempt to make geostatistical techniques accessible to the non-expert. We provide an overview of the methodology, references to the geostatistical literature, and use our system as an example. Ciliates were sampled in a 40 × 40 m grid, divided at 10 m intervals; the grid was further divided into subsets, to determine 1 to 10 m scale variation. Between 30 and 35 points were sampled on 2 occasions (January and October). Ciliates were preserved with Lugol's iodine; abundance and species composition were determined by standard inverted microscopy. The work focused on 4 abundant ciliate species. We indicate, using the variographic analysis, that the abundance of 3 of the 4 ciliates is neither randomly nor homogeneously distributed, but exhibits a structured small-scale patchy distribution. We indicate that species-specific patterns of patchiness exist in stratified and in mixed waters, supporting the notion of behavioural niche-separation of planktonic ciliates. Patches of <13, <18, and < 77 m were formed by Lohmaniella oviformis, Tintinnopsis sp. and Strombidium sp., respectively. In contrast, Pleuronema sp. formed patches below the detection limits of the analysis (<1 m). Using geostatistical techniques, we established variograms and used them to model ciliate distribution and predict ciliate behaviour. Distribution maps were then generated that depicted the shape, distinctness, and gradient of the different patches. After analysing the data, we proposed a working definition of a 'ciliate patch': regions with abundance above the cut-off of the upper quartile from the kriging prediction model. Finally, error-maps were developed, indicating the coefficient of variation of the predicted distributions. We conclude that geostatistical analysis is a powerful tool to examine microzooplankton at small-scales, and we support its further application in the field.

Role of ciliates and other microzooplankton in the Irminger Sea (NW Atlantic Ocean)

“…Spatial distribution of plankton abundance, biomass, and production were assessed by geostatistical analysis (for an overview of this method see Bulit et al 2003Bulit et al , 2004. The spatial structure of abundance was determined using the empirical variogram as the basic tool (Goovaerts 1997).…”

“…The empirical variogram is a mathematical function that allows description of the spatial variability of abundance, biomass, and production in terms of variance between pairs of samples at increasing distance. Empirical variograms were modelled to predict values at non-visited locations using ordinary kriging techniques (see Bulit et al 2003Bulit et al , 2004. Omnidirectional spherical and Gaussian models were fit to the empirical variograms, using the weighted least-squares method (Cressie 1993), and their parameters were used for kriging contour maps.…”

“…Other studies in the Northeast Atlantic have also noted localised patchiness of microzooplankton (Quevedo et al 2003) and short-term events for phytoplankton and microzooplankton dynamics (Gifford et al 1995). As microzooplankton have growth rates that are similar to their prey and are able to exploit short-term blooms of phytoplankton (Banse 1982, 1992, Montagnes 1996, it would be expected that small-scale patches, on the order of km (or less), will occur, as in the Irish Sea (Montagnes et al 1999) and in coastal lagoons (Bulit et al 2003). This raises issues regarding our ability to assess or model microzooplankton dynamics from data that are typically collected at scales of 10 to 100 km (see Lynn & Montagnes 1991, Montagnes 1996.…”

Assessing spatial and temporal patchiness of the autotrophic ciliate Myrionecta rubra: a case study in a coastal lagoon

“…Methods to obtain empirical variograms followed those outlined by Bulit et al (2003). Although several models were applied to the data, 2 standard omnidirectional models, plus a nugget effect, were used: the exponential and the Gaussian (see Isaaks & Srivastava 1989 for formulae).…”

Local adaptation among geographically distant clones of the cosmopolitan freshwater ciliate Meseres corlissi. I. Temperature response

“…There is, however, increasing evidence that protist species may have geographically patchy distributions in marine and freshwater (Bulit et al 2003, 2004, Kim et al 2004, Katz et al 2005, Foissner 2006). Freshwater protists with predominant or exclusively asexual reproduction, such as many ciliates and dinoflagellates, have a (multi-) clonal population structure (Kusch 1998, Kusch et al 2000, Kim et al 2004, Lowe et al 2005a, with divergent genotypes and phenotypes.…”