AME 30:185-196 (2003)  -  doi:10.3354/ame030185

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

Celia Bulit1,*, Carlos Díaz-Avalos2, Martha Signoret1, David J. S. Montagnes3

1Departamento El Hombre y su Ambiente, Universidad Autónoma Metropolitana-Xochimilco, Calzada del Hueso 1100, 04960 México DF, México
2Instituto de Investigaciones en Matemáticas Aplicadas y Sistemas, Universidad Nacional Autónoma de México, Apartado Postal 20-726, 01000 México DF, México
3Port Erin Marine Laboratory, School of Biological Sciences, University of Liverpool, Port Erin, Isle of Man, IM9 6JA, British Isles

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 x 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 Lugol¹s 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 Œciliate patch¹: 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.

KEY WORDS: Microzooplankton patchiness · Variographic analysis · Ordinary kriging · Tintinnopsis · Lohmaniella · Strombidium · Pleuronema · Mexico

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