MEPS 268:55-67 (2004)  -  doi:10.3354/meps268055

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

Celia Bulit1,*, Carlos Díaz-Ávalos2, David J. S. Montagnes3

1Departamento El Hombre y su Ambiente, Universidad Autónoma Metropolitana-Xochimilco, Calzada del Hueso 1100, 04960 México DF, Mexico
2Instituto de Investigaciones en Matemáticas Aplicadas y en Sistemas, Universidad Nacional Autónoma de México, Apartado Postal 20-726, 01000 México DF, Mexico
3School of Biological Sciences, University of Liverpool, Biosciences Building, Crown Street, Liverpool L69 7ZB, UK

ABSTRACT: Myrionecta rubra patchiness in a Mexican coastal lagoon was studied. The 3 objectives were to (1) characterize the spatial distribution of M. rubra patches through time; (2) characterize and model the spatial distribution of M. rubra at scales ranging from m to km, and from 1 wk to more than 1 yr; and (3) to place the patchiness patterns of M. rubra into an ecological context. Geostatistical analysis was applied to data collected from simple and nested sampling grids in different seasons; autocorrelation analysis was used to detect temporal regularities over 55 wk. Classical statistics were applied to data from 10 sites in the lagoon to identify trends relating ciliate abundance to environmental conditions. Patches were detected and characterized using empirical variograms and modelled by omnidirectional Gaussian and exponential functions. For most of the analysis variance was low in the nugget parameter, indicating a strong spatial resolution of the data, and the range parameter indicated that M. rubra formed patches of 10, 20, 80, 130, and 170 m. Spatial analysis using hierarchical grids produced a more detailed assessment of patches than single grids alone. Conditional simulation of patches indicated the presence of a >2 km patch covering most of the western lagoon. Patch densities varied from between 4 and 700 cells ml-1. M. rubra abundance exhibited a temporal, pulse-like pattern; autocorrelation revealed a 13 wk periodicity. At the lagoonal level, multiple regression revealed a trend towards higher abundance in the north-west of the lagoon and a decrease during the dry season. Finally, we speculate on the forces causing heterogeneity at large (>1000 m), meso (100 to 1000 m), and fine (1 to 100 m) scales by examining physical-chemical environmental factors and physiological behavioural properties of the ciliate and its potential predators. We propose that M. rubra patches originate by fragmentation of larger patches, growth of smaller patches, and physical-behavioural aggregation of cells.

KEY WORDS: Geostatistics · Conditional simulation · Mesodinium rubrum · Mexico · Ordinary kriging · Variographic analysis

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