The distribution of dinoflagellate cysts along the Galician (NW Spain) coast

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Abstract
We have studied the distribution of dinoflagellate cysts along 10 Galician rías and part of their adjacent continental shelf. Cyst abundance in the area averaged 856 cysts ml−1, which is of the same order of magnitude as those found in other areas of the western European coast. It was higher in the rías than in the shelf, having a very heterogeneous distribution, especially in the former. Cyst assemblages in these two areas were different, suggesting that differences are due to cyst production rather than to accumulation. Principal component analysis, cluster analysis, distribution of macroscopic characteristics of cyst populations and distribution of single species suggest that local factors control the distribution in the rías. Nevertheless, a general pattern that splits the whole area into two-to the north and to the south of the ría de Camariñas-can be distinguished. This latter trend was also observed in the shelf and, in our opinion, It should be attributed to three concurrent causes: the effect of different upwelling intensities or frequencies, the effect of the different numbers and sizes of the ría in each area, and the effect of the presence of different water masses in these areas. The cyst distribution of a number of individual species was examined and showed three general groups: species with very restricted distribution, such as Alexandrium sp2 or Scrippsiella sp4, species with a widespread distribution along the rías, such as several Scrippsiella species, and species mainly distributed along the shelf, such as Gymnodinium catenatum. The distribution of cysts belonging to red tide organisms fits quite well with that of their corresponding motile phases dunng the three previous years for most of the organisms studied and also during the 1992–1993 period (7–8 years later), but the role of this resting stage in initiating such blooms seems to be highly variable with species.

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