Distribution of microreticulate dinoflagellate cysts from the Galician and Portuguese coast

In May 1993, surface sediment samples from the west coast of the Iberian Peninsula were collected with the aim of studying the geographic distribution of G. catenatum resting cysts. The sampling area ranged from 40º 39´ N (Portugal) to 42º 38´ N (Galicia, Spain). Cysts with exactly the same morphology as G. catenatum were found in a maximum concentration of 504 cysts.cm-3 of sediment. Similar cysts but smaller (24-36 µm) were found in a maximum concentration of 4488 cysts.cm-3 of sediment. A bimodal size distribution of microreticulate cysts from the sediment indicates the probable existence of two cyst species. Differences in the microreticulation of the paracingulum were also observed. We compared the cysts from the sediment with G. catenatum cysts produced in cultures. The study on the distribution of cysts in the sediment also showed significant differences in the vertical profile concentrations of both cyst types. Differences in both the size and microreticulation morphology of the cysts found in the sediment of the continental shelf of Galicia and Portugal are also observed in the literature concerning other countries. The cysts of this species cited for the coasts of Northern Europe present characteristics similar to the cysts referred to in this communication as G. catenatum-like or small microreticulate cysts. The need to clarify the identity of cysts with microreticulation in the wall is discussed in order to identify the geographical distribution of the G. catenatum cyst.

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