Morphological Variations of Dinophysis caudata (Saville-Kent) in the Coastal Area of Samut Sakhon Province

Abstract

This study on morphological variations of Dinophysis caudata (Saville-Kent) was carried out in the coastal area of Samut Sakhon Province. Sampling stations were located on the western part of Tha Chin estuary in Khasa-khao village where there were frequent records of the red tide phenomena. Physico-chemical parameters were measured with water and phytoplankton samples being collected monthly from June 2007 to May 2008. D. caudata was isolated and photographed under a compound microscope for the measurement of cell dimensions with an Image Pro-plus program. The presence of 56 morphotypes of D. caudata were recorded with the cell width varying from 10.08 to 35.60 mm (average 21.65 ± 4.27 mm) and cell length in the range of 29.54 – 76.56 mm (average 46.03 ± 8.45 mm). These characteristics can be divided into 4 groups based on frequency of occurrence in terms of cell length and width. The most dominant cell type was the small-sized cells with cell widths and lengths in the range of 18 - 25 mm and 38 - 52 mm, respectively. The occurrence in terms of these small cells tended to follow the variation in pH and nitrate-nitrogen concentrations in seawater, while the abundance of large-sized cells (> 30 mm width and > 64 mm length) showed a significant relationship with DIN:DIP ratio in the water column.