Cadmium toxicity and random motility studies using marine dinoflagellates

The marine biota is exposed to heavy metal residues of industrial and agricultural processes. The effects of these metals on phytoplankton are of particular interest because they represent the first link in the food chain and are able to transfer the metal to higher trophic levels. Members of the phytoplankton population include the diverse community of flagellated unicellular, mostly photosynthetic, microorganisms called dinoflagellates.; The effects of cadmium (Cd) on the growth of two marine dinoflagellates Scrippsiella narragansettensis and Heterocapsa triquetra were measured under different medium composition. To investigate the role of metal speciation, experiments were carried out in media prepared with natural seawater from Narragansett Bay (NBSW) and artificial seawater (ASW) under different ionic compositions. Reproduction rates of cells grown with Cd (1 and 2 × 10−6 M Cd) showed only a slight decrease compared to cells grown without the heavy metal under all the different conditions tested. The results show that the effects were concentration-dependent. After a 10-days exposure to the metal, cell density decreased with an increase in total Cd concentration (1, 3 and 5 × 10−6 M Cd). In addition, cells exposed to the metal for a second consecutive transfer into Cd-containing media showed a greater decrease in growth rates compared to cultures exposed to the metal during the first transfer.; Because swimming activity has great significance for dinoflagellates, the stopped-flow diffusion chamber (SFDC) was tested as a tool to measure the random motility coefficient of a marine dinoflagellate (Scrippsiella narragansettensis). With the use of the chamber, random motility was modeled as diffusion in one-spatial dimension, in which the random motility coefficient is analogous to the diffusion coefficient. Migration of cells inside the chamber was observed and video recorded using a dark-field microscope connected to a TV/VCR setup. The mean random motility coefficient was found to be 5.98 × 10−4 cm2 s−1 . The SFDC proved to be an efficient tool to measure the random motility of marine dinoflagellates, showing its potential application to observe and measure how environmental stresses affect this important characteristic, as well as the chemotactic behavior of these and similar aquatic microbial populations.