Effect of Temperature, Cadmium and Pyrene on Rhodomonas Sp. (Karsten, 1898) Adapted to the Coastal Waters of Ghana

Abstract

Global projections suggest that human-induced factors such as climate change and pollution are altering the productivity of marine ecosystems with potential adverse consequences for nutrition and livelihood in many coastal communities. However, the combined effects of these stress factors remain largely unknown, particularly for tropical organisms. Using a microcosm experiment, this study investigated the response of the microalgae Rhodomonas sp., a major primary producer in many marine systems, to warming (2 – 6 °C above the average sea surface temperature of Gulf of Guinea), as well as pollution by cadmium (0.1, 1, 10 and 100 μgL-1) and pyrene (0.2, 2, 20, 200 μgL-1). Response of the species was assessed using its growth rate, dry weight, protein, lipid, carbohydrate contents and catalase activity. The results suggest that the combination of cadmium and pyrene pollution did not impact lipid content of the algae. In contrast, average dry weight (0.125 ± 0.003 μgcell-1) of the cells increased (≈ 21 %) when pyrene and cadmium pollution exceeded 2 μgL-1 and 1 μgL-1 respectively. The increase in dry weight was related to increasing protein content of the cell. This was observed even when cells were exposed to warming, indicating that Rhodomonas sp. are able to buffer impact of environmental stress by producing heat shock proteins of relatively higher molecular weights. On the other hand, carbohydrate content of the cells decreased (≈ 86 %) when cadmium pollution exceeded 10 μgL-1 irrespective of pyrene pollution. Catalase activity, which indicates mechanism used by cells to neutralise impact of the stress conditions decreased (≈ 32 %) when pyrene and cadmium exceeded 0.2 μgL-1 and 0.1 μgL-1 respectively. These observations highlight the impact of multiple human-induced factors on marine organisms.