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.
