The seasonal variation of dissolved nutrients, chlorophyll a and suspended sediments at Nelly Bay, Magnetic Island

A seasonal study of dissolved nutrients and chlorophyll a at Nelly Bay, Magnetic Island, in the central Great Barrier Reef (GBR) during 1993-1994, one of the driest climatic years in the previous century is reported. Comparison of nutrient concentrations in Nelly Bay with previous measurements suggest that significant changes in chlorophyll a, ammonium, and total dissolved nitrogen levels has occurred at this site during the last 5-6 years, prior to this study. Chlorophyll a was significantly correlated with suspended sediments (r = 0.49 P < 0.001), and dissolved inorganic phosphate (DIP) (r = 0.47, P < 0.001) throughout the study, with the correlations improving during high winds, for suspended sediments (r = 0.89, P < 0.001) and DIP (r = 0.57, P < 0.001). A highly significant correlation between DIP and chlorophyll a suggests that DIP is the main limiting nutrient in the bay. This correlation is weighted to the presence of Trichodesmium, a cyanobacterium that blooms prolifically in the GBR, and whose abundance was significantly correlated with low wind strength (r = -0.72,P < 0.02), chlorophyll a (r = 0.65), DIP (r = 0.82), and suspended sediments (r = 0.64, P < 0.02-0.05). (C) 2003 Elsevier Science B.V. All rights reserved.