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Mesoscale and Nutrient Conditions Associated with the Massive 2008 Cochlodinium polykrikoides Bloom in the Sea of Oman/Arabian Gulf
Cochlodinium polykrikoides formed large blooms in the coastal waters of Oman from October 2008 through mid-January 2009, and satellite images from Aqua-MODIS and region-wide reports suggest that this bloom was found throughout the Arabian Gulf and Sea of Oman for more than 10 months. The unusual occurrence of this species appears to have supplanted the more regularly occurring bloom species, Noctiluca scintillans, in 2008–2009. For the first 2 weeks of the coastal Omani bloom, C. polykrikoides abundance was near monospecific proportions, with cell densities ranging from 4.6 × 103 to 9 × 106 cells L−1 and very high levels of chlorophyll a (78.0 μg L−1) were also recorded. The regional progression of the bloom likely began with stronger than normal upwelling along the Iranian and northern Omani coasts during the southwest monsoon in late summer, followed by discharge of unusually warm coastal plume water along the coast of Oman with the reversal of monsoonal winds in late October. The occurrence and persistence of high densities of C. polykrikoides in Oman coastal water were also significantly influenced by an elevated nutrient load and warmer than normal temperatures. Concentrations of nutrients, especially NH4 +, urea, PO4 3−, and organic nitrogen and phosphorus, were manyfold higher than observed in the year prior or since. These findings suggest that mesoscale features were important in bloom dynamics more regionally, but locally the bloom was sustained by nutrient enrichment supplemented by its mixotrophic capabilities
Seasonal variability of size-fractionated phytoplankton biomass in a sub-tropical embayment, Muscat, Sea of Oman
The contribution of three different cell size classes of picoplankton: 0.74-2 μm, nanoplankton:2–20 μm and microplankton, >20 μm of the phytoplankton population and their relationship to environmental conditions were studied over two annual cycles at one station in Bandar Khyran Bay, Sea of Oman, from May 2006 to August 2008. Nanoplankton was the most important class contributing 54.4% to total Chl a (range 6-82%). Its seasonal highest concentrations was during the cold periods when temperature ranged from 28-29 °C in fall and near 24 C in winter when the supply of nutrients was sufficient to sustain their growth. Picoplankton had the second level of the contribution, comprising (23.5%, range 4-74 %) of the total Chl a. and their concentration was generally constant (0.04-.06 μg l–1) throughout the study period. The drop of picoplankton population coincided with an increase in the microplankton and nanoplankton populations indicating a high grazing pressure exerted on the picoplankton population. Microplankton size-class occupied the third level of the contribution comprising (22.2%, range 3-65 %). Their general concentration was below 0.1 μg l–1 and only dominant when temperatures were lowest and nitrate, nitrite, silicate and phosphate concentrations were the highest. The temporal variability observed was associated with changes in the nanaoplankton indicating that in some cases, it is the small fraction of phytoplankton that drives changes in abundances and productivity