Temporal Dynamics of Phytoplankton in The Coral Reef and Open Water in The Gulf of Aqaba, Red Sea

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Abdul Karim M. Farrah
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The major objectives in this study were to quantify the short-term (minutes to weeks) variations of phytoplankton over the coral reef (Reef site) and at a near-by the open-water (Away site ), and to evaluate the roles of currents, behavior and localized predation in the generation of the observed variations. The study was carried out on 10th of October until Zth of Dec 99 in the Gulf of Aqaba (Eilat ) / Red Sea. Phytoplankton are present throughout the lighted regions of all seas, including under ice in polar areas. Because the phytoplankton are the dominant plants in the ocean, their role in the marine food chain is very important. One of the most ubiquitous characteristics of oceanic phytoplankton is its high level of temporal and spatial variations, termed "Patchiness" due to physical and biological parameters. The low-frequency fluctuations (millennia, decadal, seasonal) are fairly well documented, but rapid changes, (The study ) on the scale of minutes to hours, are poorly understood. Possible reasons for high-frequency fluctuations in plankton abundance include, physical advection, localized population growth, interactions with patchy food or predators, and behavior. Water samples were obtained with two large submersible pumps, delivering the pumped water to shore via PVC pipes. Both pumps were deployed at 8 m depth: one at the reef site, 40 m off shore, attached to a tripod with the intake opening suspended 0.75 m above bottom, and the other at the open waters (away site), 163 m off shore, where the pump was attached to a mooring line with its intake positioned 34 m above bottom (42 m depth) . The parameter used to quantified phytoplankton abundance was extracted Chlorophyll this pigment is a good indicator for phytoplankton biomass . Over all the data sampling, the chlorophyll concentration (Away and Reef sites) varied from 135 to 509 ngr L ¹, with an average of 312 and CV of 18.1% (N=532). Phaeopigments (Away and Reef sites ) vary between 13 to 270 ngr L` , with an average of 81 and CV of 32.5% (N=529). . Shorter-term variations in the chlorophyll were much smaller for the hourly samples within single diel cycles, with average CV values 6.9 and 7.6%, for the Away and Reef sites, respectively. Even smaller variations (CV=4.3 and 5.4%, respectively) were found in the series of 15 min sampling in the eight 4 hr long sessions. Chlorophyll concentrations at day time in the (Away and Reef) were much higher than night time with an average of difference (Night minus day). Phaeopigment concentrations Away site at day time were more than Night time , but much less in the Reef site at day time with an average of different ( Night minus Day) . The phytoplankton community was dominated by Synecochoccus,which formed over 97% of the cells counted under the epi-fluorescent microscope. The Coefficient of Variation (CV) was used throughout as our principal parameter of temporal variations in the plankton. Statistical analysis were made using Statistica for Windows (Version 99).
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