Spatio-temporal variation of microphytoplankton communities in Obhur Creek, the central Red Sea

The abundance and distribution of microphyto-plankton and related physicochemical factors were assessed monthly in Obhur Creek, the central Red Sea. Sampling was carried out near the entrance, the middle and end parts of the creek. During the course of the present study, the Red Sea was characterized by predominantly oligotrophic conditions. Nutrient concentrations were relatively higher in the end part of the creek compared to the two other study sites. Chlorophyll a was also low throughout the year (average: 0.35 ± 0.32 mg m⁻³), except in May when it showed clear peaks at open-water and middle sites of the creek (1.85 and 1.04 mg m⁻³, respectively). Phytoplankton abundance followed a similar pattern to that of chlorophyll a with considerably higher abundance at these sites in May (3063.27 × 10³ and 1082.34 × 10³ individuals m⁻³, respectively). This unusually higher abundance was mostly due to the proliferation of the diatom Pseudo-nitzschia cf. delicatissima (Cleve) Heiden. Silicate concentrations were statistically significantly correlated with total phytoplankton. A total of 220 phytoplankton species were recorded during the study period (117 diatoms, 99 dinoflagellates and four cyanophytes). Diatoms dominated in the phytoplankton abundance (75%) and were followed by dinoflagellates (20%), while cyanophytes accounted for a minimal proportion. Of all phytoplankton species observed during the study, 21 diatom and four dinoflagellate species were considered as new records for the Red Sea, and two diatom and 14 dinoflagellate species were listed as harmful algal species worldwide.

Conclusion
The present study identifies a shifting pattern in the prevailing oligotrophic conditions of the Red Sea coastal waters. The major outcome of this study was the documentation of different phytoplankton species from the region, of which 21 diatom and four dinoflagellate species were considered as new records for the Red Sea. Another ecologically important aspect noted was the peculiar growth of the potentially harmful diatom species Pseudo-nitzschia cf. delicatissima. The higher density of this species observed in May was mainly due to the anthropogenic impact exerted on the system over a continuous period of time. Activities that alter the health status of the creek should be controlled and proper monitoring should be maintained in order to rejuvenate the system. Consequently, continuous monitoring of the coastal waters of the Red Sea is necessary to maintain a healthy ecosystem of ecological importance for the future generations.

Acknowledgements

This project was funded by the Deanship of Scientific Research (DSR) at King Abdulaziz University, Jeddah, Saudi Arabia, under the grant No. [G-462-150-40]. The authors, therefore, acknowledge with thanks DSR for technical and financial support. We extend our gratitude to Prof. Wafaaa Sallam for her critical reading of the manuscript and Mr. Reny P. Devassy for the assistance provided during the sampling process.

Author’s contribution

MMS conceived the idea of the project. MMS, MAA and AAK carried out the sampling and the analysis. MMS wrote the initial manuscript, MAA and AAK provided suggestions and recommendations. The authors declare that there is no conflict of interest regarding the publication of this article.

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