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As on land, plants are the real producers in the sea, and on them depend all marine living resources and the basic sustainability of ecosystems. Primary production is performed by chlorophyll-bearing plants ranging from the tiny phytoplankton to the giant kelps through the process ofphotosynthesis. Zooplankton play an important role as secondary producers, and together with phytoplankton they support the vast assemblages of marine food chain with all their diversity and complexity. Data on chlorophyll pigments, phytoplankton and zooplankton are regarded as a sound basis for environmental appraisal of ecosystems. This paper presents a set of data collected from the Saudi Arabian coastal waters near the desalination plants in AI-Jubail. Materials were collected from six different sites covering the intake and discharge zones during cruises carried out in 1997–1998. Analyses of chlorophyll pigments were made using the spectrophotometric method. Plankton samples were collected using a Nansen plankton net with a mesh size of 75 μ and analyzed following standard procedures. Chlorophyll a, b, c and phaeophytin are the most commonly occurring pigments in seawater. Their concentrations showed wide fluctuation. The phytoplankton community was composed of 35 genera representing the Diatoms, Dinoflagellates and blue- green algae. Zooplankton were composed ofProtozoa, Coelenterata, Ctenophora, Aschelminthes, Annelida, Mollusca, Arthropoda, Echinodermata and Chordata. Arthropoda, represented by Cladocera, Copepoda and Crustacean larvae, formed the largest group followed by Chordata. The distribution of phyto- and zooplankton was examined and discussed on a seasonal, annual and inter-annual basis. In terms of species, overall species composition was not affected by plant discharge. The study brings out a greater understanding of the changes experienced by biotic communities as a result of impingement, entrainment and entrapment consequent to water passage through the plant structures. The study reflects the ecological relationships that the phytoplankton and the zooplankton of the region possess with respect to intake and discharge. Further, the study has brought to light a very redeeming feature of the ecosystem to sustain its productivity and planktonic abundance. It was observed that seawater temperature, conductivity and total suspended solids did not act as limiting factors. Besides throwing much light on the little known biological aspects of desalination sites, the data provided constitute a significant addition to the knowledge base of marine living resources in an industrial zone of Gulf coastal waters.

A study was carried out in the sea adjacent to a major MSF plant where a new 24MGD SWRO plant is being commissioned. Data were collected on the topographical feature of the marine basin, water quality and plankton of the intake zone. The incidents of planktonic bloom, influx of invasive organisms like jellyfish and macrofouling organisms and ingress of marine algae were monitored regularly. The Intake Bay of the plant is a well designed man-made structure studded to the coast. The marine basin in Al-Jubail, is for geological reasons, a shallow gently sloping shelf while the bay proper is a dredged, deeper basin. The area outside the bay is a vast sea grass bed and the seafloor sediment is sandy. The drag of seawater maintained by the intake pumps facilitates the transport of sediment particles, uprooted algae and floating objects creating fouling problems inside the plant. Seawater temperatures, conductivity, pH, dissolved oxygen and trace metals were found to be very much benign to the trouble free operation of the plant. Influx of jellyfish, noticed during the summer, was not found to be very severe. Data on plankton showed the presence of many phyto and zooplankton organism of biofouling potential in the plant. Total suspended solids indicated the possibility of the intake bay becoming a source of elevated Silt Density Index (SDI) for the new SWRO plant. The paper considers the data in detail and discusses the effects of environment on the desalination plant in Al-Jubail and suggests certain strategies for the protection of seawater intakes and some points useful in the siting and design of coastal seawater intakes in the region.