Water quality in the Red Sea coastal waters (Egypt): Analysis of spatial and temporal variability

Abstract

In order to provide a background picture of the water quality of the Egyptian Red Sea a number of hydrological and chemical parameters have been measured bimonthly in 2000. Few data are available on this area, which is apparently subjected to an increasing human impact due to recreational (swimming and diving), industrial (mainly phosphate shipping and industry) and fishing=harbor activities. The results of the present study indicate that changes in the salinity and pH were not significant with highly oxygenated seawaters. The levels of suspended solids (as total suspended matter, TSM) and chlorophyll-a (Chl-a) were generally low and showed an homogeneous distribution in the study region. The ratio of chlorophyll-a to total suspended matter concentrations increased between November and March and decreased from May to September. Chlorophyll-a was significantly correlated with transparency and total suspended matter concentrations in July, September and November. Nitrogen, phosphorus and reactive silicate concentrations were generally low, and allowed classifying the Egyptian Red Sea coastal water as oligotrophic to mesotrophic. The middle region of the study area, which was located between Safaga and Qusair displayed relatively high phosphate contents when compared with other coastal areas. The high values of N:P ratios indicate that PO 4 À ÀP is the limiting factor for phytoplankton growth in the Red Sea coastal waters, with the possible exception of the middle region. Significant relationships were found between chlorophyll-a concentrations and nutrient levels in different sampling periods. Spatial distribution patterns of the studied variables revealed that productivity of the Red Sea coastal waters is mostly controlled by phosphate concentrations, salinity, temperature and dissolved oxygen.

Coral reef carbonate budgets and ecological drivers in the central Red Sea – a naturally high temperature and high total alkalinity environment

“…Central Red Sea reefs are characterized by unique environmental conditions of high temperature, salinity, TA, and oligotrophy (Fahmy, 2003;Kleypas et al, 1999;Steiner et al, 2014). On a global scale they support remarkable reef growth, sustaining well-established fringing reefs along most of the coastline.…”

“…Interestingly, our study also identified PO 3− 4 concentration as an abiotic correlate of reef growth. In the Red Sea, high N : P ratios indicate that P is a limiting micronutrient, e.g., for phytoplankton (Fahmy, 2003). PO 3− is not only essential for pelagic primary producers, but also for reef calcifiers and their photosymbionts, such as the stony corals and their micro-algal Symbiodiniaceae endosymbionts (Ferrier-Pagès et al, 2016;LaJeunesse et al, 2018).…”

“…Arguably, calcification under these conditions becomes energetically costlier (Cai et al, 2016;Cohen and Holcomb, 2009;Strahl et al, 2015;Waldbusser et al, 2016). In addition, ocean acidification stimulates destructive processes, for instance the proliferation of bioeroding endolithic organisms (e.g., Enochs, 2015;Fang et al, 2013;Tribollet et al, 2009). Apart from that, locally impaired reef growth due to an increased intensity or frequency of extreme climate events (Eakin, 2001;Schuhmacher et al, 2005), human impacts including pollution and eutrophication (Chazottes et al, 2002;Edinger et al, 2000), and other ecological events such as population outbreaks of grazing sea urchins or crown-of-thorn starfish that feed on coral can induce reef framework degradation (Bak, 1994;Pisapia et al, 2016;Uthicke et al, 2015).…”

Phosphorus physiological ecology and molecular mechanisms in marine phytoplankton

“…Historically, P-limitation was suspected in various areas in the global ocean Swift 1982, Smith 1984), and this topic has more recently seen renewed interest (Karl 2000, Wu et al 2000, Moore et al 2008. Phosphorus has been reported to occur at growth-limiting levels for phytoplankton in the subtropical Atlantic Swift 1979, Wu et al 2000), Mediterranean Sea (Berland et al 1972, Thingstad et al 2005, Red Sea (Fahmy 2003), and Gulf of Mexico (Hardison et al 2013). High N:P ratios, elevated alkaline phosphatase (AP) activity, molecular 12 SENJIE LIN ET AL.…”

Dissolved Organic Phosphorus Utilization by Phytoplankton Reveals Preferential Degradation of Polyphosphates Over Phosphomonoesters

“…P is incorporated into vital biomolecules that play essential roles in cellular structure (phospholipids), the storage and transmission of genetic information (DNA and RNA), energy transduction (adenosine 5 -triphosphate; ATP), metabolic signaling (inositol trisphosphate, (de)phosphorylated proteins and metabolites), as well as stress response and homeostasis (inorganic polyphosphate; poly-P) (Kornberg et al, 1999;Gray and Jakob, 2015). Although marine primary production is principally limited by either nitrogen or iron over most of the global surface ocean (Moore et al, 2013), P can be present at low or limiting concentrations in many marine systems, from the vast oligotrophic gyres (Rivkin and Swift, 1979;Wu et al, 2000;Moore et al, 2008;Moore et al, 2013) to coastal seas (Berland et al, 1972;Fahmy, 2003;Thingstad et al, 2005;Hardison et al, 2013). Rising anthropogenic inputs of nitrogen have also led to an increasing prevalence of P limitation in many ocean environments, especially in near-shore zones (Harrison et al, 1990;Fisher et al, 1992Fisher et al, , 1999Huang et al, 2003;Kemp et al, 2005;Zhang et al, 2007;Xu et al, 2008;Fu et al, 2012;Laurent et al, 2012;Turner and Rabalais, 2013;Kim et al, 2014).…”