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Marine causeways are becoming more common in many coastal regions to improve vehicular transportation and social integration across landscapes segmented by bays and estuaries. The construction of barrier-type structures has profound implications by altering the geomorphological, hydrodynamic, and ecological conditions in the coastal marine environment. This study investigates the impact of one such newly constructed marine causeway in an enclosed bay in the Arabian Gulf. We hypothesized that the underwater structure of the bridge affects hydrodynamic and physicochemical conditions in the bay. Through extensive physicochemical monitoring, we found that the bridge acted as a physical barrier diminishing tidal currents, thereby resulting in decreased water exchange and heightened stagnation within the bay. Consequently, environmental gradients intensified and nutrient dynamics altered across the bridge. This will have implications for the plankton dynamics, ecosystem function, and overall health of the bay and its surrounding waters. Based on these results, it is recommended to increase efforts to mitigate the stagnation in the bay. Additionally, future coastal development needs to avoid further compromising the water exchange ability of the bay. Our findings also highlight the importance of continuous monitoring and adaptive management strategies to mitigate the environmental impacts of such developments. [Display omitted] • Field surveys conducted inside and outside the marine causeway in an enclosed bay. • A rapid decrease in ocean current was observed across the bridge. • The blockage effect demonstrated the bridge piers as a significant physical barrier. • Spatial gradients in physical and chemical properties inside and outside the bridge. • Changes in chemical characteristics in the bay due to the blockage effect. [ABSTRACT FROM AUTHOR]

Hydrographic variables were monitored in northwestern Arabian Gulf over the past three decades and the time-series data were statistically analyzed. The results show that while salinity has undergone several shifts, seawater temperature exhibited a steady increasing trend since the 1980s. The observed salinity shows strong correlation with Shatt Al-Arab River discharge indicating primary contribution of freshwater to salinity among other factors (evaporation and desalination effluent). Recent data show that salinity is at its highest level in the last 30 years with less pronounced seasonal variability in response to severe decline in the freshwater runoff into the northwestern Arabian Gulf. The changes in hydrographic conditions may have significant implications on hydrodynamics, water quality, and ecosystems in the Gulf. Thus, cooperation among the concerned countries - both coastal and riparian nations - would be essential for prevention of further major changes in the Gulf. [ABSTRACT FROM AUTHOR]

Continuous measurements of hydrographic, hydrodynamic, and water quality showed marked diurnal, tidal, and seasonal variabilities in Kuwait Bay, a stressed coastal system in the northwestern Arabian/Persian Gulf. Advection of water masses and seasonality in vertical mixing regulated the Bay's hydrographic and water quality properties. Intensive stratification in summer had substantial implications on the Bay environment. Kuwait Bay constantly exports dense bottom water laden with dissolved inorganic nutrients and organic matter to the central basin of the Gulf. The export was largest in August under strong water column stratification. These in-situ findings agreed well with earlier studies that corroborated Kuwait Bay as an important area where the phenomenon of reverse estuarine circulation originates in the Gulf. Thus, Kuwait Bay is a significant source of nutrients and organic matter to the Gulf Deep Water that flows into the core of the oxygen minimum zone in the northwestern Indian Ocean. • Dynamic diurnal hydrographic and water-quality variations with marked seasonality • Advection of water masses and vertical mixing contributes to the variability • Constant export of dense water mass from Kuwait Bay to the Arabian/Persian Gulf • The largest export in August when the water column stratified [ABSTRACT FROM AUTHOR]

This study evaluates the potential area and the key environmental factors supporting Sargassum bed restoration (SBR) in the highly turbid northwestern Arabian Gulf where rapid coastal development impinges on the marine ecosystem functioning. Water depth was a primary environmental factor governing the distribution of the subtidal macroalgae beds in these turbid waters. The relationship between Sargassum coverage and water depth measured by an echo sounder indicated optimal water depths where the maximum coverage was observed. The availability of stable hard substrate was another key factor introducing heterogeneity in Sargassum coverage. Potential area for the SBR estimated based on the optimal depths was 4.26 km2, whereas only 50% of the potential area (2.19 km2) was currently vegetated due to the absence of hard substrate. The outcomes of this study offer beneficial information toward implementation of the SBR as a part of mitigation measures in future coastal development plans in the region. • Sargassum distribution in the northern Arabian Gulf was measured by echo sounder. • Water depth and substrate were the main factors affecting the distribution. • The potential restoration area was estimated based on the optimal depth. • Only 50% of the potential area was vegetated due to the absence of hard substrate. • The study supported great potential for expanding the area of Sargassum beds. [ABSTRACT FROM AUTHOR]

Environmental vicissitudes cause short-term variability in plankton dynamics. The effect would be more pronounced in shallow, semi-enclosed tidal coastal systems. Here, we analyzed diurnal fluctuations in coastal phytoplankton and environmental factors in relation to seasonal tidal cycles (October 2016, Fall and February–March 2017, Winter) in a sub-tropical coastal embayment (Kuwait Bay) in the northwestern Arabian Gulf. Water-column profiles were obtained for chlorophyll, photosynthetically active radiation (PAR), salinity, temperature, and dissolved oxygen. Winter was characterised by relatively cold, well‑oxygenated, nutrient-rich, and high saline waters than the fall. Nutrient levels were high during low tide and low during high tide. High-performance liquid chromatography (HPLC) analysis of phytoplankton marker pigments revealed the presence of twelve different phytoplankton functional groups. Diatoms and dinoflagellates were the most dominant groups with significant surface-bottom differences during both seasons. The phytoplankton biomass (Chl a) was the highest during the low light hours of the day with apparent day-night differences. The picoplankton community was mainly represented by the autotrophs Synechococcus (in Fall) and picoeukaryotes (in winter) with clear seasonal patterns. Compared to picoautotrophs, picoheterotrophic biomass was relatively high during winter. This study revealed that light availability and tidal mixing are the factors regulating variability in the phytoplankton community composition and biomass (Student''s t -test, two-tailed; (P ≤ 0.1) in Kuwait Bay. High-resolution monitoring programs are essential to capture the natural variability of phytoplankton and its implication on the biogeochemistry of the shallow tide-dominated coastal systems. • Diurnal study was conducted in Kuwait Bay, Northwestern Arabian Gulf during two climatically different seasons. • Phytoplankton community was characterised by advanced methods, HPLC and flow cytometer. • Seasonal shift in phytoplankton community was observed. • The tide driven mixing and advection play major role in community variations in the Bay. • Biomass was high in low tide period and lower during high tide. [ABSTRACT FROM AUTHOR]

Sedimentary processes are expected to play a crucial role in macronutrient cycling of the shallow Arabian Gulf. To investigate this aspect, sediment cores were collected from the shallow intertidal and subtidal expanses of the first Marine Protected Area (MPA) of Kuwait in the Northwestern Arabian Gulf (NAG). Porewater nutrient profiling and whole core incubation experiments were conducted to measure the nutrient fluxes, both with and without the addition of the nitrification inhibitor allylthiourea (ATU). The porewater data confirmed the potential of sediments to host multiple aerobic and anaerobic pathways of nutrient regeneration. The average (±SD) of net nutrient fluxes from several incubation experiments indicated that ammonium (NH 4 +) predominantly fluxed out of the sediment (3.81 ± 2.53 mmol m−2 d−1), followed by SiO 4 4− (3.07 ± 1.21 mmol m−2 d−1). In contrast, the average PO 4 3− flux was minimal, at only 0.06 ± 0.05 mmol m−2 d−1. Fluxes of NO 3 − (ranged from 0.07 ± 0.005 to 1.16 ± 0.35 mmol m−2 d−1) and NO 2 − (0.03 ± 0.003 to 0.71 ± 0.21 mmol m−2 d−1) were moderate, which either reduced or reversed in the presence of ATU (−0.001 ± 0.0001 to 0.01 ± 0.0001 mmol m−2 d−1 and -0.001 ± 0.0003 to 0.006 ± 0.001 mmol m−2 d−1 for NO 3 − and NO 2 − respectively). Thus, this study provides preliminary experimental evidence that nitrification can act as a source of NO 3 − and NO 2 − as well as contribute towards the relatively high concentrations of NO 2 − (>1 in the gulf waters. [ABSTRACT FROM AUTHOR]