Heterotrophic consumption may mask increasing primary production fuelled by anthropogenic nutrient loading in the northern Arabian/Persian Gulf.

Monthly measurements of nitrate, nitrite, ammonium and phosphate at three stations off Kuwait during 2002-2015 revealed considerable inter-annual variability, broadly corresponding to fluctuations in the Shatt-al-Arab River discharge, but a lack of secular increasing trend. Nutrient enrichment experiments during two seasons revealed nitrate uptake, chlorophyll build-up and growth of micro-phytoplankton, even in the presence of ammonium, provided the availability of phosphate. Primary production was mostly nitrogen limited, but anthropogenic nitrogen supply may eventually make it phosphorus limited, especially in summer and in the open Gulf. Anthropogenic nutrient inputs appear to have enhanced biological productivity of the northern Gulf, but heterotrophic consumption, indicated by high respiration rates, probably prevented accumulation of phytoplankton biomass, accounting for the observed lack of chlorophyll increase over the past three decades. Consequently high total organic carbon and emerging hypoxia in the Gulf may lead to expansion/intensification of the oxygen minimum zone of the Arabian Sea.

Salinity-driven decadal changes in phytoplankton community in the NW Arabian Gulf of Kuwait.

Evaluation of hydrological data obtained between 2000 and 2013 from a time series station in Kuwait Bay (station K6) and an offshore southern location (station 18) off Kuwait showed drastic increase in salinity by 6 units. We tested the hypothesis that increased salinity impacted phytoplankton community characteristics in these semiarid waters. The Arabian Gulf receives seasonal freshwater discharge in the north via Shatt Al-Arab estuary with a peak during March-July. A north to south gradient in the proportion of the freshwater exists between station A in the vicinity of Shatt Al-Arab estuary and station 18 in the southern offshore area. At station A, the proportion of freshwater was the highest (25.6-42.5%) in 1997 but decreased to 0.8-4.6% by 2012-2013. The prevailing hyperhaline conditions off Kuwait are attributed to decrease in the river flow. Phytoplankton data showed a decrease in the number of constituent taxa in the last one decade from 353 to 159 in the Kuwait Bay and from 164 to 156 in the offshore area. A shift in their biomass was caused by a decrease in diatom species from 243 to 92 in the coastal waters and from 108 to 83 in the offshore areas with a concomitant increase of smaller algae. Mutivariate agglomerative hierarchical cluster analysis, non-metric multi-dimensional scaling, and one-way analysis of similarity analyses on phytoplankton data at different taxonomic levels confirmed significant changes in their community organization on a decadal scale. These evidences support our hypothesis that the salinity-related environmental changes have resulted in a coincidental decrease in species diversity and significant changes in phytoplankton community between the years 2000-2002 and 2012-2013, off Kuwait. This in turn would affect the pelagic trophodynamics as evident from a drastic decrease in the catch landings of Tenulosa ilisha (Suboor), Carangoides sp. (Hamam), Otolithes ruber (Nowaiby), Parastromateus niger (Halwaya), and Epinephelus coioides (Hamoor) in Kuwait.