The response of microzooplankton (tintinnid) community to salinity related environmental changes in a hypersaline marine system in the northwestern Arabian Gulf

Construction of large dams often wreaks havoc on coastal marine systems through hydro-biological alterations. In this study, we have investigated how salinity changes in the northwestern Arabian Gulf (NWAG) due to water regulation activities upstream of the Shatt Al-Arab River system (SAR) has influenced the hydrography and microzooplankton (tintinnid ciliates) community in the semi-arid shallow marine environment off Kuwait. Microzooplankton and water samples for environmental variables were obtained between 2004 and 2008 across several coastal and offshore locations (n = 436). Microzooplankton samples showed the presence of sixty-two species of tintinnids belonging to sixteen genera and ten families. Hydrography data revealed a continuous decrease in salinity in the NWAG from 2004 until 2006 (mean salinity: 37.3; CV: 0.09), and an increase thereafter (mean salinity in 2007-2008: 39.9, CV: 0.08). The minimum increase was reported in the offshore waters (0.50), and maximum in the northern areas upstream of Boubiyan Island (similar to 6). These changes associated with shifts in freshwater discharge from the SAR have adversely affected the hydrographical properties and phytoplankton stock post-2006. The seasonality (and heterogeneity) in hydrography were more pronounced in the low saline period of 2004-2006 than 2007-2008. As evident from multivariate statistical analyses, these changes have generated undesirable effects on the structural property indicators (abundance, biomass, and diversity), and distribution patterns of tintinnids in 2007-2008. Although agglutinated loricates constituted the most dominant group in the 2004-2008 period, the hydrographical changes post-2006 increased the relative abundance of hyalinated loricates. The biotic-abiotic interactions and distance-based linear models (DistLM) revealed that among the measured environmental variables, the cumulative effect of salinity, water temperature, dissolved inorganic nitrogen, silicic acid, and Chl a played a key role regulating microzooplankton community in 2004-2006 (p = 0.633, P: 0.1%), while a combination of factors silicic acid, salinity, water temperature, and Chl a (p= 0.422, P: 0.1%) were more important in 2007-2008. All together, species distribution patterns and complementary evidence from biotic-abiotic interactions suggest that the salinity increase post-2006 caused a significant shift in tintinnid community properties with possible repercussions on the functioning of pelagic food-web in the coastal and offshore waters of the NWAG. The present study thus offers prima facie evidence of changes in microbial grazer communities caused by anthropogenic alterations of river discharge into the Arabian Gulf in general and NWAG in particular.