Characteristics and renewal of zooplankton communities under extreme environmental stresses in the oligotrophic hypersaline Arabian Gulf

Abstract

Impacts of the exceptionally high temperature and salinity on species composition, abundance, biomass and diversity of zooplankton communities were examined in the central Arabian (Persian) Gulf in late winter and summer of 2010 and 2011. Remarkably diverse zooplankton assemblages were characterized with small calanoids (Paracalanus aculeatus and Temora longicornis), cyclopoids (Oithona nana, Oithona plumifera, Corycaeus flaccus and Corycaeus lautus) and harpacticoids (Euterpina acutifrons) with relatively low abundance and biomass. Overall, the low biomass and abundance were not significantly associated with phytoplankton, whereas zooplankton faunal similarities were significantly correlated with water properties measured as environmental distances across sampling sites. Spatially, the lowest abundance, biomass and diversity occurred in extremely saline nearshore waters off the western Qatar peninsula, whereas the highest abundance, biomass and diversity consistently appeared at northeast offshore locations that periodically encounter nutrient and species-rich but low-salinity water entering the Arabian Gulf via the Strait of Hormuz. Numerically, the relative dominance of calanoids along with lower salinity and high chlorophyll-a concentration in the northeast Arabian Gulf implies that zooplankton populations are likely replenished by the seasonal (summer) transport of species from the Gulf of Oman and the Arabian Sea, which may explain partly the high variations of species richness and zooplankton abundance previously reported in the region. Given increasing evidence of climate-change induced responses of zooplankton, our findings suggest that in the semi-closed Arabian Gulf resident populations stressed by the harsh environment are likely to continue to be sustained only by invading water masses during the summer.