Temporal Variations in Abundance and Species Richness of Zooplankton with Emphasis on Ichthyoplankton in the Subtidal Waters of Umm Al-Namil Island, Northwestern Arabian Gulf of the ROPME Sea Area

Zooplankton, including the ichthyoplankton, abundance and species richness over time in the subtidal waters of Umm Al-Namil Island, Kuwait Bay, were sampled and quantified from September 2016 to August 2017. At the same period, physicochemical measurements (i.e., water temperature, pH, salinity, dissolved oxygen and nutrient concentrations) occurred. A total of 9 larval fish families were identified: Acropomatidae, Bregmacerotidae, Bythitidae, Clupeidae, Engraulidae, Leioganthidae, Platycephalidae, Pseudochromidae and Sparidae, in addition to fish eggs. Other zooplankton were mainly represented by Copepoda, followed by Radiolaria and Molluska larvae. Generally, some sampling events (i.e., months) had 100% fish larvae, while others had 0% fish larvae. The physicochemical parameters showed variations at each sampling event as well as within the same season. Total zooplankton (including ichthyoplankton) mean abundance was highest in summer (22.65 ± 2.85 ind.5l-1), while winter (18.13 ± 1.64 ind.5l-1) and autumn (17 ± 2 ind.5l-1) mean abundance values did not significantly vary. The lowest mean abundance was observed in spring (14.33 ± 1.67 ind.5l-1). Mean species richness was highest during spring (7.22 ± 1.66), but not significantly different from autumn (7 ± 2). No significant difference was observed between winter (6.73 ± 1.64) and summer (5.90 ± 2.85). Overall, the results indicate that zooplankton species richness and abundance in Umm Al-Namil Island varied temporally in response to fluctuations in environmental conditions. Primary among these fluctuations is water temperature at different seasons of the year.