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.

Aim: The present study aimed to understand the physico-chemical factors affecting the abundance and species richness of phytoplankton communities, with emphasis on diatoms at the end of the intertidal zone and start of subtidal zone. Methodology: Water quality and phytoplankton community species richness and abundance were measured in the subtidal waters of Umm Al-Namil Island, Kuwait Bay. Kruskal-Wallis statistical approach was used to measure the effect of various environmental parameters on abundance and species richness as well as abundance-species richness relationships using R statistical software. Results: The physico-chemical parameters showed variations at each sampling event as well as within the same season. Total phytoplankton mean abundance values in summer (22.26 ± 0.66 ind. 5l-1) and winter (21.63 ± 0.52 ind. 5l-1) did not significantly vary and the lowest mean abundance was observed during spring (26.36 ± 0.33 ind. 5l-1). Species abundance showed clear pattern with the events, resulting in somehow a negative relationship. Mean species richness was highest during autumn (24.59 ± 1.51), while no significant difference was observed between spring (11.09 ± 0.33), winter (10.47 ± 0.51) and summer (10.11 ± 0.66). The results indicate that phytoplankton species richness and species abundance in Umm Al-Namil Island varied temporally in response to fluctuations in environmental conditions. Interpretation: The end of intertidal zone and beginning of subtidal zone is affluent in diverse forms of phytoplankton species, specifically diatoms since Kuwait Bay is a eutrophic area mainly due to sewage and urbanization. Therefore, a temporal monitoring is required in order to observe any changes in either physico-chemical or biological factors with time and that will help in future conservation and restoration programs. Conservation approaches should be considered seriously since some diatoms like Melosira moniliformis, Gyrosigma diminutum, Fragilaria martyi, Hemidiscus cuneiformis, Planktoniella sol and Amphiprora plicata have been observed only at one event despite abundance and season.