Biodiversity of Mesozooplankton in the Oligotrophic Hypersaline Waters of the Western Arabian Gulf

Begum, M., Madhusoodhanan, R., Joydas, T.V., Asharaf, M., Alnuwairah, M.A., Ramakrishnan, S., Manikandan, K.P., and Al-Suwailem, A., 2024. Biodiversity of mesozooplankton in the oligotrophic hypersaline waters of the Western Arabian Gulf. In: Phillips, M.R.; Al-Naemi, S., and Duarte, C.M. (eds.), Coastlines under Global Change: Proceedings from the International Coastal Symposium (ICS) 2024 (Doha, Qatar). Journal of Coastal Research, Special Issue No. 113, pp. 915-920. Charlotte (North Carolina), ISSN 0749-0208. The biodiversity of zooplankton was assessed in the Western Arabian Gulf (WAG), a region previously understudied in this context. Through extensive sampling, this study delineates spatial (Northern, Central, Southern, Coastal, Offshore) and temporal (Fall, Winter, Spring, Onset of Summer and Summer 2002-2003) variations in zooplankton populations across WAG. The study revealed 181 species of zooplankton belonging to 92 families, with total density ranging from 1,395 to 3,494 ind./m3 (mean 2,307 ind./m3). Seasonal fluctuations were evident, with higher abundances in winter and spring. Zooplankton biomass ranged from 89.01 to 1176.3 mg/m3 (mean 504.4 ± 277 mg/m3). Dry biomass measurement revealed significant spatial and latitudinal gradients, with offshore areas (678.4 ± 344 mg/m3) recording 57% higher than coastal regions (303.4 ± 145 mg/m3). The differences between the offshore and coastal areas and the latitudinal trends were statistically significant (P< 0.05). Shannon-Wiener diversity (H') ranged from 3.1 to 4.09 (mean 3.5), exhibiting seasonal variation from 3.1 (onset of summer) to 4.09 (late fall). Copepoda, Cladocera, Appendicularia, Ostracoda, and Chaetognatha were major zooplankton groups. The southern waters had higher species richness, followed by the northern and central waters during the study period. Penilia avirostris, Oikopleura spp., Parvocalanus crassirostris, Euconchoecia aculeate, Corycaeus spp., Oithona plumifera, Oncaea coniferra were the dominant zooplankton species. The spatial and seasonal patterns in zooplankton in the coastal and offshore waters off KSA thus allude to the influence of different oceanographic variables, including physical, chemical, and biological, acting in tandem on plankton standing stock and distribution patterns in the WAG. The study also underscores the necessity of long-term oceanographic monitoring to understand planktonic food web interactions and their implications for regional fisheries management, particularly in light of climate change.