Influence of Seasonal Variation and Anthropogenic Activities on Elemental Compositions in Zooplankton: A Year-Long Case Study from the Jeddah Coast of the Red Sea

Zooplankton, one of the most important groups in the ocean, serves as a pivotal connection in food webs that sustain a variety of marine life, making it imperative to investigate their spatial–temporal variations in elemental concentrations. Here we measured the concentrations of 20 common elements (including those trace/heavy metals) in the zooplankton population along the Jeddah Coast of the Saudi Arabian Red Sea over a year from October 2013 to September 2014. Our results indicated that mean concentrations of elements were broadly consistent between coastal and offshore areas within a 2 km range, with notable exceptions being higher Zn and lower Cd levels at coastal sites. A decline in concentrations of total organic carbon (TOC), total nitrogen (TN), and Cd was observed from the south to the north in offshore areas (R < − 0.22, p < 0.05), aligned with findings from prior Red Sea studies. Notably, this pattern was less pronounced in coastal areas, hinting at possible anthropogenic impacts. Conversely, Al, Mn, Fe, and Cu concentrations were positively correlated with latitude (R > 0.18, p < 0.05), potentially due to the rapid urban development and tourism activities in Northern Jeddah. Seasonal variations were also significant: elements such as Na, Mg, K, Cr, Cu, Zn, and Mo peaked during the fall and winter. TOC, TN, P, and Cd levels rose in late winter or spring, aligning with the timing of the Spring Bloom, and exhibited a moderate increase in the summer. Al, S, Mn, Fe, Ni, Sr, and Pb concentrations escalated in the summer, possibly due to the higher energy demands, as thermal plants in Saudi Arabia predominantly utilize crude oil as fuel. Conclusively, this study is the first worldwide to outline the annual elemental fluctuation patterns within the zooplankton community, underlining the need to consider seasonality in environmental risk assessments. Graphical Abstract: (Figure presented.).