Zooplankton Diversity and Abundance in the Western Pacific Ocean

Abstract

Zooplankton plays a crucial role in marine ecosystems by linking primary producers, such as phytoplankton, to higher trophic levels. This study explains the relationship between zooplankton abundance and phytoplankton availability at different depths and times of day in the water near Guam. Sampling was conducted aboard the R/V Thomas G. Thompson at three stations N, 147 °E; N, 149 °E; and N, 148 °E three different depths, 20, 200, and 600 m 9◦4◦14◦using a 1 m ring net with a 211 μm mesh size, and CTD was used to analyze how nutrient availability, chlorophyll-a, temperature, and diel vertical migration (DVM) shape zooplankton communities. While chlorophyll-a and zooplankton abundance showed no correlation ( = 𝑅2-0.106, p = 0.932), temperature showed a strong predictor, with surface layers (0-20 m) exhibiting a significant positive correction ( = 0.568, p = 0.031). Nutrient trends revealed no 𝑅2statistically significant depth-related accumulation (p > 0.05 for nitrate, phosphate, and nitrogen). Station 18’s low zooplankton abundance, despite midday sampling coinciding with DVM, was linked to food limitation from depleted chlorophyll and nutrients. Calanoid copepods overwhelmingly dominated all stations and depths (mean abundance: 116.4 ), underscoring 𝑚−3their resilience to variable food and nutrient availability as well as their central role in the ecosystem. Diversity indices highlighted station-specific patterns: Station 8’s deep layer (0–600 m) had the highest Shannon diversity (H’ = 2.23), while Station 18’s surface layer showed the greatest Margalef richness (D = 6.06). These results emphasize the interplay of thermal stratification, localized productivity, and behavioral adaptations in structuring zooplankton communities. Understanding ecosystem dynamics like chlorophyll and nutrients is important for zooplankton responses to environmental change.