Zooplankton Diversity and Community Composition along 167°W in the Equatorial Pacific

Abstract

Zooplankton are important primary consumers in the marine food web and lead an important role in carbon cycling in the open ocean. Understanding what influences zooplankton community composition can help us understand the impacts of climate change on this delicate relationship. Data was collected from 28 December 2023, through 10 January 2024, on the R/V Thomas G. Thompson near American Samoa between 5°S and 5°N along 167°W. A closing zooplankton net with 200μm mesh was used for net tows from 200m to surface at stations between 5°S and 5°N along the 167°W longitudinal line. Zooplankton abundance was highest at the equator with 345 organisms m-3 and increased from 5°S to the equator; and decreased from the equator to 5°N in a bell-curve shape. Species diversity (Shannon-Weiner) was lowest at the equator (0.878) and highest at 1°N (1.067) and 5°N (1.059). Calanoid copepods had the highest abundance over all sites (74-88% of composition), and north of the equator, calanoid copepods and gelatinous zooplankton (larvaceans) dominated most of the species composition. There were no significant relationships between species community composition and temperature, salinity, or nutrients. Results demonstrate that higher water temperatures and different current regimes impacted abundance and species presence during the 2023 – 2024 Strong El Niño. With many processes occurring with zooplankton in the open ocean, it may be that multiple variables are impacting the resulting diversity and abundance relationships. Monitoring zooplankton composition over time is vital for monitoring the health of our oceans as it has implications for global fisheries and carbon cycling.