Impact of the Island Mass Effect on Zooplankton Community Composition Around the NAM-2 Coral Atoll in the Western Pacific Ocean

Abstract

Phytoplankton acts as the base of the marine food web, providing energy to higher tropic levels such as zooplankton. Zooplankton are an intermediate part of the food chain that can provide evidence of an area with high productivity. The focus of this study was to investigate the Island Mass Effect (IME) and its impact on zooplankton communities around the NAM-2 Atoll located to the southeast of Guam. Data was collected on the TN440 research cruise on the R/V Thomas G. Thompson from December 29th, 2024, to January 11th, 2025. Zooplankton nets were deployed at five stations around the unmapped atoll, NAM-2, (09º08’40’’N, 148º07’50’’ E), and three stations on the 149ºE WOCE line in the open ocean, specifically at latitudes 5ºN, 9ºN, and 15ºN. Zooplankton metrics of abundance and diversity, current direction, temperature, nutrients, and bathymetry were measured around the NAM-2 Atoll and the open ocean to observe the biological productivity of the IME. The highest abundance of zooplankton throughout all of the sites were the calanoid copepods, followed by the cyclopoid copepods, and then the chaetognaths. There was a statistically significant relationship between copepods and their predator, chaetognaths. There was no statistical significance between zooplankton abundance and diversity between the atoll and open ocean sites and among the variables of temperature, nutrients, current direction, and bathymetry. These factors likely still impacted the abundance and diversity of zooplankton. These factors, along with the predator-prey relationship between copepods and chaetognath, may still indicate NAM-2 as a biologically productive area, according to the IME. Also, the varying current directions may bring different compositions of zooplankton to the study stations. Further research is needed to discover the complete picture of this location, which could eventually lead to contributions to Guam’s fishing economy.