Sheridan, C.C.¹, M.R. Landry², C. Benitez-Nelson³ and J. Montoya⁴

¹University of Hawaii, Department of Oceanography, 1000 Pope Rd., Honolulu, Hawaii, 96816, USA, Tel: 808-956-6050, Fax: 808-956-9516, E-mail: sheridan@hawaii.edu, ²University of Hawaii, Department of Oceanography, 1000 Pope Rd., Honolulu, Hawaii, 96816, USA, ³Department of Geological Science, University of South Carolina, 700 Sumter Street, EWS 408, USA, ⁴School of Biology, Georgia Institute of Technology, 310 Ferst Drive, Atlanta, GA, USA

A synthesis of Hawaii Ocean Time-series (HOT) mesozooplankton data from 1994-2002: temporal variability and contribution to elemental budgets

Temporal variation in microplankton community structure at the Hawaii Ocean Time-series (HOT) Station ALOHA has challenged the notion that plankton in subtropical ocean gyres are comprised of stable “climax” communities. These observations of decadal change are now extended to mesozooplankton populations in the North Pacific subtropical gyre (NPSG). Our synthesis of mesozooplankton data collected during the past eight years of HOT program shows significant increases in standing stocks since 1994. Small (0.5 – 2.0 mm) non-migrating mesozooplankton, comprised primarily of copepod taxa (>65% in abundance), are driving the increase in total mesozooplankton biomass at Station ALOHA. Our observations support the HOT working hypothesis of a major ecosystem shift in response to climate-driven regime shifts in the NPSG since the 1970s. Seasonal variation in mesozooplankton community composition further suggests that the decadal increase in standing stock is related to summer blooms of nitrogen fixing phytoplankton. This synthesis of HOT data additionally summarizes the contributions of mesozooplankton to elemental budgets in the NPSG. We specifically highlight the role of active transport by mesozooplankton in export of carbon, phosphorus, and especially nitrogen from the euphotic zone in this stratified open-ocean ecosystem.