ASLO/TOS/AGU Ocean Sciences Meeting, Honolulu, HI, February 2006.

The ALOHA to CLIMAX transect: Understanding current vs. historical perspectives of mesozooplankton community structure in the Subtropical North Pacific Ocean

C. C. Hannides¹, M. R. Landry²

¹Department of Oceanography, University of Hawaii, 1000 Pope Road, Honolulu, HI 96822

²Integrative Oceanography Division, Scripps Institution of Oceanography, University of California, San Diego, 9500 Gilman Drive, La Jolla, CA 92093

In contrast to our recent observations of seasonal and multi-year increases in zooplankton biomass at the Hawaii Ocean Time-series (HOT) Station ALOHA (22 45' N, 158 W), historical (1964-1980) surveys conducted at the CLIMAX site (28 N, 155 W) characterized central North Pacific zooplankton as relatively constant in space and time. To evaluate the role of programmatic constraints on these contrasting philosophies, Station ALOHA to CLIMAX site (A-C) transects were conducted in 1996 and 1997 using HOT program and CLIMAX survey sampling techniques. Species-level analysis of A-C transect samples allows us to investigate the role of net system and sampling location on understanding of plankton community structure in the subtropical North Pacific gyre. We find that differences in the plankton net system used by HOT (200 µm mesh) and CLIMAX programs (505 µm mesh) have a significant effect on community structure evaluation. HOT nets collected more than an order of magnitude more zooplankton than the CLIMAX net system, primarily due to enhanced collection efficiencies for small copepods from Families Oithonidae, Oncaeidae, Clausocalanidae and Paracalanidae. HOT nets also sampled the zooplankton response to a mid-transect bloom of nitrogen-fixing plankton in 1996 more effectively than the CLIMAX net system. While we stress differences between HOT and CLIMAX net systems, comparison of species-level capture efficiencies can provide a platform for evaluation of change in the subtropical North Pacific gyre over decadal time scales.