Temporal and spatial changes in epipelagic microzooplankton and mesozooplankton biomass in warm-core Gulf Stream ring 82-B

Abstract

The vertical distributio of > 64 μ m zooplankton biomass in warm-core Gulf Stream ring (WRC) 82-B was studied when the ring was approximately 2,4 and 6 months old. Variability of zooplankton biomass estimates in 82-B was not significantly different on diel, 5 to 12 day, and seasonal (April, June, August) time scales as the ring evolved from its Sargasso Sea origin. Zooplankton biomass in 82-B was similar to concentrations found in the Slope Water. The average ratio of integrated (0 to 200 m) zooplankton ( > 64 μ m ) biomass in the surrounding Slope Water to that in 82-B was 1.6 at 2 months old and 0.7 at 4 months. Small zooplankton (64 to 333 μm), dominated by copepod nauplii and copepodite stages, increased from 376 mg C m −2 in April (26% of total zooplankton biomass ) to 427 mg C m −2 in June (35% of total biomass), suggesting that the zooplankton were producing more juveniles. Increased zooplankton biomass in WCR 82-B between April and June was likely a result of both in situ growth and the lateral advection of Slope Water zooplankton into the ring. Many zooplankton species which increased in WCR 82-B were of Slope Water origin. These apportunistic species of calanoid and cyclopoid copepods appear capable of exploiting the often high phytoplankton production and standing crops of WCRs, and result in a rapid evolution of the WCR epipelagic zooplankton community from its Sargasso Sea origin.