Grazing Impacts of Diverse Zooplankton Taxa on Thin Layers

The US Navy needs to know how distributions and abundances of light-scattering and sound-scattering organisms in the ocean vary in space and time, particularly in the vertical dimension. Recent field observations have shown that many biological properties may vary substantially over small e.g. centimeter scales, commonly referred to as thin layers e.g. Cowles et al. 1998, 1999, Hanson Donaghay 1998, Holliday et al. 1999, Dekshenieks et al. 2001, Alldredge et al. 2002, Rines et al. 2002. Our previous ONR-funded research has allowed us to begin to understand how zooplankton interact with thin layers and how they can take advantage of biomass of prey concentrated in these small-scale features Avent et al. 1998, Bollens 2000, Bochdansky Bollens 2004, Clay et al. 2004, Ignoffo et al., 2005. However, there is almost no information regarding how zooplankton can influence the characteristics and persistence of thin layers. In this project we proposed to address this issue, with two main long-term goals First, to determine to what extent zooplankton graze and export carbon from thin layers and second, to determine whether and how zooplankton influence the physical e.g. optical and acoustical, chemical, and biological characteristics of thin layers with their presence. These goals require determination of rate processes such as feeding activity and excretion, which are very difficult to assess in the field. Thus our research is focused on detailed experimental studies of biological rate processes and behaviors that contribute to the recycling and export of material in and around thin layers