Question 6

## Question 6. What detail on small scales is needed to determine and model recruitment?

Question 6 Response--The importance of small scales (mm to m) to recruitment processes received much and quite uniform attention by the workshop participants. For most secondary producers, i.e., zooplankton, coupling with biology and physics occurs at the scales of their ambit, which can range from <1 mm to >100 m in the vertical. They perceive food and predators in the mm range, and can move several cm to m in a minute. Major processes of predation occur at scales of mm to cm. For example, Kils (1991) showed how a school of juvenile herring found a 10 cm thick layer of the ciliate Stenosomella, and consumed it within 20 min. There was general agreement that our community lacks information on rate processes and their variability on these spatial and also on short temporal scales.

Specifically, observations on behavioral characteristics of various stages and species of zooplankton and fish larvae are needed, including daily ambits (range of operation) of respective species and vertical distributions of zooplankton, their food and their predators over time. Variability of these should be investigated in conjunction with physical variables such as temperature; this would include species- and stage-specific aggregation dynamics.

To develop models, functional relationships for zooplankton behavior, shear and turbulence have to be obtained; and real-world small structure and small-scale processes have to be adequately addressed in such models. It is at these scales that the interactions between the various components of the plankton occur. It is also these scales about which our knowledge is severely limited. An understanding of mechanisms governing animal's existence at small scales, as mentioned earlier, is essential to comprehend processes on much larger scales.