Small-scale planktonic structure: persistence and trophic consequences

Abstract

M O S T CONVENTIONAL s a m p l i n g m e t h ods limit our ability to resolve planktonic distributions over vertical scales less than a few meters. Estimates of in situ biological rates also are limited by equipment and sampling resolution. It has been obvious to plankton researchers for decades that the uncertainties created by sampling limitations are complicated further by vertical and horizontal variability in plankton distributions (often called patchiness). Although patches of phytoplankton (usually undetected) were recognized as essential for zooplankton growth and survival (e.g., Mullin and Brooks, 1976: Dagg, 1977), the distribution, size, and concentration of phytoplankton patches have been viewed as random or stochastic (e.g., Fasham, 1978). If phytoplankton patchiness is characterized by randomness, the contribution of this variability to our estimates of phytoplankton biomass may be removed by averaging over larger scales, and samples obtained with conventional sampling equipment can be used with some confidence. On the other hand, if patchiness is nonrandom on spatial or temporal scales that are difficult to resolve with conventional methods, then conventional sampling may alias estimates of planktonic distributions and rate processes such as grazing and growth. It is generally thought that biological structure is linked to physical processes (Denman and Powell, 1984; Mackas et al., 1985; Owen, 1989) including surface waves (and wave breaking), internal waves, Langmuir circulation, horizontal