Fluorescent microparticles: A new way of visualizing sedimentation and larval settlement

Methods for preparing fluorescently labeled microparticles and bivalve larvae (Cerastoderma edule) are presented. The labeling is cheap, easy, and allows production of great quantities of fluorescent microparticles and larvae. Fluorescent visualization can be used as a tool to analyze hydrodynamical processes in the benthic boundary layer and to directly observe behavioral patterns in settling larvae. Settlement of planktonic larvae may significantly affect the temporal and spatial variation in population size and community structure of marine, benthic invertebrates (Gaines and Roughgarden 1985; Underwood and Fairweather 1989; Sutherland 1990). It is assumed that large-scale dispersal (>km) of planktonic larvae is mainly determined by oceanic circulation (Scheltema 1971), while extensive evidence exists that larval behavior may influence settling probability at very small spatial scales (cm) (Wilson 1948; Crisp 1974). Much interest has focused on the relative importance of larval behavior and hydrodynamical processes in the boundary layer during settlement (Eckman 1983; Butman 1987). In flume experiments "hydrodynamical null hypotheses" have been tested by comparing settlement patterns of inert particles and Acknowledgments We thank Nils Jonsson for providing PVC microparticles. This research was supported by the Swedish Natural Science Foundation through contract B-BU 1860-305 to P.R. J. and through contract B-BU 3294-303 to C.A. The Royal Academy of Science and the foundations of Anna Ahrenberg, Colliander and Helge Ax:son Johnson provided additional support. larvae (Butman et al. 1988; Ertman and Jumars 1988). The traditional method used to analyze settlement patterns is by sieving samples of the sediment surface and then counting recovered particles and larvae under the microscope. This procedure is tedious and often lacks the desired spatial resolution, which may be difficult to anticipate beforehand. In addition, the sampling of the sediment may seriously affect experimental conditions and intensive sampling may preclude the possibility of sequential sampling in order to analyze settlement as a function of time. A technique which circumvents sampling and sorting was used by Mullineaux (1989); she covered Mn nodules with adhesive which made it possible to directly observe the distribution of settled particles without removing them from the nodules. This procedure is difficult to carry out in soft sediments or substrata that are not easily detached. Inert microparticles have proven a valuable tool in different fields of aquatic ecology. Studies on feeding rates as a function of prey size in various suspension-feeding organisms have gained much from use of latex (polystyrene) particles as artificial prey items (Fenchel 1980). The use of particles stained with fluorescent substances has further facilitated the tracing and analysis of ingested particles (B0rsheim 1984; McManus and Fuhrman 1986). Different methods involving fluorescent microparticles have also been applied to research concerning sediment dynamics (Lopez and Elmgren 1989; Carey 1989). The use of fluorescent particles greatly enThis content downloaded from 130.241. 16.16 on Thu, 23 May 2013 02:44:17 AM All use subject to JSTOR Terms and Conditions