Obtaining absorption spectra from individual macroalgal spores using microphotometry

Information on the ecophysiology of macroalgal planktonic propagules (e.g. spores) has been hard to obtain, given their small size and low concentrati on in the water column. Studies of the photo-physiology of macroalgal spore s, for example, have been limited by the need to aggregate many spores into bulk samples for analysis. Subsequently, physiological variability among s pores (e.g. pigment concentration, absorption characteristics) is lost, and taxonomic comparisons from multi-taxa samples are impossible. Here we pres ent a technique that utilizes a spectral microphotometer to produce visible (400-800 nm) absorption spectra from individual particles; the particles i n our case are macroalgal spores. The microphotometer consists of a microsc ope fitted with a monochromator and spectrophotometer. After mounting spore s from laboratory or field suspensions onto transparent membrane filters, a bsorption characteristics of individual spores, or even individual plastids , can be evaluated independently from the remaining particles in the sample . Use of transparent rather than opaque membrane filters allows for determi nation of absorption spectra, as well as more traditional microscopic analy ses (e.g. bright field, dark field, epi-fluorescence). Glutaraldehyde fixat ion and cold storage (-10 degrees C) were found to be appropriate for maint aining the integrity of absorption spectra for at least 3 days. To demonstr ate the utility of microphotometry for macroalgal studies, absorption spect ra were obtained and analyzed from spores of various kelps and filamentous red algae.