Obtaining absorption spectra from individual macroalgal spores using microphotometry

Abstract

Information on the ecophysiology of macroalgal planktonic propagules (e.g. spores) has been hard to obtain, given their small size and low concentration in the water column. Studies of the photo-physiology of macroalgal spores, for example, have been limited by the need to aggregate many spores into bulk samples for analysis. Subsequently, physiological variability among spores (e.g. pigment concentration, absorption characteristics) is lost, and taxonomic comparisons from multi-taxa samples are impossible. Here we present a technique that utilizes a spectral microphotometer to produce visible (400-800 nm) absorption spectra from individual particles; the particles in our case are macroalgal spores. The microphotometer consists of a microscope fitted with a monochromator and spectrophotometer. After mounting spores from laboratory or field suspensions onto transparent membrane filters, absorption characteristics of individual spores, or even individual plastids, can be evaluate d independently from the remaining particles in the sample. Use of transparent rather than opaque membrane filters allows for determination of absorption spectra, as well as more traditional microscopic analyses (e.g. bright field, dark field, epi-fluorescence). Glutaraldehyde fixation and cold storage (−10 °C) were found to be appropriate for maintaining the integrity of absorption spectra for at least 3 days. To demonstrate the utility of microphotometry for macroalgal studies, absorption spectra were obtained and analyzed from spores of various kelps and filamentous red algae.