Abstract. Cell size determination is a critical part of sampling phytoplankton communities, as size is both a fundamental trait determining species' ecological niches and a quantity necessary for generating unbiased estimates of community composition. The sizes of algal cells span orders of magnitude, driving variation in growth parameters, sinking rates, herbivore defense, and biogeochemical roles. Size variation occurs at both intra-and interspecific levels. Many central questions in community and ecosystem ecology require estimating and comparing the relative abundances of species. Cell counts provide insufficient estimates, due to interspecific variation in cell size, as they over-estimate the importance of abundant, small species. While cell size (or biovolume) estimation has become standard practice in limnology, many older data sets lack this information, limiting their interpretation and utility. To address these challenges, and advance the study of freshwater phytoplankton communities, we have compiled a database of .260 000 algal biovolume estimates, spanning ;400 genera and ;1200 species. This represents the most extensive, standardized, and taxonomically diverse data set of its kind, drawing on both publicly and privately held sources. Estimates of the sizes of colonies or filaments are included, where applicable. With these data researchers will be able to account for intra-and interspecific variation in cell size, enabling new and improved analyses of classic data sets.

Although light is a key biological driver, light additions to in‐lake experiments can be difficult, if not impossible. To address this problem, we developed an inexpensive Lighting Apparatus for Mesocosm Photo‐manipulation (LAMP), a device that can be deployed within experimental underwater enclosures to increase ambient light levels. Each apparatus consists of 12 Light Emitting Diode (LED) flashlights embedded within a watertight PVC frame. Through the use of a voltage regulator, each is wired to a 12V deep‐cycle marine battery. Twelve LAMPs were deployed during a 3.5‐week mesocosm experiment in Cranberry Lake in the Adirondack region of New York State and run 12 hours per day. LAMPs proved durable under harsh wind and weather conditions. Mesocosms with LAMPs had significantly higher average Photosynthetic Photon Flux Density (PPFD) in the water column than did controls (8% higher integrated Photosynthetic Active Radiation [PAR] over a 1.75 m depth, paired t test, P < 0.01). Other potential research applications for LAMPs include (1) testing light limitation in highly eutrophic systems where algal biomass may be self‐shading, (2) experimentation at depth (e.g., examination of light limitation at the deep chlorophyll maximum), (3) application at different depths or in water bodies where specific wavelengths have been naturally attenuated using LEDs with different spectral properties, (4) testing animal responses to light climate in the field, or (5) collection of macroinvertebrates or fish larvae in modified LAMP‐based light traps.