Estimating Rates of Growth and Grazing Mortality of Phytoplanlcton by the Dilution Method

Methodological review and meta‐analysis of dilution assays for estimates of virus‐ and grazer‐mediated phytoplankton mortality

“…Due to the labor‐intensive and time‐consuming nature of setting‐up and analyzing modified dilution assays (Kimmance and Brussaard ), as well as potential issues related to the method's power to detect significant viral lysis rates (Kimmance et al ), selecting an appropriate dilution scheme is a critical consideration. Technically, only two dilution levels are required to estimate growth and mortality rates, but most experiments incorporate replicate bottles at four to six dilution levels (Landry ). The use of a “2‐point method” has been promoted recently in the standard dilution assay literature as a reliable, accurate and easier approach for estimating phytoplankton growth and grazer‐induced mortality (Chen ; Morison and Menden‐Deuer ), though such an approach has yet to be attempted for estimating virus‐induced mortality.…”

“…The “modified dilution assay” (sensu Evans et al ) is a technique used in limnology and oceanography to measure and partition phytoplankton mortality into virus‐ and grazer‐mediated fractions. Designed as a modification to the dilution assay described by Landry and Hassett () which has been used extensively to quantify microzooplankton grazing on phytoplankton, the modified dilution assay maintains many advantages of the original technique; it provides estimates of both phytoplankton growth and mortality rates in a single experiment, involves minimal handling or disruption of the microorganisms being studied, and allows for the analysis of different components of the phytoplankton community (Landry ). Additionally, of the various methods that have been developed in an attempt to quantify phytoplankton virus‐mediated mortality rates, the modified dilution approach is advantageous as it is the only assay that provides direct estimates without conversion factors (Kimmance and Brussaard ).…”

Evaluation of the Relationship Between the 18S rRNA/rDNA Ratio and Population Growth in the Marine Diatom Skeletonema tropicum via the Application of an Exogenous Nucleic Acid Standard

“…Although phytoplankton abundance is routinely monitored in marine ecology studies, abundance is determined by both growth and mortality and is not an absolute indicator of the physiological state of phytoplankton in a specific environment. Commonly used methods for estimating phytoplankton growth rate include dilution experiments (Landry 1993), radiotracer incorporation (Goericke and Welschmeyer 1993), and cell-cycle analysis (Vaulot et al 1995). These measurements are typically time-consuming, and incubation may change the physiology and community composition of phytoplankton (Kim et al 2011).…”

Size scaling of photophysiology and growth in four freshly isolated diatom species from Ryder Bay, western Antarctic peninsula

“…It has been shown that Antarctic phytoplankton communities dominated by smaller phytoplankton species experience higher grazing pressure compared to those dominated by larger phytoplankton species (Storm and Welschmeyer 1991, Garibotti et al 2003, Smith and Lancelot 2004. Moreover, grazing is dependent on the density of phytoplankton cells in the water column (Landry 1993, Behrenfeld 2010, Garzio and Steinberg 2013. This suggests that low phytoplankton biomass earlier in the season will result in relatively low grazing pressure on both small and large diatoms, whereas during the phytoplankton bloom, grazing of small diatom species increases due to the relatively high abundance of these cells and relatively high grazing pressure, thereby increasing the competitive success of larger diatom species later in the season.…”