Development And Validation Of New Methods For Measuring Predation Rates In Mixoplanktonic Protists

Abstract

Despite the supposed relevance of mixoplankton (Stoecker et al. 2017, Flynn et al. 2019) we still lack standardized techniques to measure their grazing impact in the field. This is mostly because of the difficulty in separating grazers and prey (similar sizes and/or pigments). To date, most approaches to estimate mixoplankton grazing are based on extrapolating to the field the rates obtained in the laboratory (e.g. Yih et al. 2004). For instance, to estimate grazing on protists it is common to measure the disappearance of prey during 24h incubations under strictly controlled conditions. Given the impossibility to obtain data for all the species present at sea on a given time, and to predict the particular interactions between groups, the approach is, if not completely erroneous, at least very limited and inaccurate. Moreover, the fact that some species, like Prymnesium parvum or Karlodinium armiger, release allelopathic compounds (e.g. Shilo & Aschner 1953, Rasmussen et al. 2017) that may cause immobilization and lysis of potential prey may introduce further complications to the interpretation of the result. [...]