A Revised Interpretation of Marine Primary Productivity in the Indian Ocean: The Role of Mixoplankton

Abstract

Traditional interpretations of marine plankton ecology, such as that in the Indian Ocean, mirror the plant-animal dichotomy of terrestrial ecology. Thus, single-celled phytoplankton produce food consumed by single-celled zooplankton, and these are in turn consumed by larger zooplankton through to higher trophic levels. Our routine monitoring surveys, research, models, and water management protocols all reflect this interpretation. The last decade has witnessed the development of an important revision of that traditional vision. We now know that the phytoplankton-zooplankton dichotomy represents, at best, a gross simplification. A significant proportion of the protist plankton at the base of the oceanic food-web can photosynthesise (make food ‘like plants’) and ingest food (eat ‘like animals’), thus contributing to both primary and secondary production simultaneously in the same cell. These protists are termed ‘mixoplankton’, and include many species traditionally labelled as ‘phytoplankton’ (a term now reserved for phototrophic microbes that are incapable of phagocytosis) or labelled as ‘protist zooplankton’ (now reserved for protist plankton incapable of phototrophy). Mixoplankton include various harmful algal species, most likely all the phototrophic dinoflagellates, and even iconic exemplar ‘phytoplankton’ such as coccolithophorids (which can consume bacteria). Like all significant revisions to ecology, the mixoplankton paradigm will take time to mature but to ignore it means that we fail to properly represent plankton ecology in teaching, science, management, and policy. This chapter introduces the mixoplankton functional groups and provides the first insight into the biogeography of these organisms in the Indian Ocean. A first attempt to consider the implications of the mixoplankton paradigm on marine primary productivity and ecology in the Indian Ocean is also given.