Abstract
The term plankton describes all water-living organisms whose inherent movement abilities are small compared to the movement of the surrounding water. Strictly speaking, this includes also comprehensively large organisms like jellyfish, but most planktonic organisms are of relatively small size (micrometers to millimeters). Phytoplankton as the “plant” part of the plankton community comprises a large variety of photosynthetic active organisms, both prokaryotic and eukaryotic, which as primary producers transforming inorganic carbon into biomass using light as source of energy. Although they constitute only 1% of global primary producer biomass, these organisms are responsible for approx. 50 % of global carbon fixation and oxygen production (Field et al., 1998) and, hence, mediate carbon flux from the atmosphere to the oceans. The heterotrophic zooplankton, the “animal” part of plankton, is in contrast the primary consumer of phytoplankton, and in turn a major food source for larger organisms. Thus, zooplankton links phytoplankton production to higher trophic levels (e.g. fish), which members can have a certain relevance for human economy and nutrition. In total, the plankton constitutes the basal levels of the aquatic food web, and due to this crucial ecological position, investigation and monitoring of its dynamics in terms of biomass and community structure is a topic of ongoing importance. Plankton populations can provide an indicator of the status of the marine environment (Devlin et al., 2007; Racault et al., 2014). Thus, especially in the light of climate change, ocean acidification, introduction of foreign species, and various types of pollution due to human activities, potential changes in the plankton have to be detected and evaluated to estimate potential consequences for marine ecosystem services.
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