How to Consistently Include both Laboratory Results and Oceanic Observations into Size-Based Models of Planknton Ecosystems?

2018 Ocean Sciences Meeting, 11-16 February, in Portland, OregonOur recent size-based studies of phytoplankton communities and plankton ecosystems reveal an apparent inconsistency between laboratory-based results and oceanic observations. Uni-modal distributions of maximum phytoplankton growth rate over cell size have been reported from laboratory experiments using single-species cultures. Our models, formulated based on size-scalings derived from laboratory results, tend to predict that medium-sized (nano-) phytoplankton dominate in the most productive regions of the ocean where chlorophyll concentrations are highest. However, oceanic observations of size-fractionated chlorophyll consistently reveal that the largest size fraction (micro-size) phytoplankton increases steadily with increasing total chlorophyll and dominates at the highest chlorophyll concentrations. Including size-selective grazing with decreasing preference for larger prey has been proposed as one possible means to reconcile laboratory-based size-scalings, which do not account for the effects of grazing, with oceanic observations, which reflect the net effect of both bottom-up and top-down processes. However, including size-selective grazing has not allowed our model to reproduce consistently the observed patterns of size-fractionated chlorophyll, primary production, and specific growth rate. Indeed, ship-board experiments reveal that micro-sized diatoms (> 20 μm) tend to have the fastest growth rates. This suggests that laboratory datasets, although valuable for providing information from controlled experiments, do not represent the full range of species and sizes present in the ocean. We will briefly present other recent observation-based results constituting targets for future modeling studies. For example, the interaction of predator and prey size diversities has been reported to affect trophic transfer, suggesting a mechanistic link between size structure and an important ecosystem functionPeer Reviewe