Marine ecology: different measures of biodiversity

In their analysis of global trends of diversity in marine plankton, Irigoien et al. find that taxonomic diversity of zooplankton (consumer) is a unimodal function of community biomass that is unrelated to phytoplankton (producer) diversity. Their results are unexpected because in terrestrial organisms primary-producer diversity is a good predictor of consumer diversity. I contend that this apparent uncoupling of producer and consumer diversity in marine plankton is likely to be an artefact due to the authors' use of different measures of diversity for producers and for consumers.