Phytoplankton Bloom Dynamics

Phytoplankton diversity and diatom blooms

Phytoplankton blooms of coastal systems are the foundation for the world’s most productive ocean food webs. Succession of plankton functional types in such blooms resulting from nutrient availability and predation have been well studied, but less is known about biotic interactions that might influence the bloom. The discovery that parasites contribute a huge proportion of eukaryotic diversity in the open ocean led us to hypothesize that parasite might also be important in determining the fate of coastal blooms. We use mesocosm experiments to investigate the biogeochemistry and community composition/succession of phytoplankton in bloom conditions. Both microscopy and amplicon analysis on daily samples detect species-specific temporal patterns that indicate intra-genus adaptation to changing conditions.  The 18S amplicon analysis detects many more “species” than the microscopy, although the major diatom groups are important in both.

In a simulated bloom in the Monterey Bay upwelling system, putative parasites including fungi, dinoflagellates and cercozoans were diverse and positively connected within a co-occurrence network (Figure 6), but few direct interactions among parasites and hosts were detected. Highly diverse diatom and dinoflagellate assemblages persisted throughout the bloom, indicating much greater complexity than usually assumed for classical upwelling diatom blooms. 

Large chart with network connections using modules 1, 2 and 3

Figure 6. Community correlation network based on random matrix theory (RMT) depicting potential interactions among plankton during the bloom. Gray edges in the network represent negative interactions and blue edges are positive. Nodes are colored according to class level taxonomy. The shape of the node represents module assignment, and the size of the node represents betweenness score. (Vineis et al. 2024, Co-occurrence and successional patterns among diatoms, dinoflagellates, and potential parasites in a coastal upwelling experiment)