Monitoring of Picoplankton in Ocean Fronts

Microbes are key mediators of the biogeochemical cycling of carbon, sulfur, nitrogen, and metals in the ocean. Phytoplankton are the key primary producers in the ocean. An estimated 50 percent of primary productivity is cycled through heterotrophic picoplankton in the microbial loop. Yet these ubiquitous ocean inhabitants remain poorly understood, in part because many of them cannot be isolated and studied using traditional cultivation techniques. Furthermore, the behavior of those that can be cultivated cannot always be predicted from laboratory studies. In situ analyses are a prerequisite for understanding oceanic microbial populations. Our goal is to be able to rapidly identify, quantify, and functionally characterize the dominant microbial groups in marine planktonic ecosystems. To attain this goal, we are currently developing new tools, assays, and methods for the identification, quantization, and characterization of marine plankton. Our ultimate goal is to characterize the community structure and functional significance of picoplankton, from which we will gain a better understanding of the multiple roles that these organisms play in the ecosystem.

The community structure and dynamics of  phytoplankton and bacterioplankton in the Monterey Bay region is only partially understood. The spatio-temporal structure of microbial populations and their response to episodic hydrodynamic events, nutrient injection, or biotic changes is still largely unpredictable. The MUSE experiment  provided the Microbial Group an excellent opportunity to characterize more extensively the dynamical responses of phytoplankton and picoplankton to upwelling events, naturally occurring nutrient fertilization, and biotic succession. During the experiment, we tested several hypotheses concerning biogeochemical changes and biotic shifts precipitated by upwelling events off Monterey Bay. Scholin’s group focused specifically on the response of phytoplankton communities, especially harmful algae, to upwelled iron. DeLong's group focused on predominant picoplankton groups in the upper water column.

Scholin's Group
For Scholin’s group, gaining the analytical ability to predict and monitor dynamic blooms of harmful algae and other phytoplankton species was a high priority. 

Delong's Group
Picoplankton species, which are stratified in specific zones in the water column, strongly influence the flux of carbon, nitrogen, sulfur, and metals through the major elemental cycles. We expect that upwelling events profoundly influence the structure, dynamics, and function of microbial communities in specific ways. During the MUSE experiment, we analyzed water samples for microbial communities synoptic with biogeochemical measurements (Chavez), chemical measurements (Johnson), and phytoplankton measurements (Scholin). These data provided information about the response of the ecosystem to nutrient injection during upwelling events. They provided information about the role of picoplankton in the development and succession of microbial communities also in response to upwelling events. Our fundamental goal is to define variables that influence the development, succession, and function of key picoplankton species.

Hypotheses
With respect to the picoplankton we will test the following hypotheses :

Hypothesis 1: Deep-water picoplankton species are detectable in newly upwelled water;

Hypothesis 2: Upwelled water will initiate a rapid succession of picoplankton species not found outside the upwelling plume;

Hypothesis 3: A tight coupling exists between successional events occurring in picoplankton and phytoplankton species. Specific picoplankton species will correlate positively with specific phytoplankton species;

Hypothesis 4: Picoplankton compete with phytoplankton for iron. This competition is subject to temporal lag, and it intensifies as secondary producers (picoplankton) increase in response to blooms of primary producers.

Technology Requirements
All the above hypotheses require responsive, high resolution spatial and temporal sampling, one of the justifications for MOOS. Testing these hypotheses will also critically rely on synoptic data, gathered by drifters, AUVs. ROVs, and automated samplers, in conjuction with other MUSE investigators. The analyses critically require adequate spatial mapping and sampling, achieved by drifters and AUVs. Deployment of MBARI's recently developed environmental sample processor (ESP), on a drifter or mooring, would allow for automated sampling and measurements along the edge, or outside of, the upwelled plume, for comparative purposes.

Aggressive development of sampling technology for collecting seawater samples on AUVs is an important area for development. This is critical for groundtruthing new sensors (for instance, ISUS). Additionally, for many biological measurements, there are no currently existing sensors. Sample recovery for these biotic measurements becomes an absolute requirement. For seawater, samples of at least several hundred milliliters would be optimal. In addition, further development of filtration samplers would allow recovery of more samples of unrestricted volume, and would occupy less platform space.

Some of this technology development has already begun with the ESP.