I am very thankful to the co-authors on this paper and on @kc-freel.bsky.social's paper, including @merenbey.bsky.social, Mike Rappé, Steve Giovannoni, @theotherdrfreel.bsky.social, and Uli Stingl.

We then examined the selective pressures on the metabolic traits that associate to distinct coastal or offshore lifestyles of SAR11. We found that they generally experienced high purifying selection, and thus are likely critical to fitness in these distinct environments.

We also observed distinct patterns of molybdenum-dependent enzyme utilization, where some offshore genera have completely lost the capacity to synthesize molybdenum enzymes and other offshore genera have increased reliance on molybdenum enzymes through molybdenum-dependent purine catabolism.

Coastal & offshore genera specialized on different carbon sources. Offshore genera uniquely shared metabolisms that did not rely on glycolysis, while coastal genera uniquely shared metabolisms that did. This hints at fine-scale niche partitioning along the sugar-acid spectrum within SAR11.

We next examined the SAR11 pangenome (focused on former subclades Ia & Ib) to identify metabolic traits associated with coastal and offshore lifestyles. We found subtle metabolic differences between genera, largely limited to a handful of genes involved in organic carbon and nitrogen metabolisms.

We find SAR11 genera partition across coastal and offshore waters of the tropical Pacific. The coastal genera appear in polyphyletic clades suggesting that coastal SAR11 evolved multiple times. Also we find that the habitat preferences of these genera are mostly retained across the global ocean.

Anyone else read 50 μm on this traffic sign? 🔬 #microsky

A big thank you to my collaborators, lab mates, the community of Heʻeia and broader Kāneʻohe Bay, Paepae o Heʻeia, the Heʻeia National Estuarine Research Reserve, and funding support from the NOAA Margaret A. Davidson Fellowship!

Finally, we used our findings to identify bioindicators of environmental change. Such baseline data help to inform the management of the Heʻeia Fishpond and the Heʻeia NERR. To promote phytoplankton biomass, the flow of freshwater into the Bay is critical.

Seasonal differences in biogeochemistry and phytoplankton community composition were more subtle offshore. In the nearshore, diatoms increased during the winter, while Synechococcus increased during the summer. This seasonality likely restructures food web dynamics.

Prochlorococcus HLII was abundant offshore, while Synechococcus II was abundant within the bay. We saw similar patterns of Prochlorococcus population structure at open-ocean Station ALOHA and offshore Kāneʻohe Bay, likely representing continuous populations with ongoing gene flow.

Despite mixing of nearshore and offshore waters, phytoplankton communities clustered into 3 groups that reflect the origin of the sample, either from stations in the nearshore, offshore, or located between these two end members. Broadly, large-sized phytoplankton were more abundant nearshore.

We saw persistent shifts in phytoplanktoners between coastal and offshore waters. Episodic storms triggered phytoplankton responses at relatively large spatial scales, with these storms occurring more frequently during winter months. ☔

Near-island freshwater input from streams and groundwater deliver nutrients to a nitrogen-limited system and promote elevated phytoplankton biomass nearshore. This creates strong biogeochemical gradients that shape food web dynamics within and outside of the Bay.