Decoupling of respiration rates and abundance in marine prokaryoplankton

The ocean-atmosphere exchange of CO2 largely depends on the balance between marine microbial photosynthesis and respiration. Despite vast taxonomic and metabolic diversity among marine planktonic bacteria and archaea (prokaryoplankton)1-3, their respiration usually is measured in bulk and treated as a 'black box' in global biogeochemical models4; this limits the mechanistic understanding of the global carbon cycle. Here, using a technology for integrated phenotype analyses and genomic sequencing of individual microbial cells, we show that cell-specific respiration rates differ by more than 1,000× among prokaryoplankton genera. The majority of respiration was found to be performed by minority members of prokaryoplankton (including the Roseobacter cluster), whereas cells of the most prevalent lineages (including Pelagibacter and SAR86) had extremely low respiration rates. The decoupling of respiration rates from abundance among lineages, elevated counts of proteorhodopsin transcripts in Pelagibacter and SAR86 cells and elevated respiration of SAR86 at night indicate that proteorhodopsin-based phototrophy3,5-7 probably constitutes an important source of energy to prokaryoplankton and may increase growth efficiency. These findings suggest that the dependence of prokaryoplankton on respiration and remineralization of phytoplankton-derived organic carbon into CO2 for its energy demands and growth may be lower than commonly assumed and variable among lineages.This work was supported by awards from the US National Science Foundation (1826734 to R.S., D.E., B.N.O. and N.J.P.; 1737017 to B.N.O.; and 1335810 to R.S.), the Austrian Science Fund (FWF) project ARTEMIS (P28781-B21 to G.J.H.) and by the Simons Foundation grant (827839 to R.S.).Peer reviewe

Seawater carbonate chemistry and calcification of an estuarine coccolithophore

Ocean acidification has the capacity to impact future coccolithophore growth, photosynthesis, and calcification, but experimental culture work with coccolithophores has produced seemingly contradictory results and has focused on open-ocean species. We investigated the influence of pCO2 (between 250 and 750 µatm) on the growth, photosynthetic, and calcification rates of the estuarine coccolithophore Pleurochrysis carterae using a CO2 manipulation system that allowed for natural carbonate chemistry variability, representing the highly variable carbonate chemistry of coastal and estuarine waters. We further considered the influence of pCO2 on dark calcification. Increased pCO2 conditions had no significant impact on P. carterae growth rate or photosynthetic rate. However, P. carterae calcification rates significantly increased at elevated mean pCO2 concentrations of 750 µatm. P. carterae calcification was somewhat, but not completely, light-dependent, with increased calcification rates at elevated mean pCO2 conditions in both light and dark incubations. This trend of increased calcification at higher pCO2 conditions fits into a recently developed substrate-inhibitor concept, which demonstrates a calcification optima concept that broadly fits the experimental results of many studies on the impact of increased pCO2 on coccolithophore calcification

Support for deer herd reduction on offshore Islands of Maine, U.S.A

Over the past three decades, citizens of Maine in the northeastern United States have experienced increasing blacklegged tick (Ixodes scapularis) abundance and rising incidence of Lyme and other tick-borne diseases. White-tailed deer (Odocoileus virginianus) overabundance has been considered one cause of the high incidence of tick-borne diseases on offshore islands of New England. Most of Maine\u27s 15 offshore, unbridged island communities have a history of concern about ticks, Lyme disease, and white-tailed deer overabundance, but have been challenged to keep deer numbers down through hunting or culls. This history has led to perennial, often divisive community debates about whether and how to reduce the size of their deer herds. In 2016 we conducted a convenience sample survey of year-round and summer residents of Maine\u27s offshore islands to quantify the level of concern about Lyme disease, and assess the motivations and level of support for deer herd reduction. Among respondents, 84 % agreed Lyme disease was a problem on their island and 61 % supported deer herd reduction. Agreement that Lyme disease was a problem was associated with having acquired tick-borne disease as well as with tick bites without disease. Respondents ranked deer overabundance as a top cause of tick abundance and tick-borne disease and supported deer herd reduction as an approach to reduce the risk of Lyme disease. Other problems associated with deer overabundance (vehicle collisions, damage to landscaping, and damage to forests) also motivated support for deer reduction. Approval of doe permits, an expanded archery season, and sharpshooting as reduction methods was greater than an expanded firearms season. Respondents felt responsibility for tick control fell to the town for the most part, and recognized that multiple factors have contributed to the tick problem in Maine, not just deer

Phylogeographic reconstruction of the emergence and spread of Powassan virus in the northeastern United States

Powassan virus is an emerging tick-borne virus of concern for public health, but very little is known about its transmission patterns and ecology. Here, we expanded the genomic dataset by sequencing 279 Powassan viruses isolated from ticks from the northeastern United States. Our phylogeographic reconstructions revealed that Powassan virus lineage II was likely introduced or emerged from a relict population in the Northeast between 1940 and 1975. Sequences strongly clustered by sampling location, suggesting a highly focal geographical distribution. Our analyses further indicated that Powassan virus lineage II emerged in the northeastern United States mostly following a south-to-north pattern, with a weighted lineage dispersal velocity of ~3 km/y. Since the emergence in the Northeast, we found an overall increase in the effective population size of Powassan virus lineage II, but with growth stagnating during recent years. The cascading effect of population expansion of white-tailed deer and populations likely facilitated the emergence of Powassan virus in the northeastern United States

Massive phytoplankton blooms under Arctic sea ice

Phytoplankton blooms over Arctic Ocean continental shelves are thought to be restricted to waters free of sea ice. Here, we document a massive phytoplankton bloom beneath fully consolidated pack ice far from the ice edge in the Chukchi Sea, where light transmission has increased in recent decades because of thinning ice cover and proliferation of melt ponds. The bloom was characterized by high diatom biomass and rates of growth and primary production. Evidence suggests that under-ice phytoplankton blooms may be more widespread over nutrient-rich Arctic continental shelves and that satellite-based estimates of annual primary production in these waters may be underestimated by up to 10-fold

Massive phytoplankton blooms under arctic sea ice

Phytoplankton blooms over Arctic Ocean continental shelves are thought to be restricted to waters free of sea ice. Here, we document a massive phytoplankton bloom beneath fully consolidated pack ice far from the ice edge in the Chukchi Sea, where light transmission has increased in recent decades because of thinning ice cover and proliferation of melt ponds. The bloom was characterized by high diatom biomass and rates of growth and primary production. Evidence suggests that under-ice phytoplankton blooms may be more widespread over nutrient-rich Arctic continental shelves and that satellite-based estimates of annual primary production in these waters may be underestimated by up to 10-fold