1. The occurrence of high cyanotoxin concentrations can severely impair the use of a waterbody for drinking water and recreational purposes. Cyanotoxins are likely to occur under specific environmental conditions, and so identifying these conditions can facilitate management of the waterbody to reduce the likelihood of high cyanotoxin concentrations. 2. We analysed data collected from lakes across the contiguous United States to identify environmental variables that are strongly associated with occurrence of high concentrations of a common cyanotoxin, microcystin (MC). 3. Since many different environmental variables covary and are associated with high MC, we used least absolute shrinkage and selection operator (LASSO) regression to identify a few variables that provided accurate predictions of high MC (≥1 lg L À1 ). 4. Our analysis indicated that total nitrogen (TN) and chlorophyll a (chl a) concentrations yielded a parsimonious model that accurately predicted the occurrence of high MC. Based on this model, we identified management thresholds for TN and chl a that would maintain the probability of high MC at or below 10 and 5%.

Strain HIMB11 is a planktonic marine bacterium isolated from coastal seawater in Kaneohe Bay, Oahu, Hawaii belonging to the ubiquitous and versatile Roseobacter clade of the alphaproteobacterial family Rhodobacteraceae. Here we describe the preliminary characteristics of strain HIMB11, including annotation of the draft genome sequence and comparative genomic analysis with other members of the Roseobacter lineage. The 3,098,747 bp draft genome is arranged in 34 contigs and contains 3,183 protein-coding genes and 54 RNA genes. Phylogenomic and 16S rRNA gene analyses indicate that HIMB11 represents a unique sublineage within the Roseobacter clade. Comparison with other publicly available genome sequences from members of the Roseobacter lineage reveals that strain HIMB11 has the genomic potential to utilize a wide variety of energy sources (e.g. organic matter, reduced inorganic sulfur, light, carbon monoxide), while possessing a reduced number of substrate transporters.

Rocky intertidal productivity is traditionally thought to be sustained almost solely by upwelled nitrate with remineralized forms of minor importance. Using tidepools as natural experimental mesocosms, we conducted 15 N-tracer experiments to test whether ammonium remineralized within the rocky intertidal is also a significant source of fixed N to localized ecosystem production. Comparison of tidepools with and without the dominant bivalve Mytilus californianus allowed consideration of its role in NH z 4 cycling. Closed water-incubation bottles were used to investigate the contribution of suspended microbes to NH z 4 cycling. Tidepools with mussels had both greater NH z 4 remineralization (two times) and NH z 4 removal as compared with those without, with daytime rates greater than nighttime rates. Incorporation of 15 NH z 4 tracer by particulate organic matter and macroalgae, and the persistence of this signal in tidepools for several days following the experiment, showed retention of autochthonous NH z 4 in the system. Remineralization rates were tightly correlated to removal rates when compared over all treatments and experiments, but NH z 4 remineralization was significantly greater than removal, suggesting a surplus available to nearshore primary producers.

Abstract. Seawater microbes as well as those associated with macrobiota are increasingly recognized as a key feature affecting nutrient cycling. Tidepools are ideal natural mesocosms to test macrofauna and microbe interactions, and we quantified rates of microbial nitrogen processing using tracer enrichment of ammonium (15NNH4) or nitrate (15NNO3) when tidepools were isolated from the ocean during low intertidal periods. Experiments were conducted during both day and night as well as in control tidepools and those from which mussels had been removed, allowing us to determine the role of both mussels and daylight in microbial nitrogen processing. We paired time series observations of 15N enrichment in NH4+, NO2− and NO3− with a differential equation model to quantify multiple, simultaneous nitrogen transformations. Mussel presence and daylight increased remineralization and photosynthetic nitrogen uptake. When we compared ammonium gain or loss that was attributed to any tidepool microbes vs. photosynthetic uptake, microbes accounted for 32 % of this ammonium flux on average. Microbial transformations averaged 61 % of total nitrate use; thus, microbial activity was almost 3 times that of photosynthetic nitrate uptake. Because it accounted for processes that diluted our tracer, our differential equation model assigned higher rates of nitrogen processing compared to prior source–product models. Our in situ experiments showed that animals alone elevate microbial nitrogen transformations by 2 orders of magnitude, suggesting that coastal macrobiota are key players in complex microbial nitrogen transformations.