Interactions of marine mammals and birds with offshore membrane enclosures for growing algae (OMEGA).

BACKGROUND: OMEGA is an integrated aquatic system to produce biofuels, treat and recycle wastewater, capture CO2, and expand aquaculture production. This system includes floating photobioreactors (PBRs) that will cover hundreds of hectares in marine bays. To assess the interactions of marine mammals and birds with PBRs, 9 × 1.3 m flat panel and 9.5 × 0.2 m tubular PBRs were deployed in a harbor and monitored day and night from October 10, 2011 to Janurary 22, 2012 using infrared video. To observe interactions with pinnipeds, two trained sea lions (Zalophus californianus) and one trained harbor seal (Phoca vitulina richardii) were observed and directed to interact with PBRs in tanks. To determine the forces required to puncture PBR plastic and the effects of weathering, Instron measurements were made with a sea otter (Enhydra lutris) tooth and bird beaks. RESULTS: A total of 1,445 interactions of marine mammals and birds with PBRs were observed in the 2,424 hours of video recorded. The 95 marine mammal interactions, 94 by sea otters and one by a sea lion had average durations of three minutes (max 44 min) and represented about 1% of total recording time. The 1,350 bird interactions, primarily coots (Fulica americana) and gulls (Larus occidentalis and L. californicus) had average durations of six minutes (max. 170) and represented 5% of recording time. Interactive behaviors were characterized as passive (feeding, walking, resting, grooming, and social activity) or proactive (biting, pecking, investigating, and unspecified manipulating). Mammal interactions were predominantly proactive, whereas birds were passive. All interactions occurred primarily during the day. Ninety-six percent of otter interactions occurred in winter, whereas 73% of bird interactions in fall, correlating to their abundance in the harbor. Trained pinnipeds followed most commands to bite, drag, and haul-out onto PBRs, made no overt undirected interactions with the PBRs, but showed avoidance behavior to PBR tethers. Instron measurements indicated that sea-otter teeth and gull beaks can penetrate weathered plastic more easily than new plastic. CONCLUSIONS: Otter and bird interactions with experimental PBRs were benign. Large-scale OMEGA systems are predicted to have both positive and negative environmental consequences.

Potential impact of biofouling on the photobioreactors of the Offshore Membrane Enclosures for Growing Algae (OMEGA) system.

The influence of PBR composition [clear polyurethane (PolyU) vs. clear linear low-density polyethylene (LLDPE) (top) and black opaque high-density polyethylene (bottom)] and shape (rectangular vs. tubular) on biofouling and the influence of biofouling on algae productivity were investigated. In 9-week experiments, PBR biofouling was dominated by pennate diatoms and clear plastics developed macroalgae. LLDPE exhibited lower photosynthetic-active-radiation (PAR) light transmittance than PolyU before biofouling, but higher transmittance afterwards. Both rectangular and tubular LLDPE PBRs accumulated biofouling predominantly along their wetted edges. For a tubular LLDPE PBR after 12 weeks of biofouling, the correlation between biomass, percent surface coverage, and PAR transmittance was complex, but in general biomass inversely correlated with transmittance. Wrapping segments of this biofouled LLDPE around an algae culture reduced CO2 and NH3-N utilization, indicating that external biofouling must be controlled.

VARIATION IN THE ABUNDANCE OF SYNECHOCOCCUS SP. CC9311 NARB MRNA RELATIVE TO CHANGES IN LIGHT, NITROGEN GROWTH CONDITIONS AND NITRATE ASSIMILATION(1).

Synechococcus- and Prochlorococcus-specific narB genes that encode for an assimilatory nitrate reductase are found in coastal to open-ocean waters. However, it remains uncertain if these picocyanobacteria assimilate nitrate in situ. This unknown can potentially be addressed by examining narB mRNA from the environment, but this requires a better understanding of the influence of environmental factors on narB gene transcription. In laboratory experiments with Synechococcus sp. CC9311 cultures exposed to diel light fluctuations and grown on nitrate or ammonium, there was periodic change in narB transcript abundance. This periodicity was broken in cultures subjected to a doubling of irradiance (40-80 µmol photons · m(-2) · s(-1) ) during the mid-light period. Therefore, the irradiance level, not circadian rhythm, was the dominant factor controlling narB transcription. In nitrate-grown cultures, diel change in narB transcript abundance and nitrate assimilation rate did not correlate; suggesting narB mRNA levels better indicate nitrate assimilation activity than assimilation rate. Growth history also affected narB transcription, as changes in narB mRNA levels in nitrogen-deprived CC9311 cultures following nitrate amendment were distinct from cultures grown solely on nitrate. Environmental sampling for narB transcripts should consider time, irradiance, and the growth status of cells to ecologically interpret narB transcript abundances.

NITROGEN FIXATION, HYDROGEN CYCLING, AND ELECTRON TRANSPORT KINETICS IN TRICHODESMIUM ERYTHRAEUM (CYANOBACTERIA) STRAIN IMS101(1).

This study describes the relationships between dinitrogen (N2 ) fixation, dihydrogen (H2 ) production, and electron transport associated with photosynthesis and respiration in the marine cyanobacterium Trichodesmium erythraeum Ehrenb. strain IMS101. The ratio of H2 produced:N2 fixed (H2 :N2 ) was controlled by the light intensity and by the light spectral composition and was affected by the growth irradiance level. For Trichodesmium cells grown at 50 µmol photons · m(-2) · s(-1) , the rate of N2 fixation, as measured by acetylene reduction, saturated at light intensities of 200 µmol photons · m(-2) · s(-1) . In contrast, net H2 production continued to increase with light levels up to 1,000 µmol photons · m(-2) · s(-1) . The H2 :N2 ratios increased monotonically with irradiance, and the variable fluorescence measured using a fast repetition rate fluorometer (FRRF) revealed that this increase was accompanied by a progressive reduction of the plastoquinone (PQ) pool. Additions of 2,5-dibromo-3-methyl-6-isopropyl-p-benzoquinone (DBMIB), an inhibitor of electron transport from PQ pool to PSI, diminished both N2 fixation and net H2 production, while the H2 :N2 ratio increased with increasing level of PQ pool reduction. In the presence of 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU), nitrogenase activity declined but could be prolonged by increasing the light intensity and by removing the oxygen supply. These results on the coupling of N2 fixation and H2 cycling in Trichodesmium indicate how light intensity and light spectral quality of the open ocean can influence the H2 :N2 ratio and modulate net H2 production.

Hydrogen cycling by the unicellular marine diazotroph Crocosphaera watsonii strain WH8501.

The hydrogen (H2) cycle associated with the dinitrogen (N2) fixation process was studied in laboratory cultures of the marine cyanobacterium Crocosphaera watsonii. The rates of H2 production and acetylene (C2H2) reduction were continuously measured over the diel cycle with simultaneous measurements of fast repetition rate fluorometry and dissolved oxygen. The maximum rate of H2 production was coincident with the maximum rates of C2H2 reduction. Theoretical stoichiometry for N2 fixation predicts an equimolar ratio of H2 produced to N2 fixed. However, the maximum rate of net H2 production observed was 0.09 nmol H2 µg chlorophyll a (chl a)⁻¹ h⁻¹) compared to the N2 fixation rate of 5.5 nmol N2 µg chl a⁻¹ h⁻¹, with an H2 production/N2 fixation ratio of 0.02. The 50-fold discrepancy between expected and observed rates of H2 production was hypothesized to be a result of H2 reassimilation by uptake hydrogenase. This was confirmed by the addition of carbon monoxide (CO), a potent inhibitor of hydrogenase, which increased net H2 production rates ∼40-fold to a maximum rate of 3.5 nmol H2 µg chl a⁻¹ h⁻¹. We conclude that the reassimilation of H2 by C. watsonii is highly efficient (> 98%) and hypothesize that the tight coupling between H2 production and consumption is a consequence of fixing N2 at nighttime using a finite pool of respiratory carbon and electrons acquired from daytime solar energy capture. The H2 cycle provides unique insight into N2 fixation and associated metabolic processes in C. watsonii.

Southern Ocean iron enrichment experiment: carbon cycling in high- and low-Si waters.

The availability of iron is known to exert a controlling influence on biological productivity in surface waters over large areas of the ocean and may have been an important factor in the variation of the concentration of atmospheric carbon dioxide over glacial cycles. The effect of iron in the Southern Ocean is particularly important because of its large area and abundant nitrate, yet iron-enhanced growth of phytoplankton may be differentially expressed between waters with high silicic acid in the south and low silicic acid in the north, where diatom growth may be limited by both silicic acid and iron. Two mesoscale experiments, designed to investigate the effects of iron enrichment in regions with high and low concentrations of silicic acid, were performed in the Southern Ocean. These experiments demonstrate iron's pivotal role in controlling carbon uptake and regulating atmospheric partial pressure of carbon dioxide.