Zooplankton data of M83/1

Oxygen-deficient waters in the ocean, generally referred to as oxygen minimum zones (OMZ), are expected to expand as a consequence of global climate change. Poor oxygenation is promoting microbial loss of inorganic nitrogen (N) and increasing release of sediment-bound phosphate (P) into the water column. These intermediate water masses, nutrient-loaded but with an N deficit relative to the canonical N:P Redfield ratio of 16:1, are transported via coastal upwelling into the euphotic zone. To test the impact of nutrient supply and nutrient stoichiometry on production, partitioning and elemental composition of dissolved (DOC, DON, DOP) and particulate (POC, PON, POP) organic matter, three nutrient enrichment experiments were conducted with natural microbial communities in shipboard mesocosms, during research cruises in the tropical waters of the southeast Pacific and the northeast Atlantic. Maximum accumulation of POC and PON was observed under high N supply conditions, indicating that primary production was controlled by N availability. The stoichiometry of microbial biomass was unaffected by nutrient N:P supply during exponential growth under nutrient saturation, while it was highly variable under conditions of nutrient limitation and closely correlated to the N:P supply ratio, although PON:POP of accumulated biomass generally exceeded the supply ratio. Microbial N:P composition was constrained by a general lower limit of 5:1. Channelling of assimilated P into DOP appears to be the mechanism responsible for the consistent offset of cellular stoichiometry relative to inorganic nutrient supply and nutrient drawdown, as DOP build-up was observed to intensify under decreasing N:P supply. Low nutrient N:P conditions in coastal upwelling areas overlying O2-deficient waters seem to represent a net source for DOP, which may stimulate growth of diazotrophic phytoplankton. These results demonstrate that microbial nutrient assimilation and partitioning of organic matter between the particulate and the dissolved phase are controlled by the N:P ratio of upwelled nutrients, implying substantial consequences for nutrient cycling and organic matter pools in the course of decreasing nutrient N:P stoichiometry.

Gene expression profiling in gills of the great spider crab Hyas araneus in respond to ocean acidification and warming, supplementary data

Hypercapnia and elevated temperatures resulting from climate change may have adverse consequences for many marine organisms. While diverse physiological and ecological effects have been identified, changes in those molecular mechanisms, which shape the physiological phenotype of a species and limit its capacity to compensate, remain poorly understood. Here, we use global gene expression profiling through RNA-Sequencing to study the transcriptional responses to ocean acidification and warming in gills of the boreal spider crab Hyas araneus exposed medium-term (10 weeks) to intermediate (1,120 µatm) and high (1,960 µatm) PCO2 at different temperatures (5°C and 10°C). The analyses reveal shifts in steady state gene expression from control to intermediate and from intermediate to high CO2 exposures. At 5°C acid-base, energy metabolism and stress response related genes were upregulated at intermediate PCO2, whereas high PCO2 induced a relative reduction in expression to levels closer to controls. A similar pattern was found at elevated temperature (10°C). There was a strong coordination between acid-base, metabolic and stress-related processes. Hemolymph parameters at intermediate PCO2 indicate enhanced capacity in acid-base compensation potentially supported by upregulation of a V-ATPase. The likely enhanced energy demand might be met by the upregulation of the electron transport system (ETS), but may lead to increased oxidative stress reflected in upregulated antioxidant defense transcripts. These mechanisms were attenuated by high PCO2, possibly as a result of limited acid-base compensation and metabolic down-regulation. Our findings indicate a PCO2 dependent threshold beyond which compensation by acclimation fails progressively. They also indicate a limited ability of this stenoecious crustacean to compensate for the effects of ocean acidification with and without concomitant warming.

Seawater carbonate chemistry, clearance rates, respiration rates, condition index and cellular turnover (RNA: DNA) of Juvenile King Scallop, Pecten maximus in a laboratory experiment

The decline in ocean water pH and changes in carbonate saturation states through anthropogenically mediated increases in atmospheric CO2 levels may pose a hazard to marine organisms. This may be particularly acute for those species reliant on calcareous structures like shells and exoskeletons. This is of particular concern in the case of valuable commercially exploited species such as the king scallop, Pecten maximus. In this study we investigated the effects on oxygen consumption, clearance rates and cellular turnover in juvenile P. maximus following 3 months laboratory exposure to four pCO2 treatments (290, 380, 750 and 1140 µatm). None of the exposure levels were found to have significant effect on the clearance rates, respiration rates, condition index or cellular turnover (RNA: DNA) of individuals. While it is clear that some life stages of marine bivalves appear susceptible to future levels of ocean acidification, particularly under food limiting conditions, the results from this study suggest that where food is in abundance, bivalves like juvenile P. maximus may display a tolerance to limited changes in seawater chemistry.

Environmental conditions and habitats of GOS sites and bottle data of HOT-ALOHA station

The Global Ocean Sampling (GOS) expedition is currently the largest and geographically most comprehensive metagenomic dataset, including samples from the Atlantic, Pacific, and Indian Oceans. This study makes use of the wide range of environmental conditions and habitats encompassed within the GOS sites in order to investigate the ecological structuring of bacterial and archaeal taxon ranks. Community structures based on taxonomically classified 16S ribosomal RNA (rRNA) gene fragments at phylum, class, order, family, and genus rank levels were examined using multivariate statistical analysis, and the results were inspected in the context of oceanographic environmental variables and structured habitat classifications. At all taxon rank levels, community structures of neritic, oceanic, estuarine biomes, as well as other exotic biomes (salt marsh, lake, mangrove), were readily distinguishable from each other. A strong structuring of the communities with chlorophyll a concentration and a weaker yet significant structuring with temperature and salinity were observed. Furthermore, there were significant correlations between community structures and habitat classification. These results were used for further investigation of one-to-one relationships between taxa and environment and provided indications for ecological preferences shaped by primary production for both cultured and uncultured bacterial and archaeal clades.