Search

Marine diazotrophs convert dinitrogen (N2) gas into bioavailable nitrogen (N), supporting life in the global ocean. In 2012, the first version of the global oceanic diazotroph database (version 1) was published. Here, we present an updated version of the database (version 2), significantly increasing the number of in situ diazotrophic measurements from 13 565 to 55 286. Data points for N2 fixation rates, diazotrophic cell abundance, and nifH gene copy abundance have increased by 184 %, 86 %, and 809 %, respectively. Version 2 includes two new data sheets for the nifH gene copy abundance of non-cyanobacterial diazotrophs and cell-specific N2 fixation rates. The measurements of N2 fixation rates approximately follow a log-normal distribution in both version 1 and version 2. However, version 2 considerably extends both the left and right tails of the distribution. Consequently, when estimating global oceanic N2 fixation rates using the geometric means of different ocean basins, version 1 and version 2 yield similar rates (43–57 versus 45–63 Tg N yr−1 ; ranges based on one geometric standard error). In contrast, when using arithmetic means, version 2 suggests a significantly higher rate of 223±30 Tg N yr−1(mean ± standard error; same hereafter) compared to version 1 (74 ± 7 Tg N yr−1). Specifically, substantial rate increases are estimated for the South Pacific Ocean (88±23 versus 20±2 Tg N yr−1), primarily driven by measurements in the southwestern subtropics, and for the North Atlantic Ocean (40 ± 9 versus 10 ±2 Tg N yr−1). Moreover, version 2 estimates the N2 fixation rate in the Indian Ocean to be 35 ± 14 Tg N yr−1,which could not be estimated using version 1 due to limited data availability. Furthermore, a comparison of N2 fixation rates obtained through different measurement methods at the same months, locations, and depths reveals that the conventional 15N2 bubble method yields lower rates in 69 % cases compared to the new 15N2 dissolution method. This updated ve

Ocean acidification and warming are current global challenges that marine diazotrophs must cope with. Little is known about the effects of pH and temperature changes at elevated CO2 levels in combination with different nutrient regimes on N2 fixers, especially on heterotrophic bacteria. Here, we selected four culturable diazotrophs, i.e., cyanobacteria and heterotrophic bacteria, found in association with the endemic Mediterranean seagrass Posidonia oceanica. We tested different pH (from pH 4 to 8) and temperature levels (from 12 to 30 °C), under different nutrient concentrations of both phosphorus, P (0.1 µM and 1.5 mM), and iron, Fe (2 nM and 1 µM). We also tested different CO2 concentrations (410 and 1000 particles per million (ppm)) under different P/Fe and temperature values (12, 18, and 24 °C). Heterotrophic bacteria were more sensitive to changes in pH, temperature, and CO2 than the cyanobacterial species. Cyanobacteria were resistant to very low pH levels, while cold temperatures stimulated the growth in heterotrophic bacteria but only under nutrient-limited conditions. High CO2 levels (1000 ppm) reduced heterotrophic growth only when cultures were nutrient-limited, regardless of temperature. In contrast, cyanobacteria were insensitive to elevated CO2 levels, independently of the nutrient and temperature levels. Changes in N2 fixation were mainly controlled by changes in growth. In addition, we suggest that alkaline phosphatase activity (APA) and reactive oxidative species (ROS) can be used as biomarkers to assess the plasticity of these communities to climate change factors. Unlike other studies, the novelty of this work lies in the fact that we compared the responses of cyanobacteria vs. heterotrophic bacteria, studying which changes occur at the cell plasticity level. Our results suggest that the responses of diazotrophs to climate change may depend on their P and Fe status and lifestyle, i.e., cyanobacteria or heterotrophic bacteria.

After the first successful virtual ASLO Aquatic Sciences Meeting (ASM) in 2021 where we transformed the scientific and social events into interactive media experiences due to the COVID-19 pandemic...

Certain ultra-violet filter (UVF) components of solar creams have negative impacts on coral reefs and have been prohibited in international tourism destinations (i.e., Hawaii, Florida, and Palau) to protect coral reefs. In the Mediterranean coasts which are also hotspots of international tourism and where endemic seagrass Posidonia oceanica forms extensive meadows, the accumulation of UVF components have not been studied. We report for the first time, that the rhizomes of P. oceanica internally accumulated UVFs BP3, BP4, AVO, 4MBC and MeBZT and the paraben preservative MePB. The components BP4 and MePB occurred in higher concentrations reaching up to 129 ng g-1 dw and 512 ng g-1 dw, respectively. This work emphasizes the need for more experimental studies on the effects of UVFs on seagrasses and check if we should follow suit to prohibit certain UVFs to protect this species as what has been done in other regions to protect corals.

We investigated the effects of increasing seawater temperature and CO2 concentration based on a high business-as-usual climate change scenario by year 2100 on the photosynthetic performance and productivity of Mediterranean seagrass Posidonia oceanica and alkaline phosphatase and N2-fixing activities of microbes associated with different plant parts during winter when the plants may be thermally more vulnerable. Our results suggest that elevated CO2 and temperature benefit the overall photosynthetic performance of P. oceanica. Despite the benefits, the magnitude of respiration increased with elevated CO2 resulting in a negative carbon balance for P. oceanica in winter. This trend is contradictory to the general notion of decreased respiration in plants with increasing CO2, and warrants future investigation on the mechanisms behind the opposite trend. Changes of alkaline phosphatase activities found here may not be a direct consequence of the different treatments, but indirectly, through changes in the demand for dissolved inorganic phosphorus for N2 fixers. Of the several groups of N2 fixers tested for nifH expression (a proxy for activity of nitrogenase, the enzyme required for N2 fixation), only the unicellular N2-fixing cyanobacterial phylotypes, UCYNB and UCYNC, actively transcribed with a positive nifH transcription response of UCYNC to elevated CO2 and temperature. Our results suggest that in future climate scenarios, the structure and diversity of N2 microbial communities associated with seagrasses may change and high-light the importance of investigating the responses of different groups individually in their natural habitat substrates.

ASLO and the local and scientific committees continue working on the forthcoming aquatic sciences meeting in Palma. Given the uncertainty that the current COVID‐19 pandemic situation poses for traveling and social‐distancing measures, we are currently planning for a hybrid meeting, that is, combining an in‐person meeting with online participation. We are aiming to provide a physical venue for limnologists and oceanographers from around the world to meet, discuss, and share their science; however, this year there will be added online components and possibilities. Rescheduling of the ASLO meeting to early summer offers participants the potential to complement their scientific discussion during the meeting with plenty of social and outdoor activities.

The current global situation caused by the COVID‐19 pandemic has triggered changes in most scientific meetings worldwide. The ASLO 2021 in Palma “Aquatic Sciences for a sustainable future: nurturing cooperation,” has also been rescheduled to June 22–27. As “blessing in disguise,” this change from a winter to a summer meeting increases the options of enjoying cultural opportunities in Mallorca. Here we describe in a nutshell the most relevant options to experience during the sunny season of this unique Mediterranean Island.

The gastronomy of the Balearic Islands reflects the tradition of the Mediterranean diet, based on seafood, fruits, and olive oil (Fig. 1). For instance, dishes like the Menorcan caldereta de Langosta (lobster stew) or sepia a la mallorquina (cuttlefish with vegetables) are good examples. However, the most famous of all Mallorcan dishes sobrasada mallorquina, or the typical sweet ensaïmada served during, for example, coffee breaks, together with lots of other traditional dishes incorporate an ingredient that might not seem logical for outsiders: pork. Sobrasada is an excellent example of tasty traditional food that has deep cultural roots. The making of sobrasada is a family (including friends) affair, culminating in a festive rite that denotes the beginning of autumn and is still celebrated widely, a reflection of the long‐standing traditions of the local population. During the ritual slaughter of an autochthonous breed of pig (matança), nothing is wasted, and the pork loin and bacon are mixed with paprika, salt, and black pepper to produce the tasty cured sausage called sobrasada. Sobrasada can be incorporated as an ingredient in other traditional dishes or used as a spread on typical Mallorcan biscuits (e.g., on locally branded Quely biscuits, which date back to the 18th century). These small crackers are a sort of ship biscuit, formerly used as a long‐lasting provision but now mostly popular as kids' snacks and appetizers.

Posidonia oceanica, an endemic seagrass of the Mediterranean Sea harbors a high diversity of N-fixing prokaryotes. One of these is Halothece sp., a unicellular N-fixing cyanobacteria detected through nifH analysis from the epiphytes of P. oceanica. The most related strain in culture is Halothece sp. PCC 7418 and this was used as the test organism in this study. In the Mediterranean Sea, phosphorus (P) and iron (Fe) can be the major limiting nutrients for N fixation. However, information about the mechanisms of P-acquisition and the role of metals (i.e., Fe) in these processes for N-fixing bacteria is scarce. From our genomic analyses of the test organism and other phylogenetically related N-fixing strains, Halothece sp. PCC 7418 is one of the strains with the greatest number of gene copies (eight copies) of alkaline phosphatases (APases). Our structural analysis of PhoD (alkaline phosphatase type D) and PhoU (phosphate acquisition regulator) of Halothece sp. PCC 7418 showed the connection among metals (Ca and Fe), and the P-acquisition mechanisms. Here, we measured the rates of alkaline phosphatase activity (APA) through MUF-P hydrolysis under different combinations of concentrations of inorganic P ( PO ) and Fe in experiments under N-fixing (low NO availability) and non-N fixing (high NO availability) conditions. Our results showed that APA rates were enhanced by the increase in Fe availability under low levels of PO, especially under N-fixing conditions. Moreover, the increased PO-uptake was reflected in the increased of the P-cellular content of the cells under N fixation conditions. We also found a positive significant relationship between cellular P and cellular Fe content of the cells (r = 0.71, p < 0.05). Our results also indicated that Fe-uptake in Halothece sp. PCC 7418 was P and Fe-dependent. This study gives first insights of P-acquisition mechanisms in the N-fixing cyanobacteria (Halothece sp.) found in P. oceanica and highlights the role of Fe in these

The next Aquatic Sciences Meeting will be held in Palma, Spain. We anticipate that the topic “Aquatic Sciences for a Sustainable Future: Nurturing Cooperation” and the location of the meeting will incite researchers from all continents working in all aquatic fields to come over, communicate, interact, and share. While attending the meeting for the stimulating science, one has the opportunity to enjoy the astounding beauty of Mallorca, the larger island of the Balearics archipelago, located about 200 km (~125 miles) off the mainland Spain. The archipelago is bathed by the transparent waters of the Mediterranean Sea, harboring some of the best preserved endemic Posidonia oceanica seagrass meadows (Fig. 1) including those declared as UNESCO World Heritage between Ibiza and Formentera. The small Cabrera Archipelago, off the coast of Mallorca, was the first declared “Sea and Land National Park” in Spain, and shelters a diversity of sea life, including the last Spanish catalogued specimens of the highly endangered pen shell, Pinna nobilis (Fig. 1).

Palma de Mallorca, where the “Med mingles with history” is a jewel in the Mediterranean, has all the ingredients of a beautiful and exciting cosmopolitan city. Located in the south‐west coast of Mallorca on the nostalgic Bay of Palma, the city is bordered to the north and west sides by the Serra de Tramuntana, the island's major mountain range and a UNESCO World Heritage site. Palma dates back to the 13th‐century Christian reconquest of the island, and to the Moors, Romans and Talayotic people before that. It is famous for the immense Cathedral “La Seu” (the geographic and historical heart of the city) built on a previous mosque. The Old city behind the cathedral is a maze of streets hinting at an Arab past. Aside from this historical heritage, the endless beaches, the nearby mountain range and picturesque coastlines (Fig. 1), Palma has vibrant public squares, bohemian neighborhoods, bars, shops, cafes, a variety of restaurants (more than 1000), offering local (Mallorquin and Spanish) and international cuisines, and creations by local and international chefs of prestige.

We used 15N-labeled substrates to measure dinitrogen (N2) fixation, nitrate (NO3−) and ammonium (NH4+) uptake, regeneration and associated dissolved organic nitrogen (DON) release in a coastal upwelling system (Cape Ghir, ∼31°N) and an open ocean grid (bounded between 25°–42°N and 20°W) in the Canary Current region during the summer of 2009. New production (Pnew=NO3− uptake+N2 fixation+DON released from NO3− uptake−NO3− regeneration) was higher in the upwelling than in the open ocean zone (0.126 and 0.014 µmol N L−1 h−1, respectively), while regenerated production (Preg=NH4+ uptake+DON released from NH4+ uptake+NH4+ regeneration) was similar in both zones (0.157 and 0.133 µmol N L−1 h−1, respectively). The resulting f-ratio (Pnew/Pnew+Preg) for the open ocean and upwelling zones was 0.08 and 0.48, respectively. The availability of nitrogen in excess of that expected from Redfield stoichiometry is generally attributed to N2 fixation. A previous study indicated that our open ocean grid zone had an excess nitrogen production rate of 40±22×1010 mol N yr−1. We revisited this budget including new dissolved organic matter and NO3− fluxes through the Strait of Gibraltar and estimated a revised nitrogen excess rate of 22±19×1010 mol N yr−1. The average volumetric rate of N2 fixation for this zone was only 1.3×10−3 nmol N L−1 d−1, indicating that its influence in Pnew and nitrogen excess production in this part of the Atlantic is negligible.