Modelling nitrogen fluxes in oligotrophic environments: NW Mediterranean and NE Atlantic

Stepped Coastal Water Warming Revealed by Multiparametric Monitoring at NW Mediterranean Fixed Stations

Since 2014, the global land and sea surface temperature has scaled 0.23 °C above the decadal average (2009-2018). Reports indicate that Mediterranean Sea temperatures have been rising at faster rates than in the global ocean. Oceanographic time series of physical and biogeochemical data collected from an onboard and a multisensor mooring array in the northwestern Mediterranean Sea (Blanes submarine canyon, Balearic Sea) during 2009-2018 revealed an abrupt temperature rising since 2014, in line with regional and global warming. Since 2014, the oligotrophic conditions of the water column have intensified, with temperature increasing 0.61 °C on the surface and 0.47 °C in the whole water column in continental shelf waters. Water transparency has increased due to a decrease in turbidity anomaly of -0.1 FTU. Since 2013, inshore chlorophyll a concentration remained below the average (-0.15 mg·l-1) and silicates showed a declining trend. The mixed layer depth showed deepening in winter and remained steady in summer. The net surface heat fluxes did not show any trend linked to the local warming, probably due to the influence of incoming offshore waters produced by the interaction between the Northern Current and the submarine canyon. Present regional and global water heating pattern is increasing the stress of highly diverse coastal ecosystems at unprecedented levels, as reported by the literature. The strengthening of the oligotrophic conditions in the study area may also apply as a cautionary warning to similar coastal ecosystems around the world following the global warming trend.

Reducing nutrient impacts from shrimp effluents in a subtropical coastal lagoon

Shrimp farm aquaculture causes environmental impacts, notably decreased water quality due to the release of nutrient-rich effluents. Pond wastewater is usually discharged without treatment, and tidal conditions are not taken into account in the management plans. However, natural variability of nutrients makes difficult field evaluation and attribution of impacts. Here we implemented a three-dimensional coupled hydrodynamic-biogeochemical model (spatial resolution=50m×50m, time resolution=4s) in order to evaluate the dispersion conditions under specific tidal conditions of nutrient discharges from a semi-intensive shrimp farm during spring and neap tide. Ammonia was quickly assimilated by plankton and its concentration recovered initial levels 10days after the beginning of the harvest. Due to the higher salinity of the pond effluents, shrimp farm discharges accumulate in waters and sediments of the upper lagoon creeks, mostly affecting the benthos, thus implying a potential risk of shrimp farm self-contamination. Maximum concentrations of most biogeochemical tracers occurred when the harvest ends and the ponds are fully emptied. We show that maximum nutrient concentrations can be reduced by ~10% when the harvest ends during spring tides compared to harvests ending during neap tides. This work may be useful to improve the management of shrimp farm effluents by reducing, easily and at little cost, nutrient impacts on tropical and sub-tropical receiving ecosystems.

Microbial Diversity and Putative Diazotrophy in High- and Low-Microbial-Abundance Mediterranean Sponges

Microbial communities associated with marine sponges carry out nutrient transformations essential for benthic-pelagic coupling; however, knowledge about their composition and function is still sparse. We evaluated the richness and diversity of prokaryotic assemblages associated with three high-microbial-abundance (HMA) and three low-microbial-abundance (LMA) sympatric Mediterranean sponges to address their stability and uniqueness. Moreover, to examine functionality and because an imbalance between nitrogen ingestion and excretion has been observed for some of these species, we sequenced nitrogenase genes (nifH) and measured N2 fixation. The prokaryotic communities in the two sponge types did not differ in terms of richness, but the highest diversity was found in HMA sponges. Moreover, the discrete composition of the communities in the two sponge types relative to that in the surrounding seawater indicated that horizontal transmission and vertical transmission affect the microbiomes associated with the two sponge categories. nifH genes were found in all LMA species and sporadically in one HMA species, and about half of the nifH gene sequences were common between the different sponge species and were also found in the surrounding water, suggesting horizontal transmission. (15)N2-enriched incubations showed that N2 fixation was measurable in the water but was not associated with the sponges. Also, the analysis of the isotopic ratio of (15)N to (14)N in sponge tissue indicated that N2 fixation is not an important source of nitrogen in these Mediterranean sponges. Overall, our results suggest that compositional and functional features differ between the prokaryotic communities associated with HMA and LMA sponges, which may affect sponge ecology.

The new pelagic Operational Observatory of the Catalan Sea (OOCS) for the multisensor coordinated measurement of atmospheric and oceanographic conditions

The new pelagic Operational Observatory of the Catalan Sea (OOCS) for the coordinated multisensor measurement of atmospheric and oceanographic conditions has been recently installed (2009) in the Catalan Sea (41°39'N, 2°54'E; Western Mediterranean) and continuously operated (with minor maintenance gaps) until today. This multiparametric platform is moored at 192 m depth, 9.3 km off Blanes harbour (Girona, Spain). It is composed of a buoy holding atmospheric sensors and a set of oceanographic sensors measuring the water conditions over the upper 100 m depth. The station is located close to the head of the Blanes submarine canyon where an important multispecies pelagic and demersal fishery gives the station ecological and economic relevance. The OOCS provides important records on atmospheric and oceanographic conditions, the latter through the measurement of hydrological and biogeochemical parameters, at depths with a time resolution never attained before for this area of the Mediterranean. Twenty four moored sensors and probes operating in a coordinated fashion provide important data on Essential Ocean Variables (EOVs; UNESCO) such as temperature, salinity, pressure, dissolved oxygen, chlorophyll fluorescence, and turbidity. In comparison with other pelagic observatories presently operating in other world areas, OOCS also measures photosynthetic available radiation (PAR) from above the sea surface and at different depths in the upper 50 m. Data are recorded each 30 min and transmitted in real-time to a ground station via GPRS. This time series is published and automatically updated at the frequency of data collection on the official OOCS website (http://www.ceab.csic.es/~oceans). Under development are embedded automated routines for the in situ data treatment and assimilation into numerical models, in order to provide a reliable local marine processing forecast. In this work, our goal is to detail the OOCS multisensor architecture in relation to the coordinated capability for the remote, continuous and prolonged monitoring of atmospheric and oceanographic conditions, including data communication and storage. Accordingly, time series of measurements for a number of biological parameters will be presented for the summer months of 2011. Marine hindcast outputs from the numerical models implemented for simulating the conditions over the study area are shown. The strong changes of atmospheric conditions recorded in the last years over the area have altered the marine conditions of living organisms, but the dimension of the impact remains unclear. The OOCS multisensor coordinated monitoring has been specifically designed to address this issue, thus contributing to better understand the present environmental fluctuations and to provide a sound basis for a more accurate marine forecast system.

Chronobiology of deep-water decapod crustaceans on continental margins

Species have evolved biological rhythms in behaviour and physiology with a 24-h periodicity in order to increase their fitness, anticipating the onset of unfavourable habitat conditions. In marine organisms inhabiting deep-water continental margins (i.e. the submerged outer edges of continents), day-night activity rhythms are often referred to in three ways: vertical water column migrations (i.e. pelagic), horizontal displacements within benthic boundary layer of the continental margin, along bathymetric gradients (i.e. nektobenthic), and endobenthic movements (i.e. rhythmic emergence from the substrate). Many studies have been conducted on crustacean decapods that migrate vertically in the water column, but much less information is available for other endobenthic and nektobenthic species. Also, the types of displacement and major life habits of most marine species are still largely unknown, especially in deep-water continental margins, where steep clines in habitat factors (i.e. light intensity and its spectral quality, sediment characteristics, and hydrography) take place. This is the result of technical difficulties in performing temporally scheduled sampling and laboratory testing on living specimens. According to this scenario, there are several major issues that still need extensive research in deep-water crustacean decapods. First, the regulation of their behaviour and physiology by a biological clock is almost unknown compared to data for coastal species that are easily accessible to direct observation and sampling. Second, biological rhythms may change at different life stages (i.e. size-related variations) or at different moments of the reproductive cycle (e.g. at egg-bearing) based on different intra- and interspecific interactions. Third, there is still a major lack of knowledge on the links that exist among the observed bathymetric distributions of species and selected autoecological traits that are controlled by their biological clock, such as the diel rhythm of behaviour. Species evolved in a photically variable environment where intra- and inter-specific interactions change along with the community structure over 24 h. Accordingly, the regulation of their biology through a biological clock may be the major evolutionary constraint that is responsible for their reported bathymetric distributions. In this review, our aim is to propose a series of innovative guidelines for a discussion of the modulation of behavioural rhythms of adult decapod crustaceans, focusing on the deep waters of the continental margin areas of the Mediterranean as a paradigm for other marine zones of the world.