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The volcanic eruption that occurred in La Palma Island (Canary Islands, Spain) in 2021 resulted in molten lava flowing into the ocean and forming a delta in the coastline, besides the emission of large amounts of ashes being deposited in a vast area around the Canary Islands. In order to assess the effects of the eruption on seawater, two oceanographic cruises were carried out, one at the beginning of the eruption and a second one a month later. We used an oceanographic CTD rosette sampler for collecting seawater in different areas of La Palma coastline together with Unmanned Aerial Vehicles (UAVs) equipped with a sampling device to collect surface samples near the delta newly formed on the coastal fringe. We sequenced the 16S rRNA gene in order to assess the response of bacterioplankton to such natural disturbance. The results show that the abundance of Thiomicrospirales, Gammaproteobacteria capable of oxidizing poly-metal sulfides, increased significantly in UAV samples collected near the lava delta. Moreover, in stations where the largest physical-chemical anomalies were recorded with the CTD, sequence data showed drastic changes in the prokaryotic community structure; cyanobacterial abundance decreased while the ammonia-oxidizing archeon Nitrosopelagicus and the bacterial SAR324 clade, with potential sulfur-based chemolithoautotrophic lifestyle, dominated the communities. The combined used of shipboard operations and UAVs provided a unique opportunity to study the prokaryotic response to a massive lava input, an event that is rarely observed and sampled in real time.

Diversity of protists was researched in different coastal areas of the Mediterranean Sea by means of high throughput sequencing technologies based on the amplification of a specific region of the 18S rRNA gene. A total of 25 samples were obtained in the Mar Menor coastal lagoon (MMS) in 2016-2017 after the ecosystem suffered a so-called 'ecosystem disruptive algal bloom' which was attributed to nitrate pollution. Another set of samples (9) was harvested in 2018 at a coastal area of the northern Alboran Sea, which received urban wastewater (CS). The community structure in these two areas was compared with samples collected at stations of the Alboran Sea following a trophic gradient from coast to open sea (UP; 15 samples; OAS) located far from pollution sources. On average, Alveolata, Stramenopila and Rhizaria counted for more than 85% of the total sequence reads in the three areas although the contribution of the three groups was different. The relative abundance of Alveolata reads averaged 62% in OAS but increased notably in CS (80%) and MMS (70%). In contrast, both diversity and abundance of Rhizaria were reduced in CS (1.4% and 4.7% of reads and OTUs) and MMS (3% and 7%) compared to OAS (5.5% and 9.7%). The highest contribution of Stramenopila to total reads was obtained in OAS (20% compared to 8% and 13% in CS and MMS, respectively). a-diversity of autotrophs, dinoflagellates and heterotrophs decreased in the areas impacted by nutrient pollution. However, these was not a consistent variability pattern in b-diversity.

Microplankton is an heterogeneous group of organisms ranging between 20 and 200 microns in size. Morphological characterization of its diversity is challenging as it includes Chromista, Protozoa, and Metazoa (adults and larvae). We characterized the composition of the microzooplankton community (heterotrophic and mixotrophic) collected with a CalVET net (50 µm mesh), in a coastal area affected by urban wastewater discharges in the N Alboran Sea (SW Mediterranean). We applied an integrative taxonomic approach, combining metabarcoding of the mtDNA cytochrome oxidase I (COI) and the V4 region of the 18S rRNA (18S) genes with morphological microscopic identification of organisms. Both methods showed differentiated coastal and offshore microzooplankton assemblages. The dominant taxa varied depending on the method used, with Dinophyceae accounting for 64-85% of the microscopy counts but Arthropoda representing up to 98% or the COI and 18S reads. When computing Protozoa and Metazoa relative abundances separately, both microscopy and metabarcoding revealed unicellular communities dominated by thecate Dinophyceae, followed by Ciliophora. Metazoa microscopy counts were dominated by eggs, followed by Copepoda nauplii in offshore waters, whilst by Appendicularia and Mollusca larvae in the shallow coastal stations. COI reads also corresponded mostly to Copepoda and Mollusca. However, 18S reads were dominated by Thecostraca and Copepoda. Despite the identification level differed among methods and taxa, the integrated approach revealed higher diversity than expected.

The Alborán Sea sardine (Sardina pilchardus) is the most abundant small pelagic fish in the Mediterranean Sea. Along the northern coast of the Alborán Sea, Málaga and Almería Bay are two important nursery grounds with contrasting oceanographic characteristics. Post-larval stages of S. pilchardus were collected during the late autumn and late winter along with the mesozooplankton community. We examined the influence of feeding behavior on larval growth using environmental variables, daily growth metrics, otolith biometry, stable isotope analysis and trophodynamics. Trophic positions were calculated using mesoozooplankton as potential prey for S. pilchardus. During both seasons, we observed faster growth in larger otoliths that also corresponded to higher trophic positions. Our results indicate that the isotopic signature of larvae is highly influenced by the mesozooplankton community structure. Moreover, the trophic variables showed a significant linear relationship with the estimated ages for all larvae indicating dietary changes throughout ontogenic development.

The influence of hydrochemistry and trophic conditions on the coastal zooplankton community’s biomass and metabolic activities was investigated along the Spanish Mediterranean coastal waters, from Algeciras Bay to Barcelona, from autumn 2011 to autumn 2012. Two hydrographic regions were differentiated: NW Alboran (ALB) and W Mediterranean (MED). Zooplankton metabolism was assessed from measurements of the electron transport system (ETS) and aminoacyl-tRNA synthetases (AARS) activities, as proxies for potential respiration and somatic growth, respectively. Zooplankton showed three to fivefold higher biomass in ALB than in MED during autumn 2011 and spring 2012. However, in autumn 2012, a drastic decrease in biomass standing stock was observed in ALB, with no significant differences between the two regions. This biomass depletion event was not associated with environmental variables, food availability or zooplankton metabolic rates, but coincided with a twofold peak of Sardina pilchardus landings in ALB. A reduced standing stock coupled with high zooplankton growth rates suggests mortality by predation as the main cause for the low zooplankton biomass typically observed in MED, and in ALB during autumn 2012.

To assess the likely economic outcomes to fishing fleets of the Landing Obligation (LO), bioeconomic models covering seven European fisheries, ranging from the North East Atlantic to the Mediterranean, have been applied to estimate the economic performance of fleets before and after implementing the LO. It is shown that for most of the analysed fisheries, their economic outcome will be negatively affected in the long term by the LO, when compared to the expected outcome with no LO. Efficient mitigation strategies (exemptions, quota uplifts, improved selectivity, effort reallocation and others) may, for some of the analysed fisheries, reduce the negative economic effect of the LO. Moreover, the possibility to trade quotas, both nationally and internationally, may also reduce the economic losses caused by the LO. However, even with mitigation strategies and/or quota trade in place, most of the analysed fisheries are worse off under the LO than what could be expected if the LO was not implemented.

In the Bay of Algeciras (BA), intensive urban and industrial activityis underway, which is potentially responsible for the release of significant quantities of nutrients. However, the assessment of the impact of these discharges is complex. Nutrient concentration in the surface layer is per se strongly variable due to the variability associated with the upwelling of nutrient-enriched deep Mediterranean water (MW), which in turn is regulated by atmospheric forcing. The aim of this study is to determine the effects of changes in the upwelling intensity on the load of nitrate and phosphate in the BA and to appraise their impact on chlorophyll a variability. Based on this analysis, the possible influence of the nutrients released from land-based sources is indirectly inferred. Data and samples collected during nine research cruises carried out in different seasonal cycle periods between 2010 and 2015 in the BA were analysed. The vertical variation of temperature and salinity indicates that the MW upwelling was favoured in spring, as occurred in other coastal areas of the northern Alboran Sea. However, principal component analysis conducted on physical and chemical data reveals that shifts in nutrients and chlorophyll a in the euphotic layer are poorly explained by changes in the upwelling intensity. Furthermore, during some of these research surveys (particularly in summer), chlorophyll a concentrations were higher in the BA as compared to a nearby coastal area also affected by MW upwelling. Scarce information about land-based pollution sources precludes quantitative analysis of the impact of nutrient loads on water quality; however, the available data suggest that the main source of allochthanous inorganic nitrogen over the period 2010–2015 in the BA was nitrate. Therefore, it is reasonable to hypothesize that the high concentrations of nitrate and chlorophyll a in BA in summer are a consequence of those discharges. Our study highlights the need of more exhaustive inve

The distribution of marine productivity in the Alboran Sea responds strongly to its hydrodynamics, shaped by the influence of the Atlantic jet that enters through the Gibraltar Strait. This stream originates an oligotrophic western anticyclonic gyre (WAG) that dominates the western basin of the Alboran Sea. We studied vertical (0–900 m) diel changes in zooplankton biomass, potential respiration (electron transport system activity, ETS) and growth rates (aminoacyl-tRNA synthetases activity, AARS), to assess their variability in relation to the WAG structure. Zooplankton biomass was distributed in distinctive layers and we observed strong diel vertical migrations in the open sea. Diel vertical migrants (DVM) biomass, production and respiration rates doubled within the WAG core. The active carbon flux to mesopelagic waters mediated by DVM, estimated from respiration and mortality at depth, increased from the coast (2.0–5.7 mg C m−2 d−1) towards the gyre core (27.1–76.7 mg C m−2 d−1). The WAG enhanced the carbon export to deep waters, reinforcing the role of the Alboran Sea as sink of atmospheric carbon.

The Alboran Sea is highly dynamic from a hydrographical point of view. Depending on the strength of the currents and the direction of the wind the surface coastal water masses can be either of Atlantic or Mediterranean origin. This variability affects both the phytoplankton and zooplankton components of the community inhabiting the Bay of Málaga. In addition, fish larvae distribution varies with the diel cycle, affecting zooplankton distribution in shallow waters. In order to provide a first insight into the variability of the planktonic community composition in the area during a 24 hour cycle, we applied an integrative approach combining morphological and molecular tools.

The Alboran Sea is a highly dynamic basin which exhibits a high spatio-temporal variability of hydrographic structures (e.g. fronts, gyres, coastal upwellings). This work compares the abundance and composition of picophytoplankton observed across the northern Alboran Sea among eleven cruises between 2008 and 2012 using flow cytometry. We evaluate the seasonal and longitudinal variability of picophytoplankton on the basis of the circulation regimes at a regional scale and explore the presence of cyanobacteria ecotypes in the basin. The maximal abundances obtained for Prochlorococcus, Synechococcus and picoeukaryotes (12.7 × 104, 13.9 × 104 and 8.6 × 104 cells mL− 1 respectively) were consistent with those reported for other adjacent marine areas. Seasonal changes in the abundance of the three picophytoplankton groups were highly significant although they did not match the patterns described for other coastal waters. Higher abundances of Prochlorococcus were obtained in autumn-winter while Synechococcus and picoeukaryotes exhibited a different seasonal abundance pattern depending on the sector (e.g. Synechococcus showed higher abundance in summer in the west sector and during winter in the eastern study area). Additionally, conspicuous longitudinal gradients were observed for Prochlorococcus and Synechococcus, with Prochlorococcus decreasing from west to east and Synechococcus following the opposite pattern. The analysis of environmental variables (i.e. temperature, salinity and inorganic nutrients) and cell abundances indicates that Prochlorococcus preferred high salinity and nitrate to phosphate ratio. On the contrary, temperature did not seem to play a role in Prochlorococcus distribution as it was numerically important during the whole seasonal cycle. Variability in Synechococcus abundance could not be explained by changes in any environmental variable suggesting that different ecotypes were sampled during the surveys. In particular, our data would indicate the pr

Zooplankton play a central role as ecological/environmental indicator of the good environmental state sensu Marine Strategy Framework Directive. One of the main challenges in their practical application is the quantitative evaluation of zooplankton production with a frequency matching the spatial and temporal scales of phytoplankton variability. For this purpose indirect methods of production assessment are needed. Zooplankton production along the southeastern Spanish coast, from Algeciras to Cartagena was determined from measurements of biomass and AARS activity. The relationships between zooplankton biomass and growth variability and the hydrochemistry and trophic conditions were studied. Zooplankton had overall lower biomass-specific growth rates in Algeciras Bay and the central Alboran Sea than in the eastern stations. However, zooplankton biomass and abundance were significantly higher in the Bay of Málaga. As a result, the zooplankton community in these coastal waters presented the highest production rates of the study area.

The seasonal changes in structure and functioning of the pelagic trophic web in Málaga Bay (NW Alboran Sea) are related to the annual hydrological cycle. However, time series analyses have shown that the relationship between interannual hydrological variability and the plankton community composition is weak. This might be due to different human-induced pressures (nutrient pollution, coastal fisheries) acting on different compartments of the trophic web. The net effect of all these factors would depend on how the ecosystem channels changes in the composition and abundance of each trophic level. Interactions of phytoplankton-ciliates-zooplankton might have a central role in the regulation of the trophic web in Málaga Bay, although the trophic relations of the dominant groups remain still undefined. In order to identify the dominant trophic relationships we aimed to characterise the diet of key ichthyo- and mesozooplankton species in the field. Given that gut content preys (phyto- and microplankton) are fragile and not easy to identify visually, we developed species-specific molecular markers to detect their presence/absence within the predators gut.

The utility of three different algorithms for retrieving surface chlorophyll-a values from satellite images of MODIS-Aqua is tested in the northern Alboran Sea. The available global algorithm to calculate chlorophyll-a from reflectance of MODIS-Aqua (OC3M) overestimates the surface chlorophyll-a in the study area. Another regional algorithm specifically developed for the Mediterranean Sea (MedOC3) improves the estimates although the best outcome is obtained with OC5, which was developed for Atlantic coastal waters. The three tested algorithms perform worse at in situ chlorophyll-a concentrations higher than 1 mg m−3 and exhibit uncertainty levels higher than 35% for this range of concentrations. A new algorithm (ALBOC3) is proposed which produces a good estimation of the in situ chlorophyll-a for the whole range of concentrations normally registered in the study area (0.1–3.5 mg m−3). We hypothesize that the particular bio-optical features of the northern Alboran Sea phytoplankton explain the poor functioning of the published algorithms that have been tested in this work.

We report on results of a microcosm experiment to study the interactive effects of elevated CO2, high organic and inorganic nutrient loading, and high irradiance on phytoplankton and bacterioplankton from the Mediterranean coastal ecosystem of the Alboran Sea. This experiment was part of the Group for Aquatic Productivity 9th international workshop and was conducted by Working Group 1 (WG1: Phytoplankton of coastal waters, www.gap9.uma.es). Over a 7 d period, we measured the variation in physical and chemical variables and the characteristics of phytoplankton and bacterioplankton in microcosms incubated under 8 treatments, representing full factorial combinations of 2 levels each of CO2 supply, nutrient concentrations and solar radiation exposure. For each treatment combination, we incubated triplicate microcosms consisting of 20 l polyethylene bags which were transparent to ultraviolet radiation. Sustained growth of phytoplankton biomass (chl a) occurred in all treatments. The absence of mesozooplankton in the microcosms resulted in a trophic cascade. Picophytoplankton were initially stimulated but then decreased, apparently due to microzooplankton grazing, and were largely replaced by diatoms. Bacteria were also initially stimulated and then decreased, but eventually recovered. Responses were modified markedly by nutrient enrichment and light availability, with moderate effects of elevated CO2. Relative to ambient CO2, elevated CO2 resulted in higher chl a under low irradiance, but lower chl a under high irradiance.

We conducted a microcosm experiment aimed at studying the interactive effects of high CO2, nutrient loading and irradiance on the metabolism of a planktonic community sampled in the Western Mediterranean near the coast of Málaga. Changes in the metabolism of phytoplankton and bacterioplankton were observed for 7 d under 8 treatment conditions, representing the full factorial combinations of 2 levels each of CO2, nutrient concentration and solar radiation exposure. The initial plankton sample was collected at the surface from a stratified water column, indicating that phytoplankton were naturally acclimated to high irradiance and low nutrient concentrations. Nutrient addition combined with high irradiance resulted in a significant increase in primary production. Nitrate uptake by phytoplankton was also stimulated under high nutrient conditions. High nutrients, high irradiance and the combination of low CO2 and high irradiance positively affected bacterial production. Light was the main factor affecting the respiration rates of the community, which were higher at the high light level. After 7 d of incubation, nutrient loading was the only factor that significantly affected the amount of particulate organic carbon (POC) accumulated in the microcosms. Therefore, the changes in metabolic rates produced at high CO2 had no effect on net production of particulate organic matter. If these results are extrapolated to the natural environment, it could be hypothesized that high levels of CO2 will have a limited impact on biological pump activity in the northern Alboran Sea since it is assumed that POC export towards deeper layers determines the potential for carbon sequestration