Potential uptake of dissolved organic matter by seagrasses and macroalgae

Dissolved organic nitrogen (DON) acts as a large reservoir of fixed nitrogen. Whereas DON utilization is common in the microbial community, little is known about utilization by macrophytes. We investigated the ability of the coexisting temperate marine macrophytes Zostera noltii, Cymodocea nodosa, and Caulerpa prolifera to take up nitrogen and carbon from small organic substrates of different molecular complexities (urea, glycine, L-leucine, and L-phenylalanine) and from dissolved organic matter (DOM) derived from algal and bacterial cultures (substrates with a complex composition). In addition to inorganic nitrogen, nitrogen from small organic substrates could be taken up in significant amounts by all macrophytes. Substrate uptake by the aboveground tissue differed from that of the belowground tissue. No relationships between carbon and nitrogen uptake of small organics were found. The preference for individual organic substrates was related to their structural complexity and C:N ratio. Uptake of algae-derived organic nitrogen was of similar magnitude as inorganic nitrogen, and was preferred over bacteria-derived nitrogen. These results add to the growing evidence that direct or quick indirect DON utilization may be more widespread among aquatic macrophytes than traditionally thought.This research was supported by the regional government of Andalusia project FUNDIV (P07-RNM-2516), the Spanish Project CTM2008-00012/MAR, a European Reintegration Grant (MERG-CT-2007-205675), a travel grant from Schure-Beijerinck-Popping Fund (SBP/JK/2007-32) and the Netherlands Organization for Scientific Research. Thanks to Fidel Echevarrìa Navas (Director of CACYTMAR) for granting us access to facilities, and to Bas Koutstaal for helping with sample processing. We also thank the anonymous reviewers for their valuable comments which significantly improved this manuscript

Oxygen concentration in the water column over a Posidonia oceanica meadow in Cabrera Archipelago Marine-Terrestrial National Park between October 2019 – October 2021

[Description of methods used for collection/generation of data] For the study, environmental data were measured by sensors located in both the water column and the benthic compartment (at 4 m and 8 m, respectively). Temperature, salinity and dissolved oxygen (DO) from the water column were measured from October 2019 to October 2021 by a sensor attached to the mooring line. Data were recorded with a CT SBE37 (Conductivity, Temperature) sensor (SBE37SMP-ODO-RS232, Sea-Bird Scientific©) coupled with an SBE 63 (Sea-Bird Scientific©) dissolved oxygen (DO) sensor with accuracies of ± 0.002 °C for temperature, ± 0.002 mS cm-1 for conductivity and ± 2 % for DO. Measurements were taken with a resolution of 0.0001 ºC for temperature, 0.0001 mS cm−-1 for conductivity and 0.2 µmol kg-1 for DO. Multiparametric Hydrolab HL4 probes (OTT HydroMet) were deployed during 8 different periods covering all seasons following the procedure by Hendriks et al. (2021). Accuracy for the multiparametric probe sensors is ± 0.10 ºC for temperature and ± 0.5 % of reading + 0.001 mS cm−1 for conductivity, with resolutions of 0.01 ºC and 0.001 mS cm-−1, respectively. The DO sensor presents an accuracy of ± 0.1 mg L−1 for values lower than 8 mg L−1, and ± 0.2 mg L−1 for values higher than 8 mg L−1, and a resolution of 0.01 mg L−1. Two benthic chambers were installed during May and July 2021 using a design previously described in Barrón et al. (2006). MiniDOT sensors (PME, Inc. ©) were used for temperature and DO measurements every 15 minutes, with accuracies of ± 0.1 ºC and ± 5 %, respectively. DO sensor data were validated against water samples analysed with the Winkler method.. Three chamber replicates were installed during each deployment. Wind speed (m s−1) values at Cabrera NP Station were obtained from data provided by the Organismo Autónomo de Parques Nacionales (OAPN, Spain). For the benthic chambers, night respiration was estimated from changes in DO between one hour after sunset and one hour before sunrise. The same procedure was followed for the calculation of the net community production (NCP) during daylight hours, and the two values were summed for GPP. NCP was used along with the total meadow area coverage and residence time of water in Sta. María Bay to determine the total O2 exported by the meadow to the water column. For the metabolic rate calculation, only oxygen data from the first 24 hours were used.[Methods for processing the data] Seasonal variations in the metabolic rates were analysed with a one-way ANOVA test using the Statistics and Machine Learning ToolboxTM in Matlab® (https://mathworks.com). For this purpose, daily metabolic rates from water column sensors and multiparametric sensors were grouped by season . The same statistical analysis was performed to analyse disparities between sensors. Since benthic chamber data were only available for one day in May and one day in July, differences between deployments were tested using a Student t-test.readme provides background information for csv datafiles. Csv datafiles are processed data of oxygen concentrations used as input for the model, with a frequency of 10 minutes for hydrolab (HL) measurements and hourly for the CT measurements, and a frequency of 15 minutes for MiniDot measurements.Spanish Ministry of Science (SumaEco, RTI2018–095441-B-C21), the Government of the Balearic Islands through la Consellería d'Innovació, Recerca i Turisme (Projecte de recerca científica i tecnològica SEPPO, PRD2018/18), the Posi-COIN Project from the 2018 BBVA Foundation “Ayudas a equipos de investigación científica” call. STARTER research project funded by the 2021 call of the Càtedra de la Mar, Iberostar Foundation. This work is a contribution to CSIC's Thematic Interdisciplinary Platform PTI OCEANS+. The present research was carried out within the framework of the activities of the Spanish Government through the "Maria de Maeztu Centre of Excellence" accreditation to IMEDEA (CSIC-UIB) (CEX2021-001198).With funding from the Spanish government through the "Severo Ochoa Centre of Excellence" accreditation (CEX2021-001198).Peer reviewe

Reproductive investment of the pen shell Pinna nobilis Linnaeus, 1758 in Cabrera National Park (Spain)

The spawning period can be a period of particular vulnerability for a species. In hermaphroditic species like the long-lived pen shell Pinna nobilis different costs could be associated with female, male or hermaphrodite stages. Here we evaluate gonad development in a population with few anthropogenic pressures and describe the timing and succession of developmental stages, determine the ratio of the sexes and the condition of the animals. We assess resource mobilisation and associated costs through the relationship between stable isotopes and condition indexes with reproductive parameters and evaluate the role of the adductor muscle as storage organ used in gonad maturation. In our study area only one spawning season is observed, starting in May and peaking in June-July. The onset of spawning coincides with water temperatures of 20 °C. Condition indexes drop during the spawning period and recover afterwards to reach pre-spawning values in November. Stable isotope signals are negatively related to the gonadal condition index, while the CN ratio shows a positive correlation with the same index. Additionally, the muscle condition index sharply decreases after the start of the spawning season, which suggests that P. nobilis uses the reserves stored in the adductor muscle for reproduction as in other Pinnidae species. Reproductive indices and stable isotopes ratios indicate ‘capital breeding’ as reproductive strategy of the pen shell. Decreased muscle force could mean a higher vulnerability during the summer period, coinciding with the peak in recreational activities involving poaching and anchoringVersión del edito

Long photoperiods sustain high pH in Arctic kelp forests

Concern on the impacts of ocean acidification on calcifiers, such as bivalves, sea urchins, and foraminifers, has led to efforts to understand the controls on pH in their habitats, which include kelp forests and seagrass meadows. The metabolism of these habitats can lead to diel fluctuation in pH with increases during the day and declines at night, suggesting no net effect on pH at time scales longer than daily. We examined the capacity of subarctic and Arctic kelps to up-regulate pH in situ and experimentally tested the role of photoperiod in determining the capacity of Arctic macrophytes to up-regulate pH. Field observations at photoperiods of 15 and 24 hours in Greenland combined with experimental manipulations of photoperiod show that photoperiods longer than 21 hours, characteristic of Arctic summers, are conducive to sustained up-regulation of pH by kelp photosynthesis. We report a gradual increase in pH of 0.15 units and a parallel decline in pCO2 of 100 parts per million over a 10-day period in an Arctic kelp forest over midsummer, with ample scope for continued pH increase during the months of continuous daylight. Experimental increase in CO2 concentration further stimulated the capacity of macrophytes to deplete CO2 and increase pH. We conclude that long photoperiods in Arctic summers support sustained up-regulation of pH in kelp forests, with potential benefits for calcifiers, and propose that this mechanism may increase with the projected expansion of Arctic vegetation in response to warming and loss of sea ice.The study was funded by the Danish Environmental Protection Agency within the Danish Cooperation for Environment in the Arctic. It is also a contribution to the Greenland Ecosystem Monitoring program (www.G-E-M.dk) and the Arctic Science Partnership (www.asp-net.org). M.S.-M. was supported by a Fundación “La Caixa” fellowship (Spain). We acknowledge support by the CSIC Open Access Publication Initiative through its Unit of Information Resources for Research (URICI).Peer reviewe

The emergent fouling population after severe eutrophication in the Mar Menor coastal lagoon

Mar Menor is one of the largest coastal lagoons in the Mediterranean basin. Over the years, Mar Menor has suffered a significant environmental degradation due to multiple factors with anthropogenic origin. The transformation from a rain-fed basin to intensive irrigated agriculture has led to an rise in the water inflow and nutrients in the basin, which has provoked severe eutrophication. The increase in nutrients led to changes in the structure and function of the lagoon ecosystems. The epibenthic and suspension feeder organisms have benefited from this imbalance, proliferating and reaching a high population density. The composition and abundance of the species assemblage found in the sub-coastal bottoms of the coastal lagoon after the environmental crisis occurred in 2016, using artificial settlement structures. The variation in community density and affinity between sampling sites in 2017 and 2018, were determined. A total of 31 species belonging to 27 genera and 7 phyla were observed in 11 samples. The best represented class are polychaeta (Phylum Annelida) with 11 identified species. The genus with the greatest species richness was Hydroides with two species: H. dianthus (Verrill, 1873), and H. elegans (Haswell, 1883), both of them considered potentially invasive and opportunistic species followed by the genus Serpula, with two species: S. vermicularis (Linnaeus, 1767), and S. concharum (Langerhans, 1880) and the genus Branchiomma was represented with another exotic invasive species, B. boholense (Grube, 1878), which is only found in collectors in 2018. These results have allowed to increase the knowledge about the effect of eutrophication in the structure of the fouling community in the assemblage succession in the Mar Menor coastal lagoon.This study was supported by the research fund of the University of Alicante and Murcia University Aquarium

Effects of seagrasses and algae of the Caulerpa family on hydrodynamics and particle-trapping rates

The widespread decline of seagrass beds within the Mediterranean often results in the replacement of seagrasses by opportunistic green algae of the Caulerpa family. Because Caulerpa beds have a different height, stiffness and density compared to seagrasses, these changes in habitat type modify the interaction of the seafloor with hydrodynamics, influencing key processes such as sediment resuspension and particle trapping. Here, we compare the effects on hydrodynamics and particle trapping of Caulerpa taxifolia, C. racemosa, and C. prolifera with the Mediterranean seagrasses Cymodocea nodosa and Posidonia oceanica. All macrophyte canopies reduced near-bed volumetric flow rates compared to bare sediment, vertical profiles of turbulent kinetic energy revealed peak values around the top of the canopies, and maximum values of Reynolds stress increased by a factor of between 1.4 (C. nodosa) and 324.1 (P. oceanica) when vegetation was present. All canopies enhanced particle retention rates compared to bare sediment. The experimental C. prolifera canopy was the most effective at particle retention (m2 habitat); however, C. racemosa had the largest particle retention capacity per structure surface area. Hence, in terms of enhancing particle trapping and reducing hydrodynamic forces at the sediment surface, Caulerpa beds provided a similar or enhanced function compared to P.oceanica and C. nodosa. However, strong seasonality in the leaf area index of C. racemosa and C. taxifolia within the Mediterranean, combined with a weak rhizome structure, suggests that sediments maybe unprotected during winter storms, when most erosion occurs. Hence, replacement of seagrass beds with Caulerpa is likely to have a major influence on annual sediment dynamics at ecosystem scales.This research was funded by the European Network of Excellence ‘‘Marine Biodiversity and Ecosystem Function’’ (MarBEF); FP6, EC contract no. 505446 and a grant from the Fundacio ´n BBVA. EPM was supported by a European Union Marie Curie host fellowship for transfer of knowledge, MTKD-CT-2004-509254, the Spanish national project EVAMARIA (CTM2005-00395/MAR) and the regional government of Andalusia project FUNDIV(P07-RNM-2516)

Genetic and oceanographic tools reveal high population connectivity and diversity in the endangered pen shell Pinna nobilis

For marine meta-populations with source-sink dynamics knowledge about genetic connectivity is important to conserve biodiversity and design marine protected areas (MPAs). We evaluate connectivity of a Mediterranean sessile species, Pinna nobilis. To address a large geographical scale, partial sequences of cytochrome oxidase I (COI, 590 bp) were used to evaluate phylogeographical patterns in the Western Mediterranean, and in the whole basin using overlapping sequences from the literature (243 bp). Additionally, we combined (1) larval trajectories based on oceanographic currents and early life-history traits and (2) 10 highly polymorphic microsatellite loci collected in the Western Mediterranean. COI results provided evidence for high diversity and low inter-population differentiation. Microsatellite genotypes showed increasing genetic differentiation with oceanographic transport time (isolation by oceanographic distance (IBD) set by marine currents). Genetic differentiation was detected between Banyuls and Murcia and between Murcia and Mallorca. However, no genetic break was detected between the Balearic populations and the mainland. Migration rates together with numerical Lagrangian simulations showed that (i) the Ebro Delta is a larval source for the Balearic populations (ii) Alicante is a sink population, accumulating allelic diversity from nearby populations. The inferred connectivity can be applied in the development of MPA networks in the Western MediterraneanProject MEDEICG funded by the Spanish Ministry of Economy and Competitiveness (CTM2009-07013)IEH was supported by Ramon y Cajal Fellowship RYC2014-14970Spanish Ministry of Economy, Industry and Competitiveness IFCT Investigator Programme-Career Development (IF/00998/2014)MGW and AHE was supported by FCT fellowships SFRH/BPD/63703/2009 and SFRH/BPD/107878/2015National Science Foundation (OCE-1419450)CCMAR team via excellence research line EXCL/AAG-GLO/0661/2012Ciencias del Ma

Food supply confers calcifiers resistance to ocean acidification

Invasion of ocean surface waters by anthropogenic CO emitted to the atmosphere is expected to reduce surface seawater pH to 7.8 by the end of this century compromising marine calcifiers. A broad range of biological and mineralogical mechanisms allow marine calcifiers to cope with ocean acidification, however these mechanisms are energetically demanding which affect other biological processes (trade-offs) with important implications for the resilience of the organisms against stressful conditions. Hence, food availability may play a critical role in determining the resistance of calcifiers to OA. Here we show, based on a meta-analysis of existing experimental results assessing the role of food supply in the response of organisms to OA, that food supply consistently confers calcifiers resistance to ocean acidification.This work was funded by grants from the Danish Environmental Protection Agency within the Danish 486 Cooperation for Environment in the Arctic (DANCEA), ASSEMBLE grant agreement no. 227799 from European Community and from the Spanish Ministry of Economy and Competitiveness (ESTRESX, number CTM2012-32603). N.A.L. acknowledges support from grants Fondecyt 1140938 and NC 1200286 (Millennium Nucleus Project MUSELS) and L.R. was supported by BECAS CHILE fellowship program from Comisión Nacional de Investigación Científica y Tecnológica de Chile (CONICYT)Peer Reviewe

Warming and CO2 Enhance Arctic Heterotrophic Microbial Activity

Ocean acidification and warming are two main consequences of climate change that can directly affect biological and ecosystem processes in marine habitats. The Arctic Ocean is the region of the world experiencing climate change at the steepest rate compared with other latitudes. Since marine planktonic microorganisms play a key role in the biogeochemical cycles in the ocean it is crucial to simultaneously evaluate the effect of warming and increasing CO2 on marine microbial communities. In 20 L experimental microcosms filled with water from a high-Arctic fjord (Svalbard), we examined changes in phototrophic and heterotrophic microbial abundances and processes [bacterial production (BP) and mortality], and viral activity (lytic and lysogenic) in relation to warming and elevated CO2. The summer microbial plankton community living at 1.4°C in situ temperature, was exposed to increased CO2 concentrations (135–2,318 μatm) in three controlled temperature treatments (1, 6, and 10°C) at the UNIS installations in Longyearbyen (Svalbard), in summer 2010. Results showed that chlorophyll a concentration decreased at increasing temperatures, while BP significantly increased with pCO2 at 6 and 10°C. Lytic viral production was not affected by changes in pCO2 and temperature, while lysogeny increased significantly at increasing levels of pCO2, especially at 10°C (R2 = 0.858, p = 0.02). Moreover, protistan grazing rates showed a positive interaction between pCO2 and temperature. The averaged percentage of bacteria grazed per day was higher (19.56 ± 2.77% d-1) than the averaged percentage of lysed bacteria by virus (7.18 ± 1.50% d-1) for all treatments. Furthermore, the relationship among microbial abundances and processes showed that BP was significantly related to phototrophic pico/nanoflagellate abundance in the 1°C and the 6°C treatments, and BP triggered viral activity, mainly lysogeny at 6 and 10°C, while bacterial mortality rates was significantly related to bacterial abundances at 6°C. Consequently, our experimental results suggested that future increases in water temperature and pCO2 in Arctic waters will produce a decrease of phytoplankton biomass, enhancement of BP and changes in the carbon fluxes within the microbial food web. All these heterotrophic processes will contribute to weakening the CO2 sink capacity of the Arctic plankton community.En prens

Recruitment Disruption and the Role of Unaffected Populations for Potential Recovery After the Pinna nobilis Mass Mortality Event

A devastating mass mortality event (MME) very likely caused by the protozoan Haplosporidium pinnae first detected in 2016 in the Western Mediterranean Sea, is pushing the endemic bivalve Pinna nobilis to near extinction. Populations recovery, if possible, will rely on larval dispersal from unaffected sites and potential recolonization through recruitment of resistant juveniles. To assess the impact of the MME on the species’ larval recruitment, an unprecedented network of larval collector stations was implemented over several thousands of kilometers along the Western Mediterranean coasts during the 3 years after the onset of the MME. The findings of this network showed a generalized disruption in recruitment with dramatic consequences for the recovery of the species. However, there were exceptions to this pattern and recruits were recorded in a few sites where the resident population had been decimated. This hints to the importance of unaffected populations as larval exporting sources and the role of oceanographic currents in larval transport in the area, representing a beacon of hope in the current extremely worrying scenario for this emblematic species.En prens