Instituto de Investigacións Mariñas

Marine macrophytes play a significant role in the marine carbon cycle by releasing dissolved organic carbon (DOC), including a recalcitrant fraction with potential for long-term carbon sequestration. Here, we investigated how warming and the presence of an invasive species affect DOC dynamics in different native temperate macrophyte communities (Zostera noltei, Cymodocea nodosa and Caulerpa prolifera) from the south of the Iberian Peninsula, a transitional habitat between Atlantic and Mediterranean marine regimes. Additionally, we introduced a standardized framework to link DOC release to internal carbon content, facilitating comparisons of blue carbon pathways among macrophyte communities across diverse ecosystems. Controlled mesocosm experiments across three temperatures (24, 26 and 28 °C) revealed that the presence of the invasive seagrass Halophila stipulacea did not significantly alter the carbon metabolism or DOC fluxes of native macrophytes. However, temperature significantly affected both the quantity and composition of the released DOC. In particular, recalcitrant DOC decreased by 28%, while labile DOC increased by a similar proportion as temperature rose, and bioavailable DOC decay rates also declined significantly at higher incubation temperatures of the tested macrophytes. These results suggest that warming may enhance both net and labile DOC production, while the remaining DOC is less bioavailable than that produced at lower temperatures. This clearly indicates that warming restructures DOC composition, potentially reducing coastal carbon storage capacity and the role of recalcitrant DOC. By applying our proposed standardization, we estimate that the recalcitrant fraction produced in the tested macrophyte communities was comparable in magnitude, although 1.41 higher, to the carbon burial rates in the sediment measured in the same communities, which underscores the potential contribution of recalcitrant DOC produced by macrophyte communities to the long-term carbon storage. This standardized approach positions recalcitrant DOC as a crucial climate-sensitive blue carbon pathway that should be integrated into global carbon budget estimates.

<title>Abstract</title> Environmental DNA (eDNA) has emerged as a transformative, non-invasive tool for ecological monitoring and conservation biology. Beyond species detection and community assessments, there is growing interest in applying eDNA to evaluate genetic variability and monitor ecosystem health, particularly for elusive or endangered species where traditional sampling is invasive or limited. In this systematic review, we synthesize recent advances in eDNA based population genetics based on a final dataset of 83 studies (72 research articles and 11 reviews), with special emphasis on the use of nuclear DNA (nuDNA) to capture intraspecific genetic diversity. We identify several technical challenges, including low DNA copy number, allelic dropout and the lack of individual genotypes. To address these constraints, we highlight allele frequency-based approaches as a promising strategy to estimate effective population size (Ne) directly from eDNA. These methods are particularly suitable for non-model species without reference genomes and for contexts where invasive sampling is not feasible. We further discuss the potential of eDNA Pool-seq technologies to improve cost efficiency and to infer the minimum number of contributing individuals. Together, these advances provide a pathway to extend the use of eDNA beyond biodiversity monitoring toward a comprehensive, non-invasive framework for population genetic inference in conservation.

The sensitivity of marine microalgae to metal contamination, particularly copper (Cu), is well recognized in ecotoxicology, providing key insights into predicting marine pollution impacts. This study examined the combined effects of Cu toxicity and salinity on the diatom Chaetoceros calcitrans under controlled laboratory conditions. Toxicity assays were conducted using two environmentally relevant Cu concentrations (2 and 5μgL-1) and three salinity levels (33, 36, and 39) over 96h, with cell responses analyzed via flow cytometry. Specific growth rate (SGR), chlorophyll fluorescence, fatty acid methyl ester (FAME) composition, polyunsaturated aldehydes (PUAs), and reactive oxygen species (ROS) production were evaluated. Results showed that SGR increased from 1.7d-1at salinity 33 to 1.9d-1at 39, indicating enhanced growth at higher salinity. However, Cu exposure significantly reduced SGR, particularly under 5μg L-1 Cu at salinity 33, where SGR dropped to 0.86 d-1. ROS levels were highest under the combined low salinity (33) and 5μgL-1 Cu treatment, suggesting strong oxidative stress. PUA profiles shifted with Cu and salinity, with stress-related compounds such as 2E,4E/Z-decadienal and 2E,4E/Z,7Z-decatrienal increasing at low salinity. Fatty acid analysis revealed marked rises in saturated fatty acids, especially palmitic acid (C16:0) and myristic acid (C14:0), under Cu exposure. In the Cu2/39 treatment, C16:0 reached 1.34×104fmol cell-1 compared to 1.36×103fmol cell-1 in the control. Monounsaturated fatty acids, notably palmitoleic acid (C16:1), also increased, reaching 7. 46×103fmol cell-1 versus 1.71×103fmol cell-1 in the control. Conversely, polyunsaturated fatty acids, including arachidonic acid (C20:4) and eicosapentaenoic acid (C20:5 n-3), decreased significantly following Cu exposure. Overall, elevated salinity mitigated Cu-induced growth inhibition but intensified oxidative and biochemical stress, underscoring the complex, endpoint-specific responses of C. calcitrans to multiple environmental stressors.

Maternal effects play a fundamental role in shaping early larval growth and survival in marine fishes. This study explores the relationship between maternal trophic ecology and larval growth in bluefin tunas, with a focus on Southern Bluefin Tuna (SBT) and an expanded dataset from multiple Atlantic Bluefin Tuna (ABT) populations incorporated into the General Bluefin Model (GBM). Daily growth and stable isotopes (δ 15 N and δ 13 C) were obtained from 80 pre-flexion SBT larvae and 355 pre-flexion larvae from the GBM dataset. Results revealed a significant negative linear trend between larval age and δ 15 N values, consistent with the gradual attenuation of maternally inherited isotopic signatures during development. Faster growing larvae showed significantly lower δ 15 N and δ 13 C values, indicating that maternal trophic behaviour and prey sources critically influence larval growth potential. Maternal isotopic niche breadth, inferred from larval isotope data, was markedly narrower in groups with optimal larval growth, suggesting that specialized (stenophagous) maternal feeding strategies promote enhanced offspring performance. These patterns were observed consistently in two bluefin species across seven different populations, despite geographic and temporal variability, highlighting a robust ecological link between maternal foraging behaviour and larval development. From these findings, we introduce the hypothesis of an Optimal Maternal Feeding Isotopic Niche, representing a constrained isotopic range associated with increased larval growth and survival. This framework advances our understanding of the influence of maternal trophic ecology on offspring fitness and offers valuable insights for the conservation and management of highly migratory pelagic species with complex reproductive strategies.

<strong class="journal-contentHeaderColor">Abstract.</strong> The Mediterranean Sea (MedSea) is highly sensitive to climate-driven changes in temperature, oxygen, and pH, among other variables. To better assess these long-term trends, we developed CARIMED (CARbon, tracers, and ancillary data In the MEDiterranean Sea), the first comprehensive, harmonised data synthesis product for the MedSea. CARIMED integrates hydrographic, inorganic carbon, transient tracer, and ancillary measurements from 46 research cruises spanning the period from 1976 to 2018, containing observations for the entire water column across all MedSea sub-basins. A substantial component of the data was retrieved from fragmented or locally archived historical records, thus consolidating previously inaccessible measurements. Following global synthesis approaches, CARIMED applies a quality-controlled, and bias-adjusted framework. A key adaptation was the secondary quality control (2QC) procedure, specifically tailored to the MedSea's unique hydrography, utilising sub-basin divisions and supplementary checks (including statistical consistency assessments) to resolve complex, often contradictory, inter-cruise offsets. This rigorous process minimised systematic biases, yielding a dataset with improved consistency, and highlights the urgent need for adapted standard operating procedures and reference materials to address the MedSea biogeochemical particularities. CARIMED delivers two complementary, freely available products: the aggregated original cruise data product (<a href="https://doi.org/10.20350/digitalCSIC/17785" target="_blank" rel="noopener">https://doi.org/10.20350/digitalCSIC/17785</a>; Garc&iacute;a-Ib&aacute;&ntilde;ez et al., 2025) and the final bias-adjusted data synthesis product (<a href="https://doi.org/10.25921/cp5b-zq67" target="_blank" rel="noopener">https://doi.org/10.25921/cp5b-zq67</a>; &Aacute;lvarez et al., 2025). This essential resource establishes a new benchmark for assessing long-term biogeochemical trends, validating regional ocean models, and supporting climate-change mitigation and adaptation strategies in this rapidly changing semi-enclosed basin.

<strong class="journal-contentHeaderColor">Abstract.</strong> The North Atlantic (NA) GO-SHIP A25 OVIDE-BOCATS section is a long-term repeat hydrographic transect extending from Portugal to Greenland. Since 2002, physical and biogeochemical measurements have been carried out biennially along the OVIDE-BOCATS section, contributing to a better understanding of water mass properties, mixing, circulation, carbon storage, and climate change impacts such as ocean acidification (OA) in the NA. In particular, the high-precision pH measurements on the total hydrogen ion scale (pH_T) from the OVIDE-BOCATS program represent a key milestone in monitoring OA in this particularly climate sensitive region. The method used for pH_T determination relies on adding meta-cresol purple (mCP) dye to the seawater sample and spectrophotometrically measuring its absorbances at specific wavelengths. The OVIDE-BOCATS program has used unpurified mCP dye, which impurities have been proven to bias pH_T values. Here we quantified the bias induced by these impurities in pH_T measurements. We found that measurements carried out using the unpurified mCP dye tend to be, on average, <strong>0.011 &plusmn; 0.002</strong> pH_T units higher than those obtained using the purified mCP dye, with this difference slightly decreasing at higher pH_T values. Moreover, we tested independent methods to correct the effect of impurities in both the historical and recent OVIDE-BOCATS pH_T data, demonstrating that the correction is consistent across methods. The long-term pH_T dataset has been updated to include newly acquired data and absorbance measurements, and to standardize corrections for mCP dye impurities. This effort results in a twenty-year dataset of pH_T corrected for mCP dye impurities, that demonstrates the possibility of a global effort to improve the reliability and coherency of spectrophotometric pH_T measurements made with unpurified mCP dye. The corrections applied to our pH_T dataset have negligible implications for the OA rates previously reported, but they do affect the depth of the aragonite saturation horizon, implying a shoaling of approximately 150 m.