Response of the Calanoid Copepod Clausocalanus furcatus, to Atmospheric Deposition Events: Outcomes from a Mesocosm Study

Atmospheric deposition is assumed to stimulate heterotrophic processes in highly oligotrophic marine systems, controlling the dynamics and trophic efficiency of planktonic food webs, and is expected to be influenced by climate change. In the course of an 8-day mesocosm experiment, we examined the channeling, of the Saharan dust (SD) and mixed aerosols (A) effects on microplankton up to the copepod trophic level, in the highly oligotrophic Eastern Mediterranean Sea. Based on mesocosms with SD and A treatments, we evaluated the feeding response of the dominant copepod Clausocalanus furcatus every other day. We hypothesized that increased food availability under atmospheric deposition would result in increased copepod ingestion rates, selectivity and production. Overall, no robust pattern of food selection was documented, and daily rations on the prey assemblage of all mesocosms were very low indicating severe food limitation of C. furcatus. Although increased food availability was not true, after few days ingestion of ciliates was maximized, followed by egg production, in both the SD and A treatments, indicating their importance in the diet of this copepod as well as a response of C. furcatus feeding performance. Our results help in understanding the trophic efficiency of marine food webs in ultra-oligotrophic environments under atmospheric deposition. We suggest that future mesocosm research in oligotrophic waters should consider more than one copepod speciesVersión del edito

Large-scale testing of phytoplankton diversity indices for environmental assessment in Mediterranean sub-regions (Adriatic, Ionian and Aegean Seas)

Abstract According to the methodological standards established by Marine Strategy Framework Directive, the assessment for the pelagic habitat under the Biodiversity Descriptor should be carried out at the regional or sub-regional level. In the case of Mediterranean Sea, the sub-regional assessment seems optimal to take into account biogeographic differences in species composition and functional characteristics. Previous research has shown that phytoplankton diversity indicators are efficient for reliable environmental assessments, although more effort has been recommended to test these indicators on a wide spatial scale to cover wider gradients of natural and anthropogenic pressures. In this work, a set of eight diversity indices was tested against the pressure levels within a common data set of the structure and abundance of phytoplankton communities from the Adriatic, Ionian and Aegean Seas. Expert knowledge was used to define four categories of impacts that take into account partial pressures, such as point and non-point pollution, industry, ports and fisheries. At the level of the common data set, most of the diversity, evenness and dominance indices could only distinguish between the highest level of impact and the rest of impact categories. These indices maintained the distinction between two levels of subsequently dichotomised impacts (no to low impact vs. high impact) across latitudinal and longitudinal gradients. On average, the indices were less sensitive to impacts in the northernmost and westernmost areas than in the southernmost and easternmost areas, although they still showed a significant response. The results also suggest that phytoplankton communities become more uniform and less dominated by a single taxon as sampling depth increases at sites with low impact, while evenness and dominance at impacted sites remain similar at all depths. In order to establish meaningful definitions of good environmental status and targets for pelagic habitats in the Mediterranean Sea, it is necessary to establish spatially specific thresholds by additional examination of indices of good performance

Status of pelagic habitats within the EU-Marine Strategy Framework Directive: Proposals for improving consistency and representativeness of the assessment

Anthropogenic activities have transformed the pelagic habitat in the last decades with profound implications for its essential functions. While the EU-Marine Strategy Framework Directive 2008/56/EC and the Commission Decision (EU) 2017/848 have set criteria and methodological standards for the assessment and determination of Good Environmental Status (GES) for pelagic habitats in EU waters, there is strong evidence that Member States have not yet harmonized the pelagic GES assessment across EU marine waters. Today, pelagic habitats are assessed by evaluating whether good status is achieved by each of the pelagic indicators, but this approach fails to observe the high variability of the pelagic environment. To this end, GES is not estimated at pelagic habitats scale but only for each individual indicator. This paper synthesises the latest developments on pelagic habitats assessment and identifies the main factors limiting the consistency of the assessment across Member States: i) coarse spatial and temporal scales of sampling effort as regards to the pelagic habitat dynamics, ii) little consideration of the whole range of plankton (and, to some extent, of zooplankton) size and trophic spectra, iii) lack of integrated hydro-biogeochemical and biological studies and collaboration among experts from different scientific fields, iv) limited availability of pressure-based indicators, and v) lack of integration methods of the pelagic indicators’ status for the GES determination. This analysis demonstrates the importance of maintaining a consistent sampling frequency and a spatially extensive network of stations across the gradient of anthropogenic pressures, where spatial environmental data can help objectively extrapolating field data.The authors would like to thank the Pelagic Habitats Experts, part of the MSFD Biodiversity Expert Network for the fruitful discussions on the harmonisation of the MSFD assessment and monitoring for pelagic habitats. CM, MP, JND, and AP were funded by the Joint Research Centre of Ispra (Italy). IV wishes to acknowledge support from the program “Monitoring and recording the situation of the marine sub-regions of Greece / Upgrading and functional updating of the MSFD monitoring network”, funded by national and EU funds under National Strategic Reference Framework 2014–2020 (MIS 5010880), and the European project ABIOMMED: Support coherent and coordinated assessment of biodiversity and measures across Mediterranean for the next 6-year cycle of MSFD implementation, funded by DG Environment (11.0661/2020/839620/SUB/ENV.C2), coordinator Dr. Kalliopi Pagou, HCMR.Peer reviewe

Abundance of microplankton in the eastern Mediterranean Sea in April 2008 during SES_GR2

The dataset is based on samples taken from 12 stations in Northern Aegean Sea, Southern Aegean Sea, Ionian Sea and Libyan Sea during August-September 2008. 12 Niskin bottles (8lt) made by PVC with rubber coated o rings and stainless steel ss springs. Seawater samples (150 mL) were collected from selected depths of the water column (2, 20, 50, 75, 100 m) for the identification and enumeration of phytoplankton cells (>= 5 µm). The samples were fixed with Lugol solution and concentrated to 25 mL by sedimentation. Phytoplankton species abundance was determined with an inverted light microscope (OLYMPUS IX70) according to the Utermohl method (Utermohl, 1958)

Abundance of microplankton in the eastern Mediterranean Sea in March and April 2008 during SES_GR1

The dataset is based on samples taken from 12 stations in Southern Aegean Sea, Northern Aegean Sea, Ionian Sea and Libyan Sea during March-April 2008. 12 Niskin bottles (8lt) made by PVC with rubber coated o rings and stainless steel ss springs. Seawater samples (150 ml) were collected from selected depths of the water column (2, 20, 50, 75, 100 m) for the identification and enumeration of phytoplankton cells (>=5 µm). The samples were fixed with Lugol solution and concentrated to 25 ml by sedimentation. Phytoplankton species abundance was determined with an inverted light microscope (OLYMPUS IX70) according to the Utermohl method (Utermohl, 1958)

Ecology of harmful microalgae and impact on the marine benthic ecosystem

Harmful algae attract interest due to the increase of duration and intenseness of Harmful Algal Blooms (HABs), with serious impacts on coastal ecosystems, public health and economy. Many harmful algae are toxic microalgae that are consumed by pelagic and benthic organisms. The subject of this Doctoral Thesis was the study of ecology and toxicity of the dinoflagellates Dinophysis acuminata and Prorocentrum lima and the diatom Pseudo-nitzschia multiseries, as well as the transfer of their toxins to the bivalves Callista chione and Ruditapes decussatus. The studied microalgae species cause HABs in many coastal areas, including South Europe, e.g. Greece and Spain, while the studied bivalve species present wide distribution in these two counties and commercial interest. The aims of the Thesis were the study of: a) the natural populations and HABs of D. acuminata in relation to the availability of organic matter and other biotic/abiotic parameters in the Gulf of Thermaikos, b) the impact of nitrogen or phosphorus deficiency conditions on the growth and toxicity of P. lima, and c) the accumulation and impact of D. acuminata, P. lima και P. multiseries toxins on the bivalves C. chione from Thermaikos Gulf and R. decussatus from Ría de Vigo, Spain.Τα επιβλαβή φύκη παρουσιάζουν ενδιαφέρον καθώς η ένταση και η διάρκεια των εξάρσεών τους αυξάνονται με σοβαρές επιπτώσεις στα παράκτια οικοσυστήματα, τη δημόσια υγεία και οικονομία. Πολλά επιβλαβή φύκη είναι τοξικά μικροφύκη και καταναλώνονται από πελαγικούς και βενθικούς οργανισμούς. Αντικείμενο της Διδακτορικής Διατριβής αποτέλεσε η μελέτη της οικολογίας και τοξικότητας των δινομαστιγωτών Dinophysis acuminata και Prorocentrum lima και του διατόμου Pseudo-nitzschia multiseries, καθώς και η μεταφορά των τοξινών τους στα δίθυρα μαλάκια Callista chione και Ruditapes decussatus. Αυτά τα είδη μικροφυκών προκαλούν επιβλαβείς εξάρσεις σε πολλές παράκτιες περιοχές συμπεριλαμβανομένης της Ν Ευρώπης, όπως η Ελλάδα και η Ισπανία, τα δε είδη διθύρων παρουσιάζουν εκεί ευρεία εξάπλωση και εμπορικό ενδιαφέρον. Στόχοι της Διατριβής ήταν: α) η μελέτη των φυσικών πληθυσμών και των εξάρσεων του είδους D. acuminata σε σχέση με τη διαθεσιμότητα της οργανικής ύλης και άλλων βιοτικών/αβιοτικών παραμέτρων στον Θερμαϊκό Κόλπο, β) η μελέτη της επίδρασης των συνθηκών έλλειψης αζώτου/φωσφόρου στην αύξηση του είδους P. lima και την παραγωγή τοξίνης στα κύτταρά του, γ) η μελέτη της συσσώρευσης και της επίδρασης των τοξινών που παράγουν τα μικροφύκη D. acuminata, P. lima, P. multiseries στα δίθυρα C. chione από τον Θερμαϊκό και R. decussatus από τον Κόλπο του Vigo της Ισπανίας

Microalgae show a range of responses to exometabolites of foreign species

Studies on microalgae interspecific interactions have so far focused either on nutrient competition or allelopathic effects due to excreted substances from Harmful Algal Bloom (HAB) species. Evidence from plants, bacteria and specific microalgae groups, point to a range of responses mediated by sensing or direct chemical impact of exometabolites from foreign species. Such processes remain under-investigated, especially in non-HAB microalgae, despite the importance of such knowledge in ecology and industrial applications. Here, we study the directional effect of exometabolites of 4 “foreign” species Heterosigma akashiwo, Phaeocystis sp., Tetraselmis sp. and Thalassiosira sp. to each of three “target” species across a total of 12 treatments. We disentangle these effects from nutrient competition by adding cell free medium of each “foreign” species into our treatment cultures. We measured the biomass response, to the foreign exometabolites, as cell number and photosynthetic biomass (Chla), whereas nutrient use was measured as residual phosphorus (PO4) and intracellular phosphorus (P). Exometabolites from filtrate of foreign species were putatively annotated by untargeted metabolomics analysis and were discussed in association to observed responses of target species. Among others, these metabolites included L-histidinal, Tiliacorine and dimethylsulfoniopropionate (DMSP). Our findings show that species show a range of responses with the most common being biomass suppression, and less frequent biomass enhancement and intracellular P storage. Filtrate from the green microalgae Tetraselmis caused the most pronounced negative effects suggesting that non-HAB species can also cause negative chemical interference. A candidate metabolite inducing this response is L-histidinal which was measured in high abundance uniquely in Tetraselmis and its L-histidine form derived from bacteria was previously confirmed as a microalgal algicidal. H. akashiwo also induced biomass suppression on other microalgae and a candidate metabolite for this response is Tiliacorine, a plant-derived alkaloid with confirmed cytotoxic activity

Impact of a Dinophysis acuminata Bloom on the Copepod Acartia clausi: first indications

Faecal pellet production and content along with egg production of the dominant copepod species Acartia clausi were studied in the Thermaikos Gulf (NW Aegean Sea) during a pre-bloom and a bloom of the toxic dinoflagellate Dinophysis acuminata. Both faecal pellet production (6.8–8.6 ind−1 d−1) and egg production (15.8–47.6 ind−1 d−1) appeared unrelated to the D. acuminata bloom. Less than 11% of the copepod faecal pellets contained one or two D. acuminata cells, almost intact, whereas the other material in the pellets was broken into small pieces or amorphous shapes. The toxin outflux seemed to be insignificant when compared to the mean toxin concentration from the whole D. acuminata population. Finally, the potential grazing impact of A. clausi on D. acuminata during the study period was low.European Commission | Ref. EVK3-2001-00055European Commission | Ref. H2020, n. 87115

Impact of a Dinophysis acuminata Bloom on the Copepod Acartia clausi : First Indications

Faecal pellet production and content along with egg production of the dominant copepod species Acartia clausi were studied in the Thermaikos Gulf (NW Aegean Sea) during a pre-bloom and a bloom of the toxic dinoflagellate Dinophysis acuminata. Both faecal pellet production (6.8-8.6 ind(-1) d(-1)) and egg production (15.8-47.6 ind(-1) d(-1)) appeared unrelated to the D. acuminata bloom. Less than 11% of the copepod faecal pellets contained one or two D. acuminata cells, almost intact, whereas the other material in the pellets was broken into small pieces or amorphous shapes. The toxin outflux seemed to be insignificant when compared to the mean toxin concentration from the whole D. acuminata population. Finally, the potential grazing impact of A. clausi on D. acuminata during the study period was low