fmars-07-552047 November 7, 2020 Time: 19:27 # 1 ORIGINAL RESEARCH published: 12 November 2020 doi: 10.3389/fmars.2020.552047 A Synthesis of Marine Monitoring Methods With the Potential to Enhance the Status Assessment of the Baltic Sea 1 2 3 1 4 Edited by: Leoni Mack *, Jenni Attila , Eva Aylagas , Arne Beermann , Angel Borja , 1 5 1 6 2 Michelle Jillian Devlin, Daniel Hering , Maria Kahlert , Florian Leese , Robin Lenz , Maiju Lehtiniemi , 7 8 2 2 2 Centre for Environment, Fisheries Antonia Liess , Urmas Lips , Olli-Pekka Mattila , Kristian Meissner , Timo Pyhälahti , and Aquaculture Science (CEFAS), Outi Setälä2, Jennifer S. Strehse9, Laura Uusitalo2, Anna Willstrand Wranne10 and United Kingdom Sebastian Birk1 Reviewed by: 1 Faculty of Biology, University of Duisburg-Essen, Essen, Germany, 2 Finnish Environment Institute (SYKE), Helsinki, Finland, Bo Gustafsson, 3 Red Sea Research Center, King Abdullah University of Science and Technology, Thuwal, Saudi Arabia, 4 AZTI, Marine Stockholm University, Sweden Research Division, Pasaia, Spain, 5 Department of Aquatic Sciences and Assessment, Swedish University of Agricultural Thanos Dailianis, Sciences, Uppsala, Sweden, 6 Leibniz Institute for Baltic Sea Research Warnemünde, Rostock, Germany, 7 Rydberg Institute of Marine Biology, Laboratory of Applied Science, Halmstad University, Halmstad, Sweden, 8 Department of Marine Systems, Tallinn University Biotechnology & Aquaculture, Greece of Technology, Tallinn, Estonia, 9 Institute of Toxicology and Pharmacology for Natural Scientists, University Medical School Agnes M. L. Karlson, Schleswig-Holstein, Kiel, Germany, 10 Swedish Meteorological and Hydrological Institute, Gothenburg, Sweden Stockholm University, Sweden *Correspondence: Leoni Mack A multitude of anthropogenic pressures deteriorate the Baltic Sea, resulting in the [email protected] need to protect and restore its marine ecosystem. For an efficient conservation, comprehensive monitoring and assessment of all ecosystem elements is of fundamental Specialty section: This article was submitted to importance. The Baltic Marine Environment Protection Commission HELCOM Marine Ecosystem Ecology, coordinates conservation measures regulated by several European directives. However, a section of the journal Frontiers in Marine Science this holistic assessment is hindered by gaps within the current monitoring schemes. Received: 15 April 2020 Here, twenty-two novel methods with the potential to fill some of these gaps and Accepted: 07 September 2020 improve the monitoring of the Baltic marine environment are examined. We asked key Published: 12 November 2020 stakeholders to point out methods likely to improve current Baltic Sea monitoring. We Citation: then described these methods in a comparable way and evaluated them based on Mack L, Attila J, Aylagas E, Beermann A, Borja A, Hering D, their costs and applicability potential (i.e., possibility to make them operational). Twelve Kahlert M, Leese F, Lenz R, methods require low to very low costs, while five require moderate and two high costs. Lehtiniemi M, Liess A, Lips U, Mattila O-P, Meissner K, Pyhälahti T, Seventeen methods were rated with a high to very high applicability, whereas four Setälä O, Strehse JS, Uusitalo L, methods had moderate and one low applicability for Baltic Sea monitoring. Methods Willstrand Wranne A and Birk S with both low costs and a high applicability include the Manta Trawl, Rocket, Sediment (2020) A Synthesis of Marine Monitoring Methods With Corer, Argo Float, Artificial Substrates, Citizen Observation, Earth Observation, the the Potential to Enhance the Status HydroFIA R pH system, DNA Metabarcoding and Stable Isotope Analysis. Assessment of the Baltic Sea. Front. Mar. Sci. 7:552047. Keywords: Baltic Sea Action Plan, Marine Strategy Framework Directive, Water Framework Directive, data doi: 10.3389/fmars.2020.552047 acquisition, marine management Frontiers in Marine Science| www.frontiersin.org 1 November 2020| Volume 7| Article 552047 fmars-07-552047 November 7, 2020 Time: 19:27 # 2 Mack et al. Novel Marine Monitoring Methods HIGHLIGHTS their impacts on the marine environment and human well- being are fundamental (Söderström and Kern, 2017). HELCOM - We rated novel methods regarding their ability to improve the established the Baltic Sea Action Plan (BSAP; Backer et al., 2010) Baltic Sea monitoring. as a joint programme to protect the Baltic Sea and restore the - Methods were assessed with respect to their costs good status of its marine environment by 2021 (HELCOM, 2007). and applicability. For an efficient protection and restoration of the Baltic Sea, - All methods can potentially increase data resolution or comprehensive monitoring of all its ecosystem elements is of monitor novel ecosystem elements. fundamental importance. Monitoring comprises the acquisition - We recommend several novel methods for the Baltic status of biological, chemical, physical, hydrological and morphological assessment. data of the ecosystem to assess its status (Mack et al., 2019). The assessment of the Baltic Sea’s status is following an indicator-based approach (HELCOM, 2018a). Indicators address INTRODUCTION specific measurable attributes of selected ecosystem elements, allowing to monitor spatial or temporal changes of these The unique Baltic Sea ecosystem is in critical condition due to elements. Several indicators are defined and grouped into strong anthropogenic pressures, therefore, it urgently requires eleven thematic categories addressing characteristic ecosystem protection and restoration (Andersen et al., 2015; HELCOM, features and functions, so-called “descriptors” within the MSFD 2017). As one of the largest brackish water bodies worldwide, (Zampoukas et al., 2012). the Baltic Sea’s most distinguishing feature is a pronounced The current monitoring of the Baltic Sea, however, reveals salinity gradient. Marine and freshwater species coexist and significant gaps, which conceivably prevent a holistic assessment interact, creating a unique but sensitive biological community and impede adequate conservation of the Baltic Sea. Five main (HELCOM, 2016). The Baltic Sea is shallow with a low water gaps were identified by Emmerson et al.(2019) and Kahlert exchange rate with other marine water bodies, which makes et al.(2020), three of which relate to insufficiently monitored it especially vulnerable to human impacts (Szymczychta et al., and lacking indicators (i–iii), while two relate to regulation and 2019). Due to effluents draining from nine countries into its coordination (iv–v): basin, main environmental pressures include eutrophication and contamination. In consequence, areas with low oxygen (i) Insufficient monitoring of existing indicators in space or even anoxic conditions are expanding (Gustafsson et al., and time, which especially applies to oxygen conditions, 2012; Carstensen et al., 2014). In addition, the ecosystem phytoplankton, zooplankton, benthic habitats and species, is highly impaired by marine litter, non-indigenous species, and the monitoring of mobile species. underwater noise, fishing, as well as habitat disturbance and (ii) The lack of indicators that adequately reflect the loss (Andersen et al., 2015). Climate change already reduces descriptors of the MSFD, including food webs, the extent and duration of ice cover in the Northern parts, sea-floor integrity, contaminants, marine litter, and as well as increases riverine freshwater inflow (HELCOM, underwater noise/energy. 2018a). The critical condition of the Baltic Sea calls for (iii) Ecosystem elements and drivers of change, which are profound mitigation actions as stipulated by the present not monitored so far, including climate change and environmental legislation. ecosystem services. Several European directives and international conventions (iv) Insufficient regulations on data handling or storage, in address the protection of the Baltic Sea. The most important particular regarding some descriptors such as biodiversity directives are the Marine Strategy Framework Directive (MSFD; (i.e., benthic habitats and species), non-indigenous European Commission, 2008) and the Water Framework species, bycatch, hazardous substances, and marine litter. Directive (WFD; European Commission, 2000). The common (v) The lack in coordination of the monitoring between aim of these directives is to achieve a good status of the Baltic countries, which especially applies for the descriptors Sea. “Status” refers to the qualitative condition of the ecosystem, mentioned in the previous gap. which is classified as good if it deviates only slightly from near- natural conditions (European Commission, 2000, 2008). Further These gaps arise from various circumstances: Traditional relevant legislations are the Habitats Directive (92/43/EEC), methods require relatively high efforts regarding costs and the Birds Directive (2009/147/EC), the Common Fisheries time, and therefore cannot be conducted as often as necessary Policy (Regulation EU No 1380/2013) and the regulation on to meet the data requirements regarding spatio-temporal invasive alien species (Regulation EU No 1143/2014). The resolution and coverage. These traditional methods include implementation of the directives is regionally coordinated manual water/sediment sampling from research vessels, sampling by the Baltic Marine Environment Protection Commission and observation by trained divers, manned aircraft surveys HELCOM (i.e., “Helsinki Commission”). This intergovernmental or the morphological identification of sampled organisms.