An example for transatlantic hitchhiking by macrozoobenthic organisms with a research vessel

In 2019 the RV Meteor cruised from Guadalupe in April/May to Cape Verde in June/July and to Namibia in August/September. The distance is about 10,000 km. The ship has a moon pool for installation of instruments. In Cape Verde we had a first glimpse of the already sparsely populated moon pool. We reached Namibian waters in mid-August. In mid-September, 47 days later and 6000 km south, the ship's moon pool was sampled in the port of Walvis Bay. 13 different taxa could be identified belonging to two phyla, four classes, six orders and 10 families. Most of these species have not yet been observed in the port or in the adjacent areas and are new records for the entire Namibian coast. The goose barnacles Conchoderma auritum (Linnaeus, 1767), Conchoderma virgatum Spengler, 1789 and Lepas anatifera Linnaeus, 1758 were particularly noticeable. They were only surpassed by the large number of amphipods. The species Ericthonius brasiliensis (Dana, 1853), Jassa marmorata Holmes, 1905, Stenothoe senegalensis Krapp-Schickel, 2015 and Paracaprella pusilla Mayer, 1890 are particularly noteworthy here. In addition, the pycnogonid species Endeis straughani Clark, 1970 and the titan acorn barnacle Megabalanus coccopoma (Darwin, 1854) should be mentioned, which occurred very frequently as well. The present study shows, on the one hand, an example of the transatlantic spread of bioinvasive species by ships as vectors and, on the other hand, a convenient method for sampling ship hulls

Shell microstructures (disturbance lines) of Arctica islandica (Bivalvia) : a potential proxy for severe oxygen depletion

The spread of oxygen deficiency in nearshore coastal habitats endangers benthic communities. To better understand the mechanisms leading to oxygen depletion and eventually hypoxia, predict the future development of affected ecosystems, and define suitable mitigation strategies requires detailed knowledge of the dissolved oxygen (DO) history. Suitable high-resolution DO archives covering coherent time intervals of decades to centuries include bivalve shells. Here, we explored if the microstructure, specifically disturbance lines, in shells of Arctica islandica from the Baltic Sea can be used as an alternative or complementary proxy to Mn/Cashell to track the frequency and severity of past low-DO events. Disturbance lines differ from periodic annual growth lines by the presence of fine complex crossed lamellae instead of irregular simple prisms. Aside from a qualitative assessment of microstructural changes, the morphology of individual biomineral units (BMUs) was quantitatively determined by artificial intelligence-assisted image analysis to derive models for DO reconstruction. As demonstrated, Mn-rich disturbance lines can provide a proxy for past deoxygenation events (i.e., DO < 45 μmol/L), but it currently remains unresolved if low DO leads to microstructurally distinct features that differ from those caused by other environmental stressors. At least in studied specimens from the Baltic Sea and Iceland, low temperature, salinity near the lower physiological tolerance, or food scarcity did not result in disturbance lines. With decreasing DO supply, disturbance lines seem to become more prominent, contain more Mn, and consist of increasingly smaller and more elongated BMUs with a larger perimeter-to-area ratio. Although the relationship between DO and BMU size or elongation was statistically significant, the explained variability (<1.5%) was too small and the error too large to reconstruct DO values. BMU parameters may reveal a closer relationship with DO if studied in three dimensions and if the DO content was determined at high resolution, directly at the position where the bivalves lived, something that future work should address

Laboratory Measurements to Image Endobenthos and Bioturbation with a High-Frequency 3D Seismic Lander

The presented 3D seismic system operates three transducers (130 kHz) from a stationary lander and allows non-destructive imaging of small-scale objects within the top decimeters of silty sediments, covering a surface area of 0.2 m2. In laboratory experiments, samples such as shells, stones, and gummy worms of varied sizes (down to approx. 1 cm diameter) could be located in the 3D seismic cube to a depth of more than 20 cm and differentiated by a reflected amplitude intensity and spatial orientation. In addition, simulated bioturbation structures could be imaged. In a practical application, the system allows to determine the abundance of endobenthos and its dynamic in muddy deposits in-situ and thus identify the intensity of local bioturbation

Shell microstructures (disturbance lines) of Arctica islandica (Bivalvia): a potential proxy for severe oxygen depletion

The spread of oxygen deficiency in nearshore coastal habitats endangers benthic communities. To better understand the mechanisms leading to oxygen depletion and eventually hypoxia, predict the future development of affected ecosystems, and define suitable mitigation strategies requires detailed knowledge of the dissolved oxygen (DO) history. Suitable high-resolution DO archives covering coherent time intervals of decades to centuries include bivalve shells. Here, we explored if the microstructure, specifically disturbance lines, in shells of Arctica islandica from the Baltic Sea can be used as an alternative or complementary proxy to Mn/Cashell to track the frequency and severity of past low-DO events. Disturbance lines differ from periodic annual growth lines by the presence of fine complex crossed lamellae instead of irregular simple prisms. Aside from a qualitative assessment of microstructural changes, the morphology of individual biomineral units (BMUs) was quantitatively determined by artificial intelligence-assisted image analysis to derive models for DO reconstruction. As demonstrated, Mn-rich disturbance lines can provide a proxy for past deoxygenation events (i.e., DO &lt; 45 µmol/L), but it currently remains unresolved if low DO leads to microstructurally distinct features that differ from those caused by other environmental stressors. At least in studied specimens from the Baltic Sea and Iceland, low temperature, salinity near the lower physiological tolerance, or food scarcity did not result in disturbance lines. With decreasing DO supply, disturbance lines seem to become more prominent, contain more Mn, and consist of increasingly smaller and more elongated BMUs with a larger perimeter-to-area ratio. Although the relationship between DO and BMU size or elongation was statistically significant, the explained variability (&lt;1.5%) was too small and the error too large to reconstruct DO values. BMU parameters may reveal a closer relationship with DO if studied in three dimensions and if the DO content was determined at high resolution, directly at the position where the bivalves lived, something that future work should address

Seasonal change of multifrequency backscatter in three Baltic Sea habitats

This study investigated the seasonality of acoustic backscatter intensities, exploring three habitats in the southwestern Baltic Sea: 1) a mussel-covered reef, 2) coarse sand and gravel, and 3) seagrass meadows. Backscatter information of different, partly calibrated frequencies (200, 400, 550, and 700 kHz) was collected in three seasons (May, August, and October). The acoustic data were supported by point samples and video profiles for grain size and benthic community analysis. Angular response curves helped to quantify the seasonal backscatter response of the different frequencies. The multifrequency and multiseasonal backscatter maps distinguish the three habitats and reveal variable seasonal differences in acoustic backscatter, but not all changes in the benthic community can be recognized in the acoustic data. 1) The high-backscatter response of the mussel-covered reef shows little seasonal differences and was frequency independent. 2) The ecologically valuable coarse sand and gravel areas show small-scale seasonal alterations in the sediment composition and morphology, mainly caused by changes in local hydrodynamics. Higher frequencies were found best suited to identify coarse sand and gravel. 3) Seagrass meadows seasonality is dominated by growth of seagrass blades, increasing the backscatter response compared to bare sand. The use of multiple frequencies is beneficial as the low frequency is sensitive to changes in the shallow subsurface and benthic features such as seagrass rhizomes, while the higher frequency highlights changes related to coarser sediment

Characterization and differentiation of sublittoral sandbanks in the southeastern North Sea

Marine sublittoral sandbanks are essential offshore feeding grounds for larger crustaceans, fish and seabirds. In the southern North Sea, sandbanks are characterized by considerable natural sediment dynamics and are subject to chronic bottom trawling. However, except for the Dogger Bank, sandbanks in the southeastern North Sea have been only poorly investigated until now. We used an extensive, multi-annual dataset covering ongoing national monitoring programmes, environmental impact assessments, and basic research studies to analyse benthic communities on sublittoral sandbanks, evaluating their ecological value against the backdrop of similar seafloor habitats in this region. The analysis revealed complex spatial structuring of sandy seafloor habitats of the southeastern North Sea. Different infauna clusters were identified and could be specified by their composition of characteristic species. The sandbanks shared common structural features in their infauna community composition although they were not necessarily characterized by particularly high biodiversity compared to other sandy habitats. A close association of one of the main bioturbators in the southern North Sea, the sea urchin Echinocardium cordatum, with sandbanks was detected, which may promote the sediment-bound biogeochemical activity in this particular seafloor habitat. This would corroborate the status of sandbanks as sites of high ecological value calling for consideration in marine conservation

In Search of a Field-Based Relationship Between Benthic Macrofauna and Biogeochemistry in a Modern Brackish Coastal Sea

During several cruises in the southern Baltic Sea conducted in different seasons from 2014 to 2016, sediment cores were collected for the investigation of pore-water biogeochemistry and associated nutrient fluxes across the sediment-water interface. Six stations were positioned along a salinity gradient (ranging from 22 to 8) and covered various sedimentary habitats ranging from mud to sand. Integrated fluxes of nutrients in the supernatant water and sediment oxygen consumption were additionally derived from incubations of intact sediment cores. Subsequently, sediment from the pore-water and incubation cores was sieved for taxonomic identification and estimation of benthic macrofauna density. This combined dataset was used to determine the dominant factors influencing the vertical distribution of geochemical parameters in the pore-waters of the studied habitats and to find similarities and patterns explaining significant variations of solute fluxes across the sediment-water interface. A statistical relationship between the thickness of sulfide-free surface sediments, solute fluxes of sulfide, ammonium, and phosphate as well as oxygen consumption and taxonomic and functional characteristics of macrobenthic communities were tested. Our data and modeling results indicate that bioturbation and bioirrigation alter near-surface pore-water nutrient concentrations toward bottom water values. Besides sediment properties and microbial activity, the biogeochemical fluxes can further be explained by the functional structure of benthic macrofauna. Community bioturbation potential, species richness, and biomass of biodiffusers were the best proxies among the tested set of biotic and abiotic parameters and could explain 63% of multivariate total benthic flux variations. The effects of macrobenthos on ecosystem functioning differ between sediment types, specific locations and seasons. Both, species distribution and nutrient fluxes are temporally dynamic. Those natural patterns, as well as potential anthropogenic and natural disturbances (e.g., fishery, storm events), may cause impacts on field data in a way beyond our present capability of quantitative prediction, and require more detailed seasonal studies. The data presented here adds to our understanding of the complexity of natural ecosystem functioning under anthropogenic pressure

Seasonal SIMS δ18O record in Astarte borealis from the Baltic Sea tracks a modern regime shift in the NAO

IntroductionAstarte borealis holds great potential as an archive of seasonal paleoclimate, especially due to its long lifespan (several decades to more than a century) and ubiquitous distribution across high northern latitudes. Furthermore, recent work demonstrates that the isotope geochemistry of the aragonite shell is a faithful proxy of environmental conditions. However, the exceedingly slow growth rates of A. borealis in some locations (&lt;0.2mm/year) make it difficult to achieve seasonal resolution using standard micromilling techniques for conventional stable isotope analysis. Moreover, oxygen isotope (δ18O) records from species inhabiting brackish environments are notoriously difficult to use as paleoclimate archives because of the simultaneous variation in temperature and δ18Owater values.MethodsHere we use secondary ion mass spectrometry (SIMS) to microsample an A. borealis specimen from the southern Baltic Sea, yielding 451 SIMS δ18Oshell values at sub-monthly resolution.ResultsSIMS δ18Oshell values exhibit a quasi-sinusoidal pattern with 24 local maxima and minima coinciding with 24 annual growth increments between March 1977 and the month before specimen collection in May 2001.DiscussionAge-modeled SIMS δ18Oshell values correlate significantly with both in situ temperature measured from shipborne CTD casts (r2 = 0.52, p&lt;0.001) and sea surface temperature from the ORAS5-SST global reanalysis product for the Baltic Sea region (r2 = 0.42, p&lt;0.001). We observe the strongest correlation between SIMS δ18Oshell values and salinity when both datasets are run through a 36-month LOWESS function (r2 = 0.71, p &lt; 0.001). Similarly, we find that LOWESS-smoothed SIMS δ18Oshell values exhibit a moderate correlation with the LOWESS-smoothed North Atlantic Oscillation (NAO) Index (r2 = 0.46, p&lt;0.001). Change point analysis supports that SIMS δ18Oshell values capture a well-documented regime shift in the NAO circa 1989. We hypothesize that the correlation between the SIMS δ18Oshell time series and the NAO is enhanced by the latter’s influence on the regional covariance of water temperature and δ18Owater values on interannual and longer timescales in the Baltic Sea. These results showcase the potential for SIMS δ18Oshell values in A. borealis shells to provide robust paleoclimate information regarding hydroclimate variability from seasonal to decadal timescales

Distribution of boulders in coastal waters of Western Pomerania, German Baltic Sea

This study contributes to a better understanding of geogenic reef distribution in the southern Baltic Sea and highlights the implications of survey-related factors on automated boulder classification when utilizing data from multiple surveys. The distribution of hard grounds and reefs is needed as a baseline for geological and biological studies, but also for offshore construction, navigation and coastal management. In this study we provide maps of the distribution of geogenic reefs for about 750 km2 in the southern Baltic Sea, at the sites Wismar Bay, Darss Sill and Plantagenet Ground. The maps are based on full-coverage backscatter surveys with different side scan sonar and multibeam echo sounder systems. The distribution and number of boulders in the backscatter maps was determined using a convolutional neural network combined with quality control by human experts. The extent of the geogenic reefs was calculated on the basis of the number of boulders in 50 m x 50 m grid cells. We compare the results with previous reef maps based on point sampling, which show reefs of either biogenic or geogenic origin. According to the earlier maps, 11% of the Plantagenet Ground seabed was classified as reef habitat type. This is similar to the result of our study (12%), although we only considered reefs of geogenic origin. In the Darss Sill, geogenic reefs are larger in this study than in previous maps (30% versus 23%). In both regions, the spatial distribution of reefs differs significantly between old and new maps. For Wismar Bay, previous maps classify 3% of the seafloor as habitat type reef, whereas this study classifies 35% as geogenic reef. The use of automated classification during seafloor mapping allowed large areas to be interpreted in a few days. It also provided more information on the distribution of boulders within the geogenic reef. However, the boulder distribution maps show the negative effects of survey geometry, frequency and environmental conditions on automated boulder classification when data from different surveys are combined