Atlas of Modern Dinoflagellate Cyst Distributions in the Black Sea Corridor: from Aegean to Aral Seas, Including Marmara, Black, Azov and Caspian Seas
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1 Marine Micropaleontology Achimer June 2017, Volume 134, Pages 1-152 http://dx.doi.org/10.1016/j.marmicro.2017.05.004 http://archimer.ifremer.fr http://archimer.ifremer.fr/doc/00387/49824/ © 2017 Elsevier B.V. All rights reserved. Atlas of modern dinoflagellate cyst distributions in the Black Sea Corridor: From Aegean to Aral Seas, including Marmara, Black, Azov and Caspian Seas Mudie Peta J. 1, Marret Fabienne 2, *, Mertens Kenneth 3, Shumilovskikh Lyudmila 4, Leroy Suzanne A.G. 2, 5 1 Geological Survey of Canada, Box 1008, Dartmouth, NS B2Y 4A2, Canada 2 School of Environmental Sciences, University of Liverpool, Liverpool, L69 7ZT, UK 3 Research Unit Palaeontology, Ghent University, Krijgslaan 281 S8, 9000 Gent, Belgium 4 Department of Palynology and Climate Dynamics, University of Göttingen, Untere Karspüle 2, 37073 Göttingen, Germany 5 CEREGE, Technopôle de l’Arbois BP 80, 13545, Aix-en-Provence, cedex 4, France * Corresponding author : Fabienne Marret, email address : [email protected] Abstract : We present the first comprehensive taxonomic and environmental study of dinoflagellate cysts in 185 surface sediment samples from the Black Sea Corridor (BSC) which is a series of marine basins extending from the Aegean to the Aral Seas (including Marmara, Black, Azov and Caspian Seas). For decades, these low-salinity, semi-enclosed or endorheic basins have experienced large-scale changes because of intensive agriculture and industrialisation, with consequent eutrophication and increased algal blooms. The BSC atlas data provide a baseline for improved understanding of linkages between surface water conditions and dinoflagellate cyst (dinocyst) distribution, diversity and morphological variations. By cross-reference to dinocyst occurrences in sediment cores with radiocarbon ages covering the past c. 11,700 years, the history of recent biodiversity changes can be evaluated. The seabed cyst samples integrate seasonal and multi-year data which are not usually captured by plankton samples, and the cyst composition can point to presence of previously unrecorded motile dinoflagellate species in the BSC. Results show the presence of at least 71 dinocyst taxa of which 36% can be related to motile stages recorded in the plankton. Comparison with sediment core records shows that five new taxa appear to have entered or re-entered the region over the past century. Statistical analysis of the atlas data reveals the presence of four ecological assemblages which are primarily correlated with seasonal and annual surface water salinity and temperature; correlation with phosphate, nitrate and silicate nutrients, chlorophyll-a and bottom water oxygen is less clear but may be important for some taxa. Biodiversity indices reveal strong west − east biogeographical differences among the basins that reflect the different histories of Mediterranean versus Ponto-Caspian connections. The atlas data provide a standardised taxonomy and regional database for interpreting downcore cyst variations in terms of quantitative oceanographic changes. The atlas also provides a baseline for monitoring further changes in the BSC dinocysts that may accompany the accelerating development of the region. Please note that this is an author-produced PDF of an article accepted for publication following peer review. The definitive publisher-authenticated version is available on the publisher Web site. 2 Highlights ► Study of dinoflagellate cyst distribution in 185 surface sediment samples from the Black Sea ► Corridor ► 71 dinocyst taxa are described, illustrated, and related to motile stages and HABS. ► Spatial distribution of modern taxa is mapped and related to sediment-core time-series. ► Biogeography and relation of taxa to SST, SSS, nutrients and oxygen are discussed. Keywords : Phytoplankton, harmful algae, biodiversity, paleoceanography, surface samples Please note that this is an author-produced PDF of an article accepted for publication following peer review. The definitive publisher-authenticated version is available on the publisher Web site. ACCEPTED MANUSCRIPT 4 1. Introduction Organic-walled dinoflagellate cysts (dinocysts) are generally abundant and well-preserved in the sediments of the Black Sea Corridor (hereafter abbreviated as BSC), which is the series of marine and lacustrine basins extending from the Marmara to the Aral Seas, including the Black, Azov and Caspian Seas (Figure 1). In the low-oxygen stratified waters of these brackish water basins, dinocysts are the main proxy for studying changes in sea-surface conditions and phytoplankton biodiversity (Mudie et al. 2002a; Marret et al. 2004; Sorrel et al., 2006; Bradley and Marret, 2013). The value of the dinocysts as environmental indicators in the BSC is because 1) calcareous phytoplankton (nannofossils) are frequently sparse, poorly preserved, and of low diversity because they are at their salinity limit and carbon dissolution is high (Giunta et al., 2007); 2) in the BSC, planktonic foraminifera occur only in the Marmara Sea (Mudie et al., 2002a); and 3) siliceous fossils (mostly diatoms) are subject to dissolution (Piskaln, 1991) and to loss of opal relative to calcium carbonate (Piskaln and Pike, 2001). Calcareous dinocysts are common in the Marmara and western Black Seas: their calcareous skeletons are not always preserved (Aksu et al., 2002) but they can be traced from their organic linings recovered in the palynological residues after acid treatment. Therefore, calcareous dinocysts are included in this atlas. ACCEPTED MANUSCRIPT [Figure 1 goes here - Map of region with place names] The composition of dinocyst assemblages in modern sediments is tightly linked to the biological, physical and chemical oceanographic conditions of the surface water (0–20 m) and the bottom depositional environment (e.g. Zonneveld et al., 2013 and references therein). Modern and fossil dinocysts can therefore provide an index of environmental change in the BSC 4 ACCEPTED MANUSCRIPT 5 (e.g. Mudie et al., 2004; Leroy et al., 2006; 2012; Sorrel et al., 2006; Giosan et al., 2012; Mousing et al., 2013), and they record biodiversity shifts resulting from anthropogenic impacts (Bradley et al., 2012). Mapping of the cyst assemblages also provides information on possible dinoflagellate-induced harmful algal blooms and on invasion rates of harmful species, as shown for other areas (Anderson et al., 2012; Ribeiro et al., 2012). Global atlases (Marret and Zonneveld, 2003; Zonneveld et al., 2013) provide few data for the low salinity marine to brackish waters of the BSC. This is an important omission because these are the world’s largest semi-enclosed or land-locked seas and they are currently undergoing major anthropogenic changes, including rapid increases of salinity, eutrophication and harmful species invasions (Glantz and Zonn, 1996; Beşiktepe et al., 1997; Mee et al., 2005; Zavialov, 2005; Micklin, 2007; Boomer, 2012; Nasrollahzadeh et al., 2014). Outbreaks of harmful dinoflagellate algal blooms (including non-toxic red tides) in the Marmara and Black Seas (Koray, 1984; Velikova et al., 1999; Feyzioğlü and Öğüt, 2006; Yasakova, 2013; Balkis et al., 2011; Krakhmalny et al., 2012; Leroy et al., 2013a) point to the need for study of latent cyst reservoirs in the surface sediments (Aydin and Uzar, 2014; Balkis et al., 2016). Detailed mapping of recent−present-day dinocyst assemblages is required to investigate and quantify the relationshipACCEPTED between modern environmental MANUSCRIPT conditions and the geographic distribution of the cysts. Paleoecological transfer functions then use these linkages to quantify past oceanographic changes (e.g. de Vernal et al., 2005; Zonneveld and Siccha, 2016). Although studies involving dinocysts and dinoflagellates from the Black and Caspian seas have proliferated over the past decade (e.g. Marret et al., 2004; Mudie et al., 2004; 2011; Atanassova, 2005, Kovaleva, 2008; Giosan et al., 2012; Shumilovskikh et al., 2013, 2014; Bradley and Marret, 2013), the wide diversity of unique BSC environments poses several challenges to researchers. Firstly, the geographic range of the marginal seas extends over 3,800 km, including 5 ACCEPTED MANUSCRIPT 6 11 Eastern European–Central Asian countries with limited access to international journals and publications in 11 languages and various alphabets. This circumstance has restricted exchange of taxonomic data and prevented adoption of standardised processing and counting methods (e.g. Mertens et al. 2009a, 2012a; Mudie et al., 2011; Marret and Garcés, 2013, Price et al., 2016). Secondly, as first noted by Wall et al. (1973), several BSC dinocyst taxa are endemic, and exhibit wide morphological variation within seasonally variable ecological niches often lacking long-term observational data. Thirdly, the most common BSC dinocysts are cosmopolitan, euryhaline species such as Lingulodinium machaerophorum, which can make precise environmental reconstruction difficult because of their wide salinity and temperature tolerances. Fourthly, previously there has been little information on the cysts of freshwater dinoflagellates in the vast deltas and limans (estuaries and adjacent coastal lagoons) of rivers flowing into the BSC seas (Figure 1), including the Danube and Volga rivers which are the largest in Europe. These dinocysts are markers of deltaic environments and are crucial for understanding of the early Holocene seawater flooding history of the Black Sea which is a highly controversial topic despite decades of research (e.g. Hiscott et al., 2007;