Coccolithophore assemblage response to Black Sea Water inflow into the North Aegean Sea (NE Mediterranean)

Abstract

This study aims to presents the species composition of living coccolithophore communities in the NE Aegean Sea, investigating their spatial and temporal variations along a north-south transect in the area receiving the inflowing surface Black Sea Water (BSW) over the deeper Levantine Water (LW) layer. Coccolithophores in the area were relatively diverse and a total of 95 species over 3 sampling periods studied were recognized using Scanning Electron Microscope (SEM) techniques. R-mode hierarchical cluster analysis distinguished two coccolithophore Groups (I, IIa, IIb, IIc) with different ecological preferences. Emiliania huxleyi was the most abundant species of Group I, whereas Syracosphaera spp., Rhabdosphaera spp. and holococcolithophores were prevailing in the highly diversified Group II assemblages. Biometric analysis conducted on E. huxleyi coccoliths from Aegean water column and Black Sea sediment trap samples, indicated that during autumn, NE Aegean specimens in samples under BSW influence were featured by unimodal distribution concerning the coccolith relative tube width, with values similar to those provided by the Black Sea specimens. In early spring, coccoliths in the stations with increased BSW influx displayed a bimodal pattern of relative tube width with smaller values found mostly in the surface layers, while the distribution became again unimodal and dominated by larger values within the deeper LW layers. In the summer period, the typical LW holococcolithophore species (Group II) presented low cell numbers in the surface layer (<20 m), which is their usual ecological niche in the Aegean Sea, compared to greater depths, therefore marking LW mass flowing beneath the less saline 2 BSW surface lid. In contrast to Black Sea early summer bloom conditions, E. huxleyi was almost absent in the NE Aegean during the summer sampling period.

Emiliania huxleyi coccolith calcite mass modulation by morphological changes and ecology in the Mediterranean Sea

“…Overall, A1 was predominantly encountered in the upper photic zone of the Atlantic-Gibraltar Strait and SW Mediterranean, characterized by low salinity waters; while A3b was mainly found in the middle-lower photic zone of the SE Mediterranean, characterized by high salinity waters. A similar vertical distribution of the calcification varieties was observed, at smaller scale, in the NE Aegean Sea [ 47 ]: low-calcified E . huxleyi Type A coccoliths were particularly abundant in the upper 20 m of the water column, within the low salinity-low density layer of inflowing Black Sea water.…”

“…huxleyi coccolith mass should mainly reflect the geographical distribution of its morphotypes [ 12 ]. Still, in oceanic regions where one morphotype is largely predominant, as in the Mediterranean Sea [ 46 , 47 , 49 ], the calcification varieties of that particular morphotype can be expected to exercise a major control.…”

“…Previous field observations have demonstrated the existence of a connection between multiple environmental parameters and the calcification degree of E . huxleyi populations [ 12 , 14 , 38 , 46 , 47 , 58 ]. Besides, distinct sets of environmental parameters appear to control the average coccolith mass, depending on the oceanic region [ 21 ].…”

“…The existence of different degrees of calcification within E . huxleyi Type A has been documented in the past [ 35 ], mainly from the North Atlantic Ocean [ 37 – 39 ], the Pacific Ocean [ 40 ] and the Mediterranean Sea [ 41 – 47 ]. The region of focus for this study is the Mediterranean Sea: a ‘small-scale ocean’ with steep W−E biogeochemical and physical gradients and a fast overturning circulation (80 to 100 years) [ 48 ].…”

Phytoplankton temporal dynamics in the coastal waters of the north-eastern Adriatic Sea (Mediterranean Sea) from 2010 to 2017

“…Generally, non-redtide dinoflagellates are reported to be well-adapted to thermal stratification conditions with low nutrient availability (Latasa et al 2010). The coccolithophore Rhabdolithes claviger was also identified as a distinctive summer coccolithophore in the Adriatic Sea (Bernardi Aubry et al 2006;Godrijan et al 2013;Cerino et al 2017;Godrijan et al 2018) as well as in other Mediterranean areas (Cros and Fortuño 2002;Dimiza et al 2015;Karatsolis et al 2017) and in thermal stratified waters worldwide (Okada and McIntyre 1977;Hagino et al 2000). It is reported to be related to high temperature and low nitrate concentrations (Haidar and Thierstein 2001;Bernardi Aubry et al 2006;Godrijan et al 2013).…”