Low planktic foraminiferal diversity and abundance observed in a 2013 West-East Mediterranean Sea transect

Abstract

<p><strong>Abstract.</strong> Planktic foraminifera were collected with 150 µm BONGO nets from the upper 200 m water depth at 20 stations across the Mediterranean Sea between 02 May and 02 June, 2013. The main aim was to characterize the species distribution and size-normalized shell weight (SNW). Average foraminifera abundances and diversity are 1.42 ± 1.43 ind.∙10 m<sup>−3</sup> (ranging from 0.11 to 5.20 ind.∙10 m<sup>−3</sup>), with ten overall species found, respectively. Large differences in species assemblages and abundance values are observed between the different Mediterranean sub-basins, with an overall dominance of spinose, symbiont-bearing species indicating oligotrophic conditions. The highest values in absolute abundance are in the Strait of Gibraltar and Alboran Sea. The western basin is dominated by <i>Globorotalia inflata</i> and <i>Globigerina bulloides</i> at slightly lower standing stocks than in the eastern basin. In contrast, the planktic foraminiferal assemblage in the warmer, saltier and more nutrient-limited eastern basin is dominated by <i>Globigerinoides ruber</i> sensu stricto (s.s.). These new collective results in combination with comparison to previous findings, suggest that stratification of the surface water column, nutrient concentration and hence food availability, and temperature seem to be the main factors controlling foraminiferal abundances and distribution. Standing stocks and size-normalized weight (SNW) of <i>G. ruber</i> s.s. and <i>G. bulloides</i> are more related to food availability than seawater carbonate chemistry. Increasing temperature, salinity, surface ocean stratification and trophic conditions could be the causes of reduced abundance, diversity and species-specific changes in calcification in planktic foraminifera.</p>

Spring distribution of shelled pteropods across the Mediterranean Sea

“…Planktic foraminiferal abundance and distribution presented in Mallo et al (2017) were compared to the pteropod data from this study. The tow samples from Mallo et al (2017) were collected during the same cruise and within the same nets as the pteropods of the present study, allowing a direct comparison of the two groups of key planktic calcifiers.…”

“…Experimental evidence indicates that planktic foraminifera are vulnerable to OA conditions under which they experience reduced calcification and an increased metabolic rate (Davis et al, 2017;Lombard et al, 2010;Manno et al, 2012). Foraminiferal distribution and abundance appear to be driven more by nutrient levels than carbonate saturation levels, as suggested in Mallo et al (2017). The skeleton of foraminifera is made of calcite, a less soluble form of calcium carbonate than aragonite (Mucci et al, 1989;Subhas et al, 2018).…”

“…Both pteropods and foraminifera are sensitive to OA due to their carbonate skeletons, however it is likely that foraminifera are less sensitive to carbonate variability due to the lower solubility of their calcite skeleton compared with aragonite. Foraminifera have been shown to be nutrient limited (Gregg and Casey, 2007;Schiebel et al, 2004), and Mallo et al (2017) suggested that the lower foraminiferal abundance in the eastern Mediterranean (ultra-oligotrophic sector) results from reduced reproduction due to limiting food resources.…”

Tintinnina (Ciliophora) and Foraminifera in plankton of hypersaline Lagoon Bardawil (Egypt): spatial and temporal variability

“…High Foraminifera abundance in plankton of a hypersaline lagoon in Crimea (Black Sea) was noted earlier, from 194 to 36,372 ind./m 3 (Zagorodnyaya et al, 2008). It is currently believed that the main factor determining abundance of foraminifera in plankton is food concentration (Cifelli, 1974;Pujol and Grazzini, 1995;Mallo et al, 2017). All three species of foraminifera found in Lagoon Bardawil actively consume small animals, including copepods, along with algae (Anderson et al, 1979).…”

“…High foraminiferal abundance in the lagoon likely can be explained by high copepod density (from 17,000 to 120,000 ind./m 3 ; our data) as well as other preys (rotifers, tintinnids, etc.). All three foraminifera species are also hosts for symbiotic flagellates that supply their hosts with more food (Pujol and Grazzini, 1995;Mallo et al, 2017); the authors may assume that this may make a significant contribution to primary production of the oligotrophic lagoon. Currently, there are no data to support that idea and this question requires special study.…”