Resting stage in the biogenic fraction of surface sediments from the deep Mediterranean Sea

Abstract

The presence of resting stages in neritic areas is well known, while their occurrence in the deep sea realm has seldom been considered. Recent investigations showed strict interactions between neritic and deep sea domains, due to up- and down-welling phenomena driven by submarine canyons. To estimate the presence of resting stages in deep bottom sediments, seven sediment cores, collected along a trans-Mediterranean transect by means a multi-corer during the TRANSMED survey (1999), were studied. Most biogenic sediment was composed of Foraminifera tests (tens of thousand tests cm-3), Calciodinellum albatrosianum and Leonella granifera (Dinophyta) cysts (up to thousands cysts cm-3). Eleven dinocyst morphotypes were recorded mainly as empty shells (seven calcareous-walled: C. albatrosianum, Calciperidinium asymmetricum, Leonella granifera, Scrippsiella trochoidea, S. precaria type 1, S. precaria type 2, S. regalis; four organic-walled: Impagidinium aculeatum, unid. dinocyst 1, unid. dinocyst 2 and unid. dinocyst 3), while no metazoan resting eggs were observed. The presence of viable resting stages in deep bottom surface sediments was much lower than in neritic areas, suggesting that oceanic species do not produce cysts for a "benthic resting" strategy. Further taxonomic and biogeographic studies are needed to better understand the ecological dynamics of oceanic plankton in the Mediterranean Sea.