To determine the relationship between region specific dinoflagellate cyst distribution in the Po-river
discharge area and oceanic environmental conditions, surface sediments of 48 sites in the middle and distal
part of the discharge plume area have been studied. Establishing such a relationship is a prerequisite to
create reconstructions of the eutrophication history as well as the palaeoclimatic and palaeoceanography
history of the area.
Literature based information about the sedimentation rates based on 210Pb dating methods are available for
18 sites. This enables the calculation of cyst accumulation rates of individual cyst species which reflect their
cyst production. Correlation of the accumulation rates of individual species with environmental parameters
of the upper waters allows us to adapt and refine the ecological characteristics of a selection of cyst species.
This latter is trivial since the current concepts on the ecological significance of dinoflagellate cyst have to be
revised as a result of the current developments in the dinoflagellate research field. These developments have
elucidated that a considerable part of the relative abundance datasets that form the basis for the present day
ecological concepts of dinoflagellate cysts might have suffered from so called “closed sum effects” and have
been overprinted by early diagenetic processes.
The dinoflagellate cyst association reflects both upper and bottom water circulation. Based on the relative
abundance data four associations can be distinguished that are characteristic for the major oceanographic
settings in the region. (1) River discharge association. This association consists of Echinidinium spp., Lejeunecysta
sabrina, Lingulodinium machaerophorum, Polykrikos kofoidii, Polykrikos schwarzii, cysts of Protoperidinium
stellatum, Selenopemphix quanta and reworked cysts. These species have high relative abundances in sites where
bottom waters are low in oxygen and upper waters are influenced by river discharge waters that are
characterized by high productivity and relative low salinity. (2) Warm water association. This association
consists of Spiniferites mirabilis, Spiniferites pachydermus, Spiniferites ramosus and Spiniferites spp. which
have their highest relative abundances in the sites at the plume margin that are characterized by relative
warm upper waters and intermediate chlorophyll-a concentrations. (3) Oxygenated bottom water group.
Species of this group; Impagidinium aculeatum, Impagidinium patulum, Impagidinium sphaericum,
Operculodinium centrocarpum and Operculodinium israelianum have their highest relative abundances at
sites where bottom waters are formed by well ventilated Adriatic Deep Water or Eastern Mediterranean
Deep Water. (4) Golfo di Taranto group consisting of round brown cysts produced by Protoperidinium
species (grouped as Brigantedinium spp.).
The variation in accumulation rates can be related to gradiental changes in the trophic state of the surface
waters linked to river outflow. Most species show a positive relationship between cyst production and
nutrient/trace element availability in upper waters. No negative correlation between cyst production and
nutrient/trace element availability could be documented. Production of Brigantidinium spp., Echinidinium
spp., L. sabrina, L. machaerophorum, P. kofoidii/schwarzii, Spiniferites spp., S. mirabilis and S. quanta shows
the most pronounced increase with increasing nutrient/trace element availability. These species can be
considered as valuable indicators for reconstructing changes in the trophic state of the upper waters
within the Po-river area in palaeo-environmental studies.