Environmental Factors Affecting Spatial Dinoflagellate Cyst Distribution in Surface Sediments Off Aveiro-Figueira da Foz (Atlantic Iberian Margin)

Abstract

Resting cysts of planktonic dinoflagellates, once produced, sink to the seabed where they can remain viable for a long time. These cysts have important ecological roles, such as acting as the inoculum for the development of planktonic populations. Moreover, dinoflagellate cyst records from depth sediment cores are broadly used as a proxy to infer past environmental conditions. In this study, the main objective was to obtain information on the relationships between the spatial distribution of modern dinoflagellate cysts and present-day hydrography in the NW Iberian shelf. Cyst assemblages were analyzed in 51 surface sediment samples with varying grain sizes, collected at different water depths, following nine transects perpendicular to the coast, between Aveiro and Figueira da Foz (Atlantic Iberian margin). Multivariate statistical analyses revealed marked land-sea and latitudinal gradients in the distribution of cysts, and helped investigate how environmental factors [water depth, grain size, sea-surface temperature (SST), sea-surface salinity (SSS), bottom temperature (BTT) and surface chlorophyll-a concentration (CHL)] influence modern dinoflagellate cyst composition and abundances. Three main ecological signals were identified in the modern dinoflagellate cyst assemblages: (1) the heterotroph signal as the main upwelling signal; (2) the dominance of P. reticulatum and L. polyedra signal, indicative of warm stratified conditions, possibly reflecting transitional environments between more active inshore upwelling and warmer offshore waters; and (3) the G. catenatum signal for the presence of mid-shelf upwelling fronts. The almost absence of viable cysts of the toxic and potentially toxic species G. catenatum L. polyedra and P. reticulatum suggests that in the study area, for these species, there is no build-up of significant cyst beds and thus planktonic populations must depend on other seeding processes. These results are the first detailed modern distribution of dinoflagellate cysts in the NW Iberian Atlantic margin (off Portugal), and show a good correspondence with hydrographic features of summer upwelling season in the study area, meaning that they are reflecting water column characteristics and therefore may be used as supporting evidence for the interpretation of stratigraphic cyst records and reconstruction of past marine ecosystems in W Iberia.

Dinoflagellate cysts production, excystment and transport in the upwelling off Cape Blanc (NW Africa)

“…High concentrations and relative abundances of Echinidinium and Brigantedinium species have also been observed in surface sediments below other areas of active upwelling in the (sub)tropics (e.g. Verleye and Louwye, 2010;Limoges et al, 2010;Zonneveld et al, 2013;Ribeiro et al, 2016;Garcia-Moreiras et al, 2021).…”

“…Also in other upwelling areas, this species is typically observed in stratified upper waters later in the upwelling succession, when active upwelling has terminated (e.g. Bravo et al, 2010;Ribeiro et al, 2016;Band-Schmidt et al, 2019;Garcia-Moreiras et al, 2021). frontiersin.org Zonneveld et al 10.3389/fmars.2022.915755 Lateral and vertical transport…”

“…Apart from being of major importance for HAB studies, information about production and vertical/lateral transport of dinoflagellate cysts in the water column is of major importance for dinoflagellatecyst reconstructions of palaeoclimate, -oceanography and -environment (e.g. García-Moreiras et al, 2018;de Vernal et al, 2020 and references therein). Here, cyst associations are studied in sedimentary archives to reconstruct the past oceanographic and environmental conditions above the archive sites at times of deposition.…”

The role of physico-chemical interactions in the seasonality of toxic dinoflagellate cyst assemblages: The case of the NW Patagonian fjords system

“…The mandatory dormancy of P. reticulatum as determined for Chilean strains under laboratory conditions is 123 ± 11 days (Salgado et al, 2017), such that it may have been completed before the detections of vegetative cells in the water column, both during warmer years, such as those corresponding to the El Niño Southern Oscillation (ENSO), and during the warmer season, i.e., austral summer (Alves- de-Souza et al, 2019;Alves-de-Souza et al, 2014). Indeed, recent surveys at the Atlantic Iberian Margin identified an association of P. reticulatum cysts with the warm stratified conditions of the water column (García-Moreiras et al, 2021). Moreover, the high abundance of P. reticulatum empty cysts can also be explained by their fossilizable properties, which would preserve them in the sediments (Head, 1996), resulting in the gradual accumulation of different cohorts over time (Ribeiro et al, 2013).…”

New physical and biological evidence of lateral transport affecting dinoflagellate cyst distribution in the benthic nepheloid layer along a land-sea transect off Figueira da Foz (Atlantic Iberian margin)

“…The biological and physical mechanisms involved in the seeding and initiation of blooms (such as inoculum from cysts), may vary between species and are still not fully understood, although their assessment is critical for adequate monitoring and prediction of HABs, and coastal management (e.g., Bravo et al, 2010;Anderson, 2014;Berdalet et al, 2017;Brosnahan et al, 2020). The study region off Figueira da Foz is an area affected by recurrent blooms of G. catenatum (e.g., Botelho et al, 2019) however a cyst survey carried out in the area could not detect the presence of significant sediment cyst banks (Garcıá-Moreiras et al, 2021), suggesting local blooms may rely on other seeding strategies.…”