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Tuesday February 14, 2023, 4pm CET


García-Moreiras, I.1 , Hatherly, M.2, Zonneveld, K.3, Dubert, J.4, Nolasco, R.4, Santos, A.I.5,6, Oliveira, A. 6, Moita, T.7, Oliveira, P.B.8, Magalhães, J.9, Amorim, A.2

Physical and biological processes influencing dinoflagellate cyst distribution in the benthic nepheloid layer off Figueira da Foz (Atlantic Iberian margin)

1Centro de Investigación Mariña (CIM), Universidade de Vigo, Departamento de Bioloxía Vexetal e Ciencias do Solo, Facultade de Ciencias, Vigo, Spain
2Centro de Ciências do Mar e do Ambiente (MARE) /ARNET - Aquatic Research Network, , Faculdade de Ciências, Universidade de Lisboa, Lisbon, Portugal
3Center for Marine Environmental Sciences (MARUM) and Geosciences Department, University of Bremen, Bremen, Germany
4Centro de Estudos Do Ambiente e Do Mar (CESAM) e Departamento de Física, Universidade de Aveiro, 3810-193, Aveiro, Portugal.
5Marine Geology Division, Instituto Hidrográfico (IH), Lisbon, Portugal
6Instituto Dom Luiz, Faculdade de Ciências, Universidade de Lisboa, Lisbon, Portugal
7Centro de Ciências do Mar (CCMAR), Universidade do Algarve, Faro, Portugal
8Instituto Português do Mar e da Atmosfera (IPMA), Algés, Portugal
9Centro Interdisciplinar de Investigação Marinha e Ambiental (CIIMAR) e Departamento de Geociências, Ambiente e Ordenamento do Território (DGAOT), Universidade do Porto, Porto, Portugal


The production of benthic resting stages (cysts) in the life cycle of many dinoflagellates is recognized as a key survival and dispersal strategy. Nevertheless, the coupling of biological and physical mechanisms involved in their transport, sedimentation and the initiation of planktonic blooms are still little understood. Where are the cysts produced before they accumulate on the sea bottom? Does the Benthic Nepheloid Layer (BNL) influence cyst distribution? Are there viable cysts in the BNL that may have the potential to seed planktonic populations? Are cysts in the BNL reflecting cyst assemblages in the underlying bottom sediments? These are some of the questions that have motivated the design of this multi-disciplinary study, which included the analysis of dinoflagellate cysts (composition and abundances) in the BNL along a land-sea transect off Figueira da Foz, NW Portuguese coast (Atlantic Iberian margin). This region is affected by seasonal upwelling that brings nutrient-rich waters and contributes to the high primary productivity that characterizes these coastal ecosystems. Environmental data and water samples were collected at different depths and in two different days (14th and 19th September 2019) to study spatial and temporal changes of physical properties and cyst assemblages. BNL cyst records were compared to planktonic records (cysts and vegetative cells from cyst-forming species) collected at different levels (0-75 m) above the BNL, along the same transect. They were also compared to the cyst rain collected by a sediment trap and with sediment cyst records to study the origin of cysts in the BNL. The survey covered a change from active to relaxed upwelling conditions with an increase of thermal stratification. In this talk I will discuss the relevance of cross- and along-shore transport on the distribution of cysts in the studied coastal transect, based on physical and biological (cysts and vegetative cells) in-situ data, along with new results obtained from particle back-track Lagrangian experiments that enabled reconstructing the trajectory of cysts in the BNL. Multi-disciplinary evidence support that during the survey the cyst distribution in the water column and underlying sediments was influenced by lateral transport in the BNL. This highlights the importance of physical transport processes on the geographical segregation of cyst production and cyst deposition areas. In consequence, cysts accumulated in the sediments are a mixture of locally and regionally produced cysts. Furthermore, high abundances of viable cysts were recorded in the BNL. Evidence suggests that during the survey, the majority of these cysts were produced in the upper water column (local or regional) rather than being resuspended from surface sediments. Cysts in BNL are exposed to higher oxygen concentrations, do not have to escape the sediment matrix and are closer to the euphotic layer, this could lead to higher germination rate and germling survival than in the bottom sediments; therefore, the BNL may act as a reservoir of viable cysts that have the potential to seed planktonic blooms.