Bilbao-Urdaibai time series


Coastal marine systems offer many services that historically have attracted human populations, which, in turn, exert an increasing pressure on them. These ecosystems are characterized by their complex natural variability both at temporal (seasonal cycles, interannual and interdecadal oscillations) and spatial (thermohaline gradients, tidal and gravitational circulation) scales. In addition, they are affected by anthropogenic disturbances at local (littoral modification, exploitation of abiotic and biotic resources, pollution) and global (climate change) scales that modify their structure and function. In order to understand ongoing changes in these ecosystems and their causes, it is necessary to implement programs of systematic observations at time and space scales that are useful to interpret them properly. Time series are powerful tools to describe and interpret long-term changes in marine pelagic ecosystem and address predictive goals. Therefore, public institutions that are responsible for coastal ecosystems management are increasingly demanding studies based on time series, in order to ensure a suitable use for food supply, transport and recreation that is compatible with marine life conservation. This is evidenced by the recent creation of the GOOS (Global Ocean Observing System) by the IOC-UNESCO (Intergovernmental Oceanographic Commission), and the IGMETS (International Group for Marine Ecological Time Series), among other attempts to enhance the monitoring of marine ecosystems worldwide.


The group of Marine and Estuarine Plankton Ecology of the University of the Basque Country (UPV/EHU) started a scientific program to obtain and analyze time series from neritic and transitional plankton ecosystems of two nearby areas of the Basque coast with contrasting history of human pressure and conservation status, i.e. the estuary and port area of Bilbao, and the estuary of the Biosphere Reserve of Urdaibai. The project aim is to monitor short- and long-term natural and anthropogenic changes in water conditions and plankton communities. This effort is in agreement with worldwide scientific initiatives related to the study of climate change and marine environment conservation. Data collection was initiated in 1996, but it is carried out systematically with a monthly frequency since 1998. The approach selected to study the spatial variability was lagrangian, by sampling selected salinity zones instead of spatially fixed points.

Location of the area of study. Maps of the estuaries of Bilbao and Urdaibai showing the spatial range of the sampling salinity zones (26, 30, 33, 34 and 35)


The Marine and Estuarine Plankton Ecology group of the University of the Basque Country (UPV/EHU) is responsible for the field surveys, sample analyses in the laboratory and the maintenance and update of databases. The group is part of the Department of Plant Biology and Ecology of the Faculty of Science and Technology and of the Faculty of Pharmacy, and of the Research Centre for Experimental Marine Biology & Biotechnology (PiE-UPV/EHU). The sampling boat and field equipment is kept at the Higher Technical School of Navigation and Naval Machinery of Portugalete (UPV/EHU). Participating staff includes 3 researchers of the permanent staff of the UPV/EHU (Fernando Villate, Arantza Iriarte and Ibon Uriarte), hired collaborators, and PhD, MSc and BSc students engaged in the program to carry out their theses or final degree/master works (projects).


The Bilbao-Urdaibai Time Series program has no specific permanent financial support from public or private bodies. Funding has been obtained in competitive calls for research funds of the Spanish Government (MINECOR, MEC), the Basque Government (PIBA, GIC, ETORTEK), the UPV/EHU (GIU, UNESCO, EHU), the Aquitaine-Euskadi-Navarre Cooperative Program, and from contracts with private companies through specific university-company agreements (OTRI, EUSKOIKER).


In the sampling program, routine environmental and biotic data from plankton ecosystems are obtained monthly. In situ water column vertical profiles of salinity, temperature and dissolved oxygen are obtained, the Secchi disk depth is measured, water samples are collected with oceanographic bottles for the determination of phytoplankton photosynthetic pigments, and plankton samples are taken with 200 µm nets for the qualitative and quantitative analyses of zooplankton at mid depth, below the halocline. Samplings are performed at different salinity zones, from 35 to 30 and from 35 to 26 in the Bilbao and Urdaibai systems, respectively, to cover adequately marine and transitional habitats and the corresponding neritic and brackish zooplankton communities in both systems.



These time-series data are the property of the research group responsible for the program, but are available for any researcher interested in using them by agreement with the terms of use established by the research group in charge. They are also available for PhD, master and undergraduate students to carry out their doctoral thesis, final master or degree works (projects), as long as such theses or works are supervised by a member of the research group in charge.


There are specific databases that contain either separately or jointly the abiotic and biotic variables. Databases are available in different formats depending on the requirements of the specific study for which they have been used, but can be modified to fit with other research aims too. To date, data of environmental variables are available up to 2020 and those of the abundance and composition of zooplankton communities up to 2015.

Any query on the databases of the Bilbao-Urdaibai Time series and the terms of use may be addressed to

A) Monthly variation of the dissolved oxygen saturation (%) along the salinity gradient of the estuary of Bilbao from 1998 to 2020. B) Monthly variation of the zooplankton density (individual m-3, log x+1) along the salinity gradient of the estuary of Bilbao from 1998 to 2015. C) Monthly variation of the water temperature (ºC) in the estuary of Urdaibai from 1998 to 2020. D) Monthly variation of the relative abundance (%) of the copepods Acartia bifilosa and A. tonsa in the estuary of Urdaibai from 1998 to 2015.