Spatial and seasonal dynamics of zooplankton assemblages in the Douro Estuary
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1
Abel Salazar Institute of Biomedical Sciences, University of Porto, Portugal
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2
Interdisciplinary Center for Marine and Environmental Research, Abel Salazar Institute of Biomedical Sciences, University of Porto, Portugal
Introduction
Zooplankton plays an extremely important role in aquatic food webs, representing a link from primary producers to higher trophic levels. Therefore, it is crucial to understand this compartment in estuaries in order to feed conservation and management strategies. The present study aims the understanding of spatial and temporal dynamics of zooplankton assemblages in the Douro Estuary.
Location and methods
The Douro Estuary is the end-member of the largest Iberian watershed. The freshwater flow is controlled by a network of 50+ large dams, the last one located just 21.5 km from the river mouth.
For this study, a seasonal (spring-summer-fall-winter) sampling program was implemented in three locations corresponding to the lower (41.14631ºN/8.66677ºW), middle (41.13990ºN/8.61489ºW), and upper (41.06945ºN/8.50057ºW) estuary. At each sampling site, vertical tows were performed with a 150 μm mesh net for zooplankton collection. Key environmental descriptors (salinity, temperature, dissolved oxygen, pH, turbidity) were measured with an YSI 6000 series multiprobe CTD.
Zooplankton individuals were sorted into major taxonomic groups, namely Copepoda, Cladocera, Hydromedusae, Oykopleura, Polychaeta larvae, and fish eggs and larvae. Abundances were determined (individuals.m-3) for each taxonomic group. The Shannon-Wiener index H’ was determined as a measure of diversity of the zooplankton community in the Douro Estuary.
Main results
The zooplankton community of the Douro Estuary presented low diversity, according to the Shannon diversity index (H’=0.56±0.15) across all sampling locations and seasons. Furthermore, there was no consistent spatial trend of zooplankton diversity throughout the year. The diversity varied seasonally, reaching a minimum in spring (H’=0.47±0.11), when no clear salinity gradient from the lower (0.18) to the upper (0.10) estuary could be observed. The highest diversity occurred during the summer (H’=0.67±0.17), with a peak in the lower estuary (H’=0.86), with salinity in the polyhaline range (>18).
The abundances of zooplankton also varied seasonally, reaching a peak in summer. Copepoda was the most abundant taxonomic group, representing over 60% of the zooplankton identified, followed by Cladocera (28%). The nauplius phases of Copepoda and Cirripeda represented an important component of the zooplankton community, especially during summer. Moreover, the structure of the zooplankton community followed spatial and temporal patterns. The Copepoda were the most abundant group from summer to winter, while Cladocera (54%) were more abundant than Copepoda (43%) in the spring. The Copepoda were more abundant in the lower and middle stretches, than in upstream areas. Conversely, Cladocera abundances were higher at the upstream areas.
Conclusions
This study contributed to the understanding of the zooplankton assemblages of the Douro Estuary. In summary, few taxa dominated the zooplankton community, namely Copepoda and Cladocera, whose distribution was determined by the salinity gradient. In the context of climate change, increasing drought due to low precipitation and exacerbated by the large number of dams in the Douro River, may disrupt the present seasonal and spatial salinity patterns. Therefore, the productivity and functional roles played by the different components of the estuarine food web, including zooplankton, may be compromised.
Acknowledgements
This study was financed by the Project INNOVMAR (NORTE-01-0145-FEDER-000035), Research Line ECOSERVICES, supported by the Northern Portugal Regional Operational Programme (NORTE2020), through the European Regional Development Fund (ERDF); and Project RecBio - Operation MAR-01.04.02-FEAMP-0025, co-founded by the European Maritime and Fisheries Fund (EMFF), through the Operational Program MAR2020. We are thankful to all the team members that participated in the surveys and laboratory analysis.
Keywords:
Plankton,
Copepoda,
Cladocera,
diversity,
estuarine
Conference:
XX Iberian Symposium on Marine Biology Studies (SIEBM XX) , Braga, Portugal, 9 Sep - 12 Sep, 2019.
Presentation Type:
Poster Presentation
Topic:
Ecology, Biodiversity and Vulnerable Ecosystems
Citation:
Duarte
I,
Mendes
C,
Costa-Dias
SC and
Bordalo
A
(2019). Spatial and seasonal dynamics of zooplankton assemblages in the Douro Estuary.
Front. Mar. Sci.
Conference Abstract:
XX Iberian Symposium on Marine Biology Studies (SIEBM XX) .
doi: 10.3389/conf.fmars.2019.08.00132
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Received:
28 May 2019;
Published Online:
27 Sep 2019.
*
Correspondence:
PhD. Sérgia C Costa-Dias, Abel Salazar Institute of Biomedical Sciences, University of Porto, Porto, 4050-343, Portugal, scdias@icbas.up.pt