Spatio-temporal variability of wrack abundance and composition along the north Portuguese sandy beaches
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1
Interdisciplinary Center for Marine and Environmental Research, Abel Salazar Institute of Biomedical Sciences, University of Porto, Portugal
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2
Departament of Biology, Faculty of Sciences, University of Porto, Portugal
Many detached macroalgae and seagrasses leads in amounts of detritus on the shorelines forming accumulations commonly named as “wrack”. Wrack is exported from highly productive rocky shores to low-productive sandy beaches. This accumulation of marine macrophytes also plays key roles providing nutrients to primary producers and food for decomposers. So high is the value of wrack as a substitute for nutrients that humans have used this vegetal detritus as fertilizer for centuries. However, to the date, no study has proved the value of wrack in the sandy Portuguese coasts.
The interest of the sandy beaches as spaces for leisure, tourism and recreational activities makes authorities to remove wrack and other debris in order to improve their aesthetics, amenity and utility for the user demand. This removal of debris is usually carried out in summer and, in most of the cases, the wrack is treated as residues without any additional valorisation. The project Val-Wrack was created with the aim of exploring the ecological drivers that control the amount of wrack that arrives to Portuguese sandy beaches testing its potential use as economical resource. One of the aims of this project is to explore the natural variability of wrack abundance along the north Portuguese sandy beaches. For this aim, several beaches were visited in order to estimate the species composition and total biomass of wrack. Sampling was carried out during low spring tides. Samples were randomly collected from the base of the dune to the lowest swash level along transects of 100 m, deploying randomly10 quadrats of 100 x 100 cm and collecting macrophytes within them. To explore species composition, the wrack of each quadrat was stored separately in bags and frozen. Subsequently, seaweed and seagrass species were separated and total biomass of each one was calculated by drying samples at 60ºC. The spatial and temporal variability of biomass and number of species was explored by analysis of variance (ANOVA). Spatial and temporal changes on the structure of wrack assemblages was explored by permutational multivariate analysis of variance (PERMANOVA).
Until now, we collected the wrack supply of four sandy beaches, two at the north (Cabedelo and Âncora) and other two at the south in the Esmoriz area. Results showed that in northern beaches, wrack was predominately composed by the fucoids Fucus spp., Ascophyllum nodosum, Pelvetia canaliculata and the invasive Sargassum muticum. However, in the southern beaches wrack was composed by Fucus spp., S. muticum and the seagrass Zostera noltei. As in the north of Portugal, Fucus sp. and A. nodosum reach their southern distribution limit, in a future scenario of global change, the exportation to sandy beaches of these two macroalgae could disappear, with negative consequences because our results showed that these are the main species present in wrack. On the other hand, the presence of the seagrass Z. noltei as member of wrack in the southern most beaches indicates an important contribution from Ria de Aveiro, where this species is widely distributed. Therefore, our results highlight the importance of the conservation of Zoostera beds in the Ria de Aveiro.
The knowledge provides in this study, could help us to understand the consequences that climate change could have on the coasts of northern Portugal. In addition, this study provides us valuable information about the seasonal and spatial variability in the abundance and composition of our resource (wrack). This is a critical point to plan its exploitation and therefore, its viability as resource.
Acknowledgements
This research was developed under the Project No. 029818, co-financed by COMPETE 2020, Portugal 2020 and the European Union through the ERDF, and by FCT through national funds.
Keywords:
Wrack,
North of Portugal,
sandy beaches,
Fucoids,
seagrass
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:
Guerrero-Meseguer
L,
Torres
A,
Veiga
P and
Rubal
M
(2019). Spatio-temporal variability of wrack abundance and composition along the north Portuguese sandy beaches.
Front. Mar. Sci.
Conference Abstract:
XX Iberian Symposium on Marine Biology Studies (SIEBM XX) .
doi: 10.3389/conf.fmars.2019.08.00189
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Received:
15 May 2019;
Published Online:
27 Sep 2019.
*
Correspondence:
Miss. Ana Catarina Torres, Interdisciplinary Center for Marine and Environmental Research, Abel Salazar Institute of Biomedical Sciences, University of Porto, Matosinhos, 4450-208, Portugal, a_catarina_torres@hotmail.com