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Portuguěse Coast Associated Investigators: Related Web Sites: Related Time Series: The Cascais monitoring site is a station of the time-series CASCAIS-WATCH, the oceanographic observation programme of the Oceanography and Plankton Group of the Instituto Portuguěs do Mar e da Atmosfera (IPMA), former Instituto Nacional de Recursos Biologicos. The station is located off Cascais Bay, outside the Tagus River estuary at 38 40 N 09 26.2 W and approximately 4 km offshore from Cascais, a town 40 km west of Lisbon, in a water depth of around 38 m. The hydrography of the bay is influenced by coastal morphology, the bottom topography (submarine canyons of Lisbon and Setubal), and the discharge of freshwater from the Tagus River (Ribeiro and Amorim, 2008). Zooplankton samples are collected from 30 m to the surface (oblique hauls) on a monthly basis with a WP2 net (50 cm diameter, 200 µm mesh). Samples are divided into two with a Folsom plankton splitter: one half is preserved in 4% borax-buffered formalin in seawater and later examined for identification and counting of mesozooplankton. The other half is lyophilized and weighed for biomass determination. During the first four years of sampling (2005-2008), neuston samples were also taken with a rectangular net with a mouth opening of 0.2 x 1.0 m and 200 µm mesh size, towed horizontally at the surface for 3 min. The samples were preserved and stored for later analysis. During the first year of sampling, Calanus helgolandicus egg production was determined whenever possible. After the first year of sampling and having concluded that Acartia spp. Was the most abundant copepod present in the samples, egg production measurements were started for this taxon and stopped for C. helgolandicus. Besides zooplankton monitoring, temperature, salinity, and Chlorophyll a are measured with a CTD fluorometer. The Cascais site is thought to be under the influence of the Eastern North Atlantic Upwelling System in spring and summer. This seasonal upwelling is responsible for the high phytoplankton production that promotes stable zooplankton abundance through the year (Santos et al., 2007). in situ temperatures at Cascais demonstrate a two-tier seasonal pattern, usually < 16 C during winter and spring, and =18 C in June-November. This pattern is attributed to the station being located in an upwelling shadow (Moita et al., 2003), where winds favourable to upwelling can promote local water stratification and stability. Seasonal and interannual trends The seasonal cycle of zooplankton biomass is characterized by a bimodal pattern, as observed at sites 52 and 53 to the north, with peak biomass in April and August. Copepod abundance remains high throughout the season, with highest abundance from August through November. The observed bimodal pattern is caused by seasonal upwelling in the area. Copepods at Cascais Bay are mainly represented by the genera Acartia, Paracalanus, Oncaea, and Oithona. Other species (Temora stylifera, T. longicornis, and Centropages spp.) are also important, but occur later in the season, which explains the high copepod abundance late in the year. The short length of this time-series limits its interannual analysis. Total copepod abundance and in situ temperature interannual anomalies oscillate together and result in a significant negative correlation (r^2 = 0.7848). Total copepod abundance has been decreasing in the last two years of sampling, mainly caused by a reduction in the three most abundant genera: Acartia, Paracalanus, and Oithona. The trends in these species are positively correlated. Following the decrease in abundance of copepods, bivalve veligers have become more abundant in the area, being the most abundant taxa in 2009, representing 26.2% of total zooplankton in that year. Veliger abundance follows the increasing abundance of the invasive species Ruditapes philippinarum in the Tagus estuary since its establishment 10 years ago. This clam now supports a local fishery (Garaulet, 2011). The decrease in copepod abundance at this site (54) follows the trends shown at site 53 Vigo (north of Cascais site) where the copepods A. clausi and Calanoides carinatus have been decreasing. However, additional data are necessary to better understand this shift in species abundance at the Cascais site and the relationship with the temperature increase over the past 30 years. Also, identification of the bivalve veligers to lower taxonomic levels is necessary in order to understand the importance of introduced species in the area. The long-term temperature record for this region demonstrates that SSTs are currently at the high end of those seen in the past 100 years. References: Garaulet, L. L. 2011. Estabelecimento do bivalve exotico Ruditapes philippinarum (Adams & Reeve, 1850) no estuario do Tejo: caracterizacao da populacao actual e analise comparativa com a congenere nativa Ruditapes decussatus (Linnaeus, 1758) e macrofauna bentonica acompanhante. Msc. Thesis. University of Lisbon. 77 pp. Moita, M. Y., Oliveira, P. B., Mendes, J. C., and Palma, A. S. 2003. Distribution of chlorophyll a and Gymnodinium catenatum associated with coastal upwelling plumes off central Portugal. Acta Oecologica, 24(S1): S125-S132. Ribeiro, S., and Amorim, A. 2008. Environmental drivers of temporal succession in recent dinoflagellate cyst assemblages from a coastal site in the North-East Atlantic (Lisbon Bay, Portugal). Marine Micropaleontology, 68:156-178. Santos, F., Gomez-Gesteira, M., deCastro, M., and Alvarez, I., 2011. Upwelling along the western coast of the Iberian Peninsula: dependence of trends on fitting strategy. Climate Research, 48: 213-218. Santos, A. M. P., Chicharo, A., dos Santos, A., Moita, T., Oliveira, P. B., Peliz, A., and Re, P. 2007. Physical biological interactions in the life history of small pelagic fish in the Western Iberia Upwelling Ecosystem. Progress in Oceanography, 74: 192-209. |