Environmental gradients in a southern Europe estuarine system: Ria de Aveiro, Portugal implications for soft bottom macrofauna colonization

Abstract

Four seasonal sampling surveys were carried out between December 1985 and September 1986 in Canal de Mira (Ria de Aveiro, Portugal). A total of 40 sampling stations, distributed over 13 transects, was used. Salinity, temperature, dissolved oxygen and pH of the water mass were measured. Sediment temperature, and salinity and pH of interstitial water were determined. Sediment variables also included granulometric composition and organic matter contents. Bottom macrofauna samples were collected at each station.Ordination (PCA and MDS) and classification of the sampling stations were performed, using the physicochemical and the biological data sets separately. Average linkage cluster analysis using the unweighted paired-group method, arithmetic averages, was used for both sets of data.With a salinity range from 35.1%o to 0.0%0, Canal de Mira behaves like a tidally and seasonally poikilohaline estuary. Water temperature (8.5 -24.7~ decreased along the channel towards its inner part during the cold season; an inverse and more pronounced trend was observed during the hot season. Dissolved oxygen contents was generally high during the day (50% to 240% saturation). Oversaturation was observed throughout the growing season, with peaks in areas with large amounts of rooted vegetation.The pH values, largely correlated with dissolved oxygen, ranged from 6.8 to 8.9. Four types of sediment were present in Canal de Mira, medium and muddy sands being dominant.Two major gradients were identified: (i) a typical longitudinal estuarine gradient, associated with distance from the mouth, representing physicochemical variables such as tidal amplitude, salinity and temperature; this gradient was accompanied by an upstream increase in dominance; the community composition changes were mainly related to salinity; (ii) a lateral gradient, related to current velocity, depth and sediment composition; the subtidal community had a comparatively low species richness and abundance. Groups of stations could be recognized along the environmental gradients. Benthic community changes, however, appeared to be gradual rather than marked by abrupt transitions.

Comparison of imposex and intersex development in four prosobranch species for TBT monitoring of a southern European estuarine system (Ria de Aveiro, NW Portugal)

“…Moreira et al 1993, Cunha & Moreira 1995, Cunha et al 1999. All 3 channels present a longitudinal salinity gradient but this is less pronounced in the S. Jacinto-Ovar Channel.…”

“…2B). For the most part of the ria the bottom is formed by sediments ranging from medium sands to muds (Moreira et al 1993, Cunha et al 1999. The adjacent coastal zone consists of a very extensive sandy shore interrupted by a few man-made rocky groynes.…”

Factors affecting the distribution of epibenthic biodiversity in the Cávado estuary (NW Portugal)

“…In general, salinity was lower at most upstream stations (E1, E1a) and higher at most downstream stations (E2, E3 and E3a). Seasonal variations and along to the estuarine gradient as those indicated are very common in Portuguese estuaries (Moreira et al 1993;Azevedo et al 2008;Chainho et al 2008;Sousa et al 2008b;Costa-Dias et al 2010b;Medeiros et al 2012). Winter and spring were the wettest seasons compared to summer, which was generally drier.…”

Horizontal patterns of water temperature and salinity in an estuarine tidal channel: Ria de Aveiro

“…For the Espinheiro channel is about 40·10 6 at extreme spring tide and 15·10 6 m 3 at extreme neap tide . The total estimated freshwater input for the lagoon is very small (about 1.8·10 6 m 3 during a tidal cycle) (Moreira et al 1993) when compared with the tidal prism at the mouth or at the beginning of Espinheiro channel. Despite the fact that rivers have a small contribution in terms of water input, when compared to the tidal prism, they may have a long-term influence in the residual transport (Dias et al 2003).…”