Anxo Conde

Characterization of an estuarine environment by means of an index based on intertidal macrofauna

Macrobenthic intertidal assemblages from five Atlantic Iberian estuaries were analyzed to develop an estuarine index. An R-mode analysis revealed a close association between the isopod Cyathura carinata, the polychaete Hediste diversicolor and the bivalve Scrobicularia plana. Although these species are abundant in all the estuaries considered, they tend to be absent from sites at the marine and freshwater ends of the environmental gradient. Three different ways of calculating the estuarine index are proposed. The index is comprised in the interval [0,1] and was constructed using relative abundances rather than absolute abundances. Transformation of the raw data helped improve the performance of the index. A non-parametric statistical test is proposed for application to the estuarine index to find sites with the same values after a significant omnibus test. The index appears to be a good proxy for recognizing estuarine limits by use of indicator species.

Multivariate analysis applied to agglomerated macrobenthic data from an unpolluted estuary

We agglomerated species into higher taxonomic aggregations and functional groups to analyse environmental gradients in an unpolluted estuary. We then applied non-metric Multidimensional Scaling and Redundancy Analysis (RDA) for ordination of the agglomerated data matrices. The correlation between the ordinations produced by both methods was generally high. However, the performance of the RDA models depended on the data matrix used to fit the model. As a result, salinity and total nitrogen were only found significant when aggregated data matrices were used rather than species data matrix. We used the results to select a RDA model that explained a higher percentage of variance in the species data set than the parsimonious model. We conclude that the use of aggregated matrices may be considered complementary to the use of species data to obtain a broader insight into the distribution of macrobenthic assemblages in relation to environmental gradients.

Intertidal macrofauna and environmental stress at a riverine-marine boundary.

A field experiment was carried out to test the effect of pore water salinity on the macrobenthic assemblages in an estuarine region of the Tagus estuary (Portugal) subjected to wide fluctuations in salinity. The conditions at the experimental site ranged from freshwater (minimum salinity 0.2) to mesohaline (maximum salinity 15.3). The experimental site was affected by an unexpected deposition of fluid mud during summer. Redundancy Analysis discriminated the experimental treatments along the first canonical ordination axis. The analysis also revealed an experimental gradient of increasing environmental stress, in which the minimal presence of organisms corresponded to treatments representing a high level of environmental stress. Sediment dynamics and saline fluctuations were the major factors that, together, determined the low macrofaunal abundance and species diversity at the experimental site. The most abundant macrofaunal species in this harsh environment were the polychaetes Hediste diversicolor and Streblospio shrubsolii.

First record of Cordylophora caspia (Hydrozoa: Cnidaria) in the Tagus estuary, central Portugal

The Ponto-Caspian hydroid Cordylophora caspia has been found for the first time in the Tagus estuary. There is only one previous citation for this invasive species in Portuguese waters. The colonies of C. caspia were branched and had healthy gastrozooids and gonophores. The specimens were collected from a saline boundary zone characterized by high fluctuations in salinity (maximum of 15.3 and minimum of 0.2) and high suspended solids loading. Cordylophora caspia is capable of colonizing man-made infrastructures such as industrial facilities and can inhabit both brackish and freshwater environments. These features of C. caspia, together with its resilience when in a dormant stage (menonts), indicate that the monitoring of this invasive species is advisable in the Tagus estuary.

The presence of Mya arenaria in the Ria de Aveiro is the third confirmed record of this invasive clam on the Portuguese coast

The occurrence of the invasive clamMya arenaria is confirmed in the Ria de Aveiro (northern Portugal). Some live specimens were collected from the mid-upper intertidal zone. The population density was low (about 0.15 ind m) and the individuals were large, of mean shell length 82.22+ 14.85 mm. Large empty shells of M. arenaria, of mean shell length 85.32+ 11.31 mm, were found in a life-like position, which indicates an episode of mass mortality in the sampling area and suggests that invasion by the clam in the Ria de Aveiro is not a recent event. Differences in the size-classes of empty shells of the invasive clam indicate that the clam is able to reproduce in this habitat. Occurrence of established populations ofM. arenaria at different locations on the Portuguese coast, such as the Tagus estuary, the Lima estuary and the Ria de Aveiro, may be due to intentional introduction of M. arenaria in at least some cases.

Converse effect of flooding on intertidal macrobenthic assemblages in the Guadiana estuary

macrobenthic assemblages in the Guadiana estuary anxo conde, jose’ calva’rio, martin sprung2,†, ju’ lio m. novais and jorge domi’nguez IBB-Institute for Biotechnology and Bioengineering, Center for Biological and Chemical Engineering, Instituto Superior Tecnico (IST), 1049-001, Lisbon, Portugal, Centro de Ciencias do Mar (CCMAR), Faculdade de Ciencias do Mar e do Ambiente, Universidade do Algarve, Campus de Gambelas, 8005-139 Faro, Portugal, Departamento de Ecoloxia e Bioloxia Animal, Universidade de Vigo, Vigo E-36310, Spain, †Deceased