Browsing by Author "Silva, Gilda"
Now showing 1 - 3 of 3
Results Per Page
Sort Options
- Non-indigenous species in soft-sediments: are some estuaries more invaded than others?Publication . Cabral, Sara; Carvalho, Frederico; Gaspar, Miguel; Ramajal, Joao; Sa, Erica; Santos, Catia; Silva, Gilda; Sousa, Antonio; Costa, Jose Lino; Chainho, PaulaNon-indigenous species (NIS) are increasingly widespread and abundant in coastal areas, hence being considered indicators to assess the environmental status of marine waters under the Marine Strategy Framework Directive. However, information on the effects of biological invasions on species composition and abundance is still scarce, particularly for soft-sediment benthic communities, which remain poorly understood. Therefore, the present study aimed at monitoring the benthic communities of two Portuguese estuarine systems, with a particular focus on NIS. Sampling surveys were conducted at the Tagus and Sado estuaries, in three different years. Invertebrate communities were collected at sampling stations located along the estuarine gradient, using a clam dredge, and several water and sediment parameters were measured at the same locations. NIS represented nearly one fourth (23%) of the total observed individuals across all years and estuaries, with Ruditapes philippinarum accounting for 22% of the total abundance across estuaries and years. Although both estuaries presented a similar total number of species (91 at the Tagus and 81 at the Sado), three-fold more NIS were identified at the Tagus estuary. The frequency of occurrence of the NIS Crassostrea (Magallana) gigas, Mya arenaria and Panopeus occidentalis increased significantly over the three years at the Tagus estuary and decreased significantly for Dyspanopeus sayi from 2015 to 2018. The Tagus and Sado estuaries presented distinct and diverse communities, with the abundance of R. philippinarum being eleven-fold greater at the Tagus estuary than at the Sado estuary. This study provides a baseline list of the NIS occurring in two of the main Portuguese estuarine systems, as well as an approach to estimate NIS abundance, richness, frequency of occurrence and community diversity. Although most studies on NIS impacts have focused on single species, the assessment of the environmental status of marine waters requires that overall impacts of NIS on marine ecosystems are determined. This study indicated metrics that are appropriate to evaluate changes in soft-sediment benthic communities associated to the introduction of NIS.
- Shifts in estuarine macroinvertebrate communities associated with water quality and climate changePublication . Goulding, Thomas; Sousa, Pedro M.; Silva, Gilda; Medeiros, João Paulo; Carvalho, Frederico; Metelo, Inês; Freitas, Catarina; Lopes, Nuno; Chainho, Paula; Costa, José LinoThe present work aims to identify changes in the macroinvertebrate community of the Tagus estuary (Portugal) due to improvements in water quality and to climate change. Data was collected over a period of 16 years (1998–2014) from different sites located along the estuarine gradient. The AZTI Marine Biotic Index (AMBI) was used to assess the ecological quality status based on benthic invertebrate communities and identify possible variations associated with changes in water quality. The overall distribution of each species was examined to detect possible changes associated with climate, based on species’ affinity for more temperate or subtropical climates. Results demonstrate that there was an overall improvement of AMBI scores during the assessment period. The analysis of the geographical distribution of benthic species seems to indicate that there has been an increase of species which prefer subtropical climates in the shallower waters of the estuary, whereas in the deeper estuarine sections the propensity is for species that prefer temperate climates.
- Spatial and temporal variations of Cockle (Cerastoderma spp.) populations in two portuguese estuarine systems with low directed fishing pressurePublication . Santos, Cátia; Cabral, Sara; Carvalho, Frederico; Sousa, António; Goulding, Thomas; Ramajal, João; Medeiros, João Paulo; Silva, Gilda; Angélico, Maria Manuel; Gaspar, Miguel; Brito, Ana C.; Costa, José Lino; Chainho, PaulaCockles are amongst the most exploited bivalve species in Portugal, playing an important ecological and socioeconomic role in coastal ecosystems. Two sympatric species of cockles, Cerastoderma edule (Linnaeus, 1758) and Cerastoderma glaucum (Bruguiere, 1789-1792) may co-occur in estuaries and coastal lagoons in mixed populations along the European Atlantic coast, namely in Portugal, France and the United Kingdom. The increasing importance of shellfish harvesting in Portugal requires a good knowledge of cockle stocks and temporal variability in stock levels to better inform sustainable management practices. Therefore, this study aimed at assessing spatial and temporal variations in cockle populations in two Portuguese estuarine systems where the species are exploited at low levels. Sampling was carried out using a clam dredge, covering the entire potential area of occurrence of cockles in the Tagus and Sado estuaries at around the same time of the year in each of the three sampling years (2015, 2018, and 2019). The abundance, spatial distribution and population structure of cockles were examined at each system. Moreover, several water and sediment parameters were measured to understand the influence of environmental conditions on the spatial distribution and abundance of cockles. The results obtained showed that cockles occur mostly in the intermediate areas of both estuarine systems and are more abundant in the Tagus estuary. Depth, average sediment grain size and the species Ruditapes philippinarum were the factors that better explained the probability of species occurrence. The population structure analysis indicated that natural mortality is constraining the cockle communities given the low abundance of adult individuals with marketable size in both estuaries. This study highlights the need for appropriate management measures to ensure the sustainability of these bivalve population stocks that have significant socioeconomic importance for local populations.